fix(mcp): child workflow with response block returns error

[icecrasher321]

Summary

Undefined in response block payload is being interpreted as false returning an error flag even when executed correctly.

Type of Change

• Bug fix

Testing

Tested manually

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
docs	Skipped		Feb 2, 2026 5:25pm

[greptile-apps]

Greptile Overview

Greptile Summary

Fixed a boolean coercion bug in MCP tool execution that incorrectly flagged successful workflows with response blocks as errors. When executeResult.success is undefined (common with response blocks), the old logic !executeResult.success evaluated to true, setting isError: true incorrectly. The fix uses explicit comparison executeResult.success === false to only flag actual failures.

• Changed isError: !executeResult.success to isError: executeResult.success === false in route.ts:287
• Now correctly handles three states: undefined/true → no error, false → error
• Resolves issue where child workflows with response blocks returned error flags despite successful execution

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The change is a precise, targeted fix for a clear boolean coercion bug. The logic is sound: using strict equality (=== false) instead of negation (!) prevents undefined from being falsely interpreted as an error. The fix maintains correct behavior for all three states (undefined, true, false) and only affects the specific edge case described in the PR.
• No files require special attention

Important Files Changed

Filename	Overview
apps/sim/app/api/mcp/serve/[serverId]/route.ts	Fixed boolean coercion bug where undefined success field was incorrectly treated as error

Sequence Diagram

sequenceDiagram
participant Client
participant MCP as MCP Server Route
participant DB as Database
participant WF as Workflow Execute API
participant Executor as Workflow Executor
Client->>MCP: POST tools/call (workflow execution)
MCP->>DB: Fetch tool and workflow info
DB-->>MCP: Tool & workflow details
MCP->>WF: POST /api/workflows/{id}/execute
WF->>Executor: Execute workflow with input
Executor->>Executor: Process blocks & response block
alt Workflow with Response Block
Executor-->>WF: Result (success: undefined)
WF-->>MCP: executeResult {output, success: undefined}
Note over MCP: Bug: !undefined = true → isError: true ❌
Note over MCP: Fix: undefined === false → isError: false ✅
else Workflow Execution Failed
Executor-->>WF: Result (success: false)
WF-->>MCP: executeResult {success: false, error}
Note over MCP: false === false → isError: true ✅
else Normal Success
Executor-->>WF: Result (success: true)
WF-->>MCP: executeResult {success: true, output}
Note over MCP: true === false → isError: false ✅
end
MCP-->>Client: CallToolResult {content, isError}

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[greptile-apps]

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