Implement the engine spine: claim, outbox, machine, API

Contracts first (T02–T04): approval claim schema with issuer, freshness,
and binding digest; local transactional outbox wire; load-bearing cadence
as heartbeat or reconciliation (layer.yaml declared).

Then the object (T06–T08): SQLite closed state machine, CAS supersession,
distinct-approver fail-closed, revocation without holder cooperation,
outbox insert in the same transaction. Tests fail the mutation when
emission fails, and revoke while the drain sink is down.

Introspection GET /v1/approvals/{id}/claim is a PIP fact, not a decision.
No public consume (T05 waits on GH-WP-0002-T06). Canon T-06 coverage for
wrong binding, expiry, revoke, and supersede.

FLEX-WP-0017 T03 is unblocked on this object; T05 remains blocked only on
consumption ordering.

Assistant: grok
Assistant-Session: 01a04ceb-2057-7e20-b0f9-c282964d5dd9

tests/test_api.py

@@ -0,0 +1,69 @@
+from approval_engine.api import call
+from tests.conftest import binding, validity
+
+
+def test_readyz(app):
+    status, body = call(app, "GET", "/v1/readyz")
+    assert status == 200
+    assert body["status"] == "ok"
+
+
+def test_create_entry_claim_roundtrip(app):
+    status, created = call(
+        app,
+        "POST",
+        "/v1/approvals",
+        {"binding": binding(), "validity": validity(), "required_count": 1},
+    )
+    assert status == 201
+    aid = created["id"]
+    status, _ = call(app, "POST", f"/v1/approvals/{aid}/entries", {"subject_id": "user:alice"})
+    assert status == 200
+    status, claim = call(app, "GET", f"/v1/approvals/{aid}/claim")
+    assert status == 200
+    assert claim["kind"] == "approval-claim"
+    assert claim["valid_now"] is True
+    assert "effect" not in claim
+    assert "decision" not in claim
+
+
+def test_no_check_or_authorize_or_consume(app):
+    for path in (
+        "/v1/check",
+        "/authorize",
+        "/v1/approvals/00000000-0000-0000-0000-000000000001/consume",
+        "/v1/approvals/abc/consume",
+    ):
+        status, body = call(app, "POST", path, {})
+        assert status == 404
+        assert "consume is not implemented" in body.get("message", "") or body["error"] == "not_found"
+
+
+def test_claim_after_revoke(app):
+    _, created = call(
+        app,
+        "POST",
+        "/v1/approvals",
+        {"binding": binding(), "validity": validity()},
+    )
+    aid = created["id"]
+    call(app, "POST", f"/v1/approvals/{aid}/entries", {"subject_id": "user:alice"})
+    call(app, "POST", f"/v1/approvals/{aid}/revoke", {})
+    status, claim = call(app, "GET", f"/v1/approvals/{aid}/claim")
+    assert status == 200
+    assert claim["valid_now"] is False
+    assert claim["reason_code"] == "revoked"
+
+
+def test_store_unavailable_is_503():
+    from approval_engine.api import App
+    from approval_engine.errors import StoreUnavailable
+    from approval_engine.store import Engine
+
+    class Dead(Engine):
+        def outbox_stats(self):
+            raise StoreUnavailable("down")
+
+    status, body = call(App(Dead.__new__(Dead)), "GET", "/v1/readyz")
+    assert status == 503
+    assert body["error"] == "store_unavailable"