feat(mcp): fork existing conversations

[juliusmarminge]

Problem

Agents could create ordinary or delegated threads, but could not create a durable T3 conversation fork from a precise stable source or inspect its context-transfer provenance.

Change

Add current-project t3_thread_fork and bounded t3_thread_transfers tools backed by a focused service and the existing thread.fork V2 command through ThreadManagementService.

Behavior

Forks require a completed run, checkpoint, or latest stable source plus a retry key. Results return the committed transfer and receipt, inherited-permission enforcement, and truthful native-fork eligibility while leaving native or portable resolution to the first target turn. Derived target identities use a fork-specific namespace and cannot overwrite existing or soft-deleted threads.

Focused validation

• transfer contract, service, root-schema, production MCP, and real V2/provider-adapter tests
• retry, inherited history, caller/source race, identity collision, occupied-target, and projection-failure coverage
• 5 focused files / 16 tests passed across the complete native stack
• server and contracts scoped typechecks, targeted formatting, and git diff --check

Dependency

Bottom layer of native stack 8776, based on t3code/codex-turn-mapping at the pinned rollout target. #8697 consumes this transfer contract and service for merge-back.

Implemented by GPT-5.6-Sol via Codex in T3 Code.

Note

Add MCP conversation fork and transfer list tools

• Adds ConversationTransferMcpService exposing t3_thread_transfers for bounded read-only transfer listing and t3_thread_fork for conversation mutations.
• Orchestrator thread.fork dispatch validates caller policy ceilings (runtime and interaction modes) and checks target projection existence before issuing fork commands.
• Replaces the single command-thread lock with recursive multi-key dispatch locks (withDispatchLocks) so forks coordinate on source, target, and caller threads.
• Contracts package adds ConversationForkInput, ConversationForkResult, and TransferPageLimit schemas with strict validation (e.g., Unicode well-formedness for retry keys).
• Risk: thread.fork dispatch now fails when target projection exists or source runtime/interaction mode exceeds the caller ceiling; withDispatchLocks changes dispatch lock acquisition to multiple sorted keys.

^{Macroscope summarized 1ad23c2.}

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[macroscopeapp]

Effect service conventions review: one convention violation found in the new ConversationTransferMcpService module.

^{Posted via Macroscope — Effect Service Conventions}

[github-actions]

Thread transfer impact

⚠️ The latest CI run did not produce a thread transfer result for 1ad23c2.

This comment will update automatically after the next completed run.

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR adds production MCP tools that create durable conversation forks and context-transfer records, with new provider-resolution behavior and shared orchestration locking and permission enforcement. Its new user-facing workflow and cross-cutting runtime changes warrant human review.

^{You can add or adjust custom eligibility rules. Learn more.}

[macroscopeapp]

Macroscope skipped reviewing this pull request. Per-review cost limit exceeded (workspace setting).

This review would cost an estimated $246.19, which exceeds your per-review limit of $10.00.

The top 3 files driving up this estimate:

File	Diff Size	Estimate
apps/server/src/orchestration-v2/Orchestrator.ts	279.68KB	$13.98
apps/server/src/orchestration-v2/Adapters/AcpAdapterV2.ts	271.74KB	$13.59
apps/server/src/orchestration-v2/Adapters/CodexAdapterV2.ts	215.40KB	$10.77

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[macroscopeapp]

One convention issue found: a new single-tag Effect.catchTag in Orchestrator.ts. The rest of the new ConversationTransferMcpService module (inline Context.Service interface, environment-acquired ThreadManagementService, exported make/layer, namespace imports of Effect modules) matches the conventions.

^{Posted via Macroscope — Effect Service Conventions}

[cursor]

Stale Bugbot comment from a previous run.

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

^{Bugbot Autofix is ON, but a cloud agent failed to start.}

^{Reviewed by Cursor Bugbot for commit 6f3e626. Configure here.}

[juliusmarminge]

Superseded as the active MCP proposal by #10558 in the rebuilt MCP stack, following the maintainer request to review thin service wrappers separately from service hardening.

This is not a full feature-parity replacement. Each invocation generates a new command. No additional clientRequestId protocol, transfer journal or provider implementation. Merge targets remain in the calling project.

Closing this mixed proposal without merging. The remote branch agents/mcp-conversations/fork and exact head 1ad23c2032b0aa1ce9a55e4d50ce73cd5f6fc20a are retained so the service changes can be extracted for separate review later.