feat: add memory injection audit trail for effectiveness tracking

skills/memory/SKILL.md

@@ -215,6 +215,59 @@ Moves the lesson to `archive.jsonl` regardless of frequency.
 | Before agent spawn (run start) | Inject relevant lessons | `archeflow-memory.sh inject <domain> <archetype>` |
 | User command | Add/list/forget lessons | `archeflow-memory.sh add/list/forget` |
 
+## Audit Trail
+
+Track which lessons are injected into each run and whether they were effective.
+
+### Storage
+
+```
+.archeflow/memory/audit.jsonl    # Append-only audit log
+```
+
+### Injection Audit Record
+
+When `--audit <run_id>` is passed to the `inject` command, an audit record is written:
+
+```jsonl
+{"ts":"2026-04-04T10:00:00Z","run_id":"2026-04-04-auth-fix","domain":"code","archetype":"","lessons_injected":["m-001","m-003"],"lesson_count":2}
+```
+
+Usage:
+```bash
+./lib/archeflow-memory.sh inject "$DOMAIN" "" --audit "$RUN_ID"
+```
+
+### Effectiveness Check
+
+After a run completes, check whether injected lessons prevented issues:
+
+```bash
+./lib/archeflow-memory.sh audit-check <run_id>
+```
+
+This command:
+1. Reads `audit.jsonl` for lessons injected in the given run
+2. Reads the run's event file for `review.verdict` events
+3. For each injected lesson, checks keyword overlap between the lesson's description and review findings
+4. **No matching finding** = `helpful` (the lesson likely prevented the issue)
+5. **Matching finding** = `ineffective` (the issue repeated despite the lesson being injected)
+6. Appends effectiveness results to `audit.jsonl`
+
+### Effectiveness Over Time
+
+By querying `audit.jsonl` for effectiveness records, you can measure:
+- Which lessons consistently prevent issues (high `helpful` count)
+- Which lessons are not working (high `ineffective` count — consider rewording or removing)
+- Overall memory system ROI (ratio of helpful to ineffective across all runs)
+
+```bash
+# Count effectiveness per lesson
+jq -r 'select(.type == "effectiveness_check") | [.lesson_id, .effectiveness] | @tsv' .archeflow/memory/audit.jsonl | sort | uniq -c
+```
+
+---
+
 ## Design Principles
 
 1. **Append-only storage.** `lessons.jsonl` is append-only during writes; decay rewrites the file in place but preserves all data (archived lessons move to `archive.jsonl`).