fix(api): best-effort call logging + non-JSON 200 → ModelError (final-review)

- call_log._default_write: swallow any exception from the default file/
  stdout sink and report to stderr, so a log-write failure (disk full,
  bad permissions, misconfigured CALL_LOG_PATH) never turns a successful
  narration into a 500 (charter §13). Injected write= sinks (used by
  tests) are left to surface their own errors.
- ollama_client.chat: catch ValueError alongside httpx.HTTPError in the
  retry loop so a 200 response with a non-JSON body (JSONDecodeError is
  a ValueError subclass) counts as a failed attempt and falls through to
  ModelError after the one retry, instead of escaping chat() uncaught
  (charter §12 — one retry, then ModelError, nothing else escapes).
- main.py: update stale docstrings — /dm/narrate is now fully wired
  (routing + model call + logging); the other four roles remain stubs.

Regression tests added for both fixes (TDD: watched RED, then GREEN).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/app/main.py

@@ -3,7 +3,9 @@
 Skeleton: a health check plus the five role endpoints. Each role endpoint now
 validates the posted canon log against the contract (charter §11) before doing
 anything else — an invalid log is rejected with 422 and never reaches a prompt.
-Prompt routing, model selection, and logging land later.
+`/dm/narrate` is fully wired: prompt routing, the Ollama model call, and
+call-log logging. The other four roles remain stubs until they get the same
+treatment.
 """
 
 from fastapi import Depends, FastAPI, HTTPException
@@ -48,8 +50,9 @@ def health() -> dict:
 
 # ── Role endpoints (charter §4) ──────────────────────────────────────────────
 # The client knows these paths and nothing about which model or prompt serves
-# them. Bodies are validated against the canon log contract; the AI half is a
-# stub until prompt routing lands.
+# them. Bodies are validated against the canon log contract. /dm/narrate is
+# fully wired (routing + model call + logging); the other four roles remain
+# stubs until prompt routing, model selection, and logging land for them too.
 
 
 @app.post("/dm/narrate")