feat(workflows): output schema MCP

[kappa90]

TL;DR

Added structured output support to the agent server through a new MCP server that provides a submit_result tool for agents to return JSON Schema-validated results. This is used by workflows agents that need to return a structured output defined by the user.

What changed?

• Added ResultMcpServer class that runs an HTTP MCP server exposing a submit_result tool
• Added --outputSchema CLI option to accept JSON Schema for structured output validation
• Modified agent initialization to conditionally start the result MCP server and include it in the MCP servers list
• Updated system prompt generation to provide structured output instructions when output schema is configured
• Added automatic task completion marking when structured results are submitted
• Added proper cleanup of the result MCP server during agent shutdown

How to test?

1. Start the agent server with --outputSchema '{"type": "object", "properties": {"answer": {"type": "string"}}}'
2. Send a task to the agent that requires structured output
3. Verify the agent uses the submit_result tool to return data conforming to the schema
4. Check that the task run is marked as completed and the output is saved to the PostHog API

Why make this change?

This enables agents to return structured, validated results instead of only creating PRs or branches.

[kappa90]

• feat(workflows): output schema MCP #1221 👈 (View in Graphite)
• main

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