🤖 feat: add per-workspace MCP server and tool configuration

[ThomasK33]

Summary

Adds per-workspace MCP server and tool configuration. Users can now customize which MCP servers are enabled and which tools are exposed for each workspace, without modifying the project-level .mux/mcp.jsonc.

Changes

Backend

• Types & Schemas: Added WorkspaceMCPOverrides schema with disabledServers and toolAllowlist fields
• Config helpers: getWorkspaceMCPOverrides() and setWorkspaceMCPOverrides() methods in Config class
• ORPC endpoints: workspace.mcp.get and workspace.mcp.set for frontend access
• MCPServerManager: Updated to filter servers and tools based on workspace overrides
• AIService: Fetches and passes overrides when getting MCP tools

Frontend

• WorkspaceMCPModal: New modal component for per-workspace MCP configuration
• WorkspaceHeader: Added Server button (⚙️) to open the modal
• UI features:
  • Toggle servers enabled/disabled for the workspace
  • Fetch tools from each server
  • Checkbox allowlist to select which tools to expose
  • "Allow all" shortcut button

Tests

• 5 tests for workspace override filtering in MCPServerManager
• 6 tests for workspace MCP override Config helpers

How it works

1. Server definitions remain per-project in .mux/mcp.jsonc
2. Per-workspace overrides are stored in ~/.mux/config.json under each workspace entry
3. Effective servers = (project servers) - (workspace disabledServers)
4. Effective tools = filtered by toolAllowlist[server] if set

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📋 Implementation Plan

Plan: Selective MCP tools + per-workspace configuration

Goals

1. Selective MCP tools — For each workspace, expose only an allowlisted subset of MCP tools to the model.
2. Per-workspace MCP configuration — Allow enabling/disabling MCP servers (and tool allowlists) per workspace, without impacting other workspaces.
3. Backwards compatible — Existing per-project .mux/mcp.jsonc continues to work unchanged.

Proposed approach (recommended)

1) Keep server definitions per-project; add per-workspace overrides

• Per-project (existing): PROJECT_ROOT/.mux/mcp.jsonc
  • Source of truth for server commands.
• Per-workspace (new, stored in mux global config ~/.mux/config.json under each workspace entry):
  • Which servers are enabled for that workspace.
  • Which tools are allowlisted (per server) for that workspace.

This avoids needing to read/write config inside SSH workspaces (remote filesystem) and keeps the current "configure once per project" ergonomics, while still enabling workspace-specific behavior.

2) Workspace MCP override schema

Add an optional mcp field on WorkspaceConfigSchema:

// Stored under each workspace entry in ~/.mux/config.json
export interface WorkspaceMCPOverrides {
  /** If set, these servers are disabled for this workspace (after project config). */
  disabledServers?: string[];

  /**
   * Optional per-server allowlist of tools.
   * Key: server name (from .mux/mcp.jsonc)
   * Value: raw MCP tool names (NOT namespaced)
   *
   * If omitted for a server => expose all tools from that server.
   */
  toolAllowlist?: Record<string, string[]>;
}

Semantics:

• Effective servers for a workspace = (project-config enabled servers) minus disabledServers.
• Effective tools for a server:
  • If toolAllowlist[server] present => only expose those tool names.
  • Else => expose all tools from that server.

3) Runtime behavior changes

• MCPServerManager.getToolsForWorkspace(...) filters the returned tool map using the workspace allowlists before it is merged into getToolsForModel.
• MCPServerManager.listServers(...) gains a workspace-aware variant so the system prompt lists only the servers enabled for that workspace.
• No restart required when only tool allowlists change (servers stay running; we just filter what we expose).

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Generated with mux • Model: anthropic:claude-opus-4-5 • Thinking: high

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