feat: per-mode MCP server allowlist (allowedMcpServers)

[roomote-v0]

Related GitHub Issue

Closes: #12004

Description

This PR attempts to address Issue #12004 by adding an optional allowedMcpServers field to ModeConfig that acts as a per-mode allowlist for MCP servers. Feedback and guidance are welcome.

How it works:

• When allowedMcpServers is defined on a mode config (e.g. in .roomodes), only MCP servers whose names are in the list will have their tools injected for that mode.
• When allowedMcpServers is omitted or empty, all enabled MCP servers are included -- preserving current default behavior.

Key implementation details:

• Type definition (packages/types/src/mode.ts): Added allowedMcpServers: z.array(z.string()).optional() to modeConfigSchema.
• MCP tool generation (src/core/prompts/tools/native-tools/mcp_server.ts): getMcpServerTools() now accepts an optional allowedMcpServers parameter and filters the server list before building tool definitions.
• Build tools pipeline (src/core/task/build-tools.ts): Resolves the current mode config and passes allowedMcpServers to getMcpServerTools().
• System prompt (src/core/prompts/system.ts): The MCP capabilities section now respects allowedMcpServers -- if none of the allowed servers exist, the MCP capabilities message is omitted.

Configuration example:

{
  "customModes": [
    {
      "slug": "database-architect",
      "name": "Database Architect",
      "roleDefinition": "You manage the database schema...",
      "groups": ["read", "edit", "mcp"],
      "allowedMcpServers": ["postgres-mcp", "redis-mcp"]
    }
  ]
}

Design decisions:

• Whitelist-only approach (no blocklist) -- simpler to reason about and matches the requester's needs. A blocklist could be added later.
• Server-name matching uses the key from mcpServers config (same name shown in the UI).
• Fully backward compatible -- the field is optional; when absent, behavior is identical to current.

Test Procedure

• Added 5 new tests for modeConfigSchema in packages/types/src/__tests__/mode.test.ts verifying the new allowedMcpServers field (valid arrays, empty arrays, undefined, non-string rejection).
• Added 5 new tests for getMcpServerTools() in src/core/prompts/tools/native-tools/__tests__/mcp_server.spec.ts covering allowlist filtering (undefined passthrough, empty array passthrough, selective filtering, no-match, single server).
• All 20 tests pass locally.

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes.
• Documentation Impact: Documentation for .roomodes configuration may need updating to mention the new allowedMcpServers field.
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

• Yes, documentation updates may be needed to describe the allowedMcpServers field in custom mode configuration.

Additional Notes

• UI updates for the mode editor (showing MCP server checkboxes) are not included in this initial PR but could be a follow-up enhancement.

Interactively review PR in Roo Code Cloud