refactor(agent): extract graph-scoped durable materialization lifecycle

[Jurij89]

Problem

Graph-scoped durable materialization is currently implemented as a deeply nested closure in runLegacyDurableSyncForContextGraphDetailed. It owns chain authentication, binding-generation fences, strict binding persistence, physical-run registration, atomic materialization/quarantine, and post-commit invalidation.

The behavior is tested, but the ownership boundary is difficult to scan and future fence changes can be placed incorrectly.

Direction

Extract a named graph-scoped durable materialization coordinator or focused lifecycle helper. Keep durable-sync request construction in the existing method and move the commit lifecycle behind a small typed API.

This must be a no-behavior-change refactor. Do not add a worker, scheduler, queue, cache, or store operation.

Acceptance criteria

• Binding changes during authentication abort before materialization.
• A subscription removed after an atomic commit triggers compensating atomic quarantine.
• A public sync admitted without a subscription retains its authenticated commit.
• Strict on-chain binding persistence happens before materialization and remains fail-closed.
• Physical-run retirement and shutdown cancellation behavior are unchanged.
• Existing lifecycle-binding and graph-scoped materialization suites remain green.

Related

• Follow-up to fix(agent): relieve repeated sync pressure #2053