Support stdio transport server on the session/new request in the acp mode. #3889

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1. Angeart

   added the

   Bug

   issue type on Jun 23, 2026
2. Angeart

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   triage

   on Jun 23, 2026
3. examon

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   area:non-interactiveNon-interactive mode (-p), CI/CD, ACP protocol, and headless automationNon-interactive mode (-p), CI/CD, ACP protocol, and headless automation

   area:mcpMCP server configuration, discovery, connectivity, OAuth, policy, and registryMCP server configuration, discovery, connectivity, OAuth, policy, and registry

   on Jun 24, 2026
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5. Varun-Patkar commented on Aug 26, 2026

   

   Varun-Patkar

   on Aug 26, 2026

   More actions

   Confirmed this is still reproducible on Windows 11 with both currently available builds tested on 2026-08-26:

   • Official WinGet stable: GitHub Copilot CLI 1.0.80
   • VS Code-managed build: 1.0.81-11

   The ACP handshake and session creation succeed. A minimal session/new request containing a client-supplied stdio MCP server receives a normal successful response with a session ID:

   {
     "jsonrpc": "2.0",
     "id": 2,
     "method": "session/new",
     "params": {
       "cwd": "<absolute workspace path>",
       "mcpServers": [
         {
           "name": "echo-test",
           "command": "<absolute path to node executable>",
           "args": ["<absolute path to a minimal stdio MCP echo server>"],
           "env": []
         }
       ]
     }
   }

   However, the supplied server is not connected and is not exposed to the model. Sending /mcp list in that session shows only the built-in/plugin servers; echo-test is absent. No JSON-RPC error is returned for the MCP configuration.

   I also tested an explicit "type": "stdio" discriminator as a compatibility probe, with the same result. The standard ACP stdio shape without type matches the current ACP session setup documentation.

   Expected behavior: the stdio server supplied in session/new.params.mcpServers should be started, listed by /mcp list, and its tools should be available in that session.

   This blocks ACP clients that inject per-session tools such as isolated desktop/computer control or connected-app bridges. The command-line --additional-mcp-config workaround is not equivalent for these clients because server configuration and credentials are scoped to an individual session.

   👍React with 👍1Reacted by Angeart