debug: A/B-diag log for SHC privacy_mode write-lock race

The SHC fetcher in shc.py overwrites _shc_state_cache.privacy_mode without
honoring the _privacy_set_at write-lock that __init__.py:1690 respects.
Suspected cause of the "privacy flips back ON after user-toggle OFF" bug
(second OFF-toggle works on retry).

Pure debug-only patch — no behavior change. When debug logging is enabled
on the integration, logs an "AB-DIAG privacy_mode race" line whenever the
fetcher would have flipped a privacy state that was within the active
write-lock window. Lets us confirm the hypothesis before applying the
actual FORCE-RULE fix.

Behavior is unchanged: entry["privacy_mode"] = new_priv is still written.

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

Author: mosandlt

custom_components/bosch_shc_camera/shc.py

@@ -222,7 +222,26 @@ async def async_update_shc_states(
         )
         if isinstance(svc, dict):
             val = svc.get("state", {}).get("value", "")
-            entry["privacy_mode"] = (val.upper() == "ENABLED")
+            new_priv = (val.upper() == "ENABLED")
+            # A/B-Diag (debug-only, behavior unchanged) — see CLAUDE.md TODO
+            # 2026-04-27: privacy flips back after user-toggle OFF. Hypothesis:
+            # this fetcher overwrites _shc_state_cache without honoring the
+            # _privacy_set_at write-lock that __init__.py:1690 respects. Logs
+            # the would-be-blocked race so we can confirm before applying the
+            # FORCE-RULE fix.
+            if _LOGGER.isEnabledFor(logging.DEBUG):
+                old_priv = entry.get("privacy_mode")
+                lock_ts = coordinator._privacy_set_at.get(cam_id)
+                age = (time.monotonic() - lock_ts) if lock_ts is not None else None
+                ttl = getattr(coordinator, "_WRITE_LOCK_SECS", 0)
+                locked = age is not None and age < ttl
+                if old_priv is not None and old_priv != new_priv and locked:
+                    _LOGGER.debug(
+                        "AB-DIAG privacy_mode race: cam=%s old=%s new=%s "
+                        "lock_age=%.1fs lock_ttl=%.1fs (would-be-blocked)",
+                        cam_id[:8], old_priv, new_priv, age, ttl,
+                    )
+            entry["privacy_mode"] = new_priv
 
 
 # ── SHC setters ──────────────────────────────────────────────────────────────