fix(extension): diff_review steps=[] race condition — in-memory metadata cache (v0.3.13)

Root cause: Collector deletes pending file before Extension reads edit_step_indices.
Fix: diffReviewMetadata Map caches step indices in Extension memory.
Known issue added. Devlog entry 003.

tests/test_diff_review_e2e.py

@@ -0,0 +1,25 @@
+"""
+Diff Review E2E Test File
+Created to trigger diff_review flow in AG extension.
+This file write should be tracked by DIFF-TRACK in the extension.
+"""
+
+
+def test_diff_review():
+    """Test that diff review Accept/Reject works via Discord."""
+    # This is a dummy test file to verify the diff_review pipeline:
+    # 1. Extension detects this file write via step probe
+    # 2. On RUNNING→IDLE transition, creates diff_review pending
+    # 3. Discord shows Accept all / Reject all buttons
+    # 4. User clicks Accept → AcknowledgeCascadeCodeEdit RPC fires
+    assert True, "Diff review E2E test passed"
+
+
+def test_multi_file_tracking():
+    """Verify multiple file modifications are tracked together."""
+    results = {
+        "files_tracked": 0,
+        "pending_created": False,
+        "rpc_called": False,
+    }
+    return results