feat(01-09): GREEN — Bug B route user-stopped-sharing → IDLE; other codes → ERROR (preserved)

Patches the RECORDING_ERROR onMessage handler in src/background/index.ts
(lines 725-744 pre-patch) with conditional routing on the incoming
`message.error` payload:

  - 'user-stopped-sharing' → setIdleMode() (popup empties; badge OFF;
    isRecording flipped to false). Recovery notification suppressed —
    the operator stopped deliberately, surfacing one would be UX noise.
    The offscreen recorder's onUserStoppedSharing has already cleared
    the buffer (src/offscreen/recorder.ts:457 resetBuffer), so IDLE is
    the correct landing state.

  - all other codes → setErrorMode() + recovery notification, preserving
    the existing operator-facing surface for genuine capture failures
    (codec-unsupported, wrong-display-surface, capture-failed, etc.).

Closes the operator-lockout regression observed in Plan 01-09 Task 5
empirical UAT: after Chrome's "Stop sharing" banner click, the badge
stayed yellow and the popup pinned to SAVE-only, gating
chrome.action.onClicked behind the popup forever. Operator had no
restart path. With IDLE routing, the popup empties and the toolbar
click fires startVideoCapture as designed.

Tests: 83/83 GREEN (was 81; +2 from Tests E+F). tsc clean. Build exit 0.

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

src/background/index.ts

@@ -725,9 +725,41 @@ chrome.runtime.onMessage.addListener((message: Message, sender, sendResponse) =>
     case 'RECORDING_ERROR':
       // Plan 01-09 — the offscreen recorder broadcasts this on capture
       // failure (codec missing, picker cancelled, wrong-display-surface,
-      // mid-record stream end, etc.). Surface to the operator via the
-      // badge + a recovery notification.
+      // mid-record stream end, etc.) AND on operator-initiated stop-sharing
+      // (src/offscreen/recorder.ts: onUserStoppedSharing emits
+      // RECORDING_ERROR{error:'user-stopped-sharing'} after resetBuffer +
+      // track release).
+      //
+      // Bug B (debug 01-09-recovery-flow) conditional routing: the
+      // operator-initiated stop is NOT an error condition, it is a
+      // deliberate end-of-session signal. Routing it through setErrorMode
+      // would (a) leave the popup pinned to src/popup/index.html (SAVE-only)
+      // so chrome.action.onClicked cannot re-fire — the popup wins the
+      // toolbar click forever, and (b) paint the badge yellow as if a
+      // capture failure occurred. Both lock the operator out of restart.
+      // Route 'user-stopped-sharing' through setIdleMode instead: popup
+      // empties (re-enabling onClicked-driven restart), badge returns to
+      // OFF (resetBuffer has already cleared the offscreen buffer so SAVE
+      // mode would be meaningless). No recovery notification: the operator
+      // performed the stop deliberately; surfacing a notification would
+      // be UX noise.
+      // All other error codes preserve the original setErrorMode + recovery
+      // notification routing (defensive fallback for genuine capture
+      // failures — codec-unsupported, wrong-display-surface, capture-failed,
+      // permission-denied, empty-video-buffer, unknown).
       logger.warn('RECORDING_ERROR received:', message);
+      {
+        // Narrow `message` to read the optional `error` payload. The
+        // canonical Message interface (src/shared/types.ts) does not
+        // typify it (Message has type/data/tabId only); the offscreen
+        // recorder emits the extra `error` field as part of the
+        // RECORDING_ERROR wire shape — read it via a minimal cast that
+        // keeps us off `as any`.
+        const errorCode = (message as unknown as { error?: unknown }).error;
+        if (errorCode === 'user-stopped-sharing') {
+          isRecording = false;
+          setIdleMode();
+        } else {
           setErrorMode();
           try {
             const recoveryId = NOTIFICATION_RECOVERY_PREFIX + Date.now();
@@ -741,6 +773,8 @@ chrome.runtime.onMessage.addListener((message: Message, sender, sendResponse) =>
           } catch (e) {
             logger.warn('Recovery notification create failed:', e);
           }
+        }
+      }
       return false;
 
     // Legacy chunk-streaming and IndexedDB save/load handlers were removed