ADR-021: third review round — tx-read methods, Job.claimed_at, schedule() queue validation, drop=rollback, receiver arms

docs/architecture/engine-sqlite.md

@@ -1,6 +1,6 @@
 ---
 status: draft
-last_updated: 2026-10-06 (ADR-019/020 — handle surfaces, enqueue semantics)
+last_updated: 2026-10-07 (ADR-021 — third review round: tx reads, claimed_at, schedule queue validation, drop=rollback, receiver arms)
 ---
 
 # SQLite engine
@@ -135,6 +135,7 @@ family is `__alkstore_*` (ADR-010 §8's naming authorization).
 | [018](decisions/018-provenance-register-and-cherry-picks.md) | Substrate provenance | `src/substrate/PROVENANCE.md` (identity, delta register — cherry-picks as tagged entries); cherry-picks recorded at adoption, non-versioning |
 | [019](decisions/019-mechanism-handle-surfaces.md) | Handle surfaces | boxed handle traits (`Queue`/`StreamHandle`/`Outbox`/`Lock`/`JobHandle`); `worker_id` stamps the row's claimant column; `StopToken` core-owned |
 | [020](decisions/020-enqueue-opt-semantics-and-bridges.md) | Enqueue options | delay-over-`run_at` in the substrate's re-derived enqueue; scheduler fires stamp from derived defaults; serde_json byte encoding |
+| [021](decisions/021-tx-reads-and-value-shape-fixes.md) | Third review round | tx-read methods route through the writer-slot lease; `Job.claimed_at` (the fork's claimed_at column, surfaced in `Job`); `schedule()` queue argument validated; drop = rollback releases the lease with `ROLLBACK` |
 
 ## Open Questions