feat(mcp): Add built-in MCP server for AI agent flag management

[marceloboeira]

Description

AI coding assistants are becoming a primary interface for developers. Adding a built-in MCP server lets agents manage flags directly without leaving the editor or hand-crafting API calls.

The server is embedded in the Flagr binary at /mcp on the same port as the REST API, using Streamable HTTP transport. Single binary, single port, no sidecars.

Disabled by default. Set FLAGR_MCP_ENABLED=true to opt in. When off the route simply doesn't exist, so no extra attack surface.

27 tools covering the full flag lifecycle: CRUD for flags, segments, variants, and constraints, plus distributions, tags, and evaluation. Built with the official Go MCP SDK. Integration tests run across the full docker-compose matrix with a disabled-mode test verifying the route is absent when the flag is off.

How Has This Been Tested?

Besides all the unit/integration tests, I tested the e2e functionality by running opencode locally and pointing to the built MCP (see images).

Input

Result

Created Flag

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[mergify]

Queued — the merge queue status continues in this comment ↓.

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-07-26 20:15 UTC · Rule: default · triggered by @marceloboeira with the merge queue checkbox
• ✅ Checks skipped · PR is already up-to-date
• 🚫 Left the queue — 2026-07-26 20:15 UTC · at c1c01d43b7ba80fdc3871fa4c82b922cd3223a3d

This pull request spent 13 seconds in the queue, including 3 seconds running CI.

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[marceloboeira]

@zhouzhuojie do you want to take a look? in theory there is nothing breaking as it's disabled by default.