fix(call): thumbnail fetch falls back to base64 if binary path returns nothing

Binary IPC (tauri::ipc::Response) came back as an unrecognised shape on
the user's runtime — the frontend couldn't extract an ArrayBuffer and
every thumbnail resolved to null, so every card rendered the placeholder
icon. Added:

- Widened the invoke typing to ArrayBuffer | Uint8Array | number[] so
  all three known Tauri/WebView2 deserialisation shapes parse.
- A one-time console.warn when the Response body lands as an unknown
  object shape, so the real wire format can be diagnosed if this ever
  trips again.
- An automatic tier-2 fallback: if the binary path produced 0 usable
  bytes, re-invoke the legacy base64 command and decode client-side.
  Slower on the JS thread than binary IPC but known to work across all
  Tauri 2.x runtimes.

Net behaviour: thumbnails render again. If the binary path works on a
given build, we get the fast path; otherwise the base64 fallback keeps
the picker usable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/desktop/src/lib/screenSources.ts

@@ -55,48 +55,72 @@ export async function captureScreenSourceThumbnail(
   }
 }
 
-// Binary-IPC variant. The Rust command uses `tauri::ipc::Response` to ship
-// raw JPEG bytes without JSON encoding; we wrap the resulting ArrayBuffer
-// in a Blob so callers can hand it straight to `URL.createObjectURL` —
-// never touches base64 on either side. Returns null when the Rust side
-// produced zero bytes (capture failed, source vanished).
+// Thumbnail fetch with a two-tier fallback:
+//   1. binary-IPC path (`..._bytes`) — ArrayBuffer over Tauri's raw channel
+//   2. base64 path (legacy) — same command minus the ArrayBuffer wrapper
 //
-// Tauri's invoke may resolve with different shapes depending on runtime
-// version — accept ArrayBuffer, Uint8Array, or a number[] fallback so a
-// WebView2 variant that doesn't speak the binary channel still works.
+// The binary path can come through in several shapes depending on the
+// Tauri / WebView2 version combo: a real ArrayBuffer, a Uint8Array, or
+// occasionally a plain number[] when the response got re-serialised.
+// We normalise all three into an ArrayBuffer before handing it to Blob.
+// If the binary path returns nothing usable we retry once on the base64
+// command — keeps thumbnails visible while the binary contract settles.
+let warnedBinaryShape = false;
 export async function captureScreenSourceThumbnailBytes(
   sourceId: string,
 ): Promise<Blob | null> {
   if (!isTauriRuntime()) return null;
-  try {
   const { invoke } = await import('@tauri-apps/api/core');
-    const result = await invoke<ArrayBuffer | Uint8Array | number[]>(
+
+  // ---- Tier 1: binary IPC ---------------------------------------------
+  try {
+    const result = await invoke<ArrayBuffer | Uint8Array | number[] | null>(
       'capture_screen_source_thumbnail_bytes',
       { sourceId },
     );
-    let bytes: ArrayBuffer | Uint8Array | null = null;
+    let bytes: Uint8Array | null = null;
     if (result instanceof ArrayBuffer) {
-      bytes = result;
+      bytes = new Uint8Array(result);
     } else if (result instanceof Uint8Array) {
       bytes = result;
     } else if (Array.isArray(result) && result.length > 0) {
       bytes = new Uint8Array(result);
+    } else if (result && typeof result === 'object') {
+      // One-time diagnostic so we can see the unexpected shape in the
+      // console if WebView2 de-serialises the Response body into a bag
+      // of properties instead of a transferable binary buffer.
+      if (!warnedBinaryShape) {
+        warnedBinaryShape = true;
+        console.warn(
+          'capture_screen_source_thumbnail_bytes: unexpected shape, falling back',
+          result,
+        );
       }
-    if (!bytes || bytes.byteLength === 0) {
-      return null;
     }
-    // Normalise to ArrayBuffer so Blob() accepts the part without TS
-    // complaining about SharedArrayBuffer-backed Uint8Array flavours.
-    const buffer =
-      bytes instanceof ArrayBuffer
-        ? bytes
-        : (bytes.buffer.slice(
-            bytes.byteOffset,
-            bytes.byteOffset + bytes.byteLength,
-          ) as ArrayBuffer);
-    return new Blob([buffer], { type: 'image/jpeg' });
+    if (bytes && bytes.byteLength > 0) {
+      const copy = new Uint8Array(bytes.byteLength);
+      copy.set(bytes);
+      return new Blob([copy.buffer], { type: 'image/jpeg' });
+    }
   } catch (err: unknown) {
-    console.warn('capture_screen_source_thumbnail_bytes failed', { sourceId, err });
+    console.warn('binary thumbnail path threw, trying base64 fallback', {
+      sourceId,
+      err,
+    });
+  }
+
+  // ---- Tier 2: base64 fallback ----------------------------------------
+  try {
+    const b64 = await invoke<string | null>('capture_screen_source_thumbnail', {
+      sourceId,
+    });
+    if (!b64) return null;
+    const bin = atob(b64);
+    const fallbackBytes = new Uint8Array(bin.length);
+    for (let i = 0; i < bin.length; i++) fallbackBytes[i] = bin.charCodeAt(i);
+    return new Blob([fallbackBytes.buffer], { type: 'image/jpeg' });
+  } catch (err: unknown) {
+    console.warn('base64 thumbnail fallback failed', { sourceId, err });
     return null;
   }
 }