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feat(mcp): merge back conversation context#8697

closed3
agents/mcp-conversations/fork
agents/mcp-conversations/merge-back
openedAug 29, 2026byJJulius Marminge
16 files changed
View on GitHubTwo-way sync enabledPR last imported 2d ago

Problem

A durable conversation fork could produce a result, but agents had no safe way to return that conversation context to the fork's original parent.

Change

Add t3_thread_merge_back on top of the fork transfer service, backed by the existing thread.merge_back V2 command through ThreadManagementService.

Behavior

The tool validates original fork lineage, source and target permission ceilings, and an explicit provider-finished source before dispatch. It returns source, target, fork-base provenance, the committed receipt, superseded pending transfers, and truthful next-target-turn consumption. Stable retries replay the same accepted transfer before mutable lineage or lifecycle checks. It never performs a Git merge or changes workspace state.

Focused validation

  • transfer contract and production root-object schema tests
  • non-fork, source/target ceiling, accepted-retry, and projection-failure coverage
  • event-driven real MCP-to-V2/provider-adapter integration covering merge-back, retry, supersession, and managed-adapter consumption on the target's next turn
  • 5 focused files / 16 tests passed across the complete native stack
  • server and contracts scoped typechecks, targeted formatting, and git diff --check

Dependency

Upper layer of native stack 8776. Depends on #8696 for the focused conversation transfer contract, service, fork creation, and bounded transfer read path.

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

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Thread transfer impact

āš ļø The latest CI run did not produce a thread transfer result for afe9681.

This comment will update automatically after the next completed run.

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Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable ā€” This PR introduces a new destructive MCP workflow for durably merging forked conversation context back into a parent, including retries, permission ceilings, supersession, and next-turn consumption. It changes production orchestration and public tool contracts across several components, so human review is appropriate.

No code changes detected at afe9681. Prior analysis still applies.

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apps/server/src/mcp/ConversationTransferMcpService.tsline 511Outdated Ā· d7d2ffaOpen thread
ā€¦ā€¦@@ -360,8 +423,169 @@ export const make = Effect.gen(function* () {
508+ `Thread ${source.thread.id} can merge back only to its recorded parent ${recordedTargetId}.`,
509+ );
510+ }
511+ const { target } = yield* loadScoped(scope, requestedTargetId);
MmacroscopeappBoton line 511Aug 30, 2026

šŸŸ  High mcp/ConversationTransferMcpService.ts:511

mergeBack allows a lower-policy caller to transfer context from a fork whose runtime or interaction mode was later escalated, bypassing the source-versus-caller ceiling enforced by fork. Lines 511ā€“528 validate only the parent target against parent, so add the same checks for source.thread before dispatching the merge-back.

šŸš€ Reply "fix it for me" or copy this AI Prompt for your agent:
text
1In file @apps/server/src/mcp/ConversationTransferMcpService.ts around line 511:
2
3`mergeBack` allows a lower-policy caller to transfer context from a fork whose runtime or interaction mode was later escalated, bypassing the source-versus-caller ceiling enforced by `fork`. Lines 511ā€“528 validate only the parent target against `parent`, so add the same checks for `source.thread` before dispatching the merge-back.
JJulius MarmingeAug 30, 2026

Fixed at b8724db4928ed0f5b96abac69baa6106021dc817. Fresh merge-back now checks the source as well as the target against both the captured and current caller ceilings inside the existing total-order source/target/caller dispatch locks. Accepted stable-key retries still replay before mutable source, target, lineage, or policy checks. Focused real MCP/V2 coverage proves source escalation is denied at the mutation boundary and that an accepted merge remains replayable after the caller narrows. Transfer service plus toolkit integration tests pass 5/5; contracts and server typechecks pass.

Added 3 commits

  • fix(mcp): enforce merge-back source ceiling073dd59
  • feat(mcp): merge back conversation context9efa23d
  • test(mcp): type merge-back denial fixtureafe9681
JJulius MarmingeSep 7, 2026

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/merge-back and exact head afe96811882382ce92e911edbe21b6251a1ffee3 are retained so the service changes can be extracted for separate review later.