fix(engine): fence long-running claims and restore regression coverage

[ovasylenko]

Summary

• Fence claimed scheduler and lifecycle state transitions on the atomic claim token, including webhook outbox commits.
• Keep claim tokens unique across fixed scheduler clocks, use Postgres database time for lease age, and initialize tokens for explicitly created active rows and batch inserts.
• Carry the immutable claim token through tree step, loop, and human-gate dispatch after ordinary context writes; make retry test drivers claim scheduled fixtures through storage.
• Fix the governed-memory integrity bypass and re-enable six previously ignored regressions.
• Add cross-backend claim-fence contracts and a focused review at docs/reviews/2026-10-18-long-running-engine.md.

Verification

• cargo fmt --all -- --check and git diff --check pass.
• Storage claim-fence contract: 8/8 on SQLite, Postgres, and encrypted variants.
• API grant contract: 4/4; push outbox contract: 48/48.
• Engine suite: 3,746 passed across 57 binaries, 0 failed. Server binary suite: 73 passed, 0 failed.
• Storage suite: 880 passed across 33 binaries on SQLite and Postgres, 0 failed.
• Repository CI is validating the whole workspace.

Known follow-ups

The review report records remaining risks for in-flight output/context writes after lease loss, external handler idempotency, and lossy in-memory hook dispatch under overload.