Add retained chat and API request diagnostics

backend/app/logging.py

@@ -0,0 +1,31 @@
+"""Structured, redacted application logging for container stdout."""
+
+from __future__ import annotations
+
+import json
+from datetime import date, datetime
+from enum import Enum
+from typing import Any
+
+
+class _JSONEncoder(json.JSONEncoder):
+    def default(self, value: Any) -> Any:
+        if isinstance(value, (datetime, date)):
+            return value.isoformat()
+        if isinstance(value, Enum):
+            return value.value
+        return super().default(value)
+
+
+def configure_structured_logging() -> None:
+    """Reserved lifecycle hook for the structured stdout audit channel."""
+
+
+def log_event(event: str, **fields: Any) -> None:
+    """Write a single JSON line; callers must not pass credentials or bodies."""
+    # stdout is Docker's durable capture point. `flush=True` also makes this
+    # visible immediately in `docker compose logs` during an active SSE run.
+    print(
+        json.dumps({"event": event, **fields}, cls=_JSONEncoder, separators=(",", ":")),
+        flush=True,
+    )