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

docs/flex-auth-handoff.md

@@ -0,0 +1,26 @@
+# Handoff for `access-engine` / `FLEX-WP-0017`
+
+`FLEX-WP-0017` T03 waited on a durable object that was not the State Hub
+`/decisions/{uuid}` shape. That object is this engine.
+
+## What exists
+
+- Claim contract: [`approval-claim.md`](approval-claim.md)
+- Introspection: `GET /v1/approvals/{id}/claim`
+- Object: `POST /v1/approvals`, entries, revoke, supersede
+- Native `binding.digest` plus optional `binding.pdp_digest` for
+  `NewDecisionBinding.request_digest`
+
+T03 is unblocked on the **object**, not on a hub substitute. Validate the
+claim before privileged production actions. Fail closed if this engine is
+unreachable.
+
+## What does not exist yet
+
+Consumption ordering (`GH-WP-0002-T06` / `APPROVAL-WP-0001-T05`). There is
+no public `consume`. `FLEX-WP-0017` T05 stays blocked **only** on that
+contract, not on a missing object or a missing digest.
+
+Canon T-06 against this implementation: `tests/test_t06_replay.py` (wrong
+target, wrong action, later time, revoked, superseded). Consume-side replay
+is out of scope until T05.