Companion 0.5.28 — backup & restore (#128), NIP-46 remote signer (#139), companion-gated install pitch (#61 residual)

The companion-agent queue from the 2026-08-30 handoff, complete:

- Backup & Restore: hub sub-page, SAF export/import sealed in the
  node's ADR-005 envelope (Argon2id + ChaCha20-Poly1305, byte-compatible
  with core backup.rs), merge-only restore, no cloud.
- Remote Signer: the phone is the NIP-46 bunker — nsec generate/import,
  nostrconnect:// QR pairing (scanner + OS deep link), per-request
  approve/deny card, NIP-44 v2 transport with NIP-04 receive fallback,
  wire-faithful to rust-nostr's reference bunker. Crypto pinned to the
  official NIP-44 + BIP-340 vectors; e2e harness included.
- #61 residual: banner + manual intro trigger + overlay all gate on
  isCompanionApp() (web-side, vitest-covered).
- Hub modal: new sub-pages like Nodes/FIPS, 70% height cap, node ULA
  display/copy in the Nodes list, fipssh Termux helper (npub→ULA is a
  pure public-key function — verified against the fips crate).

Issues #61 (comment), #128, #139 closed on the tracker.

Android/app/build.gradle.kts

@@ -11,8 +11,8 @@ android {
         applicationId = "com.archipelago.app"
         minSdk = 26
         targetSdk = 35
-        versionCode = 47
-        versionName = "0.5.27"
+        versionCode = 48
+        versionName = "0.5.28"
 
         vectorDrawables {
             useSupportLibrary = true

Android/app/src/main/AndroidManifest.xml

@@ -54,6 +54,15 @@
                 <category android:name="android.intent.category.BROWSABLE" />
                 <data android:scheme="archipelago" android:host="pair" />
             </intent-filter>
+            <!-- Remote-signer pairing deep link (NIP-46, companion 0.5.28):
+                 nostrconnect://<client-pubkey>?relay=...&secret=... — the
+                 node's login QR, hand-off from any QR scanner app. -->
+            <intent-filter>
+                <action android:name="android.intent.action.VIEW" />
+                <category android:name="android.intent.category.DEFAULT" />
+                <category android:name="android.intent.category.BROWSABLE" />
+                <data android:scheme="nostrconnect" />
+            </intent-filter>
         </activity>
 
         <!-- Embedded FIPS mesh node: split-tunnel VpnService (fd00::/8 only),

Android/app/src/main/java/com/archipelago/app/NativeCore.kt

@@ -0,0 +1,69 @@
+package com.archipelago.app
+
+import org.json.JSONObject
+
+/**
+ * JNI binding to the companion's non-mesh native surface (same
+ * libarchy_fips_core.so as FipsNative — backup + nostr signer crypto, built
+ * from Android/rust/archy-fips-core).
+ *
+ * Same contract as FipsNative: JSON over strings, failures come back as
+ * {"error": "…"} rather than exceptions, and [available] is false on ABIs
+ * the .so isn't built for so every caller can degrade gracefully.
+ */
+object NativeCore {
+    val available: Boolean = try {
+        System.loadLibrary("archy_fips_core")
+        true
+    } catch (_: Throwable) {
+        false
+    }
+
+    // ── Backup (#128): the node's ADR-005 envelope ──────────────────────────
+
+    /** Encrypt a JSON payload into an ADR-005 envelope (ChaCha20-Poly1305). */
+    external fun backupEncrypt(payload: String, passphrase: String): String
+
+    /** Decrypt an ADR-005 envelope back to its payload JSON. */
+    external fun backupDecrypt(envelope: String, passphrase: String): String
+
+    // ── NIP-46 remote signer (#139) ─────────────────────────────────────────
+
+    /** Generate a fresh nostr key: {"secret","pubkey","npub","nsec"}. */
+    external fun nostrGenerateSecret(): String
+
+    /** Import a key from hex or nsec…: {"secret","pubkey","npub","nsec"}. */
+    external fun nostrSecretFromAny(secret: String): String
+
+    /** Parse nostrconnect://…: {"clientPubkey","relays":[…],"secret","perms","name","url","image"}. */
+    external fun nostrParseConnectUri(uri: String): String
+
+    /**
+     * Sign `{kind, content, tags, created_at}` with the signer key: returns
+     * the full signed event JSON. Approval happens BEFORE this call — the
+     * native side never signs unasked.
+     */
+    external fun nostrSignEvent(secretHex: String, eventJson: String): String
+
+    /** NIP-44 v2 encrypt/decrypt; result JSON: {"result": payload} or {"error": …}. */
+    external fun nostrNip44Encrypt(secretHex: String, peerPub: String, plaintext: String): String
+    external fun nostrNip44Decrypt(secretHex: String, peerPub: String, payload: String): String
+
+    /** NIP-04 fallback (deprecated but still spoken by real clients). */
+    external fun nostrNip04Encrypt(secretHex: String, peerPub: String, plaintext: String): String
+    external fun nostrNip04Decrypt(secretHex: String, peerPub: String, payload: String): String
+
+    /** True when a native reply is an error envelope. */
+    fun isErr(json: String): Boolean = try {
+        JSONObject(json).has("error")
+    } catch (_: Exception) {
+        true
+    }
+
+    /** Error text from a native reply, or a generic message if malformed. */
+    fun errMsg(json: String): String = try {
+        JSONObject(json).optString("error", "native call failed")
+    } catch (_: Exception) {
+        "native call failed"
+    }
+}

Android/app/src/main/java/com/archipelago/app/data/BackupManager.kt

@@ -0,0 +1,229 @@
+package com.archipelago.app.data
+
+import android.content.Context
+import com.archipelago.app.NativeCore
+import com.archipelago.app.fips.FipsPreferences
+import com.archipelago.app.nostr.NostrSignerPreferences
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.withContext
+import org.json.JSONArray
+import org.json.JSONObject
+
+/**
+ * Companion backup & restore (#128) — the phone side of "losing your phone,
+ * or wiping it to cross a border".
+ *
+ * The payload (servers + FIPS identity/peers + signer key + flags) is
+ * serialized to JSON and sealed into the node's ADR-005 envelope (Argon2id +
+ * ChaCha20-Poly1305) by the native core — the SAME envelope the node uses,
+ * not a second format. The passphrase never leaves the encrypt call.
+ *
+ * Transport is deliberately boring: a plain .json file the user saves via
+ * the system file picker (SAF) — on GrapheneOS there is no cloud backup and
+ * there should be none here either; the file goes wherever the user puts it
+ * (USB drive, computer, a folder synced their way).
+ */
+class BackupManager(private val context: Context) {
+
+    private val servers = ServerPreferences(context)
+    private val fips = FipsPreferences(context)
+    private val signer = NostrSignerPreferences(context)
+
+    /** Everything the backup captures, for the restore preview UI. */
+    data class PayloadSummary(
+        val serverCount: Int,
+        val hasFipsIdentity: Boolean,
+        val hasSignerKey: Boolean,
+        val appVersion: String,
+    )
+
+    /** What a restore actually did, for the result UI. */
+    data class RestoreResult(
+        val serversRestored: Int,
+        val activeSet: Boolean,
+        val fipsIdentityRestored: Boolean,
+        val signerKeyRestored: Boolean,
+    )
+
+    private fun appVersion(): String = try {
+        context.packageManager.getPackageInfo(context.packageName, 0).versionName ?: ""
+    } catch (_: Exception) {
+        ""
+    }
+
+    /**
+     * Assemble the encrypted backup envelope. Runs on IO: DataStore reads
+     * plus the Argon2id KDF (tens of ms) + AEAD.
+     */
+    suspend fun createBackup(passphrase: String): String = withContext(Dispatchers.IO) {
+        require(passphrase.isNotEmpty()) { "passphrase required" }
+
+        val active = servers.activeServer.first()
+        val saved = servers.savedServers.first()
+        val fipsId = fips.identity()
+        val peers = fips.peersJson()
+        val partyPeers = fips.partyPeers()
+        val partyName = fips.partyName()
+        val partyListen = fips.partyListen()
+        val signerSecret = signer.secret()
+
+        val payload = JSONObject().apply {
+            put("app", "archipelago-companion")
+            put("payloadVersion", 1)
+            put("appVersion", appVersion())
+            put("createdAt", System.currentTimeMillis() / 1000)
+            put("servers", JSONArray(saved.map { it.serialize() }))
+            put("active", active?.serialize() ?: JSONObject.NULL)
+            if (fipsId != null) {
+                put("fips", JSONObject().apply {
+                    put("secret", fipsId.secret)
+                    put("npub", fipsId.npub)
+                    put("address", fipsId.address)
+                    put("peers", JSONArray(peers))
+                    put("partyPeers", JSONArray().apply { partyPeers.forEach { put(JSONObject().apply {
+                        put("npub", it.npub); put("ula", it.ula); put("name", it.name)
+                        put("ip", it.ip); put("port", it.port)
+                    }) } })
+                    put("partyName", partyName)
+                    put("partyListen", partyListen)
+                })
+            }
+            if (signerSecret != null) {
+                put("signer", JSONObject().apply { put("secret", signerSecret) })
+            }
+            put("flags", JSONObject().apply {
+                put("introSeen", servers.introSeen.first())
+            })
+        }
+
+        val envelope = NativeCore.backupEncrypt(payload.toString(), passphrase)
+        if (NativeCore.isErr(envelope)) throw BackupException(NativeCore.errMsg(envelope))
+        envelope
+    }
+
+    /**
+     * Peek at a decrypted backup (passphrase already checked) to preview what
+     * a restore would do. Does NOT touch any stored state.
+     */
+    suspend fun readBackup(envelope: String, passphrase: String): Pair<PayloadSummary, JSONObject> =
+        withContext(Dispatchers.IO) {
+            val payload = NativeCore.backupDecrypt(envelope, passphrase)
+            if (NativeCore.isErr(payload)) throw BackupException(NativeCore.errMsg(payload))
+            val obj = JSONObject(payload)
+            if (obj.optString("app") != "archipelago-companion") {
+                throw BackupException("Not a companion backup (this may be a node backup — restore it on the node)")
+            }
+            val summary = PayloadSummary(
+                serverCount = obj.optJSONArray("servers")?.length() ?: 0,
+                hasFipsIdentity = obj.has("fips"),
+                hasSignerKey = obj.has("signer"),
+                appVersion = obj.optString("appVersion", ""),
+            )
+            summary to obj
+        }
+
+    /**
+     * Apply a decrypted backup to this install. Merge semantics — a restore
+     * never silently destroys what's already here:
+     *
+     * - Servers upsert (npub-first, [ServerPreferences.upsertServer]) — same
+     *   identity merges, never duplicates.
+     * - The backup's active server is set active only when none is.
+     * - FIPS identity/peers restore only when this phone has none (a phone
+     *   that already paired has a live identity the node peers with; swapping
+     *   it from a backup would strand the current pairing). Peers merge by
+     *   npub otherwise.
+     * - Signer key restores only when none exists locally.
+     */
+    suspend fun restoreBackup(payload: JSONObject): RestoreResult = withContext(Dispatchers.IO) {
+        val serverArray = payload.optJSONArray("servers") ?: JSONArray()
+        var restored = 0
+        for (i in 0 until serverArray.length()) {
+            val raw = serverArray.optString(i)
+            val entry = ServerEntry.deserialize(raw) ?: continue
+            servers.upsertServer(entry)
+            restored++
+        }
+
+        var activeSet = false
+        val activeStr = if (payload.isNull("active")) null else payload.optString("active", "")
+        val activeEntry = activeStr?.takeIf { it.isNotBlank() }?.let { ServerEntry.deserialize(it) }
+        if (activeEntry != null && servers.activeServer.first() == null) {
+            servers.setActiveServer(activeEntry)
+            activeSet = true
+        }
+
+        // FIPS identity: only adopt when this phone has none.
+        var fipsRestored = false
+        val fipsObj = payload.optJSONObject("fips")
+        if (fipsObj != null && fips.identity() == null) {
+            val secret = fipsObj.optString("secret")
+            if (secret.isNotBlank()) {
+                fips.saveIdentity(
+                    com.archipelago.app.fips.FipsNative.Identity(
+                        secret = secret,
+                        npub = fipsObj.optString("npub"),
+                        address = fipsObj.optString("address"),
+                    )
+                )
+                fipsRestored = true
+            }
+            // Peers: union by npub with whatever is already here (an empty
+            // store takes the backup's list wholesale).
+            val backupPeers = fipsObj.optJSONArray("peers")?.let { arr ->
+                (0 until arr.length()).joinToString(",", "[", "]") { arr.optString(it) }
+            } ?: "[]"
+            fips.mergePeersJson(backupPeers)
+
+            val partyArr = fipsObj.optJSONArray("partyPeers")
+            if (partyArr != null) {
+                for (i in 0 until partyArr.length()) {
+                    val p = partyArr.optJSONObject(i) ?: continue
+                    val npub = p.optString("npub")
+                    val ula = p.optString("ula")
+                    if (npub.isNotBlank() && ula.isNotBlank()) {
+                        fips.upsertPartyPeer(
+                            com.archipelago.app.fips.PartyPeer(
+                                npub = npub, ula = ula,
+                                name = p.optString("name").ifBlank { "Phone" },
+                                ip = p.optString("ip"), port = p.optInt("port"),
+                            )
+                        )
+                    }
+                }
+            }
+            if (fipsObj.optString("partyName").isNotBlank()) {
+                fips.setPartyName(fipsObj.optString("partyName"))
+            }
+            fips.setPartyListen(fipsObj.optBoolean("partyListen", false))
+        }
+
+        // Signer key: only adopt when none exists locally.
+        var signerRestored = false
+        val signerObj = payload.optJSONObject("signer")
+        if (signerObj != null && signer.secret() == null) {
+            val secret = signerObj.optString("secret")
+            if (secret.isNotBlank()) {
+                signer.saveSecret(secret)
+                signerRestored = true
+            }
+        }
+
+        // Flags: a user who completed the intro on the old phone shouldn't
+        // see it again on the new one.
+        val flags = payload.optJSONObject("flags")
+        if (flags?.optBoolean("introSeen", false) == true) {
+            servers.markIntroSeen()
+        }
+
+        RestoreResult(
+            serversRestored = restored,
+            activeSet = activeSet,
+            fipsIdentityRestored = fipsRestored,
+            signerKeyRestored = signerRestored,
+        )
+    }
+
+    class BackupException(message: String) : Exception(message)
+}

Android/app/src/main/java/com/archipelago/app/fips/FipsPreferences.kt

@@ -89,6 +89,38 @@ class FipsPreferences(private val context: Context) {
 
     suspend fun hasPeers(): Boolean = JSONArray(peersJson()).length() > 0
 
+    /**
+     * Union the stored node peers with a backup's peer list, matched by
+     * npub — the backup's copy wins for the same npub (its addresses are what
+     * the restored identity pairs against). Used by companion restore (#128)
+     * after [saveIdentity] adopted the backup's mesh identity.
+     */
+    suspend fun mergePeersJson(incomingJson: String) {
+        context.fipsDataStore.edit { prefs ->
+            val current = JSONArray(prefs[peersKey] ?: "[]")
+            val incoming = try {
+                JSONArray(incomingJson)
+            } catch (_: Exception) {
+                JSONArray()
+            }
+            val incomingNpubs = mutableSetOf<String>()
+            val merged = JSONArray()
+            for (i in 0 until incoming.length()) {
+                val peer = incoming.optJSONObject(i) ?: continue
+                val npub = peer.optString("npub")
+                if (npub.isNotBlank()) {
+                    incomingNpubs.add(npub)
+                    merged.put(peer)
+                }
+            }
+            for (i in 0 until current.length()) {
+                val peer = current.optJSONObject(i) ?: continue
+                if (peer.optString("npub") !in incomingNpubs) merged.put(peer)
+            }
+            prefs[peersKey] = merged.toString()
+        }
+    }
+
     // ── Mesh Party (phone↔phone) ────────────────────────────────────────────
 
     suspend fun partyListen(): Boolean =

Android/app/src/main/java/com/archipelago/app/nostr/BunkerManager.kt

@@ -0,0 +1,445 @@
+package com.archipelago.app.nostr
+
+import android.content.Context
+import com.archipelago.app.NativeCore
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.withContext
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.Response
+import okhttp3.WebSocket
+import okhttp3.WebSocketListener
+import org.json.JSONArray
+import org.json.JSONObject
+import java.security.SecureRandom
+import java.util.concurrent.TimeUnit
+import java.util.concurrent.atomic.AtomicReference
+
+/**
+ * NIP-46 remote-signer session (#139) — the phone side, wire-faithful to
+ * rust-nostr's reference bunker (`signer/nostr-connect/src/signer.rs`),
+ * which the node's login flow will interoperate with:
+ *
+ * 1. Client (the node's login page) shows a `nostrconnect://` QR.
+ * 2. We scan it, connect to its relay, subscribe to kind-24133 events
+ *    p-tagged to our signer key, and send a `connect` request carrying the
+ *    secret (the client validates it and answers "ack").
+ * 3. Requests arrive as NIP-44-encrypted kind-24133 events; we respond over
+ *    the same channel. `sign_event` is the one method that never runs
+ *    without a human tapping Approve on this phone.
+ *
+ * The session lives while the app is around (the login handshake takes
+ * seconds); there is no background service in v1 and no remembered-session
+ * auto-reconnect (research doc flow C — deferred deliberately).
+ */
+object BunkerManager {
+
+    sealed class SignerState {
+        /** Native core unavailable (e.g. x86 emulator) — signing impossible. */
+        object Unavailable : SignerState()
+        /** Key exists, no session. */
+        object Idle : SignerState()
+        /** No signer key generated/imported yet. */
+        object NoKey : SignerState()
+        data class Connecting(val relay: String) : SignerState()
+        /** Connect request sent; waiting for the client to ack. */
+        data class AwaitingClient(val relay: String, val clientName: String) : SignerState()
+        /** Handshake complete — this is the state where requests are answered. */
+        data class Ready(val relay: String, val clientName: String) : SignerState()
+        data class Failed(val reason: String) : SignerState()
+    }
+
+    /** One signature request awaiting a human decision. */
+    data class PendingRequest(
+        val id: String,
+        val method: String,
+        val clientPubkey: String,
+        val clientName: String,
+        val kind: Long?,
+        val content: String?,
+        /** Formatted tag lines for the approval card. */
+        val tags: List<String>,
+        val createdAt: Long?,
+        /** The full unsigned event JSON handed to the native signer on approve. */
+        val unsignedEventJson: String,
+    )
+
+    private val _state = MutableStateFlow<SignerState>(SignerState.Idle)
+    val state: StateFlow<SignerState> = _state.asStateFlow()
+
+    private val _pending = MutableStateFlow<PendingRequest?>(null)
+    val pending: StateFlow<PendingRequest?> = _pending.asStateFlow()
+
+    private val client = OkHttpClient.Builder()
+        .connectTimeout(10, TimeUnit.SECONDS)
+        .pingInterval(25, TimeUnit.SECONDS) // relay keepalive
+        .build()
+
+    private data class Session(
+        val socket: WebSocket,
+        val relay: String,
+        /** The client's pubkey (hex) from the nostrconnect URI. */
+        val clientPubkey: String,
+        val clientName: String,
+        /** The pairing secret — echoed back during handshake, then kept for
+         *  validating an incoming `connect` from the same client. */
+        val secret: String,
+        /** Our connect request id, to match the client's ack response. */
+        val connectRequestId: String,
+        /** Our signer secret (hex). */
+        val signerSecretHex: String,
+        /** Our signer pubkey (hex). */
+        val signerPubkeyHex: String,
+        /** Event ids already handled (relays may redeliver). */
+        val seen: MutableSet<String> = java.util.concurrent.ConcurrentHashMap.newKeySet(),
+    )
+
+    private val session = AtomicReference<Session?>(null)
+
+    /** Refresh Idle/NoKey state (suspend; call from a coroutine — DataStore reads hit disk). */
+    suspend fun refreshState(context: Context) {
+        if (!NativeCore.available) {
+            _state.value = SignerState.Unavailable
+            return
+        }
+        if (session.get() != null) return
+        val prefs = NostrSignerPreferences(context.applicationContext)
+        _state.value =
+            if (prefs.secret() == null) SignerState.NoKey else SignerState.Idle
+    }
+
+    /**
+     * Pair from a scanned or deep-linked `nostrconnect://…` URI. Returns a
+     * user-presentable error on failure, or null on success (state moves to
+     * Connecting → AwaitingClient).
+     */
+    suspend fun pair(context: Context, uri: String): String? {
+        if (!NativeCore.available) return "Signing is unavailable on this device"
+        val appContext = context.applicationContext
+        return withContext(Dispatchers.IO) {
+            val parsed = JSONObject(NativeCore.nostrParseConnectUri(uri.trim()))
+            if (parsed.has("error")) return@withContext parsed.getString("error")
+
+            val prefs = NostrSignerPreferences(appContext)
+            val secret = prefs.secret()
+                ?: return@withContext "No signer key yet — generate or import one first"
+            val info = JSONObject(NativeCore.nostrSecretFromAny(secret))
+            if (info.has("error")) return@withContext info.getString("error")
+
+            val clientPubkey = parsed.getString("clientPubkey")
+            val relays = mutableListOf<String>()
+            parsed.optJSONArray("relays")?.let { arr -> for (i in 0 until arr.length()) relays.add(arr.optString(i)) }
+            val clientName = parsed.optString("name").ifBlank { "client" }
+            val pairSecret = parsed.getString("secret")
+
+            if (relays.isEmpty()) return@withContext "The pairing code carries no relay to reach the client on"
+
+            teardown()
+
+            var lastError = "no relay could be reached"
+            for (relay in relays) {
+                _state.value = SignerState.Connecting(relay)
+                val opened = openSession(
+                    relay, clientPubkey, clientName, pairSecret, secret, info,
+                )
+                if (opened != null) {
+                    session.set(opened)
+                    prefs.savePairing(
+                        NostrSignerPreferences.Pairing(clientPubkey, relay, clientName)
+                    )
+                    _state.value = SignerState.AwaitingClient(relay, clientName)
+                    return@withContext null
+                }
+                lastError = "relay $relay did not answer"
+            }
+            _state.value = SignerState.Failed(lastError)
+            lastError
+        }
+    }
+
+    /** Re-establish the last saved pairing without a fresh QR. */
+    suspend fun resume(context: Context): String? {
+        if (!NativeCore.available) return "Signing is unavailable on this device"
+        val appContext = context.applicationContext
+        return withContext(Dispatchers.IO) {
+            val prefs = NostrSignerPreferences(appContext)
+            val pairing = prefs.lastPairing()
+                ?: return@withContext "Nothing to resume — no saved pairing"
+            val secret = prefs.secret()
+                ?: return@withContext "No signer key"
+            val info = JSONObject(NativeCore.nostrSecretFromAny(secret))
+            if (info.has("error")) return@withContext info.getString("error")
+            teardown()
+            _state.value = SignerState.Connecting(pairing.relay)
+            val opened = openSession(
+                pairing.relay, pairing.clientPubkey, pairing.name,
+                secret = "", signerSecretHex = secret, info = info,
+            )
+            if (opened == null) {
+                _state.value = SignerState.Failed("relay ${pairing.relay} did not answer")
+                return@withContext "Could not reach ${pairing.relay}"
+            }
+            session.set(opened)
+            _state.value = SignerState.AwaitingClient(pairing.relay, pairing.name)
+            null
+        }
+    }
+
+    fun unpair() {
+        teardown()
+        _state.value = SignerState.Idle
+    }
+
+    private fun teardown() {
+        session.getAndSet(null)?.socket?.close(1000, "unpaired")
+        _pending.value = null
+    }
+
+    private fun randomId(): String {
+        val bytes = ByteArray(8)
+        SecureRandom().nextBytes(bytes)
+        return bytes.joinToString("") { "%02x".format(it) }
+    }
+
+    private fun openSession(
+        relay: String,
+        clientPubkey: String,
+        clientName: String,
+        secret: String,
+        signerSecretHex: String,
+        info: JSONObject,
+    ): Session? {
+        val signerPubkeyHex = info.getString("pubkey")
+        val connectRequestId = randomId()
+        // The listener needs the Session, the Session needs the WebSocket:
+        // bind through a holder set right after newWebSocket returns (OkHttp
+        // invokes onOpen on its own dispatcher after the network round-trip,
+        // i.e. always after the bind below).
+        val holder = AtomicReference<Session?>()
+
+        val request = Request.Builder().url(relay).build()
+        val socket = client.newWebSocket(request, object : WebSocketListener() {
+            override fun onOpen(webSocket: WebSocket, response: Response) {
+                val s = holder.get() ?: return
+                // Subscribe to requests addressed to us (p-tag filter), from
+                // now — no history replay of stale login attempts.
+                webSocket.send(
+                    """["REQ","${s.connectRequestId}sub",{"kinds":[24133],"#p":["${s.signerPubkeyHex}"],"since":${epochSecs() - 120}}]"""
+                )
+                // Handshake: the signer sends `connect` carrying the secret
+                // (rust-nostr's NostrConnectRemoteSigner.send_connect_ack —
+                // the exact frame the node's client waits for).
+                val content = JSONObject().apply {
+                    put("id", s.connectRequestId)
+                    put("method", "connect")
+                    put("params", JSONArray().put(s.signerPubkeyHex).put(s.secret))
+                }.toString()
+                if (!sendEncrypted(s, content)) {
+                    _state.value = SignerState.Failed("Could not encrypt the connect message")
+                }
+            }
+
+            override fun onMessage(webSocket: WebSocket, text: String) {
+                val s = session.get() ?: return
+                handleRelayMessage(s, text)
+            }
+
+            override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) {
+                if (session.get()?.socket === webSocket) {
+                    _state.value = SignerState.Failed(t.message ?: "relay connection failed")
+                    session.getAndSet(null)
+                }
+            }
+
+            override fun onClosed(webSocket: WebSocket, code: Int, reason: String) {
+                if (session.get()?.socket === webSocket) {
+                    _state.value = SignerState.Idle
+                    session.getAndSet(null)
+                }
+            }
+        })
+
+        val s = Session(
+            socket = socket,
+            relay = relay,
+            clientPubkey = clientPubkey,
+            clientName = clientName,
+            secret = secret,
+            connectRequestId = connectRequestId,
+            signerSecretHex = signerSecretHex,
+            signerPubkeyHex = signerPubkeyHex,
+        )
+        holder.set(s)
+        return s
+    }
+
+    private fun epochSecs(): Long = System.currentTimeMillis() / 1000
+
+    /** Encrypt a JSON-RPC frame to the peer and publish it as kind 24133. */
+    private fun sendEncrypted(s: Session, json: String): Boolean {
+        val enc = NativeCore.nostrNip44Encrypt(s.signerSecretHex, s.clientPubkey, json)
+        if (NativeCore.isErr(enc)) return false
+        val payload = JSONObject(enc).getString("result")
+        val event = JSONObject().apply {
+            put("kind", 24133)
+            put("content", payload)
+            put("tags", JSONArray().put(JSONArray().put("p").put(s.clientPubkey)))
+            put("created_at", epochSecs())
+        }.toString()
+        val signed = NativeCore.nostrSignEvent(s.signerSecretHex, event)
+        if (NativeCore.isErr(signed)) return false
+        return s.socket.send("""["EVENT",$signed]""")
+    }
+
+    private fun handleRelayMessage(s: Session, text: String) {
+        val arr = try {
+            JSONArray(text)
+        } catch (_: Exception) {
+            return
+        }
+        if (arr.length() == 0) return
+        when (arr.optString(0)) {
+            "EVENT" -> {
+                val event = arr.optJSONObject(2) ?: return
+                if (event.optLong("kind") != 24133L) return
+                val id = event.optString("id")
+                if (id.isNotEmpty() && !s.seen.add(id)) return
+                val author = event.optString("pubkey")
+                if (author != s.clientPubkey) return // not our client
+                handleClientEvent(s, author, event.optString("content"))
+            }
+            // OK / CLOSED / NOTICE: nothing actionable for the bunker in v1.
+        }
+    }
+
+    private fun handleClientEvent(s: Session, author: String, content: String) {
+        // NIP-44 is the mandated transport; NIP-04 stays as receive fallback
+        // for clients that still speak the deprecated scheme.
+        val plain = run {
+            val nip44 = NativeCore.nostrNip44Decrypt(s.signerSecretHex, author, content)
+            if (!NativeCore.isErr(nip44)) JSONObject(nip44).getString("result") else {
+                val nip04 = NativeCore.nostrNip04Decrypt(s.signerSecretHex, author, content)
+                if (!NativeCore.isErr(nip04)) JSONObject(nip04).getString("result") else return
+            }
+        }
+
+        val msg = try {
+            JSONObject(plain)
+        } catch (_: Exception) {
+            return
+        }
+
+        val id = msg.optString("id")
+        val method = msg.optString("method", "")
+        if (method.isNotEmpty()) {
+            when (method) {
+                "connect" -> {
+                    val params = msg.optJSONArray("params") ?: return
+                    // Param 0 must be OUR pubkey (client is connecting to us,
+                    // not some other bunker through this session).
+                    val target = params.optString(0)
+                    val givenSecret = params.optString(1)
+                    val authorized = target == s.signerPubkeyHex &&
+                        (s.secret.isBlank() || givenSecret == s.secret || givenSecret.isBlank())
+                    if (authorized) {
+                        respond(s, id, result = "ack")
+                        _state.value = SignerState.Ready(s.relay, s.clientName)
+                    } else {
+                        respond(s, id, error = "unauthorized")
+                    }
+                }
+                "get_public_key" -> respond(s, id, result = s.signerPubkeyHex)
+                "describe" -> respond(s, id, result = "connect get_public_key sign_event ping")
+                "ping" -> respond(s, id, result = "pong")
+                "sign_event" -> {
+                    val params = msg.optJSONArray("params") ?: return
+                    val eventJson = params.optString(0)
+                    val ev = try {
+                        JSONObject(eventJson)
+                    } catch (_: Exception) {
+                        respond(s, id, error = "malformed event")
+                        return
+                    }
+                    // Never overwrite a pending request silently — a second
+                    // tap on the node would otherwise cancel the visible one.
+                    if (_pending.value == null) {
+                        _pending.value = PendingRequest(
+                            id = id,
+                            method = method,
+                            clientPubkey = author,
+                            clientName = s.clientName,
+                            kind = if (ev.has("kind") && !ev.isNull("kind")) ev.optLong("kind") else null,
+                            content = if (ev.has("content") && !ev.isNull("content")) ev.optString("content") else null,
+                            tags = formatTags(ev.optJSONArray("tags")),
+                            createdAt = if (ev.has("created_at") && !ev.isNull("created_at")) ev.optLong("created_at") else null,
+                            unsignedEventJson = eventJson,
+                        )
+                    } else {
+                        respond(s, id, error = "busy")
+                    }
+                }
+                else -> respond(s, id, error = "not authorized")
+            }
+        } else if (msg.has("result") || msg.has("error")) {
+            // A response to OUR connect request (the client's ack).
+            if (id == s.connectRequestId) {
+                if (msg.has("error")) {
+                    _state.value = SignerState.Failed("Client rejected the connection: ${msg.optString("error")}")
+                } else if (msg.optString("result") == "ack") {
+                    _state.value = SignerState.Ready(s.relay, s.clientName)
+                }
+            }
+        }
+    }
+
+    /** Approve the pending request: sign and send the result. */
+    suspend fun approve(): Boolean {
+        val s = session.get() ?: return false
+        val req = _pending.value ?: return false
+        val ok = withContext(Dispatchers.IO) {
+            val signed = NativeCore.nostrSignEvent(s.signerSecretHex, req.unsignedEventJson)
+            if (NativeCore.isErr(signed)) {
+                respond(s, req.id, error = "signing failed")
+                false
+            } else {
+                // Result is the signed event, JSON-stringified per the spec.
+                respond(s, req.id, result = signed)
+            }
+        }
+        _pending.value = null
+        return ok
+    }
+
+    /** Deny the pending request with an explicit error. */
+    fun deny() {
+        val s = session.get() ?: return
+        val req = _pending.value ?: return
+        respond(s, req.id, error = "denied")
+        _pending.value = null
+    }
+
+    /** Send a JSON-RPC response frame to the client. True when the WS send worked. */
+    private fun respond(s: Session, id: String, result: String? = null, error: String? = null): Boolean {
+        val frame = JSONObject().apply {
+            put("id", id)
+            if (error != null) put("error", error)
+            if (result != null) put("result", result)
+        }.toString()
+        return sendEncrypted(s, frame)
+    }
+
+    private fun formatTags(tags: JSONArray?): List<String> {
+        tags ?: return emptyList()
+        val out = mutableListOf<String>()
+        for (i in 0 until tags.length()) {
+            val tag = tags.optJSONArray(i) ?: continue
+            val parts = mutableListOf<String>()
+            for (j in 0 until tag.length()) parts.add(tag.optString(j))
+            out.add(parts.joinToString(" "))
+        }
+        return out
+    }
+}

Android/app/src/main/java/com/archipelago/app/nostr/NostrSignerPreferences.kt

@@ -0,0 +1,95 @@
+package com.archipelago.app.nostr
+
+import android.content.Context
+import androidx.datastore.core.DataStore
+import androidx.datastore.preferences.core.Preferences
+import androidx.datastore.preferences.core.edit
+import androidx.datastore.preferences.core.stringPreferencesKey
+import androidx.datastore.preferences.preferencesDataStore
+import com.archipelago.app.NativeCore
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.distinctUntilChanged
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import org.json.JSONObject
+
+private val Context.signerDataStore: DataStore<Preferences> by preferencesDataStore(name = "nostr_signer")
+
+/**
+ * Storage for the phone-side NIP-46 remote signer (#139): the signer secret
+ * key (hex) and the last pairing, so a re-opened app can resume a session
+ * without re-scanning the node's QR.
+ *
+ * Same plaintext-DataStore model as the FIPS secret (app-private storage,
+ * no extra OS keystore ceremony — the node login password lives the same way
+ * in ServerPreferences); the nsec grants the ability to sign as this identity,
+ * never node login.
+ */
+class NostrSignerPreferences(private val context: Context) {
+
+    private val secretKey = stringPreferencesKey("signer_secret")
+    private val clientPubkeyKey = stringPreferencesKey("pair_client_pubkey")
+    private val clientRelayKey = stringPreferencesKey("pair_client_relay")
+    private val clientNameKey = stringPreferencesKey("pair_client_name")
+
+    /** The signer secret (hex) or null when no key exists yet. */
+    suspend fun secret(): String? = context.signerDataStore.data.first()[secretKey]
+
+    val secretFlow: Flow<String?> = context.signerDataStore.data
+        .map { it[secretKey] }
+        .distinctUntilChanged()
+
+    suspend fun saveSecret(hex: String) {
+        context.signerDataStore.edit { it[secretKey] = hex.trim() }
+    }
+
+    /** Generate a fresh signer key (fails if the native core is missing). */
+    suspend fun generateSecret(): JSONObject = withContext(Dispatchers.IO) {
+        val json = NativeCore.nostrGenerateSecret()
+        val obj = JSONObject(json)
+        if (obj.has("error")) throw IllegalStateException(obj.getString("error"))
+        saveSecret(obj.getString("secret"))
+        obj
+    }
+
+    /** Import a secret from hex or nsec…; returns the parsed key info. */
+    suspend fun importSecret(raw: String): JSONObject = withContext(Dispatchers.IO) {
+        val json = NativeCore.nostrSecretFromAny(raw.trim())
+        val obj = JSONObject(json)
+        if (obj.has("error")) throw IllegalArgumentException(obj.getString("error"))
+        saveSecret(obj.getString("secret"))
+        obj
+    }
+
+    data class Pairing(val clientPubkey: String, val relay: String, val name: String)
+
+    suspend fun lastPairing(): Pairing? {
+        val prefs = context.signerDataStore.data.first()
+        val pubkey = prefs[clientPubkeyKey] ?: return null
+        val relay = prefs[clientRelayKey] ?: return null
+        if (pubkey.isBlank() || relay.isBlank()) return null
+        return Pairing(pubkey, relay, prefs[clientNameKey] ?: "")
+    }
+
+    suspend fun savePairing(pairing: Pairing) {
+        context.signerDataStore.edit {
+            it[clientPubkeyKey] = pairing.clientPubkey
+            it[clientRelayKey] = pairing.relay
+            it[clientNameKey] = pairing.name
+        }
+    }
+
+    suspend fun clearPairing() {
+        context.signerDataStore.edit {
+            it.remove(clientPubkeyKey)
+            it.remove(clientRelayKey)
+            it.remove(clientNameKey)
+        }
+    }
+
+    suspend fun wipeKey() {
+        context.signerDataStore.edit { it.remove(secretKey) }
+    }
+}

Android/app/src/main/java/com/archipelago/app/ui/components/BackupSection.kt

@@ -0,0 +1,294 @@
+package com.archipelago.app.ui.components
+
+import androidx.activity.compose.rememberLauncherForActivityResult
+import androidx.activity.result.contract.ActivityResultContracts
+import androidx.compose.foundation.background
+import androidx.compose.foundation.border
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Restore
+import androidx.compose.material.icons.filled.Save
+import androidx.compose.material3.Icon
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.archipelago.app.data.BackupManager
+import com.archipelago.app.ui.theme.BitcoinOrange
+import com.archipelago.app.ui.theme.SuccessGreen
+import com.archipelago.app.ui.theme.TextMuted
+import com.archipelago.app.ui.theme.TextPrimary
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+import java.text.SimpleDateFormat
+import java.util.Date
+import java.util.Locale
+
+/**
+ * Backup & Restore (#128) — the hub's BACKUP sub-page (same container as
+ * Nodes/FIPS), the phone side of losing your phone or wiping it to cross a
+ * border. See docs/companion-backup-restore.md for the envelope and merge
+ * semantics; this composable is the flow only.
+ */
+@Composable
+internal fun BackupSection() {
+    val context = LocalContext.current
+    val scope = rememberCoroutineScope()
+    val manager = remember { BackupManager(context) }
+
+    var passphrase by remember { mutableStateOf("") }
+    var confirm by remember { mutableStateOf("") }
+    var status by remember { mutableStateOf<String?>(null) }
+    var statusError by remember { mutableStateOf(false) }
+    var busy by remember { mutableStateOf(false) }
+
+    // Decrypted backup awaiting the user's go-ahead (restore flow).
+    var restorePreview by remember { mutableStateOf<Pair<BackupManager.PayloadSummary, org.json.JSONObject>?>(null) }
+
+    fun say(msg: String, error: Boolean) {
+        status = msg
+        statusError = error
+    }
+
+    val exportLauncher = rememberLauncherForActivityResult(
+        ActivityResultContracts.CreateDocument("application/json")
+    ) { uri ->
+        if (uri == null) return@rememberLauncherForActivityResult
+        scope.launch {
+            busy = true
+            try {
+                val envelope = manager.createBackup(passphrase)
+                withContext(Dispatchers.IO) {
+                    context.contentResolver.openOutputStream(uri)?.use { out ->
+                        out.write(envelope.toByteArray())
+                    } ?: throw BackupManager.BackupException("could not open the destination file")
+                }
+                say("Saved — keep the file and the passphrase somewhere safe.", false)
+            } catch (e: Exception) {
+                say(e.message ?: "backup failed", true)
+            } finally {
+                busy = false
+            }
+        }
+    }
+
+    val importLauncher = rememberLauncherForActivityResult(
+        ActivityResultContracts.OpenDocument()
+    ) { uri ->
+        if (uri == null) return@rememberLauncherForActivityResult
+        scope.launch {
+            busy = true
+            try {
+                val envelope = withContext(Dispatchers.IO) {
+                    context.contentResolver.openInputStream(uri)?.use { it.readBytes().decodeToString() }
+                        ?: throw BackupManager.BackupException("could not read the selected file")
+                }
+                val (summary, payload) = manager.readBackup(envelope, passphrase)
+                restorePreview = summary to payload
+            } catch (e: Exception) {
+                say(e.message ?: "restore failed", true)
+            } finally {
+                busy = false
+            }
+        }
+    }
+
+    Column(verticalArrangement = Arrangement.spacedBy(10.dp)) {
+        SectionCopy(
+            "An encrypted copy of everything this phone holds — nodes and their passwords, " +
+                "your mesh identity, the remote-signer key. Same envelope your node uses (ADR-005), " +
+                "one passphrase, no cloud."
+        )
+
+        // ── Create a backup ──────────────────────────────────────────────
+        SectionHeader(Icons.Default.Save, "Create a backup")
+        GlassField(
+            value = passphrase,
+            onValueChange = { passphrase = it },
+            placeholder = "Passphrase",
+            visualTransformation = androidx.compose.ui.text.input.PasswordVisualTransformation(),
+        )
+        GlassField(
+            value = confirm,
+            onValueChange = { confirm = it },
+            placeholder = "Repeat passphrase",
+            visualTransformation = androidx.compose.ui.text.input.PasswordVisualTransformation(),
+        )
+        SectionHint("The passphrase cannot be recovered — a backup nobody can open is a paperweight.")
+        WideAction(
+            text = if (busy) "Working…" else "Save backup file",
+            onClick = {
+                if (busy) return@WideAction
+                if (passphrase.length < 8) {
+                    say("Use at least 8 characters — this passphrase guards every secret in the app.", true)
+                    return@WideAction
+                }
+                if (passphrase != confirm) {
+                    say("The two passphrases don't match.", true)
+                    return@WideAction
+                }
+                val stamp = SimpleDateFormat("yyyyMMdd-HHmm", Locale.US).format(Date())
+                exportLauncher.launch("archy-companion-backup-$stamp.json")
+            },
+        )
+
+        Spacer(Modifier.height(2.dp))
+
+        // ── Restore a backup ─────────────────────────────────────────────
+        SectionHeader(Icons.Default.Restore, "Restore a backup")
+        SectionHint(
+            "Nothing is overwritten: nodes merge by identity, and the mesh identity and " +
+                "signer key only restore when this phone has none."
+        )
+        WideAction(
+            text = if (busy) "Working…" else "Choose backup file",
+            onClick = {
+                if (busy) return@WideAction
+                if (passphrase.isEmpty()) {
+                    say("Enter the backup's passphrase first.", true)
+                    return@WideAction
+                }
+                importLauncher.launch(arrayOf("application/json"))
+            },
+        )
+
+        restorePreview?.let { (summary, payload) ->
+            Spacer(Modifier.height(2.dp))
+            Column(
+                Modifier
+                    .fillMaxWidth()
+                    .clip(RoundedCornerShape(14.dp))
+                    .background(Color.White.copy(alpha = 0.04f))
+                    .border(1.dp, Color.White.copy(alpha = 0.08f), RoundedCornerShape(14.dp))
+                    .padding(12.dp),
+                verticalArrangement = Arrangement.spacedBy(6.dp),
+            ) {
+                Text(
+                    "Backup verified${if (summary.appVersion.isNotBlank()) " (made by v${summary.appVersion})" else ""}",
+                    color = SuccessGreen, fontSize = 13.sp, fontWeight = FontWeight.SemiBold,
+                )
+                SummaryRow("Nodes", summary.serverCount.toString())
+                if (summary.hasFipsIdentity) SummaryRow("Mesh identity", "included")
+                if (summary.hasSignerKey) SummaryRow("Remote-signer key", "included")
+                WideAction(
+                    text = if (busy) "Restoring…" else "Restore onto this phone",
+                    onClick = {
+                        if (busy) return@WideAction
+                        scope.launch {
+                            busy = true
+                            try {
+                                val result = manager.restoreBackup(payload)
+                                restorePreview = null
+                                passphrase = ""
+                                confirm = ""
+                                say(
+                                    "Restored ${result.serversRestored} node(s)" +
+                                        (if (result.activeSet) ", set active" else "") +
+                                        (if (result.fipsIdentityRestored) ", mesh identity" else "") +
+                                        (if (result.signerKeyRestored) ", signer key" else "") +
+                                        ". Restart the app to reconnect.",
+                                    false,
+                                )
+                            } catch (e: Exception) {
+                                say(e.message ?: "restore failed", true)
+                            } finally {
+                                busy = false
+                            }
+                        }
+                    },
+                )
+            }
+        }
+
+        status?.takeIf { it.isNotBlank() }?.let { msg ->
+            Text(
+                msg,
+                color = if (statusError) Color(0xFFFF6B6B) else SuccessGreen,
+                fontSize = 12.sp,
+                textAlign = TextAlign.Center,
+                modifier = Modifier.fillMaxWidth(),
+            )
+        }
+    }
+}
+
+@Composable
+internal fun SectionHeader(icon: androidx.compose.ui.graphics.vector.ImageVector, title: String) {
+    Row(
+        verticalAlignment = Alignment.CenterVertically,
+        horizontalArrangement = Arrangement.spacedBy(10.dp),
+    ) {
+        Icon(icon, contentDescription = null, tint = BitcoinOrange, modifier = Modifier.size(18.dp))
+        Text(title, color = TextPrimary, fontSize = 15.sp, fontWeight = FontWeight.SemiBold)
+    }
+}
+
+@Composable
+internal fun SectionCopy(text: String) {
+    Text(text, color = TextMuted, fontSize = 12.sp, lineHeight = 16.sp)
+}
+
+@Composable
+internal fun SectionHint(text: String) {
+    Text(text, color = TextMuted.copy(alpha = 0.8f), fontSize = 10.sp, lineHeight = 13.sp)
+}
+
+/** Wide orange-outline action button in the menu's visual language. */
+@Composable
+internal fun WideAction(
+    text: String,
+    onClick: () -> Unit,
+    icon: androidx.compose.ui.graphics.vector.ImageVector? = null,
+) {
+    Row(
+        Modifier
+            .fillMaxWidth()
+            .height(44.dp)
+            .clip(RoundedCornerShape(12.dp))
+            .background(BitcoinOrange.copy(alpha = 0.15f))
+            .border(1.dp, BitcoinOrange.copy(alpha = 0.4f), RoundedCornerShape(12.dp))
+            .clickable { onClick() },
+        verticalAlignment = Alignment.CenterVertically,
+        horizontalArrangement = Arrangement.Center,
+    ) {
+        if (icon != null) {
+            Icon(icon, contentDescription = null, tint = BitcoinOrange, modifier = Modifier.size(16.dp))
+            Spacer(Modifier.size(8.dp))
+        }
+        Text(text, color = BitcoinOrange, fontSize = 13.sp, fontWeight = FontWeight.Bold)
+    }
+}
+
+@Composable
+internal fun SummaryRow(label: String, value: String) {
+    Row(
+        Modifier.fillMaxWidth(),
+        horizontalArrangement = Arrangement.SpaceBetween,
+    ) {
+        Text(label, color = TextMuted, fontSize = 12.sp)
+        Text(value, color = TextPrimary, fontSize = 12.sp, fontWeight = FontWeight.Medium)
+    }
+}

Android/app/src/main/java/com/archipelago/app/ui/components/NESMenu.kt

@@ -31,6 +31,8 @@ import androidx.compose.material.icons.filled.Dns
 import androidx.compose.material.icons.filled.Groups
 import androidx.compose.material.icons.filled.Keyboard
 import androidx.compose.material.icons.filled.RestartAlt
+import androidx.compose.material.icons.filled.SettingsBackupRestore
+import androidx.compose.material.icons.filled.Key
 import androidx.compose.material.icons.filled.SportsEsports
 import androidx.compose.foundation.layout.heightIn
 import androidx.compose.foundation.shape.RoundedCornerShape
@@ -106,22 +108,62 @@ fun NESMenu(
     onKeyboard: () -> Unit,
     onBackToWebView: (() -> Unit)? = null,
     onMeshParty: (() -> Unit)? = null,
+    // Remote-signer pairing request (nostrconnect://… deep link, or a scan):
+    // non-null opens the hub on the signer sub-page and pairs. Consumed once
+    // the signer section hands it back via [onSignerPairHandled].
+    signerPairRequest: String? = null,
+    onSignerPairHandled: () -> Unit = {},
 ) {
+    // Pairing state is latched here (not passed straight through) so the
+    // source can clear itself while the request stays alive until consumed.
+    var pendingSignerPair by remember { mutableStateOf<String?>(null) }
+    var signerScan by remember { mutableStateOf(false) }
+    LaunchedEffect(signerPairRequest) {
+        if (signerPairRequest != null) pendingSignerPair = signerPairRequest
+    }
+
     AnimatedVisibility(visible = visible, enter = fadeIn(), exit = fadeOut()) {
         // Contained hub overlay: a centred glass panel (not full-screen) that
-        // holds the card page and its sub-pages (Nodes, FIPS) and scrolls
-        // inside its own bounds when content is tall. Tapping the dimmed
-        // backdrop dismisses.
+        // holds the card page and its sub-pages (Nodes, FIPS, Backup, Signer)
+        // and scrolls inside its own bounds when content is tall. Tapping the
+        // dimmed backdrop dismisses.
         Box(
             Modifier.fillMaxSize().background(Color.Black.copy(alpha = 0.7f))
                 .clickable(indication = null, interactionSource = remember { MutableInteractionSource() }) { onDismiss() },
             contentAlignment = Alignment.Center,
         ) {
             AnimatedVisibility(visible = visible, enter = fadeIn() + scaleIn(initialScale = 0.95f), exit = fadeOut() + scaleOut(targetScale = 0.95f)) {
-                MenuPanel(servers, activeServer, onDismiss, onSelectServer, onAddServer, onScanQr, onEditServer, onRemoveServer, onRemote, onKeyboard, onBackToWebView, onMeshParty)
+                MenuPanel(
+                    servers, activeServer, onDismiss, onSelectServer, onAddServer, onScanQr,
+                    onEditServer, onRemoveServer, onRemote, onKeyboard, onBackToWebView, onMeshParty,
+                    signerPairUri = pendingSignerPair,
+                    onSignerScan = { signerScan = true },
+                    onSignerPairHandled = {
+                        pendingSignerPair = null
+                        onSignerPairHandled()
+                    },
+                )
             }
         }
     }
+
+    // Pairing-QR scanner for the signer sub-page — a full-screen glass
+    // modal hosted OUTSIDE the hub panel so it isn't clipped to the panel's
+    // bounds (same layering the pairing scanner gets from WebViewScreen).
+    QrGlassModal(
+        visible = signerScan && visible,
+        title = "Scan pairing QR",
+        status = null,
+        idleHint = "Point at the nostrconnect QR the node or client shows",
+        permissionRationale = "Camera access is needed to scan the pairing code",
+        onDismiss = { signerScan = false },
+        onDecoded = { text ->
+            if (text.startsWith("nostrconnect://")) {
+                signerScan = false
+                pendingSignerPair = text
+            }
+        },
+    )
 }
 
 @Composable
@@ -138,6 +180,9 @@ private fun MenuPanel(
     onKeyboard: () -> Unit,
     onBackToWebView: (() -> Unit)?,
     onMeshParty: (() -> Unit)?,
+    signerPairUri: String?,
+    onSignerScan: () -> Unit,
+    onSignerPairHandled: () -> Unit,
 ) {
     var showAdd by remember { mutableStateOf(false) }
     // The saved server being edited, or null when adding a new one.
@@ -176,9 +221,10 @@ private fun MenuPanel(
             .widthIn(max = 420.dp)
             .fillMaxWidth()
             .padding(horizontal = 20.dp)
-            // Cap height just short of the full screen; the panel wraps short
-            // content and only scrolls in the rare case it outgrows this.
-            .heightIn(max = (LocalConfiguration.current.screenHeightDp * 0.92f).dp)
+            // Cap height at 70% of the screen — a ~15% breathing margin top
+            // and bottom — the panel wraps short content and scrolls inside
+            // its own bounds when a sub-page outgrows this.
+            .heightIn(max = (LocalConfiguration.current.screenHeightDp * 0.70f).dp)
             .clip(RoundedCornerShape(PANEL_R))
             .background(PanelBg.copy(alpha = 0.86f))
             .border(1.dp, PanelBorder, RoundedCornerShape(PANEL_R))
@@ -201,7 +247,13 @@ private fun MenuPanel(
                     IconRound(Icons.AutoMirrored.Filled.ArrowBack, "Back") { resetForm(); page = HubPage.HUB }
                     Spacer(Modifier.width(12.dp))
                     Text(
-                        if (page == HubPage.NODES) "Nodes" else "FIPS Mesh",
+                        when (page) {
+                            HubPage.NODES -> "Nodes"
+                            HubPage.FIPS -> "FIPS Mesh"
+                            HubPage.BACKUP -> "Backup & Restore"
+                            HubPage.SIGNER -> "Remote Signer"
+                            HubPage.HUB -> "Menu"
+                        },
                         color = TextPrimary, fontSize = 20.sp, fontWeight = FontWeight.SemiBold, letterSpacing = 1.sp,
                     )
                 }
@@ -233,6 +285,12 @@ private fun MenuPanel(
                 if (onMeshParty != null) {
                     HubCard(Icons.Default.Groups, "Mesh Party", "Phone-to-phone chat & beam") { onMeshParty() }
                 }
+                // Backup & Restore (#128): the phone side of losing your phone
+                // or wiping it to cross a border — encrypted export file, no cloud.
+                HubCard(Icons.Default.SettingsBackupRestore, "Backup & Restore", "Encrypted export for a wiped phone") { page = HubPage.BACKUP }
+                // Remote Signer (#139): hold a nostr key on the phone and
+                // approve/deny remote signature requests (NIP-46).
+                HubCard(Icons.Default.Key, "Remote Signer", "Approve signatures for your node") { page = HubPage.SIGNER }
                 // Dark/Classic style lives on the remote/keyboard screen next to
                 // the settings button — not here.
 
@@ -272,6 +330,11 @@ private fun MenuPanel(
                     val active = server.serialize() == activeServer?.serialize()
                     MenuItem(
                         label = server.displayName(),
+                        // FIPS nodes carry their mesh ULA — the address Termux
+                        // (or any other app) can reach over the split-tunnel,
+                        // from anywhere. Tap to copy; the node's npub stays
+                        // visible in the FIPS Mesh page.
+                        subtitle = server.meshIp.takeIf { it.isNotBlank() },
                         selected = active,
                         onClick = { onSelectServer(server) },
                         onEdit = { startEdit(server) },
@@ -391,11 +454,23 @@ private fun MenuPanel(
             HubPage.FIPS -> {
                 FipsSection(embedded = true)
             }
+
+            HubPage.BACKUP -> {
+                BackupSection()
+            }
+
+            HubPage.SIGNER -> {
+                SignerSection(
+                    pairUri = signerPairUri,
+                    onScan = onSignerScan,
+                    onPairHandled = onSignerPairHandled,
+                )
+            }
         }
     }
 }
 
-private enum class HubPage { HUB, NODES, FIPS }
+private enum class HubPage { HUB, NODES, FIPS, BACKUP, SIGNER }
 
 /** Big tappable destination card for the hub page: icon + title + subtitle. */
 @Composable
@@ -582,26 +657,52 @@ private fun MenuItem(
     onClick: () -> Unit,
     onEdit: (() -> Unit)? = null,
     onRemove: (() -> Unit)? = null,
+    /** Optional second line (the node's mesh ULA); tapping it copies. */
+    subtitle: String? = null,
 ) {
+    val clipboard = LocalClipboardManager.current
     Row(
         Modifier
             .fillMaxWidth()
-            .height(ROW_H)
+            // Rows with a second line grow to fit it.
+            .then(if (subtitle == null) Modifier.height(ROW_H) else Modifier.heightIn(min = ROW_H))
             .clip(RoundedCornerShape(ROW_R))
             .background(if (selected) BitcoinOrange.copy(alpha = 0.12f) else RowBg)
             .border(1.dp, if (selected) BitcoinOrange.copy(alpha = 0.4f) else RowBorder, RoundedCornerShape(ROW_R))
             .clickable { onClick() }
-            .padding(horizontal = 16.dp),
+            .padding(horizontal = 16.dp)
+            .then(if (subtitle == null) Modifier else Modifier.padding(vertical = 8.dp)),
         verticalAlignment = Alignment.CenterVertically,
         horizontalArrangement = Arrangement.SpaceBetween,
     ) {
+        Column(Modifier.weight(1f)) {
             Text(
                 label,
                 color = if (selected) BitcoinOrange else labelColor,
                 fontSize = 16.sp,
                 fontWeight = FontWeight.Medium,
-            modifier = Modifier.weight(1f),
             )
+            if (subtitle != null) {
+                Row(
+                    Modifier
+                        .padding(top = 2.dp)
+                        .clip(RoundedCornerShape(6.dp))
+                        .clickable { clipboard.setText(AnnotatedString(subtitle)) }
+                        .padding(horizontal = 4.dp, vertical = 2.dp),
+                    verticalAlignment = Alignment.CenterVertically,
+                ) {
+                    Text(
+                        subtitle,
+                        color = TextMuted,
+                        fontSize = 10.sp,
+                        fontFamily = androidx.compose.ui.text.font.FontFamily.Monospace,
+                        maxLines = 1,
+                        overflow = androidx.compose.ui.text.style.TextOverflow.Ellipsis,
+                    )
+                    Text("⧉", color = TextMuted.copy(alpha = 0.7f), fontSize = 11.sp, modifier = Modifier.padding(start = 6.dp))
+                }
+            }
+        }
         if (onEdit != null) {
             Text(
                 "✎",
@@ -623,7 +724,7 @@ private fun MenuItem(
 
 /** Glass text field with centered input text. */
 @Composable
-private fun GlassField(
+internal fun GlassField(
     value: String,
     onValueChange: (String) -> Unit,
     placeholder: String,

Android/app/src/main/java/com/archipelago/app/ui/components/SignerLaunch.kt

@@ -0,0 +1,14 @@
+package com.archipelago.app.ui.components
+
+import kotlinx.coroutines.flow.MutableStateFlow
+
+/**
+ * Cross-layer handoff for remote-signer pairing (#139): NavGraph's
+ * `nostrconnect://` deep link drops the URI here and routes to the session;
+ * WebViewScreen collects it, opens the hub menu, and NESMenu opens the
+ * signer sub-page with the request. Cleared once the signer section has
+ * consumed it (via NESMenu's onSignerPairHandled).
+ */
+object SignerLaunch {
+    val pendingUri = MutableStateFlow<String?>(null)
+}

Android/app/src/main/java/com/archipelago/app/ui/components/SignerSection.kt

@@ -0,0 +1,381 @@
+package com.archipelago.app.ui.components
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.border
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.heightIn
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.foundation.text.KeyboardActions
+import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Key
+import androidx.compose.material.icons.filled.QrCodeScanner
+import androidx.compose.material3.Icon
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalClipboardManager
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.text.AnnotatedString
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.text.input.ImeAction
+import androidx.compose.ui.text.style.TextAlign
+import androidx.compose.ui.text.style.TextOverflow
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.archipelago.app.NativeCore
+import com.archipelago.app.nostr.BunkerManager
+import com.archipelago.app.nostr.NostrSignerPreferences
+import com.archipelago.app.ui.theme.BitcoinOrange
+import com.archipelago.app.ui.theme.SuccessGreen
+import com.archipelago.app.ui.theme.TextMuted
+import com.archipelago.app.ui.theme.TextPrimary
+import kotlinx.coroutines.launch
+import org.json.JSONObject
+import java.text.SimpleDateFormat
+import java.util.Date
+import java.util.Locale
+
+/**
+ * Remote Signer (#139) — the hub's SIGNER sub-page (same container as
+ * Nodes/FIPS). The phone holds a nostr key; a NIP-46 client (the node's
+ * login QR, any nostrconnect:// app) pairs via [pairUri] or the scanner
+ * (hosted by NESMenu outside this panel), and every `sign_event` request
+ * lands as a legible approve/deny card. See
+ * docs/companion-nip46-remote-signer.md.
+ */
+@Composable
+internal fun SignerSection(
+    pairUri: String?,
+    onScan: () -> Unit,
+    onPairHandled: () -> Unit,
+) {
+    val context = LocalContext.current
+    val scope = rememberCoroutineScope()
+    val clipboard = LocalClipboardManager.current
+    val prefs = remember { NostrSignerPreferences(context) }
+
+    var keyInfo by remember { mutableStateOf<JSONObject?>(null) }
+    var keyError by remember { mutableStateOf<String?>(null) }
+    var importText by remember { mutableStateOf("") }
+    var showNsec by remember { mutableStateOf(false) }
+    var notice by remember { mutableStateOf<String?>(null) }
+    var noticeError by remember { mutableStateOf(false) }
+
+    val bunkerState by BunkerManager.state.collectAsState()
+    val pending by BunkerManager.pending.collectAsState()
+
+    fun say(msg: String, error: Boolean) {
+        notice = msg
+        noticeError = error
+    }
+
+    suspend fun loadKey() {
+        val secret = prefs.secret()
+        keyInfo = secret?.let {
+            val json = NativeCore.nostrSecretFromAny(it)
+            if (NativeCore.isErr(json)) null else JSONObject(json)
+        }
+    }
+
+    LaunchedEffect(Unit) {
+        BunkerManager.refreshState(context)
+        loadKey()
+    }
+
+    // Consume a pairing request (deep link or scanner) exactly once.
+    LaunchedEffect(pairUri) {
+        val uri = pairUri?.takeIf { it.isNotBlank() } ?: return@LaunchedEffect
+        if (keyInfo == null) loadKey()
+        val err = BunkerManager.pair(context, uri)
+        if (err != null) say(err, true) else say("Pairing started…", false)
+        onPairHandled()
+    }
+
+    Column(verticalArrangement = Arrangement.spacedBy(10.dp)) {
+        SectionCopy(
+            "Hold a nostr key on this phone and sign for it remotely — pair with your " +
+                "node's login QR (or any NIP-46 client), then approve each signature " +
+                "request as it arrives. Nothing signs without you."
+        )
+
+        if (bunkerState is BunkerManager.SignerState.Unavailable) {
+            Text(
+                "Signing is unavailable on this device (native core missing).",
+                color = Color(0xFFFF6B6B), fontSize = 12.sp,
+            )
+        }
+
+        val info = keyInfo
+        if (info == null) {
+            // ── No key yet: generate or import ──────────────────────────
+            keyError?.let { Text(it, color = Color(0xFFFF6B6B), fontSize = 11.sp) }
+            WideAction(text = "Generate signer key", onClick = {
+                scope.launch {
+                    try {
+                        keyInfo = prefs.generateSecret()
+                        keyError = null
+                        BunkerManager.refreshState(context)
+                    } catch (e: Exception) {
+                        keyError = e.message ?: "could not generate a key"
+                    }
+                }
+            })
+            GlassField(
+                value = importText,
+                onValueChange = { importText = it },
+                placeholder = "or import nsec…",
+                keyboardOptions = KeyboardOptions(imeAction = ImeAction.Done),
+                keyboardActions = KeyboardActions(onGo = {
+                    if (importText.isNotBlank()) {
+                        scope.launch {
+                            try {
+                                keyInfo = prefs.importSecret(importText)
+                                importText = ""
+                                keyError = null
+                                BunkerManager.refreshState(context)
+                            } catch (e: Exception) {
+                                keyError = e.message ?: "not a valid nsec"
+                            }
+                        }
+                    }
+                }),
+            )
+            WideAction(text = "Import", onClick = {
+                if (importText.isBlank()) return@WideAction
+                scope.launch {
+                    try {
+                        keyInfo = prefs.importSecret(importText)
+                        importText = ""
+                        keyError = null
+                        BunkerManager.refreshState(context)
+                    } catch (e: Exception) {
+                        keyError = e.message ?: "not a valid nsec"
+                    }
+                }
+            })
+        } else {
+            // ── Identity ─────────────────────────────────────────────────
+            SectionHeader(Icons.Default.Key, "Signer identity")
+            MonoValue("npub", info.optString("npub")) {
+                clipboard.setText(AnnotatedString(info.optString("npub")))
+            }
+            if (showNsec) {
+                MonoValue("nsec", info.optString("nsec"), secret = true) {
+                    clipboard.setText(AnnotatedString(info.optString("nsec")))
+                }
+                SectionHint("Anyone with the nsec can sign as you — clear the clipboard after copying.")
+            } else {
+                Text(
+                    "Show nsec",
+                    color = TextMuted, fontSize = 11.sp,
+                    modifier = Modifier
+                        .clip(RoundedCornerShape(8.dp))
+                        .clickable { showNsec = true }
+                        .padding(vertical = 2.dp, horizontal = 6.dp),
+                )
+            }
+
+            // ── Session ──────────────────────────────────────────────────
+            Spacer(Modifier.height(2.dp))
+            val label = when (val s = bunkerState) {
+                BunkerManager.SignerState.Unavailable -> "Unavailable on this device"
+                BunkerManager.SignerState.NoKey -> "No signer key yet"
+                BunkerManager.SignerState.Idle -> "Idle — pair to start"
+                is BunkerManager.SignerState.Connecting -> "Connecting to ${s.relay}…"
+                is BunkerManager.SignerState.AwaitingClient -> "Paired with \"${s.clientName}\" — waiting for the handshake to finish"
+                is BunkerManager.SignerState.Ready -> "Ready for \"${s.clientName}\""
+                is BunkerManager.SignerState.Failed -> s.reason
+            }
+            Text("Session", color = TextMuted, fontSize = 11.sp)
+            Text(
+                label,
+                color = if (bunkerState is BunkerManager.SignerState.Failed) Color(0xFFFF6B6B)
+                else if (bunkerState is BunkerManager.SignerState.Ready) SuccessGreen
+                else TextPrimary,
+                fontSize = 13.sp,
+                lineHeight = 17.sp,
+            )
+            WideAction(
+                text = "Scan pairing QR",
+                onClick = {
+                    if (bunkerState is BunkerManager.SignerState.NoKey) {
+                        say("Generate or import a signer key first.", true)
+                        return@WideAction
+                    }
+                    onScan()
+                },
+                icon = Icons.Default.QrCodeScanner,
+            )
+            if (bunkerState is BunkerManager.SignerState.Ready ||
+                bunkerState is BunkerManager.SignerState.AwaitingClient ||
+                bunkerState is BunkerManager.SignerState.Connecting
+            ) {
+                Text(
+                    "End session",
+                    color = TextMuted, fontSize = 11.sp,
+                    modifier = Modifier
+                        .clip(RoundedCornerShape(8.dp))
+                        .clickable { BunkerManager.unpair() }
+                        .padding(vertical = 2.dp, horizontal = 6.dp),
+                )
+            }
+
+            // ── Pending signature request — the whole point ──────────────
+            pending?.let { req ->
+                Spacer(Modifier.height(2.dp))
+                Column(
+                    Modifier
+                        .fillMaxWidth()
+                        .clip(RoundedCornerShape(14.dp))
+                        .background(Color.White.copy(alpha = 0.04f))
+                        .border(1.dp, BitcoinOrange.copy(alpha = 0.35f), RoundedCornerShape(14.dp))
+                        .padding(12.dp),
+                    verticalArrangement = Arrangement.spacedBy(6.dp),
+                ) {
+                    Text("Signature request", color = BitcoinOrange, fontSize = 13.sp, fontWeight = FontWeight.Bold)
+                    SummaryRow("Client", req.clientName.ifBlank { req.clientPubkey.take(12) + "…" })
+                    SummaryRow("Kind", kindLabel(req.kind))
+                    req.createdAt?.let {
+                        SummaryRow("Time", SimpleDateFormat("HH:mm:ss", Locale.US).format(Date(it * 1000)))
+                    }
+                    req.content?.takeIf { it.isNotBlank() }?.let { content ->
+                        Text(
+                            content,
+                            color = TextPrimary, fontSize = 10.sp, lineHeight = 14.sp,
+                            fontFamily = FontFamily.Monospace,
+                            modifier = Modifier
+                                .fillMaxWidth()
+                                .clip(RoundedCornerShape(10.dp))
+                                .background(Color.Black.copy(alpha = 0.45f))
+                                .padding(8.dp)
+                                .heightIn(max = 160.dp),
+                        )
+                    }
+                    if (req.tags.isNotEmpty()) {
+                        Column(
+                            Modifier
+                                .fillMaxWidth()
+                                .clip(RoundedCornerShape(10.dp))
+                                .background(Color.Black.copy(alpha = 0.45f))
+                                .padding(8.dp),
+                            verticalArrangement = Arrangement.spacedBy(2.dp),
+                        ) {
+                            req.tags.take(6).forEach {
+                                Text(
+                                    it,
+                                    color = TextMuted, fontSize = 9.sp,
+                                    fontFamily = FontFamily.Monospace,
+                                    maxLines = 1,
+                                    overflow = TextOverflow.Ellipsis,
+                                )
+                            }
+                            if (req.tags.size > 6) {
+                                Text("+${req.tags.size - 6} more", color = TextMuted, fontSize = 9.sp)
+                            }
+                        }
+                    }
+                    Row(horizontalArrangement = Arrangement.spacedBy(10.dp)) {
+                        Box(
+                            Modifier
+                                .weight(1f)
+                                .height(40.dp)
+                                .clip(RoundedCornerShape(12.dp))
+                                .background(Color(0xFFE5484D).copy(alpha = 0.16f))
+                                .border(1.dp, Color(0xFFE5484D).copy(alpha = 0.5f), RoundedCornerShape(12.dp))
+                                .clickable { BunkerManager.deny() },
+                            contentAlignment = Alignment.Center,
+                        ) { Text("Deny", color = Color(0xFFFF8A8D), fontSize = 13.sp, fontWeight = FontWeight.Bold) }
+                        Box(
+                            Modifier
+                                .weight(1f)
+                                .height(40.dp)
+                                .clip(RoundedCornerShape(12.dp))
+                                .background(BitcoinOrange.copy(alpha = 0.2f))
+                                .border(1.dp, BitcoinOrange.copy(alpha = 0.6f), RoundedCornerShape(12.dp))
+                                .clickable {
+                                    scope.launch {
+                                        val ok = BunkerManager.approve()
+                                        say(if (ok) "Signed and sent." else "Could not send the signature.", !ok)
+                                    }
+                                },
+                            contentAlignment = Alignment.Center,
+                        ) { Text("Approve", color = BitcoinOrange, fontSize = 13.sp, fontWeight = FontWeight.Bold) }
+                    }
+                }
+            }
+        }
+
+        notice?.takeIf { it.isNotBlank() }?.let { msg ->
+            Text(
+                msg,
+                color = if (noticeError) Color(0xFFFF6B6B) else SuccessGreen,
+                fontSize = 12.sp,
+                textAlign = TextAlign.Center,
+                modifier = Modifier.fillMaxWidth(),
+            )
+        }
+    }
+}
+
+/** Kind number → legible label, so the approve/deny card reads like a sentence. */
+private fun kindLabel(kind: Long?): String = when (kind) {
+    0L -> "Metadata (kind 0)"
+    1L -> "Text note (kind 1)"
+    3L -> "Contact list (kind 3)"
+    4L -> "Direct message (kind 4)"
+    7L -> "Reaction (kind 7)"
+    14L -> "Chat message (kind 14)"
+    22242L -> "Client authentication (kind 22242)"
+    30078L -> "App-stored data (kind 30078)"
+    null -> "Unknown kind"
+    else -> "Kind $kind"
+}
+
+/** Monospace value chip with a copy affordance (tap the row). */
+@Composable
+private fun MonoValue(label: String, value: String, secret: Boolean = false, onCopy: () -> Unit) {
+    Column(Modifier.fillMaxWidth()) {
+        Text(label, color = TextMuted, fontSize = 10.sp)
+        Row(
+            Modifier
+                .fillMaxWidth()
+                .clip(RoundedCornerShape(10.dp))
+                .background(Color.Black.copy(alpha = 0.45f))
+                .clickable { onCopy() }
+                .padding(horizontal = 10.dp, vertical = 8.dp),
+            verticalAlignment = Alignment.CenterVertically,
+        ) {
+            Text(
+                value,
+                color = if (secret) Color(0xFFFFB86B) else TextPrimary,
+                fontSize = 10.sp,
+                fontFamily = FontFamily.Monospace,
+                modifier = Modifier.weight(1f),
+                maxLines = 1,
+                overflow = TextOverflow.Ellipsis,
+            )
+            Text("⧉", color = TextMuted, fontSize = 13.sp, modifier = Modifier.padding(start = 8.dp))
+        }
+    }
+}

Android/app/src/main/java/com/archipelago/app/ui/navigation/NavGraph.kt

@@ -22,6 +22,7 @@ import com.archipelago.app.data.ServerEntry
 import com.archipelago.app.data.ServerPreferences
 import com.archipelago.app.data.ServerQrParser
 import com.archipelago.app.fips.FipsManager
+import com.archipelago.app.ui.components.SignerLaunch
 import com.archipelago.app.ui.screens.FlareScreen
 import com.archipelago.app.ui.screens.IntroScreen
 import com.archipelago.app.ui.screens.NodePickerScreen
@@ -133,7 +134,20 @@ fun AppNavHost(
     LaunchedEffect(pairUri) {
         val raw = pairUri ?: return@LaunchedEffect
         onPairUriConsumed()
-        when (val result = ServerQrParser.parse(raw)) {
+        when {
+            // Remote-signer pairing deep link (NIP-46): nostrconnect://…
+            // from the node's login QR — any QR scanner app can hand it over.
+            // The signer UI lives inside the hub menu: drop the URI where
+            // WebViewScreen picks it up and route to the session, which opens
+            // the hub on its signer sub-page.
+            raw.startsWith("nostrconnect://") -> {
+                prefs.markIntroSeen()
+                SignerLaunch.pendingUri.value = raw
+                navController.navigate(Routes.WEB_VIEW) {
+                    popUpTo(0) { inclusive = true }
+                }
+            }
+            else -> when (val result = ServerQrParser.parse(raw)) {
                 is PairResult.Success -> {
                     // Pairing implies the app is installed and in use — skip the intro.
                     prefs.markIntroSeen()
@@ -157,6 +171,7 @@ fun AppNavHost(
                 }
             }
         }
+    }
 
     val startDestination = when {
         introSeen == false -> Routes.INTRO

Android/app/src/main/java/com/archipelago/app/ui/screens/WebViewScreen.kt

@@ -101,6 +101,7 @@ import com.archipelago.app.fips.FipsManager
 import com.archipelago.app.ui.components.GestureHintOverlay
 import com.archipelago.app.ui.components.MeshLoadingScreen
 import com.archipelago.app.ui.components.NESMenu
+import com.archipelago.app.ui.components.SignerLaunch
 import com.archipelago.app.ui.components.QrScannerOverlay
 import com.archipelago.app.ui.components.SlidingLoader
 import com.archipelago.app.ui.components.WalletQrScannerModal
@@ -1373,6 +1374,16 @@ fun WebViewScreen(
         // Hub menu overlay — opened by the three-finger hold, drawn above
         // everything (also reachable from the error screen, where switching
         // servers is exactly what's needed).
+        // Remote-signer deep link: route to the session and pop the hub open
+        // on its signer sub-page (the request itself is consumed by NESMenu).
+        var signerPairRequest by remember { mutableStateOf<String?>(null) }
+        val signerLaunch by SignerLaunch.pendingUri.collectAsState()
+        LaunchedEffect(signerLaunch) {
+            val uri = signerLaunch ?: return@LaunchedEffect
+            signerPairRequest = uri
+            SignerLaunch.pendingUri.value = null
+            showHubMenu = true
+        }
         NESMenu(
             visible = showHubMenu,
             servers = savedServers,
@@ -1427,6 +1438,8 @@ fun WebViewScreen(
             onKeyboard = { showHubMenu = false; onRemoteKeyboard() },
             onBackToWebView = { showHubMenu = false },
             onMeshParty = onMeshParty?.let { open -> { showHubMenu = false; open() } },
+            signerPairRequest = signerPairRequest,
+            onSignerPairHandled = { signerPairRequest = null },
         )
 
         // Pairing-QR scan launched from the menu's Nodes page; the menu stays

Android/rust/archy-fips-core/Cargo.lock

@@ -12,6 +12,17 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "aes"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b169f7a6d4742236a0a00c541b845991d0ac43e546831af1249753ab4c3aa3a0"
+dependencies = [
+ "cfg-if",
+ "cipher",
+ "cpufeatures 0.2.17",
+]
+
 [[package]]
 name = "aho-corasick"
 version = "1.1.4"
@@ -81,17 +92,41 @@ checksum = "330a5ed07fa54e4702c9d6c4174f74427fc0ef6e214bbd677ae50a5099946470"
 name = "archy-fips-core"
 version = "0.1.0"
 dependencies = [
+ "aes",
  "anyhow",
+ "argon2",
+ "base64",
+ "bech32",
+ "cbc",
+ "chacha20 0.9.1",
+ "chacha20poly1305",
  "fips",
  "getrandom 0.2.17",
  "hex",
+ "hkdf",
+ "hmac",
  "jni",
  "libc",
  "paranoid-android",
+ "secp256k1 0.29.1",
  "serde_json",
+ "sha2",
  "tokio",
  "tracing",
  "tracing-subscriber",
+ "url",
+]
+
+[[package]]
+name = "argon2"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c3610892ee6e0cbce8ae2700349fcf8f98adb0dbfbee85aec3c9179d29cc072"
+dependencies = [
+ "base64ct",
+ "blake2",
+ "cpufeatures 0.2.17",
+ "password-hash",
 ]
 
 [[package]]
@@ -124,6 +159,18 @@ version = "1.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1505bd5d3d116872e7271a6d4e16d81d0c8570876c8de68093a09ac269d8aac0"
 
+[[package]]
+name = "base64"
+version = "0.22.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
+
+[[package]]
+name = "base64ct"
+version = "1.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2af50177e190e07a26ab74f8b1efbfe2ef87da2116221318cb1c2e82baf7de06"
+
 [[package]]
 name = "bech32"
 version = "0.11.1"
@@ -172,6 +219,15 @@ version = "2.13.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b588b76d00fde79687d7646a9b5bdf3cc0f655e0bbd080335a95d7e96f3587da"
 
+[[package]]
+name = "blake2"
+version = "0.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "46502ad458c9a52b69d4d4d32775c788b7a1b85e8bc9d482d92250fc0e3f8efe"
+dependencies = [
+ "digest",
+]
+
 [[package]]
 name = "block-buffer"
 version = "0.10.4"
@@ -181,6 +237,15 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "block-padding"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a8894febbff9f758034a5b8e12d87918f56dfc64a8e1fe757d65e29041538d93"
+dependencies = [
+ "generic-array",
+]
+
 [[package]]
 name = "blocking"
 version = "1.6.2"
@@ -200,6 +265,15 @@ version = "1.12.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc652a48c352aef3ea3aed32080501cf3ef6ed5da78602a020c991775b0aff04"
 
+[[package]]
+name = "cbc"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "26b52a9543ae338f279b96b0b9fed9c8093744685043739079ce85cd58f289a6"
+dependencies = [
+ "cipher",
+]
+
 [[package]]
 name = "cc"
 version = "1.3.0"
@@ -406,6 +480,17 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "displaydoc"
+version = "0.2.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c6232dd377dcc64799954cbd3a9bb882e9cdc1308ccd87b1c098f1fb2eaf82a8"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.3",
+]
+
 [[package]]
 name = "either"
 version = "1.16.0"
@@ -476,7 +561,7 @@ dependencies = [
  "libc",
  "rand 0.10.2",
  "rtnetlink",
- "secp256k1",
+ "secp256k1 0.30.0",
  "serde",
  "serde_json",
  "serde_yaml",
@@ -491,6 +576,15 @@ dependencies = [
  "tun",
 ]
 
+[[package]]
+name = "form_urlencoded"
+version = "1.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb4cb245038516f5f85277875cdaa4f7d2c9a0fa0468de06ed190163b1581fcf"
+dependencies = [
+ "percent-encoding",
+]
+
 [[package]]
 name = "futures"
 version = "0.3.33"
@@ -676,6 +770,110 @@ dependencies = [
  "digest",
 ]
 
+[[package]]
+name = "icu_collections"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fa68d21081c4a05d5a901a1c62add574c77048b6a1c67be3b50ce0b60d4ca513"
+dependencies = [
+ "displaydoc",
+ "potential_utf",
+ "utf8_iter",
+ "yoke",
+ "zerofrom",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_locale_core"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d56e28588da92eee5c3201a6eff33fabdd49b62269c8938d4ff050ce4d900deb"
+dependencies = [
+ "displaydoc",
+ "litemap",
+ "tinystr",
+ "writeable",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_normalizer"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "12f9cf5f235641ed274641dd81c3f28d870e276763d0797aeeab72317b1c646f"
+dependencies = [
+ "icu_collections",
+ "icu_normalizer_data",
+ "icu_properties",
+ "icu_provider",
+ "smallvec",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_normalizer_data"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1563da1ed3e0b3bf3d74c9b85917ac9c56464d2f57242270c09c9e752f8021a0"
+
+[[package]]
+name = "icu_properties"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7e7ca276ad3145661a65914e6daf131ca5120cd3dcee8f8f3214b8875184a148"
+dependencies = [
+ "displaydoc",
+ "icu_collections",
+ "icu_locale_core",
+ "icu_properties_data",
+ "icu_provider",
+ "zerotrie",
+ "zerovec",
+]
+
+[[package]]
+name = "icu_properties_data"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e590f038c1464a96894fd6d10127e90a8be4509f56ff7ecef851b15cee0b7caa"
+
+[[package]]
+name = "icu_provider"
+version = "2.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d27bbb9d3abbefac45d55f647c9de1d44aafcd1186eb91879afef17c396c3e73"
+dependencies = [
+ "displaydoc",
+ "icu_locale_core",
+ "writeable",
+ "yoke",
+ "zerofrom",
+ "zerotrie",
+ "zerovec",
+]
+
+[[package]]
+name = "idna"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3b0875f23caa03898994f6ddc501886a45c7d3d62d04d2d90788d47be1b1e4de"
+dependencies = [
+ "idna_adapter",
+ "smallvec",
+ "utf8_iter",
+]
+
+[[package]]
+name = "idna_adapter"
+version = "1.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb68373c0d6620ef8105e855e7745e18b0d00d3bdb07fb532e434244cdb9a714"
+dependencies = [
+ "icu_normalizer",
+ "icu_properties",
+]
+
 [[package]]
 name = "indexmap"
 version = "2.14.0"
@@ -692,6 +890,7 @@ version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "879f10e63c20629ecabbb64a8010319738c66a5cd0c29b02d63d272b03751d01"
 dependencies = [
+ "block-padding",
  "generic-array",
 ]
 
@@ -788,6 +987,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "litemap"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47d9d19d1d6efa0109d2f65ff4c85cddd50bd572e5a00127ab10987290bcefae"
+
 [[package]]
 name = "log"
 version = "0.4.33"
@@ -954,12 +1159,29 @@ version = "2.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f38d5652c16fde515bb1ecef450ab0f6a219d619a7274976324d5e377f7dceba"
 
+[[package]]
+name = "password-hash"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "346f04948ba92c43e8469c1ee6736c7563d71012b17d40745260fe106aac2166"
+dependencies = [
+ "base64ct",
+ "rand_core 0.6.4",
+ "subtle",
+]
+
 [[package]]
 name = "paste"
 version = "1.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "57c0d7b74b563b49d38dae00a0c37d4d6de9b432382b2892f0574ddcae73fd0a"
 
+[[package]]
+name = "percent-encoding"
+version = "2.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
+
 [[package]]
 name = "pin-project-lite"
 version = "0.2.17"
@@ -988,6 +1210,15 @@ dependencies = [
  "universal-hash",
 ]
 
+[[package]]
+name = "potential_utf"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d83eb9bc6d8e5cf568e7a1101d60ee05e81ed50ea106026f3d18deeb046d7661"
+dependencies = [
+ "zerovec",
+]
+
 [[package]]
 name = "ppv-lite86"
 version = "0.2.21"
@@ -1129,6 +1360,15 @@ dependencies = [
  "winapi-util",
 ]
 
+[[package]]
+name = "secp256k1"
+version = "0.29.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9465315bc9d4566e1724f0fffcbcc446268cb522e60f9a27bcded6b19c108113"
+dependencies = [
+ "secp256k1-sys",
+]
+
 [[package]]
 name = "secp256k1"
 version = "0.30.0"
@@ -1272,6 +1512,12 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "stable_deref_trait"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ce2be8dc25455e1f91df71bfa12ad37d7af1092ae736f3a6cd0e37bc7810596"
+
 [[package]]
 name = "strsim"
 version = "0.11.1"
@@ -1306,6 +1552,17 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "synstructure"
+version = "0.13.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "728a70f3dbaf5bab7f0c4b1ac8d7ae5ea60a4b5549c8a5914361c99147a709d2"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.119",
+]
+
 [[package]]
 name = "thiserror"
 version = "1.0.69"
@@ -1355,6 +1612,16 @@ dependencies = [
  "cfg-if",
 ]
 
+[[package]]
+name = "tinystr"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1e27c91459209c2986af3dcf603a5a74a4368754ce37414f59acc971167f643"
+dependencies = [
+ "displaydoc",
+ "zerovec",
+]
+
 [[package]]
 name = "tokio"
 version = "1.53.1"
@@ -1519,6 +1786,24 @@ version = "0.2.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "673aac59facbab8a9007c7f6108d11f63b603f7cabff99fabf650fea5c32b861"
 
+[[package]]
+name = "url"
+version = "2.5.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff67a8a4397373c3ef660812acab3268222035010ab8680ec4215f38ba3d0eed"
+dependencies = [
+ "form_urlencoded",
+ "idna",
+ "percent-encoding",
+ "serde",
+]
+
+[[package]]
+name = "utf8_iter"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6c140620e7ffbb22c2dee59cafe6084a59b5ffc27a8859a5f0d494b5d52b6be"
+
 [[package]]
 name = "utf8parse"
 version = "0.2.2"
@@ -1657,6 +1942,35 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "writeable"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ad82d2a33cdc9674dc7465672f271e096168fcdbe0f799d9e6db8c5892679dc"
+
+[[package]]
+name = "yoke"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "709fe23a0424b6a435d82152b1bd3fdfb0833487d5fa90d05d42762a9891fef5"
+dependencies = [
+ "stable_deref_trait",
+ "yoke-derive",
+ "zerofrom",
+]
+
+[[package]]
+name = "yoke-derive"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "de844c262c8848816172cef550288e7dc6c7b7814b4ee56b3e1553f275f1858e"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.119",
+ "synstructure",
+]
+
 [[package]]
 name = "zerocopy"
 version = "0.8.55"
@@ -1677,12 +1991,66 @@ dependencies = [
  "syn 2.0.119",
 ]
 
+[[package]]
+name = "zerofrom"
+version = "0.1.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ec05a11813ea801ff6d75110ad09cd0824ddba17dfe17128ea0d5f68e6c5272"
+dependencies = [
+ "zerofrom-derive",
+]
+
+[[package]]
+name = "zerofrom-derive"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "11532158c46691caf0f2593ea8358fed6bbf68a0315e80aae9bd41fbade684a1"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.119",
+ "synstructure",
+]
+
 [[package]]
 name = "zeroize"
 version = "1.9.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e13c156562582aa81c60cb29407084cdb54c4164760106ab78e6c5b0858cf64e"
 
+[[package]]
+name = "zerotrie"
+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ea269c3bd32f0a32c321907a2ae912ba6f4649bb0fc764a15627e99a7095a3f"
+dependencies = [
+ "displaydoc",
+ "yoke",
+ "zerofrom",
+]
+
+[[package]]
+name = "zerovec"
+version = "0.11.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb0464e17806c1d976d5cba29399c7f08e516e279e2ba493f63123b5fca67dd8"
+dependencies = [
+ "yoke",
+ "zerofrom",
+ "zerovec-derive",
+]
+
+[[package]]
+name = "zerovec-derive"
+version = "0.11.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34df6fc39dbd26ddc9c10e6a2984476e13acce22e64e4487636ef494369225da"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.3",
+]
+
 [[package]]
 name = "zmij"
 version = "1.0.23"

Android/rust/archy-fips-core/Cargo.toml

@@ -37,6 +37,35 @@ tracing = "0.1"
 # fcntl: force the VpnService TUN fd into blocking mode (see mesh::start).
 libc = "0.2"
 
+# ── Companion backup (#128) ───────────────────────────────────────────────
+# ADR-005 envelope: the SAME crates and blob layout as the node's backup code
+# (core/archipelago/src/backup/identity.rs) — Argon2id KDF + ChaCha20-Poly1305
+# AEAD — applied to the companion's own JSON payload. Do not diverge from
+# those parameters: a companion backup and a node backup must decrypt with
+# the same code path on either side.
+argon2 = "0.5"
+chacha20poly1305 = "0.10"
+base64 = "0.22"
+
+# ── NIP-46 remote signer (#139) ───────────────────────────────────────────
+# BIP340 schnorr signing + secp256k1 ECDH (NIP-44/NIP-04 conversation keys).
+# Audited libsecp256k1 via cc; cargo-ndk provides the NDK clang on Android.
+secp256k1 = "0.29"
+# NIP-44 v2: HKDF-SHA256 (conversation/message keys) + HMAC-SHA256 (MAC).
+sha2 = "0.10"
+hmac = "0.12"
+hkdf = "0.12"
+# NIP-44 v2 stream cipher (raw ChaCha20, RFC 8439 — NOT the AEAD).
+chacha20 = "0.9"
+# NIP-04 fallback (deprecated in the spec but still sent by real clients):
+# AES-256-CBC, key = raw ECDH x-coordinate.
+aes = "0.8"
+cbc = { version = "0.1", features = ["alloc"] }
+# npub/nsec (bech32, BIP173 variant — NOT Bech32m).
+bech32 = "0.11"
+# nostrconnect:// URI parsing (repeated relay params + percent-decoding).
+url = "2.5"
+
 # The JNI surface only exists on Android; host builds skip it and drive the
 # mesh module directly (tests).
 [target.'cfg(target_os = "android")'.dependencies]

Android/rust/archy-fips-core/src/backup.rs

@@ -0,0 +1,246 @@
+//! Companion app backup — the ADR-005 encrypted-backup envelope.
+//!
+//! Reuses the node's backup format exactly (ADR-005:
+//! `core/archipelago/src/backup/identity.rs`): Argon2id key derivation with
+//! default params, ChaCha20-Poly1305 AEAD, and the same blob layout
+//! `base64(salt[16] || nonce[12] || ciphertext)`. A companion backup and a
+//! node backup share one crypto story — the payload differs (the companion
+//! serializes its servers, FIPS identity and signer key instead of a node
+//! key), the envelope does not.
+//!
+//! The envelope is JSON with `version`, `kind`, `encrypted`, `blob` and
+//! `timestamp`; [`decrypt`] ignores any extra fields, so node envelopes
+//! (which carry `did`/`pubkey`/`kid`) decrypt here too.
+
+use anyhow::{bail, Context, Result};
+use argon2::Argon2;
+use base64::engine::general_purpose::STANDARD as BASE64;
+use base64::Engine;
+use chacha20poly1305::aead::{Aead, KeyInit};
+use chacha20poly1305::{ChaCha20Poly1305, Key, Nonce};
+use serde_json::json;
+
+/// Envelope version. Bump only when the blob layout itself changes — and
+/// then only with a reader for the old layout (same policy as the node).
+const BACKUP_VERSION: u32 = 1;
+const SALT_LEN: usize = 16;
+const NONCE_LEN: usize = 12;
+const KEY_LEN: usize = 32;
+
+/// Encrypt a JSON payload into an ADR-005 envelope.
+///
+/// The passphrase never leaves this call; the envelope carries only the
+/// salt (Argon2id parameter), the AEAD nonce, and the ciphertext.
+pub fn encrypt(payload: &str, passphrase: &str) -> Result<String> {
+    if payload.is_empty() {
+        bail!("backup payload is empty");
+    }
+    if passphrase.is_empty() {
+        bail!("backup passphrase must not be empty");
+    }
+
+    let mut salt = [0u8; SALT_LEN];
+    let mut nonce = [0u8; NONCE_LEN];
+    // Same CSPRNG discipline as identity generation (getrandom, see mesh.rs):
+    // OS RNG, never thread-local or derived-from-content randomness for key
+    // material or nonces.
+    getrandom::getrandom(&mut salt).context("OS RNG")?;
+    getrandom::getrandom(&mut nonce).context("OS RNG")?;
+
+    let key = derive_key(passphrase, &salt)?;
+    let cipher = ChaCha20Poly1305::new(Key::from_slice(&key));
+    let ciphertext = cipher
+        .encrypt(Nonce::from_slice(&nonce), payload.as_bytes())
+        .map_err(|_| anyhow::anyhow!("encryption failed"))?;
+
+    let mut blob = Vec::with_capacity(SALT_LEN + NONCE_LEN + ciphertext.len());
+    blob.extend_from_slice(&salt);
+    blob.extend_from_slice(&nonce);
+    blob.extend_from_slice(&ciphertext);
+
+    Ok(json!({
+        "version": BACKUP_VERSION,
+        "kind": "companion",
+        "encrypted": true,
+        "blob": BASE64.encode(&blob),
+        "timestamp": chrono_like_now(),
+    })
+    .to_string())
+}
+
+/// Decrypt an ADR-005 envelope back into its JSON payload.
+///
+/// Accepts `version: 1` envelopes regardless of `kind` or extra fields —
+/// the node's identity backups use the same blob, and being able to decrypt
+/// one here is free interop (the caller decides what to do with it).
+pub fn decrypt(envelope: &str, passphrase: &str) -> Result<String> {
+    let obj: serde_json::Value =
+        serde_json::from_str(envelope).context("not a JSON backup envelope")?;
+
+    if obj.get("version").and_then(|v| v.as_u64()) != Some(BACKUP_VERSION as u64) {
+        bail!("unsupported backup version (expected {BACKUP_VERSION})");
+    }
+
+    let blob_b64 = obj
+        .get("blob")
+        .and_then(|v| v.as_str())
+        .context("missing 'blob' in backup envelope")?;
+    let blob = BASE64
+        .decode(blob_b64)
+        .context("invalid base64 in backup blob")?;
+    if blob.len() < SALT_LEN + NONCE_LEN {
+        bail!("backup blob too short");
+    }
+
+    let salt = &blob[..SALT_LEN];
+    let nonce = &blob[SALT_LEN..SALT_LEN + NONCE_LEN];
+    let ciphertext = &blob[SALT_LEN + NONCE_LEN..];
+
+    let key = derive_key(passphrase, salt)?;
+    let cipher = ChaCha20Poly1305::new(Key::from_slice(&key));
+    let plaintext = cipher
+        .decrypt(Nonce::from_slice(nonce), ciphertext)
+        .map_err(|_| anyhow::anyhow!("decryption failed — wrong passphrase or corrupted backup"))?;
+
+    String::from_utf8(plaintext).context("decrypted payload is not valid UTF-8")
+}
+
+fn derive_key(passphrase: &str, salt: &[u8]) -> Result<[u8; KEY_LEN]> {
+    let mut key = [0u8; KEY_LEN];
+    Argon2::default()
+        .hash_password_into(passphrase.as_bytes(), salt, &mut key)
+        .map_err(|e| anyhow::anyhow!("Argon2 key derivation failed: {e}"))?;
+    Ok(key)
+}
+
+/// RFC 3339 UTC timestamp without pulling chrono into the .so — the node's
+/// envelope field is informational (display), not part of the authenticated
+/// or derived material.
+fn chrono_like_now() -> String {
+    let secs = std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| d.as_secs())
+        .unwrap_or(0);
+    let days = secs / 86_400;
+    let rem = secs % 86_400;
+    let (h, m, s) = (rem / 3600, (rem % 3600) / 60, rem % 60);
+    // Civil-from-days (Howard Hinnant's algorithm), valid for 1970-2100+.
+    let z = days as i64 + 719_468;
+    let era = z.div_euclid(146_097);
+    let doe = z.rem_euclid(146_097);
+    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365;
+    let y = yoe + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100);
+    let mp = (5 * doy + 2) / 153;
+    let d = doy - (153 * mp + 2) / 5 + 1;
+    let mo = if mp < 10 { mp + 3 } else { mp - 9 };
+    let y = if mo <= 2 { y + 1 } else { y };
+    format!("{y:04}-{mo:02}-{d:02}T{h:02}:{m:02}:{s:02}Z")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PAYLOAD: &str = r#"{"app":"archipelago-companion","servers":["192.168.1.10|false|1301||Lab Node|fd00::1|npub1abc"]}"#;
+
+    #[test]
+    fn round_trip() {
+        let envelope = encrypt(PAYLOAD, "correct horse battery staple").unwrap();
+        let decrypted = decrypt(&envelope, "correct horse battery staple").unwrap();
+        assert_eq!(decrypted, PAYLOAD);
+    }
+
+    #[test]
+    fn wrong_passphrase_fails() {
+        let envelope = encrypt(PAYLOAD, "right").unwrap();
+        let err = decrypt(&envelope, "wrong").unwrap_err();
+        assert!(
+            err.to_string().contains("wrong passphrase"),
+            "error should name the likely cause: {err}"
+        );
+    }
+
+    #[test]
+    fn envelope_shape_matches_node_format() {
+        let envelope = encrypt(PAYLOAD, "pw").unwrap();
+        let obj: serde_json::Value = serde_json::from_str(&envelope).unwrap();
+
+        assert_eq!(obj["version"], 1);
+        assert_eq!(obj["encrypted"], true);
+        assert!(obj["kind"].as_str().is_some());
+        assert!(obj["timestamp"].as_str().is_some());
+
+        // Blob layout is exactly the node's: base64(salt||nonce||ct) with the
+        // AEAD tag inside the ciphertext — at least 16+12+16+1 bytes.
+        let blob = BASE64
+            .decode(obj["blob"].as_str().unwrap())
+            .expect("blob is base64");
+        assert!(blob.len() >= SALT_LEN + NONCE_LEN + 16 + PAYLOAD.len());
+    }
+
+    #[test]
+    fn fresh_salt_and_nonce_every_time() {
+        let a = encrypt(PAYLOAD, "pw").unwrap();
+        let b = encrypt(PAYLOAD, "pw").unwrap();
+        let (oa, ob): (serde_json::Value, serde_json::Value) = (
+            serde_json::from_str(&a).unwrap(),
+            serde_json::from_str(&b).unwrap(),
+        );
+        assert_ne!(oa["blob"], ob["blob"], "salt/nonce must never repeat");
+    }
+
+    #[test]
+    fn tampered_blob_fails_to_decrypt() {
+        let envelope = encrypt(PAYLOAD, "pw").unwrap();
+        let mut obj: serde_json::Value = serde_json::from_str(&envelope).unwrap();
+        let blob = BASE64.decode(obj["blob"].as_str().unwrap()).unwrap();
+        let mut tampered = blob.clone();
+        // Flip a bit inside the ciphertext (past salt+nonce).
+        tampered[SALT_LEN + NONCE_LEN] ^= 0x01;
+        obj["blob"] = serde_json::Value::String(BASE64.encode(&tampered));
+        assert!(decrypt(&obj.to_string(), "pw").is_err());
+    }
+
+    /// Node identity backups use the same blob layout but carry their own
+    /// envelope fields (did/pubkey/kid). Decrypt must ignore those extras —
+    /// one envelope reader, two producers.
+    #[test]
+    fn node_style_envelope_with_extra_fields_decrypts() {
+        let envelope = encrypt(PAYLOAD, "pw").unwrap();
+        let mut obj: serde_json::Value = serde_json::from_str(&envelope).unwrap();
+        obj["kind"] = serde_json::Value::String("node-identity".into());
+        obj["did"] = serde_json::Value::String("did:key:z6Mktest".into());
+        obj["pubkey"] = serde_json::Value::String("aabbcc".into());
+        obj["kid"] = serde_json::Value::String("did:key:z6Mktest#key-1".into());
+        let decrypted = decrypt(&obj.to_string(), "pw").unwrap();
+        assert_eq!(decrypted, PAYLOAD);
+    }
+
+    #[test]
+    fn rejects_unknown_version_and_garbage() {
+        let err = decrypt("{\"version\":99,\"blob\":\"AAAA\"}", "pw").unwrap_err();
+        assert!(err.to_string().contains("version"));
+        assert!(decrypt("not json", "pw").is_err());
+        assert!(decrypt("{\"version\":1}", "pw").is_err());
+    }
+
+    #[test]
+    fn rejects_empty_passphrase_and_payload() {
+        assert!(encrypt(PAYLOAD, "").is_err());
+        assert!(encrypt("", "pw").is_err());
+    }
+
+    #[test]
+    fn timestamp_is_rfc3339_utc() {
+        let envelope = encrypt(PAYLOAD, "pw").unwrap();
+        let obj: serde_json::Value = serde_json::from_str(&envelope).unwrap();
+        let ts = obj["timestamp"].as_str().unwrap();
+        // 2026-08-31T12:34:56Z — 20 chars, RFC 3339 UTC.
+        assert_eq!(ts.len(), 20);
+        assert!(ts.ends_with('Z'));
+        assert_eq!(&ts[4..5], "-");
+        assert_eq!(&ts[10..11], "T");
+        assert!(ts.starts_with("20"));
+    }
+}

Android/rust/archy-fips-core/src/jni_glue.rs

@@ -1,5 +1,6 @@
-//! JNI surface for `com.archipelago.app.fips.FipsNative` — JSON over strings,
-//! no codegen (the myco / nostr-vpn embedding pattern). Errors come back as
+//! JNI surface for `com.archipelago.app.fips.FipsNative` and
+//! `com.archipelago.app.NativeCore` — JSON over strings, no codegen (the
+//! myco / nostr-vpn embedding pattern). Errors come back as
 //! `{"error": "…"}` so Kotlin never sees a raw exception from native code.
 
 use std::sync::Once;
@@ -127,3 +128,177 @@ pub extern "system" fn Java_com_archipelago_app_fips_FipsNative_statusJson(
 ) -> jstring {
     out(&env, mesh::status_json())
 }
+
+// ─────────────────────────────────────────────────────────────────────────────
+// com.archipelago.app.NativeCore — companion backup (#128) and NIP-46 remote
+// signer crypto (#139). Same library, JSON-over-strings contract.
+// ─────────────────────────────────────────────────────────────────────────────
+
+/// Kotlin: `external fun backupEncrypt(payload: String, passphrase: String): String`
+/// Returns the ADR-005 envelope JSON or `{"error": …}`.
+#[no_mangle]
+pub extern "system" fn Java_com_archipelago_app_NativeCore_backupEncrypt(
+    mut env: JNIEnv,
+    _class: JClass,
+    payload: JString,
+    passphrase: JString,
+) -> jstring {
+    init_logging();
+    let payload = jstr(&mut env, &payload);
+    let passphrase = jstr(&mut env, &passphrase);
+    let json = match crate::backup::encrypt(&payload, &passphrase) {
+        Ok(envelope) => envelope,
+        Err(e) => err_json(e),
+    };
+    out(&env, json)
+}
+
+/// Kotlin: `external fun backupDecrypt(envelope: String, passphrase: String): String`
+/// Returns the decrypted payload JSON or `{"error": …}`.
+#[no_mangle]
+pub extern "system" fn Java_com_archipelago_app_NativeCore_backupDecrypt(
+    mut env: JNIEnv,
+    _class: JClass,
+    envelope: JString,
+    passphrase: JString,
+) -> jstring {
+    init_logging();
+    let envelope = jstr(&mut env, &envelope);
+    let passphrase = jstr(&mut env, &passphrase);
+    let json = match crate::backup::decrypt(&envelope, &passphrase) {
+        Ok(payload) => payload,
+        Err(e) => err_json(e),
+    };
+    out(&env, json)
+}
+
+/// Kotlin: `external fun nostrGenerateSecret(): String`
+/// Returns `{"secret": hex, "pubkey": hex, "npub": …, "nsec": …}` or `{"error": …}`.
+#[no_mangle]
+pub extern "system" fn Java_com_archipelago_app_NativeCore_nostrGenerateSecret(
+    env: JNIEnv,
+    _class: JClass,
+) -> jstring {
+    init_logging();
+    let json = match crate::nostr::generate_secret() {
+        Ok(secret) => nostr_key_info_json(&secret),
+        Err(e) => err_json(e),
+    };
+    out(&env, json)
+}
+
+/// Kotlin: `external fun nostrSecretFromAny(secret: String): String`
+/// Accepts hex or `nsec…`; returns key-info JSON or `{"error": …}`.
+#[no_mangle]
+pub extern "system" fn Java_com_archipelago_app_NativeCore_nostrSecretFromAny(
+    mut env: JNIEnv,
+    _class: JClass,
+    secret: JString,
+) -> jstring {
+    init_logging();
+    let secret = jstr(&mut env, &secret);
+    let json = match crate::nostr::secret_from_any(&secret) {
+        Ok(hex) => nostr_key_info_json(&hex),
+        Err(e) => err_json(e),
+    };
+    out(&env, json)
+}
+
+fn nostr_key_info_json(secret_hex: &str) -> String {
+    match (
+        crate::nostr::pubkey_hex(secret_hex),
+        crate::nostr::npub_from_pubkey(&crate::nostr::pubkey_hex(secret_hex).unwrap_or_default()),
+        crate::nostr::nsec_from_secret(secret_hex),
+    ) {
+        (Ok(pubkey), Ok(npub), Ok(nsec)) => serde_json::json!({
+            "secret": secret_hex,
+            "pubkey": pubkey,
+            "npub": npub,
+            "nsec": nsec,
+        })
+        .to_string(),
+        (e, _, _) => err_json(e.unwrap_err()),
+    }
+}
+
+/// Kotlin: `external fun nostrParseConnectUri(uri: String): String`
+/// Returns the parsed URI fields or `{"error": …}`.
+#[no_mangle]
+pub extern "system" fn Java_com_archipelago_app_NativeCore_nostrParseConnectUri(
+    mut env: JNIEnv,
+    _class: JClass,
+    uri: JString,
+) -> jstring {
+    init_logging();
+    let uri = jstr(&mut env, &uri);
+    let json = match crate::nostr::parse_connect_uri(&uri) {
+        Ok(info) => info.to_json().to_string(),
+        Err(e) => err_json(e),
+    };
+    out(&env, json)
+}
+
+/// Kotlin: `external fun nostrSignEvent(secretHex: String, eventJson: String): String`
+/// Returns the signed event JSON or `{"error": …}`. The approve/deny decision
+/// is made in Kotlin BEFORE this is called — native code never signs unasked.
+#[no_mangle]
+pub extern "system" fn Java_com_archipelago_app_NativeCore_nostrSignEvent(
+    mut env: JNIEnv,
+    _class: JClass,
+    secret_hex: JString,
+    event_json: JString,
+) -> jstring {
+    init_logging();
+    let secret = jstr(&mut env, &secret_hex);
+    let event = jstr(&mut env, &event_json);
+    let json = match crate::nostr::sign_event(&secret, &event) {
+        Ok(signed) => signed,
+        Err(e) => err_json(e),
+    };
+    out(&env, json)
+}
+
+macro_rules! nostr_cipher {
+    ($name:ident, $doc:literal, $fn:path) => {
+        #[doc = $doc]
+        #[no_mangle]
+        pub extern "system" fn $name(
+            mut env: JNIEnv,
+            _class: JClass,
+            secret_hex: JString,
+            peer_pub: JString,
+            text: JString,
+        ) -> jstring {
+            init_logging();
+            let secret = jstr(&mut env, &secret_hex);
+            let peer = jstr(&mut env, &peer_pub);
+            let text = jstr(&mut env, &text);
+            let json = match $fn(&secret, &peer, &text) {
+                Ok(out) => serde_json::json!({ "result": out }).to_string(),
+                Err(e) => err_json(e),
+            };
+            out(&env, json)
+        }
+    };
+}
+
+nostr_cipher!(
+    Java_com_archipelago_app_NativeCore_nostrNip44Encrypt,
+    "Kotlin: `external fun nostrNip44Encrypt(secretHex: String, peerPub: String, plaintext: String): String` — returns `{\"result\": payload}` or `{\"error\": …}`.",
+    crate::nostr::nip44_encrypt
+);
+nostr_cipher!(
+    Java_com_archipelago_app_NativeCore_nostrNip44Decrypt,
+    "Kotlin: `external fun nostrNip44Decrypt(secretHex: String, peerPub: String, payload: String): String`",
+    crate::nostr::nip44_decrypt
+);
+nostr_cipher!(
+    Java_com_archipelago_app_NativeCore_nostrNip04Encrypt,
+    "Kotlin: `external fun nostrNip04Encrypt(secretHex: String, peerPub: String, plaintext: String): String`",
+    crate::nostr::nip04_encrypt
+);
+nostr_cipher!(
+    Java_com_archipelago_app_NativeCore_nostrNip04Decrypt,
+    "Kotlin: `external fun nostrNip04Decrypt(secretHex: String, peerPub: String, payload: String): String`",
+    crate::nostr::nip04_decrypt
+);

Android/rust/archy-fips-core/src/lib.rs

@@ -11,7 +11,9 @@
 //! JSON-over-strings, mirroring the myco / nostr-vpn embedding pattern:
 //! `generateIdentity`, `deriveIdentity`, `start`, `stop`, `isRunning`.
 
+pub mod backup;
 pub mod mesh;
+pub mod nostr;
 
 #[cfg(target_os = "android")]
 mod jni_glue;

Android/rust/archy-fips-core/src/nostr.rs

@@ -0,0 +1,824 @@
+//! NIP-46 phone-side remote signer ("bunker") crypto core.
+//!
+//! Everything that must be constant-time correct for the companion to act as
+//! a nostr remote signer: key handling (nsec/npub bech32), BIP340 schnorr
+//! event signing, NIP-44 v2 payload encryption (the mandated NIP-46
+//! transport), NIP-04 fallback decryption (deprecated, but real clients
+//! still speak it), and `nostrconnect://` URI parsing. The protocol session
+//! — relay WebSocket, JSON-RPC dispatch, approve/deny UX — lives in Kotlin;
+//! this module is the crypto and nothing but.
+//!
+//! Verified against the official NIP-44 vectors and BIP-340 reference
+//! vectors (see tests below).
+
+use anyhow::{bail, Context, Result};
+use base64::engine::general_purpose::{STANDARD as BASE64, URL_SAFE as BASE64_URL};
+use base64::Engine;
+use bech32::{Bech32, Hrp};
+use chacha20::cipher::{KeyIvInit, StreamCipher};
+use chacha20::ChaCha20;
+use hmac::{Hmac, Mac};
+use hkdf::Hkdf;
+use secp256k1::ecdh;
+use secp256k1::schnorr::Signature;
+use secp256k1::{
+    Keypair, Message, PublicKey, Secp256k1, SecretKey, XOnlyPublicKey,
+};
+use sha2::{Digest, Sha256};
+
+type HmacSha256 = Hmac<Sha256>;
+
+const NIP44_VERSION: u8 = 2;
+const NIP44_SALT: &[u8] = b"nip44-v2";
+const NIP44_MIN_PAYLOAD_LEN: usize = 99; // 1 ver + 32 nonce + 32 ct + 32 mac
+const NIP44_MIN_B64_LEN: usize = 132;
+
+// ── keys ──────────────────────────────────────────────────────────────────
+
+/// Generate a fresh nostr secret key (hex) from the OS CSPRNG.
+pub fn generate_secret() -> Result<String> {
+    loop {
+        let mut bytes = [0u8; 32];
+        getrandom::getrandom(&mut bytes).context("OS RNG")?;
+        // Reject zero and >= curve order — the valid scalar range (mirrors
+        // the mesh identity loop; rejection is astronomically unlikely).
+        if bytes.iter().all(|&b| b == 0) {
+            continue;
+        }
+        if SecretKey::from_slice(&bytes).is_ok() {
+            return Ok(hex::encode(bytes));
+        }
+    }
+}
+
+/// Parse a secret key from hex or bech32 `nsec…` form into hex.
+pub fn secret_from_any(s: &str) -> Result<String> {
+    let s = s.trim();
+    if s.starts_with("nsec") {
+        return secret_from_nsec(s);
+    }
+    let bytes = hex::decode(s.trim()).context("secret key must be hex or nsec")?;
+    let sk = SecretKey::from_slice(&bytes).context("invalid nostr secret key")?;
+    Ok(hex::encode(sk.secret_bytes()))
+}
+
+pub fn secret_from_nsec(nsec: &str) -> Result<String> {
+    let (hrp, data) = bech32::decode(nsec).context("bad nsec encoding")?;
+    if hrp.as_str() != "nsec" {
+        bail!("not an nsec");
+    }
+    let sk = SecretKey::from_slice(&data).context("invalid nostr secret key")?;
+    Ok(hex::encode(sk.secret_bytes()))
+}
+
+pub fn nsec_from_secret(secret_hex: &str) -> Result<String> {
+    let bytes = hex::decode(secret_hex.trim()).context("bad secret hex")?;
+    let hrp = Hrp::parse("nsec").context("nsec hrp")?;
+    bech32::encode::<Bech32>(hrp, &bytes).context("nsec encoding")
+}
+
+/// x-only public key (hex) for a secret key.
+/// NOTE: `Keypair::public_key()` in secp256k1 0.29 is the full compressed
+/// (33-byte) key — nostr uses x-only pubkeys, so serialize `.x_only_public_key().0`.
+pub fn pubkey_hex(secret_hex: &str) -> Result<String> {
+    let kp = keypair(secret_hex)?;
+    Ok(hex::encode(kp.public_key().x_only_public_key().0.serialize()))
+}
+
+pub fn npub_from_pubkey(pub_hex: &str) -> Result<String> {
+    let bytes = hex::decode(pub_hex.trim()).context("bad pubkey hex")?;
+    let hrp = Hrp::parse("npub").context("npub hrp")?;
+    bech32::encode::<Bech32>(hrp, &bytes).context("npub encoding")
+}
+
+/// Parse an x-only pubkey from hex or bech32 `npub…` form into hex.
+pub fn pubkey_from_any(s: &str) -> Result<String> {
+    let s = s.trim();
+    let bytes = if s.starts_with("npub") {
+        let (hrp, data) = bech32::decode(s).context("bad npub encoding")?;
+        if hrp.as_str() != "npub" {
+            bail!("not an npub");
+        }
+        data
+    } else {
+        hex::decode(s).context("pubkey must be hex or npub")?
+    };
+    XOnlyPublicKey::from_slice(&bytes).context("invalid x-only pubkey")?;
+    Ok(hex::encode(bytes))
+}
+
+fn keypair(secret_hex: &str) -> Result<Keypair> {
+    let bytes = hex::decode(secret_hex.trim()).context("bad secret hex")?;
+    let sk = SecretKey::from_slice(&bytes).context("invalid nostr secret key")?;
+    Ok(Keypair::from_secret_key(&Secp256k1::new(), &sk))
+}
+
+// ── nostrconnect:// URI ───────────────────────────────────────────────────
+
+#[derive(Debug, Clone)]
+pub struct ConnectUri {
+    /// The client's pubkey, hex.
+    pub client_pubkey: String,
+    /// Relays the client is listening on (≥1 by spec; kept in URI order).
+    pub relays: Vec<String>,
+    /// One-time pairing secret the client expects to see echoed back.
+    pub secret: String,
+    /// Comma-separated permission grants the client requests (display hint
+    /// only — approval always stays with the human).
+    pub perms: Vec<String>,
+    pub name: String,
+    pub url: String,
+    pub image: String,
+}
+
+impl ConnectUri {
+    /// JSON shape for the JNI boundary (flat strings/arrays — easy to parse
+    /// with org.json on the Kotlin side).
+    pub fn to_json(&self) -> serde_json::Value {
+        serde_json::json!({
+            "clientPubkey": self.client_pubkey,
+            "relays": self.relays,
+            "secret": self.secret,
+            "perms": self.perms,
+            "name": self.name,
+            "url": self.url,
+            "image": self.image,
+        })
+    }
+}
+
+/// Parse `nostrconnect://<client-pubkey>?relay=…&secret=…&perms=…&name=…`.
+///
+/// Query values are percent-decoded; `relay` may repeat. The pubkey in the
+/// host position may be hex or (non-spec but harmless) `npub…`.
+pub fn parse_connect_uri(uri: &str) -> Result<ConnectUri> {
+    let uri = uri.trim();
+    let rest = uri
+        .strip_prefix("nostrconnect://")
+        .ok_or_else(|| anyhow::anyhow!("not a nostrconnect:// URI"))?;
+
+    let (host, query) = match rest.split_once('?') {
+        Some((h, q)) => (h, q),
+        None => bail!("nostrconnect URI has no query parameters"),
+    };
+    let client_pubkey = pubkey_from_any(host).context("nostrconnect URI: bad client pubkey")?;
+
+    let mut relays = Vec::new();
+    let mut secret = String::new();
+    let mut perms: Vec<String> = Vec::new();
+    let mut name = String::new();
+    let mut url = String::new();
+    let mut image = String::new();
+
+    for (k, v) in url::form_urlencoded::parse(query.as_bytes()) {
+        let v = v.into_owned();
+        match k.as_ref() {
+            "relay" => {
+                if v.starts_with("ws://") || v.starts_with("wss://") {
+                    relays.push(v);
+                }
+            }
+            "secret" => secret = v,
+            "perms" => perms = v.split(',').filter(|s| !s.is_empty()).map(String::from).collect(),
+            "name" => name = v,
+            "url" => url = v,
+            "image" => image = v,
+            _ => {} // forward-compat: ignore unknown params
+        }
+    }
+
+    if relays.is_empty() {
+        bail!("nostrconnect URI carries no relay");
+    }
+    if secret.is_empty() {
+        bail!("nostrconnect URI carries no secret");
+    }
+
+    Ok(ConnectUri {
+        client_pubkey,
+        relays,
+        secret,
+        perms,
+        name,
+        url,
+        image,
+    })
+}
+
+// ── events (NIP-01 id + BIP340 signature) ─────────────────────────────────
+
+/// Compute the NIP-01 event id: sha256 over the compact serialization
+/// `[0, pubkey, created_at, kind, tags, content]`.
+fn event_id(pubkey: &str, created_at: u64, kind: u64, tags: &serde_json::Value, content: &str) -> [u8; 32] {
+    let serialized = serde_json::json!([
+        0,
+        pubkey,
+        created_at,
+        kind,
+        tags,
+        content,
+    ]);
+    let mut hasher = Sha256::new();
+    hasher.update(serialized.to_string().as_bytes());
+    hasher.finalize().into()
+}
+
+/// Sign an unsigned event `{kind, content, tags, created_at}` (pubkey filled
+/// from the secret key; `pubkey` in the input ignored) and return the signed
+/// event JSON. This is the `sign_event` NIP-46 method's core — the approve
+/// happens before this call, never inside it.
+pub fn sign_event(secret_hex: &str, event_json: &str) -> Result<String> {
+    let ev: serde_json::Value = serde_json::from_str(event_json).context("event is not JSON")?;
+    let kind = ev
+        .get("kind")
+        .and_then(|v| v.as_u64())
+        .context("event has no kind")?;
+    let created_at = ev
+        .get("created_at")
+        .and_then(|v| v.as_u64())
+        .context("event has no created_at")?;
+    let tags = ev
+        .get("tags")
+        .cloned()
+        .unwrap_or_else(|| serde_json::json!([]));
+    let content = ev
+        .get("content")
+        .and_then(|v| v.as_str())
+        .unwrap_or("")
+        .to_string();
+
+    let kp = keypair(secret_hex)?;
+    let pubkey = hex::encode(kp.public_key().x_only_public_key().0.serialize());
+    let id = event_id(&pubkey, created_at, kind, &tags, &content);
+
+    let mut aux = [0u8; 32];
+    getrandom::getrandom(&mut aux).context("OS RNG")?;
+    let sig = Secp256k1::new().sign_schnorr_with_aux_rand(
+        &Message::from_digest(id),
+        &kp,
+        &aux,
+    );
+
+    Ok(serde_json::json!({
+        "id": hex::encode(id),
+        "pubkey": pubkey,
+        "created_at": created_at,
+        "kind": kind,
+        "tags": tags,
+        "content": content,
+        "sig": hex::encode(sig.serialize()),
+    })
+    .to_string())
+}
+
+/// Verify a signed event's id and schnorr signature (tests + defensive use).
+pub fn verify_event(event_json: &str) -> Result<()> {
+    let ev: serde_json::Value = serde_json::from_str(event_json).context("event is not JSON")?;
+    let pubkey = ev.get("pubkey").and_then(|v| v.as_str()).context("no pubkey")?;
+    let id_hex = ev.get("id").and_then(|v| v.as_str()).context("no id")?;
+    let sig_hex = ev.get("sig").and_then(|v| v.as_str()).context("no sig")?;
+    let kind = ev.get("kind").and_then(|v| v.as_u64()).context("no kind")?;
+    let created_at = ev.get("created_at").and_then(|v| v.as_u64()).context("no created_at")?;
+    let tags = ev.get("tags").cloned().unwrap_or_else(|| serde_json::json!([]));
+    let content = ev.get("content").and_then(|v| v.as_str()).unwrap_or("");
+
+    let expected = event_id(pubkey, created_at, kind, &tags, content);
+    if hex::encode(expected) != id_hex {
+        bail!("event id mismatch");
+    }
+
+    let pk = XOnlyPublicKey::from_slice(&hex::decode(pubkey)?)
+        .context("bad pubkey")?;
+    let sig = Signature::from_slice(&hex::decode(sig_hex)?)
+        .context("bad signature")?;
+    Secp256k1::new()
+        .verify_schnorr(&sig, &Message::from_digest(expected), &pk)
+        .context("signature verification failed")?;
+    Ok(())
+}
+
+// ── NIP-44 v2 ──────────────────────────────────────────────────────────────
+
+/// ECDH shared x-coordinate (unhashed, 32 bytes) between our secret key and
+/// the peer's x-only public key. Lifting the x-only key with even-y parity
+/// is safe here: negating a point flips only y, so the shared x — the only
+/// thing NIP-44/NIP-04 consume — is unchanged.
+fn shared_x(secret_hex: &str, peer_pubkey_hex: &str) -> Result<[u8; 32]> {
+    let sk_bytes = hex::decode(secret_hex.trim()).context("bad secret hex")?;
+    let sk = SecretKey::from_slice(&sk_bytes).context("invalid secret key")?;
+    let peer_hex = pubkey_from_any(peer_pubkey_hex)?;
+    let peer = XOnlyPublicKey::from_slice(&hex::decode(&peer_hex)?)
+        .context("invalid peer pubkey")?;
+    // Lift x-only key to a full public key (even-y representative).
+    let full = PublicKey::from_x_only_public_key(peer, secp256k1::Parity::Even);
+    let point = ecdh::shared_secret_point(&full, &sk); // 64 bytes: x || y
+    let mut x = [0u8; 32];
+    x.copy_from_slice(&point[..32]);
+    Ok(x)
+}
+
+/// NIP-44 v2 conversation key: HKDF-extract(IKM = ECDH x, salt = 'nip44-v2').
+fn conversation_key(secret_hex: &str, peer_pubkey_hex: &str) -> Result<[u8; 32]> {
+    let x = shared_x(secret_hex, peer_pubkey_hex)?;
+    let mut hk = HkdfExtractSha256::new(Some(NIP44_SALT));
+    hk.input_ikm(&x);
+    let (prk, _) = hk.finalize();
+    let mut ck = [0u8; 32];
+    ck.copy_from_slice(prk.as_slice());
+    Ok(ck)
+}
+
+/// HKDF-SHA256 extract step, exposing the raw PRK (Hkdf::expand hashes with
+/// an info suffix even when info is empty, which is NOT the extract output;
+/// finalize returns (PRK, ready-to-expand Hkdf)).
+type HkdfExtractSha256 = hkdf::HkdfExtract<Sha256>;
+
+/// Per-message keys: HKDF-expand(PRK = conversation key, info = nonce, L = 76)
+/// sliced into chacha_key[32] chacha_nonce[12] hmac_key[32].
+fn message_keys(ck: &[u8; 32], nonce: &[u8; 32]) -> ([u8; 32], [u8; 12], [u8; 32]) {
+    let hk = Hkdf::<Sha256>::from_prk(ck).expect("conversation key is 32 bytes");
+    let mut okm = [0u8; 76];
+    hk.expand(nonce, &mut okm).expect("76 <= 255 * hash len");
+    let mut chacha_key = [0u8; 32];
+    let mut chacha_nonce = [0u8; 12];
+    let mut hmac_key = [0u8; 32];
+    chacha_key.copy_from_slice(&okm[..32]);
+    chacha_nonce.copy_from_slice(&okm[32..44]);
+    hmac_key.copy_from_slice(&okm[44..76]);
+    (chacha_key, chacha_nonce, hmac_key)
+}
+
+/// NIP-44 padding: 2-byte big-endian plaintext length (6 bytes, `0x0000` +
+/// u32, when ≥ 65536), zero-padded to the next power-of-two-ish chunk.
+fn calc_padded_len(unpadded: usize) -> usize {
+    let unpadded: u64 = unpadded as u64;
+    if unpadded <= 32 {
+        return 32;
+    }
+    let next_power = 1u64 << ((63 - (unpadded - 1).leading_zeros()) + 1);
+    let chunk = if next_power <= 256 { 32 } else { next_power / 8 };
+    (chunk * ((unpadded - 1) / chunk + 1)) as usize
+}
+
+fn pad(plaintext: &[u8]) -> Result<Vec<u8>> {
+    if plaintext.is_empty() || plaintext.len() > u32::MAX as usize {
+        bail!("invalid plaintext length");
+    }
+    let prefix: Vec<u8> = if plaintext.len() >= 65536 {
+        let mut p = vec![0u8, 0u8];
+        p.extend_from_slice(&(plaintext.len() as u32).to_be_bytes());
+        p
+    } else {
+        (plaintext.len() as u16).to_be_bytes().to_vec()
+    };
+    let padded_len = calc_padded_len(plaintext.len());
+    let mut out = Vec::with_capacity(prefix.len() + padded_len);
+    out.extend_from_slice(&prefix);
+    out.extend_from_slice(plaintext);
+    out.resize(prefix.len() + padded_len, 0);
+    Ok(out)
+}
+
+fn unpad(padded: &[u8]) -> Result<Vec<u8>> {
+    if padded.len() < 2 {
+        bail!("invalid padding");
+    }
+    let first_two = u16::from_be_bytes([padded[0], padded[1]]);
+    let (unpadded_len, prefix_len) = if first_two == 0 {
+        if padded.len() < 6 {
+            bail!("invalid padding");
+        }
+        (u32::from_be_bytes([padded[2], padded[3], padded[4], padded[5]]) as usize, 6)
+    } else {
+        (first_two as usize, 2)
+    };
+    if unpadded_len == 0
+        || padded.len() < prefix_len + unpadded_len
+        || padded.len() != prefix_len + calc_padded_len(unpadded_len)
+    {
+        bail!("invalid padding");
+    }
+    Ok(padded[prefix_len..prefix_len + unpadded_len].to_vec())
+}
+
+/// Constant-time equality (length differs → false; content comparison never
+/// short-circuits on a byte).
+fn ct_eq(a: &[u8], b: &[u8]) -> bool {
+    if a.len() != b.len() {
+        return false;
+    }
+    let mut diff = 0u8;
+    for (x, y) in a.iter().zip(b.iter()) {
+        diff |= x ^ y;
+    }
+    diff == 0
+}
+
+/// NIP-44 v2 encrypt: returns `base64(0x02 || nonce || ciphertext || mac)`.
+pub fn nip44_encrypt(secret_hex: &str, peer_pubkey_hex: &str, plaintext: &str) -> Result<String> {
+    let ck = conversation_key(secret_hex, peer_pubkey_hex)?;
+    let mut nonce = [0u8; 32];
+    getrandom::getrandom(&mut nonce).context("OS RNG")?;
+    let (chacha_key, chacha_nonce, hmac_key) = message_keys(&ck, &nonce);
+
+    let mut padded = pad(plaintext.as_bytes())?;
+    ChaCha20::new(&chacha_key.into(), &chacha_nonce.into()).apply_keystream(&mut padded);
+
+    let mut mac = <HmacSha256 as Mac>::new_from_slice(&hmac_key).expect("hmac accepts any key len");
+    mac.update(&nonce);
+    mac.update(&padded);
+    let tag = mac.finalize().into_bytes();
+
+    let mut out = Vec::with_capacity(1 + 32 + padded.len() + 32);
+    out.push(NIP44_VERSION);
+    out.extend_from_slice(&nonce);
+    out.extend_from_slice(&padded);
+    out.extend_from_slice(&tag);
+    Ok(BASE64.encode(&out))
+}
+
+/// NIP-44 v2 decrypt of a `base64(0x02 || …)` payload.
+pub fn nip44_decrypt(secret_hex: &str, peer_pubkey_hex: &str, payload: &str) -> Result<String> {
+    if payload.starts_with('#') {
+        bail!("unknown NIP-44 version (non-base64 payload)");
+    }
+    let data = BASE64
+        .decode(payload.trim())
+        .context("payload is not base64")?;
+    if payload.len() < NIP44_MIN_B64_LEN || data.len() < NIP44_MIN_PAYLOAD_LEN {
+        bail!("invalid NIP-44 payload size");
+    }
+    if data[0] != NIP44_VERSION {
+        bail!("unknown NIP-44 version {}", data[0]);
+    }
+    let nonce: [u8; 32] = data[1..33].try_into().expect("slice is 32");
+    let ciphertext = &data[33..data.len() - 32];
+    let mac_bytes = &data[data.len() - 32..];
+
+    let ck = conversation_key(secret_hex, peer_pubkey_hex)?;
+    let (chacha_key, chacha_nonce, hmac_key) = message_keys(&ck, &nonce);
+
+    let mut mac = <HmacSha256 as Mac>::new_from_slice(&hmac_key).expect("hmac accepts any key len");
+    mac.update(&nonce);
+    mac.update(ciphertext);
+    let expected = mac.finalize().into_bytes();
+    if !ct_eq(&expected, mac_bytes) {
+        bail!("invalid NIP-44 MAC");
+    }
+
+    let mut buf = ciphertext.to_vec();
+    ChaCha20::new(&chacha_key.into(), &chacha_nonce.into()).apply_keystream(&mut buf);
+    let plaintext = unpad(&buf)?;
+    String::from_utf8(plaintext).context("decrypted payload is not UTF-8")
+}
+
+// ── NIP-04 (deprecated transport, still spoken by real clients) ────────────
+
+/// NIP-04 encrypt: AES-256-CBC, key = raw ECDH x-coordinate (unhashed — the
+/// spec's quirk), output `<base64 ct>?iv=<base64 iv>`.
+pub fn nip04_encrypt(secret_hex: &str, peer_pubkey_hex: &str, plaintext: &str) -> Result<String> {
+    use aes::cipher::{BlockEncryptMut, KeyIvInit};
+    type Enc = cbc::Encryptor<aes::Aes256>;
+
+    let key = shared_x(secret_hex, peer_pubkey_hex)?;
+    let mut iv = [0u8; 16];
+    getrandom::getrandom(&mut iv).context("OS RNG")?;
+    let ct = Enc::new(&key.into(), &iv.into()).encrypt_padded_vec_mut::<aes::cipher::block_padding::Pkcs7>(plaintext.as_bytes());
+    Ok(format!("{}?iv={}", BASE64.encode(&ct), BASE64.encode(iv)))
+}
+
+/// NIP-04 decrypt of `<base64 ct>?iv=<base64 iv>`.
+pub fn nip04_decrypt(secret_hex: &str, peer_pubkey_hex: &str, payload: &str) -> Result<String> {
+    use aes::cipher::{BlockDecryptMut, KeyIvInit};
+    type Dec = cbc::Decryptor<aes::Aes256>;
+
+    let (ct_b64, iv_b64) = payload
+        .trim()
+        .split_once("?iv=")
+        .ok_or_else(|| anyhow::anyhow!("not a NIP-04 payload (no iv)"))?;
+    let ct = BASE64.decode(ct_b64).context("bad NIP-04 ciphertext base64")?;
+    let iv: [u8; 16] = BASE64
+        .decode(iv_b64)
+        .context("bad NIP-04 iv base64")?
+        .try_into()
+        .map_err(|_| anyhow::anyhow!("NIP-04 iv must be 16 bytes"))?;
+    let key = shared_x(secret_hex, peer_pubkey_hex)?;
+    let pt = Dec::new(&key.into(), &iv.into())
+        .decrypt_padded_vec_mut::<aes::cipher::block_padding::Pkcs7>(&ct)
+        .map_err(|_| anyhow::anyhow!("NIP-04 decryption failed"))?;
+    String::from_utf8(pt).context("decrypted payload is not UTF-8")
+}
+
+/// URL-safe base64 for keys that cross the JNI boundary — unused by the
+/// protocol but handy for the Kotlin side; keep the engine in one place.
+pub fn b64_url(data: &[u8]) -> String {
+    BASE64_URL.encode(data)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // ── official NIP-44 vectors (paulmillr/nip44 nip44.vectors.json) ──────
+
+    #[test]
+    fn nip44_official_conversation_keys() {
+        let vectors: &[(&str, &str, &str)] = &[
+            ("315e59ff51cb9209768cf7da80791ddcaae56ac9775eb25b6dee1234bc5d2268", "c2f9d9948dc8c7c38321e4b85c8558872eafa0641cd269db76848a6073e69133", "3dfef0ce2a4d80a25e7a328accf73448ef67096f65f79588e358d9a0eb9013f1"),
+            ("98a5902fd67518a0c900f0fb62158f278f94a21d6f9d33d30cd3091195500311", "aae65c15f98e5e677b5050de82e3aba47a6fe49b3dab7863cf35d9478ba9f7d1", "9c00b769d5f54d02bf175b7284a1cbd28b6911b06cda6666b2243561ac96bad7"),
+            ("86ae5ac8034eb2542ce23ec2f84375655dab7f836836bbd3c54cefe9fdc9c19f", "59f90272378089d73f1339710c02e2be6db584e9cdbe86eed3578f0c67c23585", "19f934aafd3324e8415299b64df42049afaa051c71c98d0aa10e1081f2e3e2ba"),
+            // sec1 == pub2 (ECDH with self)
+            ("0000000000000000000000000000000000000000000000000000000000000001", "79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798", "3b4610cb7189beb9cc29eb3716ecc6102f1247e8f3101a03a1787d8908aeb54e"),
+        ];
+        for (sec1, pub2, expected) in vectors {
+            let ck = conversation_key(sec1, pub2).unwrap();
+            assert_eq!(hex::encode(ck), *expected);
+        }
+    }
+
+    #[test]
+    fn nip44_official_message_keys() {
+        let ck_bytes: [u8; 32] = hex::decode("a1a3d60f3470a8612633924e91febf96dc5366ce130f658b1f0fc652c20b3b54")
+            .unwrap()
+            .try_into()
+            .unwrap();
+        let vectors: &[(&str, &str, &str, &str)] = &[
+            ("e1e6f880560d6d149ed83dcc7e5861ee62a5ee051f7fde9975fe5d25d2a02d72", "f145f3bed47cb70dbeaac07f3a3fe683e822b3715edb7c4fe310829014ce7d76", "c4ad129bb01180c0933a160c", "027c1db445f05e2eee864a0975b0ddef5b7110583c8c192de3732571ca5838c4"),
+            ("ea6eb84cac23c5c1607c334e8bdf66f7977a7e374052327ec28c6906cbe25967", "ff68db24b34fa62c78ac5ffeeaf19533afaedf651fb6a08384e46787f6ce94be", "50bb859aa2dde938cc49ec7a", "06ff32e1f7b29753a727d7927b25c2dd175aca47751462d37a2039023ec6b5a6"),
+        ];
+        for (nonce_h, ck_exp, cn_exp, hk_exp) in vectors {
+            let nonce: [u8; 32] = hex::decode(nonce_h).unwrap().try_into().unwrap();
+            let (chacha_key, chacha_nonce, hmac_key) = message_keys(&ck_bytes, &nonce);
+            assert_eq!(hex::encode(chacha_key), *ck_exp);
+            assert_eq!(hex::encode(chacha_nonce), *cn_exp);
+            assert_eq!(hex::encode(hmac_key), *hk_exp);
+        }
+    }
+
+    #[test]
+    fn nip44_offical_padded_len() {
+        let vectors: &[(usize, usize)] = &[
+            (16, 32), (32, 32), (33, 64), (37, 64), (45, 64), (49, 64), (64, 64),
+            (65, 96), (100, 128), (111, 128), (200, 224), (250, 256), (320, 320),
+            (383, 384), (384, 384), (400, 448), (500, 512), (512, 512), (515, 640),
+            (700, 768), (800, 896), (900, 1024), (1020, 1024), (65536, 65536),
+        ];
+        for (unpadded, padded) in vectors {
+            assert_eq!(calc_padded_len(*unpadded), *padded, "unpadded {unpadded}");
+        }
+    }
+
+    #[test]
+    fn nip44_official_encrypt_vectors() {
+        // (sec1, sec2, nonce, plaintext, payload) — decrypt with the peer's
+        // view (sec2, pub(sec1)) so this also proves key symmetry.
+        let vectors: &[(&str, &str, &str, &str, &str)] = &[
+            ("0000000000000000000000000000000000000000000000000000000000000001",
+             "0000000000000000000000000000000000000000000000000000000000000002",
+             "0000000000000000000000000000000000000000000000000000000000000001",
+             "a",
+             "AgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABee0G5VSK0/9YypIObAtDKfYEAjD35uVkHyB0F4DwrcNaCXlCWZKaArsGrY6M9wnuTMxWfp1RTN9Xga8no+kF5Vsb"),
+            ("0000000000000000000000000000000000000000000000000000000000000002",
+             "0000000000000000000000000000000000000000000000000000000000000001",
+             "f00000000000000000000000000000f00000000000000000000000000000000f",
+             "🍕🫃",
+             "AvAAAAAAAAAAAAAAAAAAAPAAAAAAAAAAAAAAAAAAAAAPSKSK6is9ngkX2+cSq85Th16oRTISAOfhStnixqZziKMDvB0QQzgFZdjLTPicCJaV8nDITO+QfaQ61+KbWQIOO2Yj"),
+            ("5c0c523f52a5b6fad39ed2403092df8cebc36318b39383bca6c00808626fab3a",
+             "4b22aa260e4acb7021e32f38a6cdf4b673c6a277755bfce287e370c924dc936d",
+             "b635236c42db20f021bb8d1cdff5ca75dd1a0cc72ea742ad750f33010b24f73b",
+             "表ポあA鷗ŒéＢ逍Üߪąñ丂㐀𠀀",
+             "ArY1I2xC2yDwIbuNHN/1ynXdGgzHLqdCrXUPMwELJPc7s7JqlCMJBAIIjfkpHReBPXeoMCyuClwgbT419jUWU1PwaNl4FEQYKCDKVJz+97Mp3K+Q2YGa77B6gpxB/lr1QgoqpDf7wDVrDmOqGoiPjWDqy8KzLueKDcm9BVP8xeTJIxs="),
+            ("eba1687cab6a3101bfc68fd70f214aa4cc059e9ec1b79fdb9ad0a0a4e259829f",
+             "dff20d262bef9dfd94666548f556393085e6ea421c8af86e9d333fa8747e94b3",
+             "2180b52ae645fcf9f5080d81b1f0b5d6f2cd77ff3c986882bb549158462f3407",
+             "( ͡° ͜ʖ ͡°)",
+             "AiGAtSrmRfz59QgNgbHwtdbyzXf/PJhogrtUkVhGLzQHv4qhKQwnFQ54OjVMgqCea/Vj0YqBSdhqNR777TJ4zIUk7R0fnizp6l1zwgzWv7+ee6u+0/89KIjY5q1wu6inyuiv"),
+            ("d5633530f5bcfebceb5584cfbbf718a30df0751b729dd9a789b9f30c0587d74e",
+             "b74e6a341fb134127272b795a08b59250e5fa45a82a2eb4095e4ce9ed5f5e214",
+             "a3e219242d85465e70adcd640b564b3feff57d2ef8745d5e7a0663b2dccceb54",
+             "🙈 🙉 🙊 0️⃣ 1️⃣ 2️⃣ 3️⃣ 4️⃣ 5️⃣ 6️⃣ 7️⃣ 8️⃣ 9️⃣ 🔟 Powerلُلُصّبُلُلصّبُررً ॣ ॣh ॣ ॣ冗",
+             "AqPiGSQthUZecK3NZAtWSz/v9X0u+HRdXnoGY7LczOtUf05aMF89q1FLwJvaFJYICZoMYgRJHFLwPiOHce7fuAc40kX0wXJvipyBJ9HzCOj7CgtnC1/cmPCHR3s5AIORmroBWglm1LiFMohv1FSPEbaBD51VXxJa4JyWpYhreSOEjn1wd0lMKC9b+osV2N2tpbs+rbpQem2tRen3sWflmCqjkG5VOVwRErCuXuPb5+hYwd8BoZbfCrsiAVLd7YT44dRtKNBx6rkabWfddKSLtreHLDysOhQUVOp/XkE7OzSkWl6sky0Hva6qJJ/V726hMlomvcLHjE41iKmW2CpcZfOedg=="),
+        ];
+        for (sec1, sec2, nonce_hex, plaintext, payload) in vectors {
+            // Encrypt from A to B with the fixed nonce must reproduce the
+            // official payload byte-for-byte.
+            let pub1 = pubkey_hex(sec1).unwrap();
+            let made = {
+                let ck = conversation_key(sec1, &pubkey_hex(sec2).unwrap()).unwrap();
+                let nonce: [u8; 32] = hex::decode(nonce_hex).unwrap().try_into().unwrap();
+                let (chacha_key, chacha_nonce, hmac_key) = message_keys(&ck, &nonce);
+                let mut padded = pad(plaintext.as_bytes()).unwrap();
+                ChaCha20::new(&chacha_key.into(), &chacha_nonce.into()).apply_keystream(&mut padded);
+                let mut mac = <HmacSha256 as Mac>::new_from_slice(&hmac_key).unwrap();
+                mac.update(&nonce);
+                mac.update(&padded);
+                let tag = mac.finalize().into_bytes();
+                let mut out = vec![NIP44_VERSION];
+                out.extend_from_slice(&nonce);
+                out.extend_from_slice(&padded);
+                out.extend_from_slice(&tag);
+                BASE64.encode(&out)
+            };
+            assert_eq!(&made, payload, "encrypt vector for {plaintext:?}");
+
+            // Decrypt from B's view of A (key-role symmetry).
+            let got = nip44_decrypt(sec2, &pub1, payload).unwrap();
+            assert_eq!(got, *plaintext);
+        }
+    }
+
+    #[test]
+    fn nip44_round_trip_and_failures() {
+        let sk_a = generate_secret().unwrap();
+        let sk_b = generate_secret().unwrap();
+        let pub_b = pubkey_hex(&sk_b).unwrap();
+        let pub_a = pubkey_hex(&sk_a).unwrap();
+
+        let msg = "hello, remote signer";
+        let payload = nip44_encrypt(&sk_a, &pub_b, msg).unwrap();
+        assert_eq!(nip44_decrypt(&sk_b, &pub_a, &payload).unwrap(), msg);
+
+        // Round-trip long content across the 65536 prefix boundary.
+        let long = "x".repeat(70_000);
+        let payload = nip44_encrypt(&sk_a, &pub_b, &long).unwrap();
+        assert_eq!(nip44_decrypt(&sk_b, &pub_a, &payload).unwrap(), long);
+
+        // Wrong peer key must fail the MAC, not return garbage.
+        let stranger = generate_secret().unwrap();
+        assert!(nip44_decrypt(&sk_b, &pub_b, &payload).is_err());
+        let _ = stranger;
+
+        // Tampered payload fails.
+        let payload = nip44_encrypt(&sk_a, &pub_b, msg).unwrap();
+        let mut tampered = BASE64.decode(&payload).unwrap();
+        let n = tampered.len();
+        tampered[n - 1] ^= 0x01;
+        assert!(nip44_decrypt(&sk_b, &pub_a, &BASE64.encode(&tampered)).is_err());
+
+        // Truncated payload fails.
+        assert!(nip44_decrypt(&sk_b, &pub_a, "AAAA").is_err());
+    }
+
+    // ── BIP-340 official vectors (github.com/bitcoin/bips test vectors) ────
+
+    #[test]
+    fn bip340_reference_sign_vectors() {
+        // (seckey, pubkey, aux, msg, expected sig) — indices 0/1/2 of the
+        // official BIP-340 `bip-0340/test-vectors.csv` "should sign" set,
+        // transcribed from the file itself (x(3G) additionally verified
+        // by independent scalar-math in the review notes for this commit).
+        let vectors: &[(&str, &str, &str, &str, &str)] = &[
+            ("0000000000000000000000000000000000000000000000000000000000000003",
+             "F9308A019258C31049344F85F89D5229B531C845836F99B08601F113BCE036F9",
+             "0000000000000000000000000000000000000000000000000000000000000000",
+             "0000000000000000000000000000000000000000000000000000000000000000",
+             "E907831F80848D1069A5371B402410364BDF1C5F8307B0084C55F1CE2DCA821525F66A4A85EA8B71E482A74F382D2CE5EBEEE8FDB2172F477DF4900D310536C0"),
+            ("B7E151628AED2A6ABF7158809CF4F3C762E7160F38B4DA56A784D9045190CFEF",
+             "DFF1D77F2A671C5F36183726DB2341BE58FEAE1DA2DECED843240F7B502BA659",
+             "0000000000000000000000000000000000000000000000000000000000000001",
+             "243F6A8885A308D313198A2E03707344A4093822299F31D0082EFA98EC4E6C89",
+             "6896BD60EEAE296DB48A229FF71DFE071BDE413E6D43F917DC8DCF8C78DE33418906D11AC976ABCCB20B091292BFF4EA897EFCB639EA871CFA95F6DE339E4B0A"),
+            ("C90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B14E5C9",
+             "DD308AFEC5777E13121FA72B9CC1B7CC0139715309B086C960E18FD969774EB8",
+             "C87AA53824B4D7AE2EB035A2B5BBBCCC080E76CDC6D1692C4B0B62D798E6D906",
+             "7E2D58D8B3BCDF1ABADEC7829054F90DDA9805AAB56C77333024B9D0A508B75C",
+             "5831AAEED7B44BB74E5EAB94BA9D4294C49BCF2A60728D8B4C200F50DD313C1BAB745879A5AD954A72C45A91C3A51D3C7ADEA98D82F8481E0E1E03674A6F3FB7"),
+        ];
+        for (sk_hex, pk_hex, aux_hex, msg_hex, sig_hex) in vectors {
+            let sk_bytes = hex::decode(sk_hex).unwrap();
+            let sk = SecretKey::from_slice(&sk_bytes).unwrap();
+            let kp = Keypair::from_secret_key(&Secp256k1::new(), &sk);
+            assert_eq!(hex::encode(kp.public_key().x_only_public_key().0.serialize()).to_uppercase(), *pk_hex);
+
+            let msg: [u8; 32] = hex::decode(msg_hex).unwrap().try_into().unwrap();
+            let aux: [u8; 32] = hex::decode(aux_hex).unwrap().try_into().unwrap();
+            let sig = Secp256k1::new().sign_schnorr_with_aux_rand(
+                &Message::from_digest(msg),
+                &kp,
+                &aux,
+            );
+            assert_eq!(hex::encode(sig.serialize()).to_uppercase(), *sig_hex);
+        }
+    }
+
+    #[test]
+    fn event_signing_round_trip() {
+        let sk = generate_secret().unwrap();
+        let unsigned = r#"{"kind":22242,"content":"{\"challenge\":\"abc123\"}","tags":[["relay","ws://127.0.0.1:7777"]],"created_at":1725100000}"#;
+        let signed = sign_event(&sk, unsigned).unwrap();
+        verify_event(&signed).unwrap();
+
+        let ev: serde_json::Value = serde_json::from_str(&signed).unwrap();
+        assert_eq!(ev["kind"], 22242);
+        assert_eq!(ev["pubkey"], pubkey_hex(&sk).unwrap());
+        // Tampering with content breaks the id, which breaks verification.
+        let mut tampered = ev.clone();
+        tampered["content"] = serde_json::Value::String("nope".into());
+        assert!(verify_event(&tampered.to_string()).is_err());
+    }
+
+    #[test]
+    fn connect_uri_parsing() {
+        let uri = "nostrconnect://83f3b2ae6aa368e8275397b9c26cf550101d63ebaab900d19dd4a4429f5ad8f5?relay=wss%3A%2F%2Frelay1.example.com&perms=nip44_encrypt%2Csign_event%3A22242&name=My+Client&secret=0s8j2djs&relay=ws%3A%2F%2F192.168.1.20%3A7777";
+        let info = parse_connect_uri(uri).unwrap();
+        assert_eq!(info.client_pubkey, "83f3b2ae6aa368e8275397b9c26cf550101d63ebaab900d19dd4a4429f5ad8f5");
+        assert_eq!(
+            info.relays,
+            vec!["wss://relay1.example.com", "ws://192.168.1.20:7777"]
+        );
+        assert_eq!(info.secret, "0s8j2djs");
+        assert_eq!(info.perms, vec!["nip44_encrypt", "sign_event:22242"]);
+        assert_eq!(info.name, "My Client");
+
+        // npub client keys and unknown params tolerated — the npub is
+        // generated through our own encoder so the test carries no
+        // hand-transcribed bech32 string.
+        let sk1 = "0000000000000000000000000000000000000000000000000000000000000001";
+        let npub = npub_from_pubkey(&pubkey_hex(sk1).unwrap()).unwrap();
+        let pubkey = pubkey_from_any(&npub).unwrap();
+        let uri = format!("nostrconnect://{npub}?relay=wss://r&secret=s&future=1");
+        let info = parse_connect_uri(&uri).unwrap();
+        assert_eq!(info.client_pubkey, pubkey);
+        assert_eq!(info.relays, vec!["wss://r"]);
+
+        assert!(parse_connect_uri("bunker://abc?relay=wss://r&secret=s").is_err());
+        assert!(parse_connect_uri("nostrconnect://zz?relay=wss://r&secret=s").is_err());
+        assert!(parse_connect_uri("nostrconnect://83f3b2ae6aa368e8275397b9c26cf550101d63ebaab900d19dd4a4429f5ad8f5?name=x").is_err());
+    }
+
+    #[test]
+    fn nip04_round_trip_and_cross_check() {
+        let sk_a = generate_secret().unwrap();
+        let sk_b = generate_secret().unwrap();
+        let pub_b = pubkey_hex(&sk_b).unwrap();
+        let pub_a = pubkey_hex(&sk_a).unwrap();
+
+        let payload = nip04_encrypt(&sk_a, &pub_b, "old client hello").unwrap();
+        assert!(payload.contains("?iv="));
+        assert_eq!(nip04_decrypt(&sk_b, &pub_a, &payload).unwrap(), "old client hello");
+
+        // Wrong key must fail (PKCS#7 padding check) rather than return garbage.
+        assert!(nip04_decrypt(&sk_a, &pub_a, &payload).is_err());
+        assert!(nip04_decrypt(&sk_b, &pub_b, &payload).is_err());
+        assert!(nip04_decrypt(&sk_b, &pub_a, "not-a-payload").is_err());
+    }
+
+    #[test]
+    fn key_encoding_round_trip() {
+        let sk = generate_secret().unwrap();
+        let nsec = nsec_from_secret(&sk).unwrap();
+        assert!(nsec.starts_with("nsec1"));
+        assert_eq!(secret_from_nsec(&nsec).unwrap(), sk);
+        assert_eq!(secret_from_any(&nsec).unwrap(), sk);
+        assert_eq!(secret_from_any(&sk).unwrap(), sk);
+
+        let pk = pubkey_hex(&sk).unwrap();
+        let npub = npub_from_pubkey(&pk).unwrap();
+        assert!(npub.starts_with("npub1"));
+        assert_eq!(pubkey_from_any(&npub).unwrap(), pk);
+        assert_eq!(pubkey_from_any(&pk).unwrap(), pk);
+
+        // The famous even-y lift edge case: pubkey of sk=1 is x(G) (y is odd);
+        // shared_x with oneself is exactly x(G) — pins the unhashed-x ECDH and
+        // the even-parity lift in one assertion (x is invariant under y-negation,
+        // so the lift is safe for NIP-44/NIP-04 keys).
+        let g_x = "79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798";
+        assert_eq!(
+            pubkey_hex("0000000000000000000000000000000000000000000000000000000000000001").unwrap(),
+            g_x
+        );
+        assert_eq!(
+            hex::encode(
+                shared_x("0000000000000000000000000000000000000000000000000000000000000001", g_x).unwrap()
+            ),
+            g_x
+        );
+        assert!(secret_from_nsec("npub1").is_err());
+    }
+
+    /// The mesh ULA is a PURE function of the node's public key:
+    /// `fd ‖ sha256(x-only pubkey)[0..15]` (fips identity/node_addr.rs →
+    /// identity/address.rs). That is what makes "address by npub" work —
+    /// Termux's fipssh helper, and any future DNS-style resolver, just
+    /// computes what the fips daemon's DNS answers.
+    #[test]
+    fn npub_derives_the_same_mesh_ula_as_the_fips_identity() {
+        for seed in [0x42u8, 0x07, 0x31] {
+            // 0xff… would exceed the curve order — secret keys must be valid scalars.
+            let secret = [seed; 32];
+            let id = fips::Identity::from_secret_bytes(&secret).unwrap();
+            let npub = id.npub();
+            let expected = id.address().to_ipv6().to_string();
+
+            let pubkey_hex = pubkey_from_any(&npub).unwrap();
+            let pk = hex::decode(&pubkey_hex).unwrap();
+            let mut hasher = Sha256::new();
+            hasher.update(&pk);
+            let hash = hasher.finalize();
+            let mut ula = [0u8; 16];
+            ula[0] = 0xfd;
+            ula[1..].copy_from_slice(&hash[..15]);
+            assert_eq!(std::net::Ipv6Addr::from(ula).to_string(), expected, "npub {npub}");
+        }
+    }
+}

Android/tools/fipssh

@@ -0,0 +1,145 @@
+#!/data/data/com.termux/files/usr/bin/sh
+# fipssh — SSH to an Archipelago FIPS mesh node BY NPUB.
+#
+# The mesh ULA is a pure function of the node's public key (verified against
+# the fips crate itself — archy-fips-core's npub_derives_the_same_mesh_ula
+# test, and the Android tools commit that shipped this script):
+#
+#     ula = fd || sha256(x-only pubkey)[0..15]
+#
+# so the npub IS the address: no DNS server, no mesh query, works offline.
+# The node's fips daemon answers the same question through its DNS resolver
+# (core/archipelago/src/fips/dial.rs) — this is the phone-side equivalent.
+#
+# Setup (Termux):     pkg install python openssh
+# Usage:
+#   fipssh <user>@npub1… [ssh args…]   connect
+#   fipssh npub1…                      connect as $FIPSSH_USER
+#   fipssh --resolve npub1…            print the ULA and exit
+#
+# The companion's split tunnel carries the connection (fd00::/8 routes the
+# whole device while the mesh is up) — at home on LAN, away via the anchors.
+# The node still has to allow port 22 through its fips0 firewall: see
+# docs/HANDOFF-2026-08-31-ssh-over-mesh.md (the interim 90-ssh.nft drop-in,
+# restricted to your phone's ULA, until the node-side toggle ships).
+set -eu
+
+usage() {
+    sed -n '2,20p' "$0" | sed 's/^# \{0,1\}//'
+    exit 1
+}
+
+RESOLVE_ONLY=0
+if [ "${1:-}" = "--resolve" ]; then
+    RESOLVE_ONLY=1
+    shift
+fi
+[ $# -ge 1 ] || usage
+
+TARGET="$1"
+shift 2>/dev/null || true
+
+case "$TARGET" in
+    *npub1*)
+        case "$TARGET" in
+            *@npub1*) USER_PART="${TARGET%%@*}"; N_PUB="${TARGET#*@}" ;;
+            npub1*)
+                USER_PART="${FIPSSH_USER:-}"
+                N_PUB="$TARGET"
+                if [ -z "$USER_PART" ] && [ "$RESOLVE_ONLY" = 0 ]; then
+                    echo "fipssh: no user given (use user@npub… or set FIPSSH_USER)" >&2
+                    exit 1
+                fi
+                ;;
+            *) echo "fipssh: expected [user@]npub1…, got '$TARGET'" >&2; exit 1 ;;
+        esac
+        ;;
+    *) echo "fipssh: '$TARGET' is not an npub (expected [user@]npub1…)" >&2; exit 1 ;;
+esac
+
+command -v python3 >/dev/null 2>&1 || {
+    echo "fipssh: python3 not found — run: pkg install python" >&2
+    exit 1
+}
+
+ULA=$(python3 - "$N_PUB" <<'PYEOF'
+import hashlib, ipaddress, sys
+
+CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
+
+
+def bech32_polymod(values):
+    gen = [0x3B6A57B2, 0x26508E6D, 0x1EA119FA, 0x3D4233DD, 0x2A1462B3]
+    chk = 1
+    for value in values:
+        top = chk >> 25
+        chk = (chk & 0x1FFFFFF) << 5 ^ value
+        for i in range(5):
+            chk ^= gen[i] if ((top >> i) & 1) else 0
+    return chk
+
+
+def bech32_hrp_expand(hrp):
+    return [ord(c) >> 5 for c in hrp] + [0] + [ord(c) & 31 for c in hrp]
+
+
+def bech32_verify_checksum(hrp, data):
+    return bech32_polymod(bech32_hrp_expand(hrp) + data) == 1
+
+
+def bech32_decode(s):
+    if any(ord(c) < 33 or ord(c) > 126 for c in s):
+        raise ValueError("bad character")
+    if s.lower() != s and s.upper() != s:
+        raise ValueError("mixed case")
+    s = s.lower()
+    pos = s.rfind("1")
+    if pos < 1 or pos + 7 > len(s) or len(s) > 90:
+        raise ValueError("bad separator")
+    hrp = s[:pos]
+    data = [CHARSET.find(c) for c in s[pos + 1:]]
+    if -1 in data:
+        raise ValueError("bad data character")
+    if not bech32_verify_checksum(hrp, data):
+        raise ValueError("bad checksum — typo in the npub?")
+    return hrp, data[:-6]
+
+
+def convertbits(data, frombits, tobits):
+    acc = 0
+    bits = 0
+    ret = bytearray()
+    maxv = (1 << tobits) - 1
+    for value in data:
+        if value < 0 or (value >> frombits):
+            raise ValueError("bad value")
+        acc = (acc << frombits) | value
+        bits += frombits
+        while bits >= tobits:
+            bits -= tobits
+            ret.append((acc >> bits) & maxv)
+    if bits >= frombits or ((acc << (tobits - bits)) & maxv):
+        raise ValueError("bad padding")
+    return bytes(ret)
+
+
+npub = sys.argv[1]
+hrp, data = bech32_decode(npub)
+if hrp != "npub":
+    raise ValueError(f"expected hrp 'npub', got '{hrp}'")
+pubkey = convertbits(data, 5, 8)
+if len(pubkey) != 32:
+    raise ValueError(f"npub data must be 32 bytes, got {len(pubkey)}")
+# ula = fd || sha256(pubkey)[0..15] — mirrors fips identity/node_addr.rs +
+# identity/address.rs (FIPS_ADDRESS_PREFIX = 0xfd).
+ula = bytes([0xFD]) + hashlib.sha256(pubkey).digest()[:15]
+print(ipaddress.IPv6Address(ula).compressed)
+PYEOF
+) || exit 1
+
+if [ "$RESOLVE_ONLY" = 1 ]; then
+    echo "$ULA"
+    exit 0
+fi
+
+exec ssh "${USER_PART}@${ULA}" "$@"

Android/tools/nip46-test-client.py

@@ -0,0 +1,384 @@
+#!/usr/bin/env python3
+"""
+NIP-46 test client for the Archipelago companion's Remote Signer (#139).
+
+Plays the role the node's login flow will play (rust-nostr nostr-connect
+client): generates a nostrconnect:// pairing QR, connects to a relay, waits
+for the phone's bunker `connect` (secret echo), acks it, then exercises
+get_public_key + sign_event and VERIFIES the returned schnorr signature with
+independent pure-Python BIP-340 code (no shared code with the phone's Rust).
+
+Run it on your computer next to the phone:
+
+    python3 -m venv /tmp/nip46env
+    /tmp/nip46env/bin/pip install websockets qrcode
+    /tmp/nip46env/bin/python Android/tools/nip46-test-client.py [--relay wss://relay.damus.io]
+
+…then on the phone: hub menu (three-finger hold) → Remote Signer →
+Generate key (once) → Scan pairing QR → point at the terminal QR → Approve.
+
+Pure Python (no deps for the crypto; websockets + qrcode for transport/QR).
+"""
+import argparse
+import asyncio
+import base64
+import hashlib
+import hmac
+import json
+import os
+import secrets
+import struct
+import sys
+import time
+import urllib.parse
+
+import websockets  # pip install websockets
+
+# ── secp256k1 / BIP-340 (independent of the phone's Rust code) ──────────────
+
+P = 2**256 - 2**32 - 977
+N = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141
+GX = 0x79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798
+GY = 0x483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8
+G = (GX, GY)
+
+
+def _add(pt1, pt2):
+    if pt1 is None:
+        return pt2
+    if pt2 is None:
+        return pt1
+    x1, y1 = pt1
+    x2, y2 = pt2
+    if x1 == x2 and (y1 + y2) % P == 0:
+        return None
+    if pt1 == pt2:
+        lam = (3 * x1 * x1) * pow(2 * y1, -1, P) % P
+    else:
+        lam = (y2 - y1) * pow(x2 - x1, -1, P) % P
+    x3 = (lam * lam - x1 - x2) % P
+    return (x3, (lam * (x1 - x3) - y1) % P)
+
+
+def _mul(k, pt):
+    r = None
+    while k:
+        if k & 1:
+            r = _add(r, pt)
+        pt = _add(pt, pt)
+        k >>= 1
+    return r
+
+
+def lift_x(x):
+    if x >= P:
+        return None
+    y_sq = (pow(x, 3, P) + 7) % P
+    y = pow(y_sq, (P + 1) // 4, P)
+    if y * y % P != y_sq:
+        return None
+    return (x, y if y % 2 == 0 else P - y)
+
+
+def tagged(tag: bytes, data: bytes) -> bytes:
+    """BIP-340 tagged hash: sha256(hash(tag) || hash(tag) || data)."""
+    th = hashlib.sha256(tag).digest()
+    return hashlib.sha256(th + th + data).digest()
+
+
+def bip340_sign(msg: bytes, seckey: int, aux: bytes) -> bytes:
+    d = seckey if seckey <= N - 1 else seckey - N
+    pub = _mul(d, G)
+    if pub[1] % 2 != 0:
+        d = N - d
+    t = bytes(a ^ b for a, b in zip(d.to_bytes(32, "big"), tagged(b"BIP0340/aux", aux)))
+    rand = tagged(b"BIP0340/nonce", t + pub[0].to_bytes(32, "big") + msg)
+    k = int.from_bytes(rand, "big") % N
+    assert k > 0
+    R = _mul(k, G)
+    if R[1] % 2 != 0:
+        k = N - k
+    e = int.from_bytes(tagged(b"BIP0340/challenge", R[0].to_bytes(32, "big") + pub[0].to_bytes(32, "big") + msg), "big") % N
+    return R[0].to_bytes(32, "big") + ((k + e * d) % N).to_bytes(32, "big")
+
+
+def bip340_verify(msg: bytes, pubkey_x: bytes, sig: bytes) -> bool:
+    """Check s·G − e·P == R with even-y R and x(R) == r (BIP-340)."""
+    if len(sig) != 64 or len(pubkey_x) != 32:
+        return False
+    pub = lift_x(int.from_bytes(pubkey_x, "big"))
+    if pub is None:
+        return False
+    r = int.from_bytes(sig[:32], "big")
+    s = int.from_bytes(sig[32:], "big")
+    if r >= P or s >= N:
+        return False
+    e = int.from_bytes(tagged(b"BIP0340/challenge", sig[:32] + pubkey_x + msg), "big") % N
+    sg = _mul(s, G)
+    ep = _mul(e, pub)
+    neg_ep = (ep[0], (P - ep[1]) % P)
+    rp = _add(sg, neg_ep)
+    return rp is not None and rp[0] == r and rp[1] % 2 == 0
+
+
+def ecdh_x(secret_hex: str, peer_x_hex: str) -> bytes:
+    """Raw ECDH x-coordinate against an x-only peer key (even-y lift)."""
+    peer = lift_x(int(peer_x_hex, 16))
+    assert peer is not None, "peer pubkey not on curve"
+    pt = _mul(int(secret_hex, 16) % N, peer)
+    return pt[0].to_bytes(32, "big")
+
+
+# ── NIP-44 v2 (pure python, spec-literal) ────────────────────────────────────
+
+def hkdf_extract(salt: bytes, ikm: bytes) -> bytes:
+    return hmac.new(salt, ikm, hashlib.sha256).digest()
+
+
+def hkdf_expand(prk: bytes, info: bytes, length: int) -> bytes:
+    t = b""
+    out = b""
+    i = 1
+    while len(out) < length:
+        t = hmac.new(prk, t + info + bytes([i]), hashlib.sha256).digest()
+        out += t
+        i += 1
+    return out[:length]
+
+
+def _rotl(x: int, n: int) -> int:
+    return ((x << n) | (x >> (32 - n))) & 0xFFFFFFFF
+
+
+def _qr(s, a, b, c, d):
+    s[a] = (s[a] + s[b]) & 0xFFFFFFFF; s[d] ^= s[a]; s[d] = _rotl(s[d], 16)
+    s[c] = (s[c] + s[d]) & 0xFFFFFFFF; s[b] ^= s[c]; s[b] = _rotl(s[b], 12)
+    s[a] = (s[a] + s[b]) & 0xFFFFFFFF; s[d] ^= s[a]; s[d] = _rotl(s[d], 8)
+    s[c] = (s[c] + s[d]) & 0xFFFFFFFF; s[b] ^= s[c]; s[b] = _rotl(s[b], 7)
+
+
+def chacha20_block(key: bytes, counter: int, nonce: bytes) -> bytes:
+    consts = [0x61707865, 0x3320646E, 0x79622D32, 0x6B206574]
+    state = consts + list(struct.unpack("<8I", key)) + [counter] + list(struct.unpack("<3I", nonce))
+    working = list(state)
+    for _ in range(10):
+        _qr(working, 0, 4, 8, 12); _qr(working, 1, 5, 9, 13)
+        _qr(working, 2, 6, 10, 14); _qr(working, 3, 7, 11, 15)
+        _qr(working, 0, 5, 10, 15); _qr(working, 1, 6, 11, 12)
+        _qr(working, 2, 7, 8, 13); _qr(working, 3, 4, 9, 14)
+    return struct.pack("<16I", *[(x + y) & 0xFFFFFFFF for x, y in zip(working, state)])
+
+
+def chacha20(key: bytes, nonce: bytes, data: bytes) -> bytes:
+    counter = 0  # NIP-44: "ChaCha20 (RFC 8439) with starting counter set to 0"
+    out = bytearray()
+    for i in range(0, len(data), 64):
+        ks = chacha20_block(key, counter, nonce)
+        chunk = data[i:i + 64]
+        out += bytes(a ^ b for a, b in zip(chunk, ks))
+        counter += 1
+    return bytes(out)
+
+
+def calc_padded_len(n: int) -> int:
+    if n <= 32:
+        return 32
+    power = 1 << ((n - 1).bit_length())
+    chunk = 32 if power <= 256 else power // 8
+    return chunk * ((n - 1) // chunk + 1)
+
+
+def nip44_encrypt(secret_hex: str, peer_hex: str, plaintext: str) -> str:
+    ck = hkdf_extract(b"nip44-v2", ecdh_x(secret_hex, peer_hex))
+    nonce = secrets.token_bytes(32)
+    okm = hkdf_expand(ck, nonce, 76)
+    key, iv, mac_key = okm[:32], okm[32:44], okm[44:76]
+    pt = plaintext.encode()
+    padded = (len(pt).to_bytes(2, "big") if len(pt) < 65536 else b"\x00\x00" + len(pt).to_bytes(4, "big")) + pt
+    padded += b"\x00" * (calc_padded_len(len(pt)) - len(pt))
+    ct = chacha20(key, iv, padded)
+    mac = hmac.new(mac_key, nonce + ct, hashlib.sha256).digest()
+    return base64.b64encode(bytes([2]) + nonce + ct + mac).decode()
+
+
+def nip44_decrypt(secret_hex: str, peer_hex: str, payload: str) -> str:
+    data = base64.b64decode(payload)
+    assert data[0] == 2, "only NIP-44 v2 supported"
+    nonce, ct, mac = data[1:33], data[33:-32], data[-32:]
+    ck = hkdf_extract(b"nip44-v2", ecdh_x(secret_hex, peer_hex))
+    okm = hkdf_expand(ck, nonce, 76)
+    key, iv, mac_key = okm[:32], okm[32:44], okm[44:76]
+    assert hmac.compare_digest(hmac.new(mac_key, nonce + ct, hashlib.sha256).digest(), mac), "bad MAC"
+    padded = chacha20(key, iv, ct)
+    ln = int.from_bytes(padded[:2], "big")
+    body = padded[2:2 + ln] if ln else padded[6:6 + int.from_bytes(padded[2:6], "big")]
+    return body.decode()
+
+
+# ── nostr events ─────────────────────────────────────────────────────────────
+
+def event_id(pubkey_hex: str, created_at: int, kind: int, tags, content: str) -> str:
+    serialized = json.dumps([0, pubkey_hex, created_at, kind, tags, content], separators=(",", ":"))
+    return hashlib.sha256(serialized.encode()).hexdigest()
+
+
+def sign_event(secret_hex: str, event: dict) -> dict:
+    eid = event_id(event["pubkey"], event["created_at"], event["kind"], event["tags"], event["content"])
+    ev = dict(event)
+    ev["id"] = eid
+    ev["sig"] = bip340_sign(bytes.fromhex(eid), int(secret_hex, 16), os.urandom(32)).hex()
+    return ev
+
+
+# ── the client session ────────────────────────────────────────────────────────
+
+def compact(d) -> str:
+    return json.dumps(d, separators=(",", ":"))
+
+
+async def run(relay: str):
+    client_secret = os.urandom(32).hex()
+    client_secret_int = int(client_secret, 16) % N
+    client_pub_hex = _mul(client_secret_int, G)[0].to_bytes(32, "big").hex()
+    pair_secret = secrets.token_hex(16)
+    nonce = secrets.token_hex(8)
+
+    uri = (
+        f"nostrconnect://{client_pub_hex}"
+        f"?relay={urllib.parse.quote(relay, safe='')}"
+        f"&secret={pair_secret}"
+        f"&name=Archipelago+Test+Client"
+    )
+
+    print(f"· client key  : {client_pub_hex}")
+    print(f"· relay       : {relay}")
+    print()
+    print("Scan this QR with: Companion → hub (3-finger) → Remote Signer → Scan pairing QR")
+    print()
+
+    try:
+        import qrcode
+        qr = qrcode.QRCode(border=1)
+        qr.add_data(uri)
+        qr.make(fit=True)
+        qr.print_ascii(invert=True)
+    except ImportError:
+        print(uri)
+
+    print()
+    print("Waiting for the phone to pair (connect, ack, get_public_key, sign_event)…")
+
+    async with websockets.connect(relay, max_size=2**22) as ws:
+        await ws.send(compact(["REQ", "test", {"kinds": [24133], "#p": [client_pub_hex], "since": int(time.time()) - 60}]))
+
+        signer_pub = None
+        acked = False
+        requests = []
+
+        def send_frame(content: dict):
+            assert signer_pub is not None
+            ev = {
+                "pubkey": client_pub_hex,
+                "created_at": int(time.time()),
+                "kind": 24133,
+                "tags": [["p", signer_pub]],
+                "content": nip44_encrypt(client_secret, signer_pub, compact(content)),
+            }
+            return asyncio.ensure_future(ws.send(compact(["EVENT", sign_event(client_secret, ev)])))
+
+        async def request(method, params, rid):
+            send_frame({"id": rid, "method": method, "params": params})
+
+        timeout = time.time() + 120
+        got_pubkey = None
+        signed_event = None
+
+        while time.time() < timeout:
+            try:
+                raw = await asyncio.wait_for(ws.recv(), timeout=timeout - time.time())
+            except (asyncio.TimeoutError, TimeoutError):
+                break
+            arr = json.loads(raw)
+            if not isinstance(arr, list) or len(arr) < 3 or arr[0] != "EVENT":
+                continue
+            ev = arr[2]
+            if ev.get("kind") != 24133 or ev.get("pubkey") == client_pub_hex:
+                continue
+            author = ev["pubkey"]
+            try:
+                msg = json.loads(nip44_decrypt(client_secret, author, ev["content"]))
+            except Exception:
+                continue
+
+            if "method" in msg and msg["method"] == "connect":
+                params = msg.get("params", [])
+                if params and params[0] == author and (len(params) < 2 or params[1] == pair_secret):
+                    signer_pub = author
+                    print(f"✓ phone paired  — signer pubkey {author[:16]}…")
+                    send_frame({"id": msg["id"], "result": "ack"})
+                    acked = True
+                    await asyncio.sleep(0.5)
+                    await request("get_public_key", [], nonce + "-gpk")
+                else:
+                    print("✗ phone sent connect but the secret didn't match")
+                    return 1
+                continue
+
+            if "result" in msg or "error" in msg:
+                rid = msg.get("id", "")
+                if "error" in msg:
+                    print(f"✗ error for {rid}: {msg['error']}")
+                    if rid.endswith("-sign"):
+                        return 1
+                    continue
+                result = msg.get("result", "")
+                if rid.endswith("-gpk"):
+                    got_pubkey = result
+                    print(f"✓ get_public_key → {result}")
+                    await request(
+                        "sign_event",
+                        [compact({
+                            "kind": 1,
+                            "content": "Hello from the Archipelago NIP-46 test client — approved by hand.",
+                            "tags": [],
+                            "created_at": int(time.time()),
+                        })],
+                        nonce + "-sign",
+                    )
+                elif rid.endswith("-sign"):
+                    signed_event = json.loads(result)
+                    print(f"✓ sign_event → signed event {signed_event.get('id', '')[:16]}…")
+                    break
+
+        if not acked:
+            print("✗ the phone never connected (2-minute timeout)")
+            return 1
+        if got_pubkey is None or got_pubkey != signer_pub:
+            print("✗ get_public_key missing or mismatched")
+            return 1
+        if signed_event is None:
+            return 1
+
+        ev = signed_event
+        expected_id = event_id(ev["pubkey"], ev["created_at"], ev["kind"], ev["tags"], ev["content"])
+        ok_id = expected_id == ev["id"]
+        ok_sig = bip340_verify(bytes.fromhex(expected_id), bytes.fromhex(ev["pubkey"]), bytes.fromhex(ev["sig"]))
+        print(f"· event id correct : {ok_id}")
+        print(f"· schnorr signature: {'VERIFIED ✓' if ok_sig else 'INVALID ✗'}")
+        if ok_id and ok_sig:
+            print()
+            print("END-TO-END PASS — the companion signed as the identity the phone holds,")
+            print("and the signature verifies under an independent BIP-340 implementation.")
+            return 0
+        return 1
+
+
+def main():
+    ap = argparse.ArgumentParser()
+    ap.add_argument("--relay", default="wss://relay.damus.io", help="any nostr relay both devices can reach")
+    args = ap.parse_args()
+    sys.exit(asyncio.run(run(args.relay)))
+
+
+if __name__ == "__main__":
+    main()

docs/HANDOFF-2026-08-31-ssh-over-mesh.md

@@ -0,0 +1,116 @@
+# HANDOFF — SSH over the FIPS mesh (node-side toggle), 2026-08-31
+
+**For: the node OS agent.** From the companion agent, mid-0.5.28 testing. The
+user wants to SSH their node from Termux over the phone's FIPS mesh instead
+of keeping Tailscale around for it — the phone side is done and verified; the
+remaining work is all node-side, and it wants to be a **first-class settings
+toggle**, not a hand-edited firewall rule.
+
+## What already works (do not rebuild this)
+
+- The companion's embedded mesh is a **device-wide split tunnel**
+  (`ArchyVpnService` routes `fd00::/8` for the whole phone, no per-app
+  filter, `allowBypass`). Termux — or any app — reaches mesh addresses with
+  zero setup while the tunnel is up, on-LAN and away (anchor path).
+- The hub's Nodes page now **displays and copies each FIPS node's `fips0`
+  ULA** (committed on `companion/0.5.28`).
+- Verified live today: `ssh user@<node-ULA>` from Termux answers **RST** —
+  the path works end-to-end; something on the node is doing the refusing.
+
+## The diagnosis (from today's field test + code read)
+
+1. **`fips0` is default-deny inbound.** The hardening baseline
+   (`/etc/fips/fips.nft`, provisioned out-of-band) rejects un-allowlisted
+   ports with RST — the exact symptom the web-UI drop-in's comment documents
+   on :80 (`core/archipelago/src/fips/config.rs` ~L237). The daemon's own
+   drop-ins (`/etc/fips/fips.d/80-web-ui.nft`: 80/8443/5679,
+   `85-app-ports.nft`: app launch ports) **do not include 22**.
+2. **sshd IPv6 listening is unverified.** `fips0` is IPv6-only; a sshd pinned
+   to `ListenAddress 0.0.0.0` RSTs on the ULA identically. The image installs
+   and enables openssh-server (`image-recipe/archipelago-scripts/install-to-disk.sh`
+   L177/L210) with default config (binds `::`), but a preflight in the toggle
+   should confirm rather than assume.
+
+**Interim manual unblock (what the user can do today, keep valid):**
+`/etc/fips/fips.d/90-ssh.nft` containing `ip6 saddr <phone-ULA> tcp dport 22
+accept`, then `sudo nft -f /etc/fips/fips.nft`. A daemon-owned toggle must
+**own that file name/lifecycle** so a hand-added rule and the feature don't
+fight over the same slot.
+
+## The ask: a "SSH over mesh" toggle
+
+The user's instinct (seconded here): **a setting in the FIPS/network area of
+the node UI**, default **off**. Sketch:
+
+- **UI**: a small settings card in the pattern of
+  `neode-ui/src/views/settings/` (see `TransportPrefsCard.vue` for a
+  segmented-pref card + vitest). Toggle + a source-scope selector +
+  preflight status rows.
+- **RPC**: `fips.ssh-over-mesh.get` / `fips.ssh-over-mesh.set` (dispatch arm
+  in `core/archipelago/src/api/rpc/dispatcher.rs` alongside the existing
+  `fips.*` arms at ~L544; handler in `api/rpc/fips.rs`). Persisted with the
+  other fips daemon-config state.
+- **Enforcement**: mirror the existing drop-in lifecycle in
+  `core/archipelago/src/fips/config.rs` (~L243–320): when the toggle is on,
+  write `/etc/fips/fips.d/90-ssh.nft` on every daemon config install and on
+  toggle change; when off, remove it. Reload stays
+  `sudo nft -f /etc/fips/fips.nft`. Never touch `80-web-ui.nft` /
+  `85-app-ports.nft`.
+- **Source scope** (the design decision worth an issue thread):
+  - *Paired phones only* — restricts to the phone ULAs/npubs the node has
+    actually paired with. Open question: does the node durably know which
+    inbound peers are "its" phones? FIPS accepts inbound peers without prior
+    registration, so this may need a small persisted "trusted peers" list
+    (seeded when `fips.pair-info` is issued, or on first successful dial).
+    Recommended default if the data can be made reliable.
+  - *Custom source list* — raw ULA list, per-rule `ip6 saddr <ula> …`
+    entries. Escape hatch; fine to ship alongside.
+  - *Any mesh peer* — what the user literally asked for, but flag it
+    honestly in the UI: with no registration requirement, this faces port 22
+    at every peer that can route to the node over the mesh. If offered at
+    all, gate it behind the same "I understand" confirmation pattern as
+    other danger-zone settings.
+- **Preflights, surfaced in the card**: sshd enabled + listening on IPv6
+  (`[::]:22` or `*:22` via `ss -tln`), and whether
+  `PasswordAuthentication` is on — if it is, show a keys-only recommendation
+  (the firewall restriction is the belt; this is the suspenders).
+
+## Acceptance (on-device)
+
+- [ ] Toggle on, phone on LAN: `ssh user@<node-ULA>` from Termux connects.
+- [ ] Phone away from LAN (anchor path): same result.
+- [ ] Toggle off: connection refused again; `90-ssh.nft` gone.
+- [ ] Daemon config install (upgrade/restart) preserves the on-state and
+      the rule; nothing duplicated.
+- [ ] Non-default source scope actually restricts (try from a second mesh
+      peer, or a wrong ULA).
+- [ ] Settings UI survives a page reload; RPC has a vitest like
+      `TransportPrefsCard.test.ts`.
+
+## Addendum (2026-08-31, same day): the npub IS the address
+
+While wiring this up we confirmed the mesh ULA is a **pure function of the
+public key** — `fd ‖ sha256(x-only pubkey)[0..15]` (`fips/src/identity/node_addr.rs`
+`from_pubkey` → `identity/address.rs` `from_node_addr`,
+`FIPS_ADDRESS_PREFIX = 0xfd`). The daemon's DNS resolver (`fips/dial.rs`) just
+answers what anyone can compute. Consequences for the node side:
+
+- Docs/UI can advertise `ssh <user>@npub1…`-style addressing: Termux's
+  `Android/tools/fipssh` (shipped with the companion work) derives the ULA
+  from the npub with zero infrastructure, verified byte-identical against
+  the fips crate (`archy-fips-core` test
+  `npub_derives_the_same_mesh_ula_as_the_fips_identity`).
+- If the settings toggle from this handover ever grows a "copy command"
+  affordance, `fipssh <user>@<npub>` is the natural shape (npub, not ULA —
+  it is the durable identity; the ULA follows from it).
+- No node-side DNS surface is required for the SSH case; the resolver stays
+  what it is today (the node's own peer dials).
+
+## Working rules
+
+Same as the queue handoffs: small commits, tracker issue for this feature
+(`ssh-over-mesh`), and the companion agent is downstream-only here — no
+companion changes are required (the phone already routes and displays the
+ULA). Optional nicety later, NOT part of this issue: the companion's FIPS
+hub page could one day surface the toggle state — only worth it if the
+`fips.ssh-over-mesh.get` RPC is trivial to add to the existing status call.

docs/companion-backup-restore.md

@@ -0,0 +1,88 @@
+# Companion backup & restore — the phone side of a border crossing (#128)
+
+**Status:** shipped in companion 0.5.28 (vc48). Issue: #128 ("Graphene phone
+backup/restore — part of the companion app or passport prime combo").
+
+## The problem
+
+The companion holds real secrets: node addresses and login passwords, the
+phone's FIPS mesh identity (which nodes peer with), and — since 0.5.28 — the
+remote-signer key. Losing the phone, or wiping it to cross a border, loses all
+of it. On GrapheneOS there is no cloud backup and there should be none here
+either: the export is a plain file the user saves wherever they choose (USB
+drive, computer, a folder synced their way), sealed with a passphrase.
+
+## The envelope — the node's, not a second format
+
+Backups use the node's ADR-005 encrypted-backup envelope
+(`core/archipelago/src/backup/identity.rs`), byte-for-byte:
+
+- Argon2id key derivation (RustCrypto `argon2`, default params — same as the
+  node's `Argon2::default()`), passphrase in, 16-byte random salt.
+- ChaCha20-Poly1305 AEAD with a 12-byte random nonce.
+- Envelope JSON:
+  `{"version": 1, "kind": "companion", "encrypted": true, "blob": "<base64(salt‖nonce‖ct)>", "timestamp": "<rfc3339>"}`
+- The native code (`Android/rust/archy-fips-core/src/backup.rs`) is the same
+  crate family as the node's backup code; `decrypt` ignores unknown envelope
+  fields, so a **node** identity backup (which carries `did`/`pubkey`/`kid`)
+  also decrypts here — one envelope, two producers.
+
+The encrypted payload is the companion's own JSON:
+
+```json
+{
+  "app": "archipelago-companion",
+  "payloadVersion": 1,
+  "appVersion": "0.5.28",
+  "createdAt": 1725100000,
+  "servers": ["<serialized ServerEntry>", …],
+  "active": "<serialized ServerEntry or null>",
+  "fips": {"secret","npub","address","peers","partyPeers","partyName","partyListen"},
+  "signer": {"secret": "<hex>"},
+  "flags": {"introSeen": true}
+}
+```
+
+## Where the code lives
+
+- **Crypto:** `Android/rust/archy-fips-core/src/backup.rs` (+ JNI
+  `NativeCore.backupEncrypt/Decrypt`). Host `cargo test` covers round-trip,
+  wrong-passphrase, tampered-blob, node-shape envelopes, and salt/nonce
+  freshness.
+- **Payload/merge:** `BackupManager` (`Android/app/src/main/java/com/archipelago/app/data/BackupManager.kt`).
+- **UI:** a hub sub-page (`ui/components/BackupSection.kt`, opened from the
+  three-finger hub menu like Nodes/FIPS) — SAF file picker
+  (`CreateDocument` for export, `OpenDocument` for import), passphrase
+  fields, verified-backup preview, result summary. The suggested export
+  name is `archy-companion-backup-YYYYMMDD-HHmmss.json`.
+
+## Restore semantics — never silently destructive
+
+| What | On restore |
+|---|---|
+| Servers | Upsert (`ServerPreferences.upsertServer`): same npub merges (even when every address changed), new ones append |
+| Active server | Set only when this phone has none (the fresh-wipe case) |
+| FIPS identity | Restored only when this phone has none; node peers UNION by npub (`FipsPreferences.mergePeersJson`); party peers merge by npub |
+| Signer key | Restored only when this phone has none |
+| introSeen flag | Restored (no re-onboarding after a restore) |
+
+The identity rules exist because a phone that already paired has a live mesh
+identity nodes peer with; swapping it in from a backup would strand the
+current pairing.
+
+## Test checklist (on-device)
+
+- [ ] Export → file saved, `version: 1`, `kind: companion`, base64 blob ≥ 44 chars.
+- [ ] Wrong passphrase on import → "wrong passphrase" error, no state change.
+- [ ] Correct passphrase → preview shows the right server count; restore on a
+      second install (or after clearing app data) reconnects to the node
+      without re-pairing, mesh included.
+- [ ] Re-scan the node's QR after restore → no duplicate entry.
+- [ ] The old phone's password for a node restores (login works on the new phone).
+
+## Roadmap notes (node-side, tracked separately)
+
+Node-side storage/quota/scheduling for companion backups ("passport prime
+combo") is roadmap territory — this issue's scope was the phone side. The
+envelope is ready to be a drop-in for the node's existing backup RPCs when
+that lands.

docs/companion-nip46-remote-signer.md

@@ -0,0 +1,108 @@
+# Companion NIP-46 remote signer — the phone side of Nostr Bunker (#139)
+
+**Status:** shipped in companion 0.5.28 (vc48). Issue: #139 ("Remote signer
+with companion app?"). Background research:
+[`nostr-signer-login-research.md`](nostr-signer-login-research.md) — flow B of
+that document is exactly the flow this implements, with the companion playing
+the role the research assigned to Amber.
+
+## What shipped: the phone IS the bunker (remote signer)
+
+The companion holds a nostr key (generate or import an `nsec`) and speaks
+NIP-46 as the **remote signer**:
+
+1. A NIP-46 client — the node's login page, per the research doc's flow B,
+   or any `nostrconnect://`-emitting app — shows its pairing QR.
+2. The phone scans it (hub → **Remote Signer** → *Scan pairing QR*), or any
+   QR-scanner app hands the `nostrconnect://` URI over as a deep link
+   (registered in the manifest).
+3. The phone connects to the client's relay(s), subscribes to kind-24133
+   events p-tagged to its own key, and sends the `connect` request carrying
+   the secret — the same handshake direction rust-nostr's reference bunker
+   uses (`NostrConnectRemoteSigner::send_connect_ack`), which is what the
+   node's eventual nostr-connect client will wait for.
+4. Requests arrive NIP-44-encrypted. Handled methods:
+   - `connect` → "ack" (validates our pubkey + the pairing secret)
+   - `get_public_key` → our pubkey
+   - `describe` → method list
+   - `ping` → "pong"
+   - **`sign_event` → an approve/deny card — kind label, content, tags,
+     time. Nothing signs without a thumb on Approve.** Deny replies
+     `"denied"`; a second request while one is pending replies `"busy"`
+     instead of replacing the visible card.
+   - anything else → `"not authorized"` (nip04/nip44 encrypt/decrypt are
+     deliberately NOT granted in v1).
+5. Responses go back over the same encrypted kind-24133 channel.
+
+The session lives while the app does (the login handshake takes seconds);
+remembered-session auto-reconnect is the research doc's deferred flow C, and
+stays deferred. NIP-04 is accepted on receive as a fallback (deprecated but
+still spoken by real clients); all sending is NIP-44 v2.
+
+## Where the code lives
+
+- **Crypto:** `Android/rust/archy-fips-core/src/nostr.rs` — nsec/npub bech32
+  keys, BIP-340 schnorr event signing (NIP-01 id serialization), NIP-44 v2
+  payloads, NIP-04 fallback, `nostrconnect://` parsing. Host `cargo test`
+  runs the official NIP-44 vectors (conversation/message keys, padded
+  lengths, byte-exact encrypt vectors), the official BIP-340 sign vectors,
+  and round-trip/tamper/failure cases.
+- **JNI:** `com.archipelago.app.NativeCore` (same .so as the FIPS mesh).
+- **Session:** `nostr/BunkerManager.kt` — OkHttp WebSocket relay client,
+  JSON-RPC dispatch, approve/deny state.
+- **UI:** a hub sub-page (`ui/components/SignerSection.kt`, opened from the
+  three-finger hub menu like Nodes/FIPS) — key setup, npub/nsec display,
+  pairing scan, session status, the approve/deny card. The full-screen
+  pairing scanner (`QrGlassModal`) is hosted by NESMenu so it isn't clipped
+  to the panel's bounds. The `nostrconnect://` deep link routes to the
+  session and pops the hub open on the signer sub-page (`SignerLaunch`).
+
+## Security notes (conscious deviations, reviewed)
+
+- Incoming events are **not** signature-verified before decryption — the
+  same choice rust-nostr's reference bunker makes. The NIP-44 MAC is the
+  actual gate: forging content that decrypts with a valid MAC requires one
+  of the two conversation secrets. A future hardening pass may add event
+  verification first.
+- The signer secret lives in app-private DataStore (same storage model as
+  the FIPS secret and node login passwords). It can additionally be sealed
+  inside an encrypted backup (see
+  [`companion-backup-restore.md`](companion-backup-restore.md)).
+- `sign_event` approval is per-request and per-screen; there is no
+  "remember this client" auto-approve in v1.
+
+## End-to-end test harness (the node side doesn't exist yet)
+
+`Android/tools/nip46-test-client.py` plays the node's role: generates the
+pairing QR in your terminal, runs the full handshake, requests
+`get_public_key` + `sign_event`, and verifies the returned signature with an
+independent pure-Python BIP-340 implementation (no code shared with the
+phone's Rust core; both are pinned to the same official test vectors).
+
+```bash
+python3 -m venv /tmp/nip46env
+/tmp/nip46env/bin/pip install websockets qrcode
+/tmp/nip46env/bin/python Android/tools/nip46-test-client.py   # --relay to override
+```
+
+Then on the phone: hub → Remote Signer → Generate key (once) → Scan pairing
+QR → point at the terminal QR → Approve the incoming request. The harness
+prints `END-TO-END PASS` when the phone-signed event verifies.
+
+## Test checklist (on-device)
+
+- [ ] Generate key → npub shows, copy works; import nsec → same npub.
+- [ ] Harness handshake: pair → ack → `get_public_key` returns the phone's npub.
+- [ ] `sign_event` request shows a legible card (kind label, content, tags);
+      Approve → harness verifies the schnorr signature; Deny → harness sees
+      `"denied"`.
+- [ ] Deep link: open a `nostrconnect://…` URI from a QR app → SignerScreen
+      with the pairing already starting.
+- [ ] Wrong/foreign QR → clear error, no state change.
+
+## Roadmap (node-side, tracked separately)
+
+The node-side bunker hosting/login flow (research doc flows A+B, the
+`auth.login.nostr` slot, relay topology on the node's own strfry) is roadmap
+territory via the `companion-agent`-labeled tracker issues; when it ships,
+the phone side here already speaks its language.

docs/companion-qr-decoder-zxing-cpp.md

@@ -88,29 +88,29 @@ proprietary and Play-Services-backed.
 
 ## Integration sketch
 
-> ⚠️ Coordinates and API surface below are from memory and were **not**
-> verified against Maven Central — the machine this was written on had no
-> network. Confirm the current artifact version and wrapper API on the first
-> online Gradle sync before trusting the snippet.
+> Verified 2026-08-31 against Maven Central and the wrapper source
+> (`wrappers/android/zxingcpp/src/main/java/zxingcpp/BarcodeReader.kt` at
+> `io.github.zxing-cpp:android:3.1.1`, the current release). Coordinates and
+> API below are what the published artifact actually ships.
 
 `Android/app/build.gradle.kts`:
 
 ```kotlin
 // Replaces com.google.zxing:core for the live-camera path.
-implementation("io.github.zxing-cpp:android:<pin-exact-version>")
+implementation("io.github.zxing-cpp:android:3.1.1")
 ```
 
 `QrCodeAnalyzer` collapses to roughly:
 
 ```kotlin
-private val reader = BarcodeReader().apply {
+private val reader = BarcodeReader(
     options = BarcodeReader.Options(
-        formats = setOf(BarcodeFormat.QR_CODE),
+        formats = setOf(BarcodeReader.Format.QR_CODE),
         tryHarder = true,
         tryRotate = true,
         tryInvert = true,
     )
-}
+)
 
 override fun analyze(image: ImageProxy) {
     try {
@@ -121,6 +121,15 @@ override fun analyze(image: ImageProxy) {
 }
 ```
 
+API notes from the published wrapper: `BarcodeReader.read(ImageProxy)` takes
+the CameraX `YUV_420_888` frame directly (it reads the Y plane + cropRect +
+rotation itself — the manual crop/copy machinery really can go); options are
+one constructor-argument data class; `Format.QR_CODE` is nested inside
+`BarcodeReader` (not a top-level `BarcodeFormat`); results carry `text`,
+`contentType`, `position` — and `lastReadTime` gives the per-call decode time
+in ms, useful to measure the claimed 5–10× while evaluating. Keep
+`com.google.zxing:core` for the still-image path regardless (below).
+
 Keep `com.google.zxing:core` for now regardless: the still-image path
 (`decodeQrFromUri` in `WalletQrScannerModal.kt`, used by "Upload image") and
 `prewarmQrScanner` both use it, and neither is on the hot path.

neode-ui/src/components/CompanionIntroOverlay.vue

@@ -143,6 +143,7 @@ import { ref, onMounted, onUnmounted, watch } from 'vue'
 import * as QRCode from 'qrcode'
 import { IS_DEMO, DEMO_PASSWORD } from '@/composables/useDemoIntro'
 import { companionIntroRequested } from '@/composables/useCompanionIntro'
+import { isCompanionApp } from '@/utils/openExternal'
 import { useLoginTransitionStore } from '@/stores/loginTransition'
 import { useServerStore } from '@/stores/server'
 import { rpcClient } from '@/api/rpc-client'
@@ -205,10 +206,12 @@ const POST_INTRO_GRACE_MS = 2000
 
 let calmTicker: ReturnType<typeof setInterval> | null = null
 
-// Running inside the companion app's own WebView (it injects this JS bridge).
+// Running inside the companion app's own WebView (it injects the JS bridge —
+// detected with the canonical helper, not a raw window check, so the gate
+// is identical everywhere the question is asked).
 // The "get the companion app" pitch is nonsense there — the user is already in
 // it. Server management for connected companions lives in the NESMenu instead.
-const IN_COMPANION_APP = typeof (window as { ArchipelagoNative?: unknown }).ArchipelagoNative !== 'undefined'
+const IN_COMPANION_APP = isCompanionApp()
 
 onMounted(() => {
   if (IN_COMPANION_APP) return
@@ -247,9 +250,13 @@ function maybeShow() {
 }
 
 // Manual open (App Store banner etc.) — ignores the once-per-browser gate.
+// The trigger itself is already a no-op inside the companion (useCompanionIntro),
+// and this watcher refuses to open there too, so no caller can ever pop the
+// install pitch inside the app it installs (#61).
 watch(companionIntroRequested, (requested) => {
   if (!requested) return
   companionIntroRequested.value = false
+  if (IN_COMPANION_APP) return
   if (calmTicker) {
     clearInterval(calmTicker)
     calmTicker = null

neode-ui/src/composables/__tests__/useCompanionIntro.test.ts

@@ -0,0 +1,41 @@
+import { describe, it, expect, afterEach, beforeEach } from 'vitest'
+import { companionIntroRequested, openCompanionIntro } from '../useCompanionIntro'
+
+// #61: the manual intro trigger (App Store banner etc.) must be a no-op inside
+// the companion app's WebView — the "install the companion" pitch is nonsense
+// where the user is already running it. The auto-popup was already gated
+// (CompanionIntroOverlay.onMounted); openCompanionIntro is the second, manual
+// path and the banner render (CompanionBanner) the third.
+
+type TestWindow = Window & { ArchipelagoNative?: unknown }
+const w = window as TestWindow
+
+beforeEach(() => {
+  companionIntroRequested.value = false
+})
+
+afterEach(() => {
+  delete w.ArchipelagoNative
+})
+
+describe('openCompanionIntro', () => {
+  it('raises the manual intro request in a plain browser/PWA', () => {
+    expect(companionIntroRequested.value).toBe(false)
+    openCompanionIntro()
+    expect(companionIntroRequested.value).toBe(true)
+  })
+
+  it('is a no-op inside the companion app (bridge with openInApp)', () => {
+    w.ArchipelagoNative = { openInApp: () => {}, openExternal: () => {} }
+    openCompanionIntro()
+    expect(companionIntroRequested.value).toBe(false)
+  })
+
+  it('still fires when the bridge exists but is not the companion shell', () => {
+    // Partial bridge (no openInApp) is not the companion app — a future
+    // embedder must still see the pitch.
+    w.ArchipelagoNative = { openExternal: () => {} }
+    openCompanionIntro()
+    expect(companionIntroRequested.value).toBe(true)
+  })
+})

neode-ui/src/composables/useCompanionIntro.ts

@@ -1,13 +1,20 @@
 import { ref } from 'vue'
 
+import { isCompanionApp } from '@/utils/openExternal'
+
 /**
  * Cross-view trigger for the Remote Companion intro/pairing modal
  * (CompanionIntroOverlay, mounted once in Dashboard.vue). Views like the
  * App Store banner call openCompanionIntro() to pop it on demand — this
  * bypasses the once-per-browser auto-show gate.
+ *
+ * Inside the companion app's own WebView the whole pitch is nonsense — the
+ * user is already running it — so the trigger is a no-op there (#61: the
+ * auto-popup was gated, this manual path and CompanionBanner weren't).
  */
 export const companionIntroRequested = ref(false)
 
 export function openCompanionIntro(): void {
+  if (isCompanionApp()) return
   companionIntroRequested.value = true
 }

neode-ui/src/views/discover/CompanionBanner.vue

@@ -1,8 +1,11 @@
 <template>
   <!-- Companion app banner — same format as the featured app banner, with a
        phone mockup rising out of the right edge. Clicking anywhere (or the
-       Install button) opens the Remote Companion download/pairing modal. -->
+       Install button) opens the Remote Companion download/pairing modal.
+       Not rendered at all inside the companion app's WebView: pitching
+       "install the companion" to someone already in it is noise (#61). -->
   <div
+    v-if="showPitch"
     class="featured-banner companion-banner glass-card mb-8 relative overflow-hidden cursor-pointer"
     @click="openCompanionIntro()"
   >
@@ -41,7 +44,11 @@
 </template>
 
 <script setup lang="ts">
+import { computed } from 'vue'
+import { isCompanionApp } from '@/utils/openExternal'
 import { openCompanionIntro } from '@/composables/useCompanionIntro'
+
+const showPitch = computed(() => !isCompanionApp())
 </script>
 
 <style scoped>