core/archipelago/src/api/handler/content.rs

@@ -162,11 +162,28 @@ impl ApiHandler {
                     r#"{"error":"This file is shared with the host's federation peers only. Federate with that node (exchange invites) so it recognizes you, then try again."}"#,
                 ),
             )),
-            Ok(content_server::ServeResult::NotFound) | Err(_) => Ok(build_response(
+            Ok(content_server::ServeResult::Unavailable) => Ok(build_response(
+                StatusCode::SERVICE_UNAVAILABLE,
+                "application/json",
+                hyper::Body::from(
+                    r#"{"error":"The seller's node can't read this file right now. No payment was taken."}"#,
+                ),
+            )),
+            Ok(content_server::ServeResult::NotFound) => Ok(build_response(
                 StatusCode::NOT_FOUND,
                 "text/plain",
                 hyper::Body::from("Content not found"),
             )),
+            // Not a 404: a paid request may already have been charged by the
+            // time this fails, and "not found" hid the real error entirely.
+            Err(e) => {
+                tracing::error!("Serving content {content_id} failed: {e:#}");
+                Ok(build_response(
+                    StatusCode::INTERNAL_SERVER_ERROR,
+                    "text/plain",
+                    hyper::Body::from("Failed to serve content"),
+                ))
+            }
         }
     }
 

core/archipelago/src/api/rpc/content.rs

@@ -555,6 +555,9 @@ impl RpcHandler {
         .service(crate::settings::transport::PeerService::PeerFiles)
         .header("X-Federation-DID", local_did)
         .header("X-Payment-Token", token_str.clone())
+        // The token is a bearer instrument the seller redeems on first sight:
+        // a Tor replay after FIPS delivered it can only arrive spent.
+        .single_delivery()
         .timeout(std::time::Duration::from_secs(900))
         .send_get()
         .await
@@ -610,8 +613,12 @@ impl RpcHandler {
             let body = response.text().await.unwrap_or_default();
             tracing::warn!("paid download: seller {onion} returned {status}: {body}");
             reclaim_spent_ecash(&self.config.data_dir, &token_str, used_backend).await;
+            let reason = serde_json::from_str::<serde_json::Value>(&body)
+                .ok()
+                .and_then(|v| v.get("error").and_then(|e| e.as_str()).map(str::to_string))
+                .unwrap_or_else(|| format!("Peer returned an error ({status})."));
             return Ok(serde_json::json!({
-                "error": format!("Peer returned an error ({status}). Your ecash was refunded to your wallet.")
+                "error": format!("{reason} Your ecash was refunded to your wallet.")
             }));
         }
 

core/archipelago/src/content_server.rs

@@ -7,7 +7,7 @@ use anyhow::{Context, Result};
 use serde::{Deserialize, Serialize};
 use std::path::{Path, PathBuf};
 use tokio::fs;
-use tracing::{debug, warn};
+use tracing::{debug, info, warn};
 
 const CATALOG_FILE: &str = "content/catalog.json";
 const CONTENT_DIR: &str = "content/files";
@@ -238,6 +238,9 @@ pub enum ServeResult {
     Forbidden,
     /// Content not found.
     NotFound,
+    /// The catalog entry and file exist but this node can't read the file.
+    /// Returned before any payment is taken.
+    Unavailable,
 }
 
 /// Serve a content item by ID with access control and optional range request.
@@ -296,6 +299,37 @@ pub async fn serve_content(
         }
     }
 
+    let file_path = content_file_path(data_dir, item);
+    if !file_path.exists() {
+        // The catalog entry survived (it's a separate JSON file) but its
+        // backing file is gone — most likely lost in an unrelated data-dir
+        // reset (a shared filebrowser file, 2026-07-01: two catalog entries
+        // outlived a filebrowser reinstall that wiped the files themselves).
+        // Leaving the entry in place would keep advertising it as available
+        // to every peer forever, each hitting the exact same dead end this
+        // one just did. Prune it so it stops being offered.
+        warn!(
+            content_id = %id,
+            filename = %item.filename,
+            "content catalog entry's file is missing on disk — pruning the stale entry"
+        );
+        prune_missing_content_entry(data_dir, id).await;
+        return Ok(ServeResult::NotFound);
+    }
+
+    // Confirm the file is readable BEFORE the paid gate below redeems the
+    // buyer's token. Reading it only afterwards meant a permission error
+    // surfaced after the sale: the buyer was charged and got an error
+    // instead of the file (2026-09-29, a FileBrowser upload left 0640).
+    if let Err(e) = ensure_readable(&file_path).await {
+        warn!(
+            content_id = %id,
+            path = %file_path.display(),
+            "shared content file is not readable by this node: {e:#}"
+        );
+        return Ok(ServeResult::Unavailable);
+    }
+
     // Check access control
     if !owner_session {
         match &item.access {
@@ -336,23 +370,6 @@ pub async fn serve_content(
         }
     }
 
-    let file_path = content_file_path(data_dir, item);
-    if !file_path.exists() {
-        // The catalog entry survived (it's a separate JSON file) but its
-        // backing file is gone — most likely lost in an unrelated data-dir
-        // reset (a shared filebrowser file, 2026-07-01: two catalog entries
-        // outlived a filebrowser reinstall that wiped the files themselves).
-        // Leaving the entry in place would keep advertising it as available
-        // to every peer forever, each hitting the exact same dead end this
-        // one just did. Prune it so it stops being offered.
-        warn!(
-            content_id = %id,
-            filename = %item.filename,
-            "content catalog entry's file is missing on disk — pruning the stale entry"
-        );
-        prune_missing_content_entry(data_dir, id).await;
-        return Ok(ServeResult::NotFound);
-    }
 
     let metadata = fs::metadata(&file_path)
         .await
@@ -572,6 +589,38 @@ pub async fn serve_content_preview(data_dir: &Path, id: &str) -> Result<PreviewR
     }
 }
 
+/// Make sure this service can open `path`, granting read access if it can't.
+///
+/// FileBrowser writes uploads as its container user (a rootless subuid such
+/// as 100999), and some arrive 0640 — unreadable by this service, although
+/// most shared files are already 0644. Inside the rootless user namespace
+/// that subuid is ours, so `podman unshare chmod a+r` grants the same read
+/// access the other shared files have, without sudo.
+async fn ensure_readable(path: &Path) -> Result<()> {
+    match fs::File::open(path).await {
+        Ok(_) => return Ok(()),
+        Err(e) if e.kind() == std::io::ErrorKind::PermissionDenied => {}
+        Err(e) => return Err(e).context("Failed to open content file"),
+    }
+    let out = tokio::process::Command::new("podman")
+        .args(["unshare", "chmod", "a+r"])
+        .arg(path)
+        .output()
+        .await
+        .context("Failed to run podman unshare chmod")?;
+    if !out.status.success() {
+        anyhow::bail!(
+            "podman unshare chmod a+r failed: {}",
+            String::from_utf8_lossy(&out.stderr).trim()
+        );
+    }
+    info!("Granted read access to shared content file {}", path.display());
+    fs::File::open(path)
+        .await
+        .context("Content file still unreadable after chmod")?;
+    Ok(())
+}
+
 /// Verify a payment token covers the required amount.
 /// Accepts both cashuA tokens (real Cashu) and legacy cashuSend_ format.
 /// Swaps proofs at the mint to verify they're unspent before accepting.

core/archipelago/src/fips/dial.rs

@@ -130,10 +130,18 @@ pub fn client_with_timeout(timeout: Duration) -> reqwest::Client {
 /// robust". Only connect/timeout errors are retried (a real HTTP response,
 /// including 4xx/5xx, is returned as-is for the caller to interpret).
 async fn send_with_retry(rb: reqwest::RequestBuilder) -> Result<reqwest::Response, reqwest::Error> {
+    send_with_retry_if(rb, |e| e.is_connect() || e.is_timeout()).await
+}
+
+/// [`send_with_retry`], retrying only on errors `retryable` accepts.
+async fn send_with_retry_if(
+    rb: reqwest::RequestBuilder,
+    retryable: impl Fn(&reqwest::Error) -> bool,
+) -> Result<reqwest::Response, reqwest::Error> {
     let retry = rb.try_clone();
     match rb.send().await {
         Ok(resp) => Ok(resp),
-        Err(e) if (e.is_connect() || e.is_timeout()) && retry.is_some() => {
+        Err(e) if retryable(&e) && retry.is_some() => {
             // Brief pause so the hole-punch packets from the first attempt can
             // traverse before we re-dial onto the warmed path.
             tokio::time::sleep(Duration::from_millis(600)).await;
@@ -350,6 +358,9 @@ pub struct PeerRequest<'a> {
     /// the per-peer FIPS/Tor badge reflects reality. Opt-in because not
     /// every caller has a data dir in scope.
     pub record_data_dir: Option<std::path::PathBuf>,
+    /// The request carries something that must reach the peer at most once
+    /// (a bearer ecash token). See [`PeerRequest::single_delivery`].
+    pub single_delivery: bool,
 }
 
 impl<'a> PeerRequest<'a> {
@@ -363,9 +374,25 @@ impl<'a> PeerRequest<'a> {
             fips_timeout: None,
             service: None,
             record_data_dir: None,
+            single_delivery: false,
         }
     }
 
+    /// Never send this request twice. A paid download carries a bearer ecash
+    /// token that the seller redeems on first sight; replaying it over Tor
+    /// after FIPS already delivered it hands the seller a spent token, so the
+    /// buyer is charged and gets a 402 instead of the file (2026-09-29: FIPS
+    /// answered 404 after the seller redeemed, the Tor retry got 402).
+    ///
+    /// With this set, whatever FIPS answers is final, the FIPS retry fires
+    /// only when the first attempt never connected, and Tor is used only when
+    /// FIPS could not have delivered the request. An attempt that may have
+    /// been delivered but timed out is an error, not a fallback.
+    pub fn single_delivery(mut self) -> Self {
+        self.single_delivery = true;
+        self
+    }
+
     /// Record the transport that serves this request into federation storage
     /// (matched by this request's onion host). Best-effort, off the hot path.
     pub fn record_transport(mut self, data_dir: impl Into<std::path::PathBuf>) -> Self {
@@ -481,7 +508,10 @@ impl<'a> PeerRequest<'a> {
         if matches!(pref, TransportPref::Auto | TransportPref::Fips) {
             match self.try_fips_get().await? {
                 Some(resp) => {
-                    if pref == TransportPref::Fips || !fips_should_fall_back(resp.status()) {
+                    if pref == TransportPref::Fips
+                        || self.single_delivery
+                        || !fips_should_fall_back(resp.status())
+                    {
                         telemetry::record_fips_ok();
                         self.spawn_record(crate::transport::TransportKind::Fips);
                         return Ok((resp, crate::transport::TransportKind::Fips));
@@ -617,8 +647,25 @@ impl<'a> PeerRequest<'a> {
         for (k, v) in &self.headers {
             rb = rb.header(*k, v);
         }
-        match tokio::time::timeout(budget, send_with_retry(rb)).await {
+        let single = self.single_delivery;
+        let attempt = send_with_retry_if(rb, |e| {
+            e.is_connect() || (!single && e.is_timeout())
+        });
+        match tokio::time::timeout(budget, attempt).await {
             Ok(Ok(r)) => Ok(Some(r)),
+            // Anything but a failed connect may have reached the peer.
+            Ok(Err(e)) if single && !e.is_connect() => Err(anyhow::anyhow!(
+                "FIPS GET {} failed after the request may have been delivered \
+                 (not retrying over Tor): {}",
+                self.path,
+                e
+            )),
+            Err(_) if single => Err(anyhow::anyhow!(
+                "FIPS GET {} exceeded its {:?} budget after the request may have \
+                 been delivered (not retrying over Tor)",
+                self.path,
+                budget
+            )),
             Ok(Err(e)) => {
                 telemetry::record_fallback(FallbackReason::ConnectFail);
                 tracing::info!(