refactor(ai_client): extract _delete_gemini_cache_result helper (Phase 10 sites 2+3)

Sites L1680 (cache.delete on context change) and L1692 (cache.delete on
TTL expiry) had identical patterns:
  try: _gemini_client.caches.delete(name=_gemini_cache.name)
  except Exception as e: _append_comms('OUT', 'request', {'message': f'[CACHE DELETE WARN] {e}'})

Per TIER1_REVIEW: logging is NOT a drain. MIGRATE to Result[T].

Single helper _delete_gemini_cache_result() -> Result[None]:
- Returns Result(data=None) on success
- Returns Result(data=None, errors=[ErrorInfo]) on SDK failure + logs warning to comms
- Caller (_send_gemini) ignores errors (best-effort cleanup)

Audit: ai_client BC 8 -> 6. Both sites migrated.

src/ai_client.py

@@ -1616,6 +1616,25 @@ def _ensure_gemini_client() -> None:
    creds          = _load_credentials()
    _gemini_client = genai.Client(api_key=creds["gemini"]["api_key"])
 
+def _delete_gemini_cache_result() -> Result[None]:
+ """Delete the active Gemini cache. Returns Result[None].
+
+ On SDK failure, returns Result(data=None, errors=[ErrorInfo]) and logs
+ a warning to comms. The caller ignores errors (cache-delete is a
+ best-effort cleanup; the caller proceeds to rebuild cache state).
+ """
+ if _gemini_cache is None or _gemini_client is None:
+  return Result(data=None)
+ try:
+  _gemini_client.caches.delete(name=_gemini_cache.name)
+  return Result(data=None)
+ except Exception as e:
+  _append_comms("OUT", "request", {"message": f"[CACHE DELETE WARN] {e}"})
+  return Result(
+   data=None,
+   errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=f"failed to delete gemini cache: {e}", source="ai_client._delete_gemini_cache_result", original=e)],
+  )
+
 def _extract_gemini_thoughts(resp: Any) -> str:
  """
   Extracts concatenated thinking text from a Gemini response object's parts.
@@ -1675,9 +1694,7 @@ def _send_gemini(md_content: str, user_message: str, base_dir: str,
   if _gemini_chat and _gemini_cache_md_hash != current_md_hash:
    old_history = list(_get_gemini_history_list(_gemini_chat)) if _get_gemini_history_list(_gemini_chat) else []
    if _gemini_cache:
-    #TODO(Ed): Review(Exception)
-    try: _gemini_client.caches.delete(name=_gemini_cache.name)
-    except Exception as e: _append_comms("OUT", "request", {"message": f"[CACHE DELETE WARN] {e}"})
+    _delete_gemini_cache_result()
    _gemini_chat              = None
    _gemini_cache             = None
    _gemini_cache_created_at  = None
@@ -1687,9 +1704,7 @@ def _send_gemini(md_content: str, user_message: str, base_dir: str,
    elapsed = time.time() - _gemini_cache_created_at
    if elapsed > _GEMINI_CACHE_TTL * 0.9:
     old_history = list(_get_gemini_history_list(_gemini_chat)) if _get_gemini_history_list(_gemini_chat) else []
-    #TODO(Ed): Review(Exception)
-    try: _gemini_client.caches.delete(name=_gemini_cache.name)
-    except Exception as e: _append_comms("OUT", "request", {"message": f"[CACHE DELETE WARN] {e}"})
+    _delete_gemini_cache_result()
     _gemini_chat              = None
     _gemini_cache             = None
     _gemini_cache_created_at  = None

tests/tier2/phase10_site23_test.py

@@ -0,0 +1,26 @@
+"""Phase 10 invariant tests (RED) — sites 2+3: _delete_gemini_cache_result.
+
+Sites 2 (L1680) and 3 (L1692): both are
+    try: _gemini_client.caches.delete(name=_gemini_cache.name)
+    except Exception as e: _append_comms("OUT", "request", {"message": f"[CACHE DELETE WARN] {e}"})
+
+Migrate via single helper _delete_gemini_cache_result() -> Result[None].
+"""
+import sys
+sys.path.insert(0, ".")
+
+
+def test_phase10_site23_delete_gemini_cache_result_exists():
+    import src.ai_client
+    assert hasattr(src.ai_client, "_delete_gemini_cache_result"), \
+        "_delete_gemini_cache_result helper missing"
+
+
+def test_phase10_site23_delete_gemini_cache_result_returns_result():
+    """The helper must return Result[None]."""
+    import src.ai_client
+    import inspect
+    fn = src.ai_client._delete_gemini_cache_result
+    sig = inspect.signature(fn)
+    assert "Result" in str(sig.return_annotation), \
+        f"_delete_gemini_cache_result return must be Result, got {sig.return_annotation}"