---
phase: 18-monitor-validation-gates
plan: 02
subsystem: monitoring
tags: [heartbeat, aion, freshness, ouroboros, yesterday-check]

requires:
  - phase: 18-monitor-validation-gates
    provides: "Phase 18 research: per-symbol ouroboros_mode branching patterns"
provides:
  - "Aion rolling-window freshness check in yesterday completion"
  - "AION_FRESHNESS_WINDOW_MIN configurable constant (default 30 min)"
  - "Per-symbol mode-branching in collect_yesterday_completion()"
affects: [heartbeat, sidecar, deploy]

tech-stack:
  added: []
  patterns: ["per-symbol ouroboros_mode branching via getattr safe fallback"]

key-files:
  created: []
  modified:
    - scripts/heartbeat/checks/yesterday.py
    - scripts/heartbeat/config.py
    - tests/test_heartbeat_yesterday_junction.py

key-decisions:
  - "Use getattr chain for ouroboros_mode access -- safe fallback to day when field absent"
  - "30 min default freshness window -- generous for high thresholds (1000 dbps)"

patterns-established:
  - "Per-symbol mode branching: getattr(getattr(entry, 'ouroboros_mode', None), 'value', 'day')"
  - "Aion freshness: max(close_time_us) vs configurable window"

requirements-completed: [MON-01]

duration: 6min
completed: 2026-03-27
---

# Phase 18 Plan 02: Yesterday Check Aion Freshness Summary

**Rolling-window freshness check for Aion symbols replacing meaningless crossover_tid orphan check, with configurable AION_FRESHNESS_WINDOW_MIN and safe day-mode fallback**

## Performance

- **Duration:** 6 min
- **Started:** 2026-03-27T15:54:30Z
- **Completed:** 2026-03-27T16:00:35Z
- **Tasks:** 1 (TDD: RED + GREEN)
- **Files modified:** 3

## Accomplishments

- Aion symbols now get rolling-window freshness check (last bar within N minutes) instead of crossover_tid orphan check
- Day-mode symbols retain existing orphan bar completion behavior unchanged
- AION_FRESHNESS_WINDOW_MIN configurable via environment variable (default 30 min)
- Safe fallback: registry failure or missing ouroboros_mode field -> day-mode check
- 5 new test cases covering fresh/stale/mixed/no-bars/fallback scenarios

## Task Commits

Each task was committed atomically:

1. **Task 1 RED: Aion freshness failing tests** - `5e2aac6` (test)
2. **Task 1 GREEN: Implementation + all tests pass** - `7ee6c7e` (feat)

## Files Created/Modified

- `scripts/heartbeat/checks/yesterday.py` - Refactored into \_check_aion_freshness() and_check_day_completion() with per-symbol mode branching
- `scripts/heartbeat/config.py` - Added AION_FRESHNESS_WINDOW_MIN constant (default 30, env override)
- `tests/test_heartbeat_yesterday_junction.py` - Added TestAionFreshness class (5 tests), ouroboros_mode to FakeSymbolEntry

## Decisions Made

- Used `getattr` chain (`getattr(getattr(entry, 'ouroboros_mode', None), 'value', 'day')`) instead of direct attribute access -- SymbolEntry may not have ouroboros_mode field yet (added by parallel phase), so this is forward-compatible
- Freshness query uses `max(close_time_us)` across all thresholds for the symbol (same pattern as existing freshness.py) -- simplest correct approach
- Kept yesterday_completion at DEGRADED health tier for consistency with existing behavior

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered

None.

## User Setup Required

None - no external service configuration required.

## Known Stubs

None - all data paths are fully wired.

## Next Phase Readiness

- Yesterday check is now Aion-aware and ready for production use
- Requires ouroboros_mode field on SymbolEntry (from Phase 13/18 registry changes) for actual Aion routing; until then, all symbols safely default to day-mode

---

_Phase: 18-monitor-validation-gates_
_Completed: 2026-03-27_
