feat: Phase 4 V1 — Robustness Hardening

Adds the observability + safety layer that turns AtoCore from
"works until something silently breaks" into "every mutation is
traceable, drift is detected, failures raise alerts."

1. Audit log (memory_audit table):
   - New table with id, memory_id, action, actor, before/after JSON,
     note, timestamp; 3 indexes for memory_id/timestamp/action
   - _audit_memory() helper called from every mutation:
     create_memory, update_memory, promote_memory,
     reject_candidate_memory, invalidate_memory, supersede_memory,
     reinforce_memory, auto_promote_reinforced, expire_stale_candidates
   - Action verb auto-selected: promoted/rejected/invalidated/
     superseded/updated based on state transition
   - "actor" threaded through: api-http, human-triage, phase10-auto-
     promote, candidate-expiry, reinforcement, etc.
   - Fail-open: audit write failure logs but never breaks the mutation
   - GET /memory/{id}/audit: full history for one memory
   - GET /admin/audit/recent: last 50 mutations across the system

2. Alerts framework (src/atocore/observability/alerts.py):
   - emit_alert(severity, title, message, context) fans out to:
     - structlog logger (always)
     - ~/atocore-logs/alerts.log append (configurable via
       ATOCORE_ALERT_LOG)
     - project_state atocore/alert/last_{severity} (dashboard surface)
     - ATOCORE_ALERT_WEBHOOK POST if set (auto-detects Discord webhook
       format for nice embeds; generic JSON otherwise)
   - Every sink fail-open — one failure doesn't prevent the others
   - Pipeline alert step in nightly cron: harness < 85% → warning;
     candidate queue > 200 → warning

3. Integrity checks (scripts/integrity_check.py):
   - Nightly scan for drift:
     - Memories → missing source_chunk_id references
     - Duplicate active memories (same type+content+project)
     - project_state → missing projects
     - Orphaned source_chunks (no parent document)
   - Results persisted to atocore/status/integrity_check_result
   - Any finding emits a warning alert
   - Added as Step G in deploy/dalidou/batch-extract.sh nightly cron

4. Dashboard surfaces it all:
   - integrity (findings + details)
   - alerts (last info/warning/critical per severity)
   - recent_audit (last 10 mutations with actor + action + preview)

Tests: 308 → 317 (9 new):
  - test_audit_create_logs_entry
  - test_audit_promote_logs_entry
  - test_audit_reject_logs_entry
  - test_audit_update_captures_before_after
  - test_audit_reinforce_logs_entry
  - test_recent_audit_returns_cross_memory_entries
  - test_emit_alert_writes_log_file
  - test_emit_alert_invalid_severity_falls_back_to_info
  - test_emit_alert_fails_open_on_log_write_error

Deferred: formal migration framework with rollback (current additive
pattern is fine for V1); memory detail wiki page with audit view
(quick follow-up).

To enable Discord alerts: set ATOCORE_ALERT_WEBHOOK to a Discord
webhook URL in Dalidou's environment. Default = log-only.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atocore/models/database.py

@@ -136,6 +136,30 @@ def _apply_migrations(conn: sqlite3.Connection) -> None:
         "CREATE INDEX IF NOT EXISTS idx_memories_valid_until ON memories(valid_until)"
     )
 
+    # Phase 4 (Robustness V1): append-only audit log for memory mutations.
+    # Every create/update/promote/reject/supersede/invalidate/reinforce/expire/
+    # auto_promote writes one row here. before/after are JSON snapshots of the
+    # relevant fields. actor lets us distinguish auto-triage vs human-triage vs
+    # api vs cron. This is the "how did this memory get to its current state"
+    # trail — essential once the brain starts auto-organizing itself.
+    conn.execute(
+        """
+        CREATE TABLE IF NOT EXISTS memory_audit (
+            id TEXT PRIMARY KEY,
+            memory_id TEXT NOT NULL,
+            action TEXT NOT NULL,
+            actor TEXT DEFAULT 'api',
+            before_json TEXT DEFAULT '{}',
+            after_json TEXT DEFAULT '{}',
+            note TEXT DEFAULT '',
+            timestamp DATETIME DEFAULT CURRENT_TIMESTAMP
+        )
+        """
+    )
+    conn.execute("CREATE INDEX IF NOT EXISTS idx_memory_audit_memory ON memory_audit(memory_id)")
+    conn.execute("CREATE INDEX IF NOT EXISTS idx_memory_audit_timestamp ON memory_audit(timestamp)")
+    conn.execute("CREATE INDEX IF NOT EXISTS idx_memory_audit_action ON memory_audit(action)")
+
     # Phase 9 Commit A: capture loop columns on the interactions table.
     # The original schema only carried prompt + project_id + a context_pack
     # JSON blob. To make interactions a real audit trail of what AtoCore fed