feat(mcp): settle the caller thread after successful completion [L23]

[Mjones13]

Agents can request settlement of their own thread through t3_thread_settle({clientRequestId}) while finishing a reply. The request leaves that run active and settles the thread only after its durable successful completion, using the existing settlement and provider-detach flow.

The request requires the exact attached provider session, instance, thread, issued MCP credential, and active attempt. A repeated request key returns its original run receipt. New user work, conflicting lifecycle actions, unsuccessful completion, or startup recovery cancels the intent; automatic completion wakeups preserve the existing behavior. Optional persisted metadata remains compatible with historical projections. No schema migration or additional runtime service is introduced.

This rebuild ports owner #85 onto the pinned nightly V2 implementation. It targets work/jones-rebuild/staging after a normal integration of the qualified capacity/account-switch parent. Original #85 remains a reference-only, unmerged branch.

Validation of the combined candidate:

• 484 tests passed across 20 affected and parent-interaction modules, with no skips. The initial combined invocation contained a wrong selection-restart path; its verified module was then run separately and passed all 13 tests, completing the deduplicated union.
• Server and contracts typechecks pass. A deterministic parent-tool substitution fails the new discovery assertion as expected; the candidate was restored.
• Scoped formatting/lint and commit hooks pass. Three new fixture schema-compilation advisory warnings and one existing unused declaration warning remain.
• Full dependency analysis and the production server bundle build pass.

Tests exercise synthetic/in-memory/SQLite state, durable effects, replay, rejection, and lifecycle cancellation. They do not qualify live provider shutdown, actual checkpoint capture, restart execution, or installed-runtime adoption. No deployment occurred.

Contributing thread: 40439454-5570-42fd-85f6-b370799bc9e4. Source-only builder handoff and coordinator fixture repairs are recorded in the rebuild task evidence. Root owns Git, validation, and publication.

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Hosted CI repair: register t3_thread_settle in the shared tool presentation inventory and add a request-specific client summary. An accepted receipt is described as requested settlement, never completed settlement. The original failing core test remains unchanged. Repair validation: 191 tests across seven modules, shared/client/server typechecks, scoped formatting/lint and commit hooks. New-head hosted CI remains pending.