[codex] gate scorer registration on readiness

[V-SK]

What changed

This PR hardens the public scorer worker so it does not register itself as available before it is actually ready to score.

Changes in scorer/scoring_server.py:

• add explicit runtime state fields (state, state_detail, ready, last_ready_at)
• add startup baseline warmup before the worker is considered ready
• add GET /status and GET /ready
• return 503 worker_not_ready from /score and /validate until warmup completes
• delay periodic endpoint registration until the local /ready probe returns 200
• re-run baseline warmup after reload and successful auto-update paths
• mark the worker degraded instead of silently advertising readiness when warmup fails

Why this changed

The live scoring path was suffering from a cold-start window where the scorer endpoint could be registered with the PS/Aggregator while the process was still loading the model or warming caches. That led to avoidable connection failures, bad-gateway behavior, and deferred scoring candidates getting stuck behind a scorer that looked registered but was not actually ready.

The fix is to make readiness explicit and only register the scorer after the worker can answer real requests.

Impact

• scorers now stay out of rotation until startup warmup has completed
• first real score avoids the worst cold-cache penalty because baseline validation is prepaid at startup
• control-plane consumers can distinguish alive from ready
• failed warmup becomes visible as degraded/not ready instead of causing false-positive registration

Root cause

The old worker exposed only /health and registered its public endpoint immediately at startup. That conflated process liveness with scoring readiness.

Validation

• python3 -m py_compile scorer/scoring_server.py
• live audit on the production scorer/aggregator pair after deploying the same readiness design:
  • scorer /ready returned 200
  • aggregator observed scorer_ready=true
  • deferred scoring candidate cleared
  • scorer evaluation count advanced successfully