feat(agent): survive + auto-recover when curator is unreachable

For redeploying curator while away with nobody to restart the agent:

- _process now distinguishes a TRANSPORT error (curator down/redeploying, 5xx,
  401/403/408/409/429, or our lease reclaimed mid-flight) from a genuine job
  fault. On a transport error it hands the job back (best effort) and signals
  the loop to back off — instead of calling fail(), which would burn the job's
  server-side attempt budget (MAX_ATTEMPTS=3) and permanently error good jobs
  across a redeploy. Job-specific 4xx (404 image gone) still fail so they don't
  re-lease forever.
- lease loop retries with capped exponential backoff (poll_idle → 60s) and
  resets on the first successful lease, so a long outage is gentle and recovery
  is automatic within ≤60s of curator returning. Sleeps are interruptible so
  Stop / pool-shrink stays responsive.
- AUTO_START env (default on in compose) resumes the worker on container start,
  so a host reboot / crash-restart (restart: unless-stopped) self-heals with
  nobody at the desktop.
- control UI shows a "waited out" counter + an "curator unreachable, holding
  work" banner so the recovering state reads as recovery, not failure.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

agent/fc_agent/config.py

@@ -16,6 +16,8 @@ class Config:
     embed_dtype: str     # torch dtype for the crop embedder: float16|float32
     embed_model_override: str  # force a SigLIP-family model ("" → use the one
     #                            the server announces in the lease)
+    auto_start: bool     # start the worker pool on boot (so a container restart
+    #                      resumes processing without anyone clicking Start)
 
     @classmethod
     def from_env(cls) -> "Config":
@@ -30,4 +32,5 @@ class Config:
             poll_idle_seconds=float(os.environ.get("POLL_IDLE_SECONDS", "10")),
             embed_dtype=os.environ.get("SIGLIP_DTYPE", "float16"),
             embed_model_override=os.environ.get("EMBED_MODEL_NAME", ""),
+            auto_start=os.environ.get("AUTO_START", "").lower() in ("1", "true", "yes"),
         )