---
phase: 02-sidecar-fill-pipeline
plan: 02
subsystem: sidecar
tags: [telemetry, junction, stathera, websocket, http-api]

requires:
  - phase: 02-sidecar-fill-pipeline/01
    provides: Stathera validation in sync_flush, rest_first_tid/rest_last_tid in _junction_state

provides:
  - ws_first_tid one-shot tracking in _main_loop per symbol
  - Full junction telemetry (rest_first_tid, rest_last_tid, ws_first_tid) in /status endpoint
  - Post-startup Stathera junction verification capability

affects: [heartbeat, monitoring, phase-03-parquet-first-catchup]

tech-stack:
  added: []
  patterns: [one-shot state recording via dict key existence check]

key-files:
  created: []
  modified:
    - python/opendeviationbar/sidecar/__init__.py
    - python/opendeviationbar/sidecar/http_server.py
    - tests/test_sync_flush_atomic_replace.py

key-decisions:
  - "ws_first_tid recorded only for symbols that went through fill_from_rest (symbol in _junction_state guard)"
  - "One-shot pattern uses dict key existence check, not a separate set tracker"

patterns-established:
  - "Junction telemetry one-shot: use 'key not in dict[sym]' guard for write-once per-symbol state"

requirements-completed: [STREAM-02]

duration: 3min
completed: 2026-03-24
---

# Phase 02 Plan 02: Gap Closure Summary

**ws_first_tid one-shot tracking in \_main_loop with full REST-to-WS junction telemetry exposed via /status endpoint**

## Performance

- **Duration:** 3 min
- **Started:** 2026-03-24T19:48:07Z
- **Completed:** 2026-03-24T19:53:00Z
- **Tasks:** 1 (TDD: RED + GREEN)
- **Files modified:** 3

## Accomplishments

- ws_first_tid recorded per symbol on first WS bar arrival in \_main_loop (one-shot, never overwritten)
- /status endpoint now exposes rest_first_tid, rest_last_tid, and ws_first_tid per symbol
- Post-startup consumers (heartbeat, monitoring) can verify Stathera junction: ws_first_tid == rest_last_tid + 1
- STREAM-02 observability requirement complete

## Task Commits

Each task was committed atomically:

1. **Task 1 RED: Failing tests for junction telemetry** - `12573a5` (test)
2. **Task 1 GREEN: ws_first_tid tracking + /status exposure** - `63de1fe` (feat)

## Files Created/Modified

- `python/opendeviationbar/sidecar/__init__.py` - ws_first_tid one-shot recording in \_main_loop burst bar processing
- `python/opendeviationbar/sidecar/http_server.py` - rest_first_tid and ws_first_tid added to /status symbols dict
- `tests/test_sync_flush_atomic_replace.py` - Test 8 (full junction fields in /status) and Test 9 (one-shot behavior)

## Decisions Made

- ws_first_tid only recorded for symbols present in \_junction_state (i.e., symbols that went through fill_from_rest). This prevents tracking symbols that bypassed the REST fill pipeline.
- One-shot guard uses dict key existence (`"ws_first_tid" not in _junction_state[symbol]`) rather than a separate tracking set, keeping state co-located.

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered

Pre-existing test failure in TestSyncFlushCrossMidnightFilter (Test 4) unrelated to this plan's changes. Verified by running the test against the commit before any changes. Out of scope.

## User Setup Required

None - no external service configuration required.

## Next Phase Readiness

- Phase 02 (Sidecar Fill Pipeline) complete: both plans shipped
- Junction telemetry is fully observable via /status, ready for heartbeat integration
- Phase 03 (Parquet-First Catchup) can proceed -- depends on Phase 02 completion

---

_Phase: 02-sidecar-fill-pipeline_
_Completed: 2026-03-24_
