tauri-app: 8a review fixes

- fetchBlob cache keyed by (did, cid), not just cid.
  Security: future per-DID access control on getBlob would
  otherwise leak the first responder's bytes to subsequent
  viewers.
- EmbedImage: pass did to releaseBlob, release previous cid
  on cid change (no leaked URLs).
- ComposeBox: releaseBlob called with both did and cid.
- pds-server: rename test
  get_blob_after_upload_with_different_did ->
  get_blob_returns_404_for_cross_did_cid_lookup. The
  docstring was misleading — the test only verifies the
  (did,cid) PK on the PDS row, not auth. The renamed name
  matches what the test actually checks.
- vitest: update releaseBlob call sites to the new
  (did, cid) signature.

crates/tauri-app/src-tauri/src/lib.rs

@@ -112,15 +112,24 @@ async fn current_session(state: tauri::State<'_, AppState>) -> Result<Option<Acc
 async fn post_create(
     state: tauri::State<'_, AppState>,
     text: String,
+    embed: Option<serde_json::Value>,
 ) -> Result<serde_json::Value, String> {
     let sess = state
         .store
         .load()
         .ok_or_else(|| "not logged in".to_string())?;
-    let record = serde_json::json!({
+    let mut record = serde_json::json!({
         "text": text,
         "createdAt": chrono::Utc::now().to_rfc3339(),
     });
+    if let Some(emb) = embed {
+        // Only attach when the caller passes a non-null object — null
+        // / missing means "no embed". The lexicon's `embed` field is
+        // optional, so leaving it absent is the safe default.
+        if !emb.is_null() {
+            record["embed"] = emb;
+        }
+    }
     let resp = state
         .pds
         .create_record(&sess.did, "app.twi.post", record, &sess.access_jwt)
@@ -348,6 +357,115 @@ async fn fetch_blob(
         .map_err(|e| e.to_string())
 }
 
+/// `pick_and_upload_image()` — open a native file picker, read the
+/// chosen file, and upload its bytes to the user's PDS via
+/// `com.atproto.uploadBlob`.
+///
+/// Returns the parsed `com.atproto.uploadBlob` response verbatim —
+/// `{ blob: { $type, ref: { $link }, mimeType, size } }` — so the
+/// frontend can drop the blob reference straight into a record's
+/// `embed.images[].image` field. Returns `None` when the user
+/// cancels the dialog.
+///
+/// MIME-type resolution:
+///   1. Sniff the file extension (`.png` → `image/png`, `.jpg`/`.jpeg`
+///      → `image/jpeg`, `.gif` → `image/gif`, `.webp` → `image/webp`).
+///   2. If the extension is unknown, fall back to
+///      `application/octet-stream`. The PDS will then re-sniff via
+///      its magic-byte detector (`at_blob::detect_mime`).
+///
+/// Size cap: the dialog plugin's selection isn't bounded; the PDS
+/// enforces a 1 MiB body limit (`MAX_BLOB_SIZE` in
+/// `pds-server/src/routes/blob.rs`) and returns 413 if exceeded.
+/// We pre-check here so we can surface a clean error before the
+/// upload round trip.
+#[tauri::command]
+async fn pick_and_upload_image(
+    app: tauri::AppHandle,
+    state: tauri::State<'_, AppState>,
+) -> Result<Option<pds_client::UploadBlobResp>, String> {
+    use tauri_plugin_dialog::DialogExt;
+
+    // Confirm we have a session — uploading without auth is a no-op
+    // on the server side (401), but we'd rather tell the caller
+    // upfront than surface a confusing PDS error.
+    let sess = state
+        .store
+        .load()
+        .ok_or_else(|| "not logged in".to_string())?;
+
+    // `blocking_pick_file` is the documented way to drive the
+    // dialog plugin's file picker from a Tauri command. We constrain
+    // the picker to common image extensions — a future change can
+    // allow arbitrary file types if we add a video / audio embed
+    // pipeline.
+    let picked = app
+        .dialog()
+        .file()
+        .add_filter("Image", &["png", "jpg", "jpeg", "gif", "webp"])
+        .set_title("Attach image")
+        .blocking_pick_file();
+
+    let Some(file_path) = picked else {
+        return Ok(None);
+    };
+
+    // The dialog plugin returns a `FilePath` enum (Path | Url). On
+    // desktop we always get a path; the URL branch exists for the
+    // mobile / scoped-access pickers but those don't apply here.
+    let path = match file_path.into_path() {
+        Ok(p) => p,
+        Err(e) => return Err(format!("invalid picked file: {e}")),
+    };
+
+    let bytes = tokio::fs::read(&path)
+        .await
+        .map_err(|e| format!("read {}: {e}", path.display()))?;
+
+    if bytes.is_empty() {
+        return Err("picked file is empty".into());
+    }
+    // Mirror the PDS body cap (1 MiB) locally so we fail fast instead
+    // of sending the request only to receive a 413.
+    const MAX_BLOB_SIZE: usize = 1024 * 1024;
+    if bytes.len() > MAX_BLOB_SIZE {
+        return Err(format!(
+            "file is {} bytes; max is {MAX_BLOB_SIZE}",
+            bytes.len()
+        ));
+    }
+
+    let mime = mime_from_extension(&path);
+    let resp = state
+        .pds
+        .upload_blob(bytes, &mime, &sess.access_jwt)
+        .await
+        .map_err(|e| e.to_string())?;
+    Ok(Some(resp))
+}
+
+/// Map a file extension to a MIME type. Returns
+/// `application/octet-stream` when the extension is unrecognised —
+/// the PDS's magic-byte sniffer will take over from there.
+fn mime_from_extension(path: &std::path::Path) -> String {
+    let ext = path
+        .extension()
+        .and_then(|s| s.to_str())
+        .unwrap_or("")
+        .to_ascii_lowercase();
+    match ext.as_str() {
+        "png" => "image/png",
+        "jpg" | "jpeg" => "image/jpeg",
+        "gif" => "image/gif",
+        "webp" => "image/webp",
+        // The PDS still accepts the upload and stores the bytes; the
+        // sniffed MIME type from magic-byte detection will fill in
+        // `mime_type` server-side on the next getBlob.
+        _ => "application/octet-stream",
+    }
+    .to_string()
+}
+
 /// Fire a native OS notification with an optional click target. The
 /// payload is also broadcast as an `app://notification` event so the
 /// frontend can route to `url` on click (via a notification listener
@@ -514,6 +632,7 @@ pub fn run() {
             unrepost_post,
             status_pds,
             fetch_blob,
+            pick_and_upload_image,
             show_notification,
         ])
         .run(tauri::generate_context!())