Bug Report: Custom agent `mcp-servers` not connected in CLI sub-agent or `--prompt` contexts

[sbdoroff]

Describe the bug

Custom agents defined in ~/.copilot/agents/ with mcp-servers declared in their YAML frontmatter do NOT receive MCP tool connections when invoked as sub-agents (via the task tool) or as the primary agent via --prompt mode. The agent only receives basic tools (view, skill, report_intent) instead of the MCP server tools declared in its profile.

Affected version

1.0.23

Steps to reproduce the behavior

Steps to reproduce

1. Configure MCP servers globally in ~/.copilot/mcp-config.json:

   {
     "mcpServers": {
       "my-mcp-server": {
         "type": "http",
         "url": "https://example.com/mcp",
         "tools": ["*"]
       }
     }
   }

2. Create a custom agent in ~/.copilot/agents/my-agent.agent.md:

   ---
   name: my-agent
   description: Agent that uses MCP tools
   tools:
     - "my-mcp-server/*"
   mcp-servers:
     my-mcp-server:
       type: 'http'
       url: 'https://example.com/mcp'
       tools: ["*"]
   ---
   Agent prompt here.

3. In the interactive CLI session, MCP tools work perfectly — the main agent can call my-mcp-server tools without issues.

4. Invoke the custom agent as a sub-agent via the task tool:

   Use my-agent to perform a task that requires my-mcp-server tools
   

5. Result: The custom agent reports it only has access to view, skill, and report_intent. None of the MCP server tools declared in its mcp-servers frontmatter are available.

6. Also fails with --prompt mode:

   copilot --agent=my-agent --prompt "List your available tools" --allow-all

   Same result — no MCP tools available.

Expected behavior

Expected behavior

When a custom agent declares mcp-servers in its YAML frontmatter, those MCP connections should be established and the tools should be available to the agent, regardless of whether the agent runs as:

• A sub-agent via the task tool
• The primary agent via --agent + --prompt
• The primary agent in interactive mode

The Custom agents configuration docs confirm that mcp-servers is a supported YAML frontmatter property. The tools property is documented to control tool access including from MCP servers.

Additional context

Actual behavior

• Interactive session (main agent): ✅ MCP tools from mcp-config.json work
• Sub-agent via task tool: ❌ Only view, skill, report_intent available
• Primary agent via --prompt: ❌ Only skill, report_intent available
• Primary agent via --agent + --prompt: ❌ Same — no MCP tools

Impact

This prevents custom agents from being used for any workflow that depends on MCP server tools (e.g., Teams, Mail, Calendar, database, or any external API). The workaround is to have the main agent execute the MCP calls directly instead of delegating to the custom agent — which defeats the purpose of agent specialization.

Environment

• OS: Windows 11
• Copilot CLI: v1.0.23
• MCP server type: HTTP (Streamable HTTP)
• Agent location: ~/.copilot/agents/
• MCP config location: ~/.copilot/mcp-config.json