## Summary
Two minimum-viable fixes after today's 0.44.0 → 0.47.3 release train and the production 30-user launch. Devil's advocate review of a 3-PR / 7-item plan cut scope to these 2 — the rest is deferred to a separate "operate-first, instrument-second" backlog item.
### B2 — Docker session_collector log skip
`services/session_collector` was logging `Collection complete: 0 users, 0 files copied` + `WARNING: Group 'data-ops' not found, using default group` every 10 minutes in the Docker layout (where `/home/*/user/sessions/` doesn't exist). New env var `AGNES_SKIP_LEGACY_COLLECTOR=1` set by default in `docker-compose.yml` short-circuits the collector pass.
The bare-VM deployment path (where /home/* IS populated by Claude Code) leaves the env var unset and continues to scan normally — including the data-ops warning, which is load-bearing for catching missing-group mis-deploys.
### O2 — FIFO check in `_check_session_pipeline`
The existing check compares `MAX(processed_at)` to newest jsonl mtime — catches "detector hasn't run lately" but blind to "old file was skipped while newer ones were processed". New code finds the oldest FS jsonl that's NOT in `session_extraction_state.session_file` and flags if its mtime is older than `SESSION_PIPELINE_STUCK_FILE_GRACE_SECONDS` (default 4× the existing grace = 2h).
Severity intentionally starts at `info` so we can collect prod data on false-positive rate before tightening to `warning`. The aggregator already treats `info` as non-promoting (see the severity vocabulary docstring at the top of `app/api/health.py`), so the headline `status` stays at `healthy` even when this fires — the operator sees the entry in the per-check breakdown but no spurious `degraded` overall.
## Test plan
- [x] `pytest tests/test_session_collector.py` — 17 tests pass (existing 9 + new 8 covering env-set/unset, truthy variants, falsy non-skip).
- [x] `pytest tests/test_health_session_pipeline.py` — 8 tests pass (existing 4 + new 4 FIFO tests covering stuck-file, under-threshold, all-processed, env-override).
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