Phase 15: B-003 post-fix E2E notes — unit gate pass, RPC deferred

Record b003-repro and npm test results; full two-compact RPC needs long
session like production repro in lost-reinject.jsonl.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/e2e-b003-post-fix.md

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+# B-003 post-fix E2E notes (Phase 15)
+
+**Date:** 2026-06-18  
+**Backlog:** B-003 — second auto compaction missed reinject; `last compaction: none`
+
+## Automated gate (this session)
+
+```bash
+node scripts/b003-repro.mjs   # 22 unit tests + lost-reinject.jsonl audit
+npm test                      # 93 tests, all green
+```
+
+**Artifact audit:** `lost-reinject.jsonl` shows pre-fix signature — compaction #2 at `07:25:14` with `lastCompactionSource: null` after compaction #1 with `auto`. Post-fix: `ensureCompactionSourceMarked` on `session_compact` infers `auto`.
+
+## Fixes verified by unit tests
+
+| Area | Test file |
+|------|-----------|
+| Source fallback when `session_before_compact` skipped | `compaction-source-fallback.test.ts` |
+| `skill-reinject:inject` counts in kept window | `kept-window.test.ts` |
+| Mid-turn `sendMessage`/`steer` + dedup | `reinject-mid-turn.test.ts` |
+| Each compact recalculates pending | `reinject-double-compact.test.ts` |
+
+## Full manual RPC E2E (deferred)
+
+Reproducing two compactions in one short RPC session (like production `gitlab-mr-review` + pi-auto-compact mid-turn) needs a long context fill or reduced `keepRecentTokens`. Checklist when LLM available:
+
+1. `/skill-reinject on` + `debug: true` in settings
+2. `/skill:…` → session until two auto compactions (second mid-turn after tool use)
+3. After each compact: skill in context **or** diag shows `deliveryBranch: "steer"` / `skipped-kept`
+4. `/skill-reinject` → `last compaction: auto` (not `none`)
+
+**Status:** unit + artifact gate pass; full two-compact RPC not run in this session (same constraint as B-002 full compact path).