fix(mcp): coalesce replayed write requests - #1814
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Session-Id: 01a0bc9a-7729-72e3-a533-412163a3eff1
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Included review availability: Your plan provides up to 4 included reviews per hour; 1 remains after this review. 📝 WalkthroughWalkthroughMCP request replay now coalesces concurrent duplicate ChangesMCP request replay
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant MCPClient
participant MCPServer
participant McpRequestReplay
participant RelayBackend
MCPClient->>MCPServer: spawn or send_dm with request ID and optional idempotency_key
MCPServer->>McpRequestReplay: run tool operation
McpRequestReplay->>RelayBackend: invoke once for matching in-flight or keyed request
RelayBackend-->>McpRequestReplay: operation result
McpRequestReplay-->>MCPServer: replayed or new result
MCPServer-->>MCPClient: MCP response
🚥 Pre-merge checks | ✅ 3 | ❌ 2❌ Failed checks (2 warnings)
✅ Passed checks (3 passed)
Full details: Description checkExplanation The description explains the problem, implementation, behavior, and validation commands, but it does not follow the required template. It omits the Test Plan checklist, RelayFlow Proof fields, and Screenshots section. Resolution Add the required Test Plan section with both checklist items, set the RelayFlow Proof Change type to feature or bugfix, provide exactly one RelayFlow case under tests/relayflows/cases/<case-id>/, and add the Screenshots section or state that it is not applicable. Full details: Docstring CoverageExplanation Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 4 files. (1 skipped: 1 unsupported.)
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Devin Review found 3 potential issues.
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Actionable comments posted: 2
- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
In `@packages/cli/src/cli/mcp/request-replay.ts`:
- Line 24: Update the replay-cache cleanup timer in the request replay promise’s
finally handler to call unref() on the timeout returned by setTimeout, while
preserving the existing five-minute requests.delete(key) cleanup.
- Line 15: Update the replay-key construction near requestId to preserve numeric
and string JSON-RPC IDs as distinct values, using a collision-safe tuple
encoding instead of String(requestId). Bypass replay deduplication for
unsupported ID types while preserving normal operation behavior. Add a
concurrent test covering numeric 41 and string "41" to verify they do not share
a promise or receipt.
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CHANGELOG.mdpackages/cli/src/cli/agent-relay-mcp.startup.test.tspackages/cli/src/cli/agent-relay-mcp.tspackages/cli/src/cli/mcp/messaging-tools.tspackages/cli/src/cli/mcp/request-replay.ts
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Session-Id: 01a0bc9a-7729-72e3-a533-412163a3eff1
Session-Id: 01a0bc9a-7729-72e3-a533-412163a3eff1
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Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.
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Reviewed by Cursor Bugbot for commit c111797. Configure here.
Session-Id: 01a0bc9a-7729-72e3-a533-412163a3eff1
Session-Id: 01a0bc9a-7729-72e3-a533-412163a3eff1
Session-Id: 01a0bc9a-7729-72e3-a533-412163a3eff1
2 participants
MCP transport replays could run one write request twice because the server did not retain a receipt keyed to the JSON-RPC request. A duplicate fleet spawn created a second Cloud invocation that then failed with
spawn_agent_name_in_use, even when the original invocation had already completed successfully. The same gap duplicated DMs.This adds a per-server replay cache keyed by MCP session, tool name, and JSON-RPC request ID. It shares the original result for a replay while separate requests, including identical message contents or a deliberate second same-name spawn, remain independent.
Validation:
npm exec vitest -- run packages/cli/src/cli/agent-relay-mcp.startup.test.ts packages/cli/src/cli/mcp/messaging-tools.delivery.test.ts packages/cli/src/cli/mcp/messaging-tools.protocol.test.tsnpm exec tsc -- -p packages/cli/tsconfig.json --noEmitNote
Medium Risk
Changes deduplication for state-changing MCP tools (spawn, add_agent, DMs); mis-keyed retries could still duplicate work, but the scope is bounded to MCP write paths with new tests.
Overview
Fixes duplicate side effects when the MCP transport replays the same JSON-RPC call: fleet
spawn, legacyadd_agent, andsend_dmnow run through a per-serverMcpRequestReplaythat shares one in-flight execution for the same MCP session, tool, and request id (numeric and string ids stay distinct).Clients can pass optional
idempotency_keyon those tools to retry after a lost response without spawning twice or sending duplicate DMs; completed results for a key are kept briefly (5 minutes). Dedup keys intentionally ignore message/spawn arguments, so identical content with different request ids still sends separately, and a later reuse of the same JSON-RPC id with a new idempotency key is not treated as a replay.Tool metadata marks these writes as non-idempotent unless the client supplies a key. Startup tests cover replay coalescing, idempotency retries, and DM behavior.
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