---
phase: 01-junction-fix-root-cause
plan: 01
subsystem: streaming
tags: [rust, live-engine, junction-fill, puck-fill, gap-detection]

requires:
  - phase: none
    provides: n/a
provides:
  - Junction fill phase in symbol_task bridging REST-to-WS gap
  - Monotonicity guard preventing duplicate trade processing at junction
  - Gap detector re-seeding past junction boundary
affects: [02-junction-telemetry-audit, 08-integration-testing]

tech-stack:
  added: []
  patterns:
    - "One-shot junction fill between REST seed and main select loop"
    - "Monotonicity guard via trade-ID comparison before processing"

key-files:
  created: []
  modified:
    - crates/opendeviationbar-streaming/src/live_engine.rs

key-decisions:
  - "Junction fill inserted between last_days init and main loop — only valid position since process_trade_through_processors requires last_days"
  - "Re-seed gap detector unconditionally after junction (whether gap existed or not) to prevent Puck double-fire"

patterns-established:
  - "JUNC-01..04: Four-invariant junction fill pattern for REST-to-WS transitions"

requirements-completed: [JUNC-01, JUNC-02, JUNC-03, JUNC-04]

duration: 1min
completed: 2026-03-19
---

# Phase 01 Plan 01: Junction Fill Implementation Summary

**One-shot junction fill in symbol_task() bridges REST-to-WS gap using puck_fill with same processors, preventing forming-bar abandonment across 18 symbols x 4 thresholds**

## Performance

- **Duration:** 1 min
- **Started:** 2026-03-19T21:37:16Z
- **Completed:** 2026-03-19T21:38:11Z
- **Tasks:** 1
- **Files modified:** 1

## Accomplishments

- Inserted 65-line junction fill block in symbol_task() between gap detector seed and main select loop
- Junction fill peeks first WS trade, detects gap via processor last_agg_trade_id, fills via puck_fill with same processors (JUNC-01/JUNC-02)
- Gap detector re-seeded past junction so Puck won't re-fire in main loop (JUNC-03)
- Monotonicity guard silently drops overlapping WS trade if already processed during junction fill (JUNC-04)

## Task Commits

Each task was committed atomically:

1. **Task 1: Add junction fill between gap detector seed and main loop** - `4d2b9a9` (feat)

## Files Created/Modified

- `crates/opendeviationbar-streaming/src/live_engine.rs` - Added junction fill block (lines 1284-1347) between last_days init and main select loop

## Decisions Made

- Junction fill placed after `let mut last_days` and before `loop {` — the only valid position since `process_trade_through_processors` requires `last_days`
- Gap detector re-seeded unconditionally after junction (not just when gap exists) to ensure Puck starts clean in main loop

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered

None

## User Setup Required

None - no external service configuration required.

## Next Phase Readiness

- Junction fill implementation complete, ready for plan 01-02 (if it exists) or phase 02 (junction telemetry + audit)
- All 4 JUNC requirements satisfied and verified via acceptance criteria
- `cargo check -p opendeviationbar-streaming` passes with zero errors

---

_Phase: 01-junction-fix-root-cause_
_Completed: 2026-03-19_
