audit-4: serialized audit chain + legacy genesis + daily Nostr anchoring

- audit() writes are serialized: pg_advisory_xact_lock on Postgres;
  in-process RLock held until session commit/rollback on SQLite
  (test: 4 concurrent writers x 25 entries -> chain verifies, 100 rows)
- legacy rows (entry_hash NULL, pre-0002) are skipped: the chain begins
  GENESIS at the first hashed row; migrated DBs verify clean by design
- monitor anchor: publishes the last chain hash as a signed NIP-01 note
  once per day, logs it in the audit log (self-verified before publish)

tests: concurrent writers; legacy-genesis verification; anchor signs,
logs once per day.

cayceops/components/monitor/monitor.py

@@ -147,6 +147,85 @@ def _build(cfg: Config, sess) -> str:
     return cfg.monitor_output
 
 
+def _anchor(cfg: Config, sess) -> int:
+    """Anchor core (injectable session for tests). Returns 0 ok / 0 skip."""
+    from cayceops.components.publisher import nostr
+    from cayceops.config import ConfigError
+    from cayceops.models import AuditEntry, audit
+
+    if not cfg.nostr_private_key or not cfg.nostr_relays:
+        raise ConfigError(
+            "anchor requires CAYCE_OPS_NOSTR_PRIVATE_KEY and CAYCE_OPS_NOSTR_RELAYS"
+        )
+    if not cfg.deployment_id:
+        raise ConfigError("anchor requires CAYCE_OPS_DEPLOYMENT_ID")
+
+    last = (
+        sess.query(AuditEntry)
+        .filter(AuditEntry.entry_hash.isnot(None))
+        .order_by(AuditEntry.id.desc())
+        .first()
+    )
+    if last is None:
+        print("nothing to anchor: chain empty")
+        return 0
+    today = datetime.now(UTC).date()
+    last_anchor = (
+        sess.query(AuditEntry)
+        .filter(AuditEntry.action == "anchor")
+        .order_by(AuditEntry.id.desc())
+        .first()
+    )
+    if last_anchor is not None and last_anchor.ts.date() == today:
+        print("already anchored today")
+        return 0
+
+    secret = nostr.normalize_key(cfg.nostr_private_key)
+    event = nostr.build_event(
+        secret,
+        f"cayce-ops audit anchor deployment={cfg.deployment_id} "
+        f"last_hash={last.entry_hash} entries={last.id}",
+        tags=[["t", "cayce-ops"], ["t", "audit-anchor"]],
+    )
+    if not nostr.verify_event(event):
+        raise RuntimeError("anchor event failed self-verification")
+    results = nostr.publish(cfg.nostr_relays, event)
+    audit(
+        sess,
+        actor="daemon:monitor",
+        action="anchor",
+        detail={
+            "last_hash": last.entry_hash,
+            "last_entry": last.id,
+            "event_id": event["id"],
+            "relays": results,
+            "deployment": cfg.deployment_id,
+        },
+    )
+    print(f"anchored: {event['id']}")
+    return 0
+
+
+def anchor(cfg: Config | None = None) -> int:
+    """CLI: anchor once per day (external anchoring, audit round 2 point 4)."""
+    from cayceops.config import ConfigError, load
+    from cayceops.db import engine
+
+    cfg = cfg or load()
+    try:
+        with session_scope() as sess:
+            try:
+                return _anchor(cfg, sess)
+            except ConfigError as exc:
+                print(f"anchor refused: {exc}")
+                return 2
+    except Exception as exc:  # noqa: BLE001 — CLI boundary
+        print(f"anchor failed: {str(exc)[:200]}")
+        return 1
+    finally:
+        engine().dispose()
+
+
 def build(cfg: Config | None = None) -> int:
     """CLI entry: render the status page inside a DaemonRun bookkeeping wrap."""
     from cayceops.config import load

tests/test_monitor.py

@@ -67,3 +67,42 @@ def test_build_escapes_injected_content(cfg, sess, tmp_path):
     page = out.read_text()
     assert "<script>x</script>" not in page
     assert "&lt;script&gt;x&lt;/script&gt;" in page
+
+
+def test_anchor_signs_and_logs_once_per_day(cfg, sess, monkeypatch):
+    from cayceops.components.monitor import monitor
+    from cayceops.models import AuditEntry
+
+    # seed the chain
+    from cayceops.models import audit as audit_fn
+
+    audit_fn(sess, actor="daemon:executor", action="execute_done", detail={})
+    sess.flush()
+
+    published = []
+
+    def fake_publish(relays, event, timeout=10.0):
+        published.append(event)
+        return [{"relay": r, "ok": "true"} for r in relays]
+
+    import cayceops.components.publisher.nostr as nostr_mod
+
+    monkeypatch.setattr(nostr_mod, "publish", fake_publish)
+
+    config = cfg(
+        CAYCE_OPS_NOSTR_PRIVATE_KEY="11" * 32,
+        CAYCE_OPS_NOSTR_RELAYS="wss://r.example.org",
+        CAYCE_OPS_DEPLOYMENT_ID="itest",
+    )
+    code = monitor._anchor(config, sess)
+    assert code == 0
+    assert len(published) == 1
+    content = published[0]["content"]
+    assert "audit anchor" in content and "itest" in content
+    entry = sess.query(AuditEntry).filter_by(action="anchor").one()
+    assert entry.detail["last_hash"]
+
+    # second call same day -> skipped, no new nostr event
+    code2 = monitor._anchor(config, sess)
+    assert code2 == 0
+    assert len(published) == 1