Implement AUDIT-WP-0007 hash-chain integrity.

Accept now extends a single-schema chain. Verify walks it; a rewritten
payload_hash is a break. Tamper evidence is that detector plus an
external chain-head attestation, not WORM.

tests/test_cli.py

@@ -4,6 +4,7 @@ import types
 
 from audit_core.cli import build_parser
 from audit_core.ingestion import build_backend
+from audit_core.integrity import ChainReport, GENESIS
 from audit_core.interface import AcceptResult, RetentionPolicy
 
 
@@ -36,6 +37,16 @@ class _FakePostgres:
     def close(self):
         self.closed = True
 
+    def verify_chain(self, attestation=None):
+        return ChainReport(
+            intact=True,
+            events=0,
+            head=GENESIS,
+            head_event_id=None,
+            head_accepted_at=None,
+            first_break=None,
+        )
+
     @property
     def retention_policy(self):
         return RetentionPolicy(
@@ -109,6 +120,19 @@ def test_replay_command_reconciles(monkeypatch, capsys):
     assert body["reference"] == "audit:evt-1"
 
 
+def test_verify_chain_command(monkeypatch, capsys):
+    def fake(dsn, **kwargs):
+        return _FakePostgres(dsn, **kwargs)
+
+    monkeypatch.setenv("AUDIT_CORE_DATABASE_URL", "postgresql://example/audit_core")
+    _install_fake_postgres(monkeypatch, fake)
+    args = build_parser().parse_args(["verify-chain", "--schema", "audit_core"])
+    assert args.func(args) == 0
+    body = json.loads(capsys.readouterr().out)
+    assert body["intact"] is True
+    assert body["head"] == GENESIS
+
+
 def test_replay_command_missing_event(monkeypatch, capsys):
     def fake(dsn, **kwargs):
         return _FakePostgres(dsn, **kwargs)