refactor(ai_client): migrate cleanup + reset_session cache.delete to helper (Phase 11 sites 3+4)

Sites L432 (cleanup) and L450 (reset_session) had:
    try: _gemini_client.caches.delete(name=_gemini_cache.name)
    except Exception: pass

This is bare 'except: pass' = INTERNAL_SILENT_SWALLOW violation (logging is NOT
a drain; 'pass' is the worst form of silent recovery).

Migration: use existing _delete_gemini_cache_result() helper (added Phase 10).
The helper returns Result[None]; on SDK error logs a warning to comms.
The caller ignores the Result (cleanup is best-effort).

Audit: ai_client SS 11 -> 9.

src/ai_client.py

@@ -426,11 +426,7 @@ def cleanup() -> None:
  """Performs cleanup operations like deleting server-side Gemini caches."""
  global _gemini_client,    _gemini_cache, _gemini_cached_file_paths
  if     _gemini_client and _gemini_cache:
-  #TODO(Ed): Exception(Review)
-  try:
-   _gemini_client.caches.delete(name=_gemini_cache.name)
-  except Exception:
-   pass
+  _delete_gemini_cache_result()
  _gemini_cached_file_paths = []
 
 def reset_session() -> None:
@@ -444,11 +440,7 @@ def reset_session() -> None:
  global _CACHED_ANTHROPIC_TOOLS, _CACHED_DEEPSEEK_TOOLS
  global _gemini_cli_adapter
  if _gemini_client and _gemini_cache:
-  #TODO(Ed): Review(Exception)
-  try:
-   _gemini_client.caches.delete(name=_gemini_cache.name)
-  except Exception:
-   pass
+  _delete_gemini_cache_result()
  _gemini_client            = None
  _gemini_chat              = None
  _gemini_cache             = None

tests/tier2/phase11_sites34_test.py

@@ -0,0 +1,34 @@
+"""Phase 11 sites 3+4: cleanup + reset_session cache.delete.
+
+Both have:
+    try: _gemini_client.caches.delete(name=_gemini_cache.name)
+    except Exception: pass
+
+Migration: use _delete_gemini_cache_result() (already added in Phase 10).
+The helper returns Result[None]; on error it logs a warning and resets
+cache state. Caller ignores the Result.
+"""
+import sys
+sys.path.insert(0, ".")
+
+
+def test_phase11_sites34_cleanup_calls_delete_helper():
+    """cleanup() must call _delete_gemini_cache_result, not raw caches.delete."""
+    import inspect
+    import src.ai_client
+    src_text = inspect.getsource(src.ai_client.cleanup)
+    assert "_delete_gemini_cache_result" in src_text, \
+        "cleanup() should call _delete_gemini_cache_result helper"
+    assert "except Exception" not in src_text, \
+        "cleanup() must NOT have a bare 'except Exception: pass'"
+
+
+def test_phase11_sites34_reset_session_calls_delete_helper():
+    """reset_session() must call _delete_gemini_cache_result, not raw caches.delete."""
+    import inspect
+    import src.ai_client
+    src_text = inspect.getsource(src.ai_client.reset_session)
+    assert "_delete_gemini_cache_result" in src_text, \
+        "reset_session() should call _delete_gemini_cache_result helper"
+    assert "except Exception" not in src_text, \
+        "reset_session() must NOT have a bare 'except Exception: pass'"