feat: disable subagent summaries, label subagent observations (#2073)

* feat: disable subagent summaries and label subagent observations

Detect Claude Code subagent hook context via `agent_id`/`agent_type` on
stdin, short-circuit the Stop-hook summary path when present, and thread
the subagent identity end-to-end onto observation rows (new `agent_type`
and `agent_id` columns, migration 010 at version 27). Main-session rows
remain NULL; content-hash dedup is unchanged.

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

* fix: address PR #2073 review feedback

- Narrow summarize subagent guard to agentId only so --agent-started
  main sessions still own their summary (agentType alone is main-session).
- Remove now-dead agentId/agentType spreads from the summarize POST body.
- Always overwrite pendingAgentId/pendingAgentType in SDK/Gemini/OpenRouter
  agents (clears stale subagent identity on main-session messages after
  a subagent message in the same batch).
- Add idx_observations_agent_id index in migration 010 + the mirror
  migration in SessionStore + the runner.
- Replace console.log in migration010 with logger.debug.
- Update summarize test: agentType alone no longer short-circuits.

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

* fix: address CodeRabbit + claude-review iteration 4 feedback

- SessionRoutes.handleSummarizeByClaudeId: narrow worker-side guard to
  agentId only (matches hook-side). agentType alone = --agent main
  session, which still owns its summary.
- ResponseProcessor: wrap storeObservations in try/finally so
  pendingAgentId/Type clear even if storage throws. Prevents stale
  subagent identity from leaking into the next batch on error.
- SessionStore.importObservation + bulk.importObservation: persist
  agent_type/agent_id so backup/import round-trips preserve subagent
  attribution.

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

* polish: claude-review iteration 5 cleanup

- Use ?? not || for nullable subagent fields in PendingMessageStore
  (prevents treating empty string as null).
- Simplify observation.ts body spread — include fields unconditionally;
  JSON.stringify drops undefined anyway.
- Narrow any[] to Array<{ name: string }> in migration010 column checks.
- Add trailing newline to migrations.ts.
- Document in observations/store.ts why the dedup hash intentionally
  excludes agent fields.

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

* polish: claude-review iteration 7 feedback

- claude-code adapter: add 128-char safety cap on agent_id/agent_type
  so a malformed Claude Code payload cannot balloon DB rows. Empty
  strings now also treated as absent.
- migration010: state-aware debug log lists only columns actually
  added; idempotent re-runs log "already present; ensured indexes".
- Add 3 adapter tests covering the length cap boundary and empty-string
  rejection.

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

* perf: skip subagent summary before worker bootstrap

Move the agentId short-circuit above ensureWorkerRunning() so a Stop
hook fired inside a subagent does not trigger worker startup just to
return early. Addresses CodeRabbit nit on summarize.ts:36-47.

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

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