fix(content): double-pay is now impossible + purchases auto-file + Paid Files tab

The double-share/double-pay chain (user hit it live, 2026-07-22):
ShareModal's already-shared lookup compared the slash-stripped stored
path against the leading-slash filepath — never matched — so every
re-share minted a NEW catalog entry with a new id, and the buyer's
owned-guard (keyed by id) saw the duplicate as unowned and paid again.
Three independent walls now: (1) ShareModal normalizes both sides so
re-shares reuse the entry; (2) content_server::add_item dedupes by
filename server-side (updates in place, keeps the id so buyers' owned
records stay valid); (3) the buyer REFUSES to pay for content it
already owns — matched by (onion, content_id) OR (onion, filename) —
and serves the cached copy instead, before any ecash is minted.

Purchases also auto-file into Photos/Music/Documents on the node (same
buckets as the Cloud view, collision-safe naming) so bought files show
up where files live on every device, and Cloud gains a Paid Files tab
listing every purchase (name, size, sats paid, date) with in-app view.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

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

@@ -412,6 +412,55 @@ impl RpcHandler {
             return Err(anyhow::anyhow!("Invalid v3 onion address"));
         }
 
+        // NEVER pay twice for content we already own (2026-07-22: a file
+        // shared twice produced two catalog ids for the same bytes and the
+        // buyer paid both). Guard BEFORE any ecash is minted, matching both
+        // by exact (onion, content_id) and by (onion, filename) — the latter
+        // catches duplicate ids pointing at the same file on the same
+        // seller. The owned copy is served from the local cache instead.
+        {
+            let filename = params.get("filename").and_then(|v| v.as_str());
+            let owned = crate::content_owned::list_owned(&self.config.data_dir).await;
+            let already = owned.iter().find(|o| {
+                o.onion == onion
+                    && (o.content_id == content_id
+                        || filename.is_some_and(|f| {
+                            !f.is_empty()
+                                && o.filename.trim_start_matches('/')
+                                    == f.trim_start_matches('/')
+                        }))
+            });
+            if let Some(o) = already {
+                tracing::info!(
+                    onion,
+                    content_id,
+                    owned_as = %o.content_id,
+                    "paid download: already owned — serving cached copy, NOT paying again"
+                );
+                if let Some((mime, bytes)) = crate::content_owned::read_owned(
+                    &self.config.data_dir,
+                    &o.onion,
+                    &o.content_id,
+                )
+                .await
+                {
+                    use base64::Engine;
+                    return Ok(serde_json::json!({
+                        "owned": true,
+                        "already_owned": true,
+                        "filename": o.filename,
+                        "mime_type": mime,
+                        "size_bytes": bytes.len(),
+                        "paid_sats": 0,
+                        "data_base64":
+                            base64::engine::general_purpose::STANDARD.encode(&bytes),
+                    }));
+                }
+                // Cache record exists but bytes are gone — fall through and
+                // repurchase rather than stranding the user.
+            }
+        }
+
         // `method` pins the backend the user confirmed in the UI ("cashu" |
         // "fedimint"); absent = auto (Cashu first, then Fedimint). The seller's
         // verify_payment_token accepts either, so a node whose balance lives in
@@ -590,6 +639,54 @@ impl RpcHandler {
             tracing::warn!("paid download: failed to cache purchased content (non-fatal): {e:#}");
         }
 
+        // Auto-file the purchase into the user's Files area (2026-07-22):
+        // Photos for images/video, Music for audio, Documents otherwise —
+        // same buckets the Cloud view uses. The in-app viewer still plays
+        // from the purchase cache; this makes the file ALSO show up where
+        // files live, on every device, without relying on a browser
+        // download. Best-effort: never fail a paid download over it.
+        {
+            let folder = if mime_type.starts_with("image/") || mime_type.starts_with("video/") {
+                "Photos"
+            } else if mime_type.starts_with("audio/") {
+                "Music"
+            } else {
+                "Documents"
+            };
+            let base = std::path::Path::new(&filename)
+                .file_name()
+                .and_then(|n| n.to_str())
+                .unwrap_or("download")
+                .to_string();
+            let dir = self.config.data_dir.join("filebrowser").join(folder);
+            if let Err(e) = tokio::fs::create_dir_all(&dir).await {
+                tracing::warn!("paid download: cannot create {}: {e}", dir.display());
+            } else {
+                // Don't clobber an existing file of the same name: "x.jpg"
+                // → "x (2).jpg" etc.
+                let mut target = dir.join(&base);
+                let (stem, ext) = match base.rsplit_once('.') {
+                    Some((s, e)) if !s.is_empty() => (s.to_string(), format!(".{e}")),
+                    _ => (base.clone(), String::new()),
+                };
+                let mut n = 2;
+                while target.exists() {
+                    target = dir.join(format!("{stem} ({n}){ext}"));
+                    n += 1;
+                }
+                match tokio::fs::write(&target, &bytes).await {
+                    Ok(()) => tracing::info!(
+                        "paid download: filed into {}",
+                        target.display()
+                    ),
+                    Err(e) => tracing::warn!(
+                        "paid download: filing into {} failed (non-fatal): {e}",
+                        target.display()
+                    ),
+                }
+            }
+        }
+
         use base64::Engine;
         let encoded = base64::engine::general_purpose::STANDARD.encode(&bytes);