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     superseded/updated based on state transition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>

tests/test_alerts.py

@@ -0,0 +1,58 @@
+"""Tests for the Phase 4 alerts framework."""
+
+from __future__ import annotations
+
+import os
+import tempfile
+from pathlib import Path
+
+import pytest
+
+import atocore.config as _config
+
+
+@pytest.fixture(autouse=True)
+def isolated_env(monkeypatch):
+    """Isolate alerts sinks per test."""
+    tmpdir = tempfile.mkdtemp()
+    log_file = Path(tmpdir) / "alerts.log"
+    monkeypatch.setenv("ATOCORE_ALERT_LOG", str(log_file))
+    monkeypatch.delenv("ATOCORE_ALERT_WEBHOOK", raising=False)
+
+    # Data dir for any state writes
+    monkeypatch.setenv("ATOCORE_DATA_DIR", tmpdir)
+    _config.settings = _config.Settings()
+
+    from atocore.models.database import init_db
+    init_db()
+
+    yield {"tmpdir": tmpdir, "log_file": log_file}
+
+
+def test_emit_alert_writes_log_file(isolated_env):
+    from atocore.observability.alerts import emit_alert
+
+    emit_alert("warning", "test title", "test message body", context={"count": 5})
+
+    content = isolated_env["log_file"].read_text(encoding="utf-8")
+    assert "test title" in content
+    assert "test message body" in content
+    assert "WARNING" in content
+    assert '"count": 5' in content
+
+
+def test_emit_alert_invalid_severity_falls_back_to_info(isolated_env):
+    from atocore.observability.alerts import emit_alert
+
+    emit_alert("made-up-severity", "t", "m")
+    content = isolated_env["log_file"].read_text(encoding="utf-8")
+    assert "INFO" in content
+
+
+def test_emit_alert_fails_open_on_log_write_error(monkeypatch, isolated_env):
+    """An unwritable log path should not crash the emit."""
+    from atocore.observability.alerts import emit_alert
+
+    monkeypatch.setenv("ATOCORE_ALERT_LOG", "/nonexistent/path/that/definitely/is/not/writable/alerts.log")
+    # Must not raise
+    emit_alert("info", "t", "m")