MCP tools from a .mcpb Desktop Extension are not exposed to the model in Chat (works in Cowork) — connector shows connected in both

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report
• [x] I am using the latest version

What's Wrong?

Summary — A local (stdio Node) MCP server installed as a Desktop Extension
(.mcpb) shows as connected in both Chat and Cowork (Settings → Connectors), but its
tools only reach the model in Cowork:

• Cowork: the extension's tools are available and work normally.
• Chat: the model reports it cannot see the tools — they never reach the model —

even though the connector shows connected.

The identical server installed via claude_desktop_config.json (shown as "Local")
works in both Chat and Cowork. Only the .mcpb install method fails to expose tools in Chat.

Connectors list — all show connected; the difference is whether the tools actually reach the model:

| Connector | How installed | Listed/connected | Tools work in Chat | Tools work in Cowork |
|------------------|------------------------------|:----------------:|:------------------:|:--------------------:|
| my-mcp | claude_desktop_config.json | both | ✅ | ✅ |
| My MCP (env) | .mcpb Desktop Extension | both | ❌ | ✅ |
| Claude in Chrome | built-in | both | ✅ | ✅ |

Steps to Reproduce

1. Build a stdio Node MCP server.
2. Install it two ways: (a) add to claude_desktop_config.json; (b) package as .mcpb and install via Settings → Extensions. Both show "connected".
3. In a Chat conversation, ask the model to use the tools → the config-file server's tools work; the .mcpb server's tools are reported as not visible / unavailable.
4. In a Cowork session, both work.

Same server code; only the install method differs.

Expected Behavior

Tools from a .mcpb Desktop Extension should be available to the model in Chat too (or the docs should state which surfaces expose Desktop-Extension tools).

Environment

• Claude Desktop version: latest (auto-updated), as of 2026-07-14
• OS: macOS (latest), as of 2026-07-14
• Plan: Max

Possibly Related (opposite surface / related symptom)

• #26259, #20377, #67185 — Desktop Extension / local MCP tools not exposed in Cowork (opposite surface; mine fails in Chat). Possible version-specific flip.
• #68240 — .mcpb install no-op while the identical server works via claude_desktop_config.json.

Questions

1. Is a .mcpb extension's tools being unavailable in Chat (while connected) intended, a bug, or transitional?
2. Is there a manifest flag/setting to expose .mcpb tools in Chat too?
3. Is claude_desktop_config.json ("Local") the recommended cross-surface method for stdio servers?