MCP naming conflict: /mcp UI lists user-level entry but runtime uses repo-level settings #3379

Describe the bug

When the same MCP server name appears in both the user-level config ($HOME/.copilot/mcp-config.json) and a project-level config (./.mcp.json or .github/mcp-config.json), the CLI silently uses different sources for the displayed metadata vs. the actually-launched process:

• The /mcp UI shows the server under the user-level section (with the source path of the user config), strongly implying the user-level definition is in effect.
• But the process that actually gets launched uses the project-level args/command — the repo-level entry shadows the user-level one at runtime.

This is extremely confusing because you have no in-CLI indication that the displayed config isn't the one being used. In my case the user-level entry passed --browser msedge to @playwright/mcp, while the project's .mcp.json defined the same server with no --browser flag (defaulting to chrome). /mcp showed me the user-level entry with msedge, but the actually-running playwright process was looking for chrome and failing.

The naming conflict should at minimum be surfaced clearly (e.g., a warning in /mcp like "this server is also defined in ./.mcp.json and the project definition is being used"), and ideally a documented precedence policy with an easy way to opt into whichever scope the user prefers.

Affected version

1.0.49-6

Steps to reproduce the behavior

1. Define an MCP server in $HOME/.copilot/mcp-config.json with distinct args, e.g.:

   "playwright": {
     "type": "stdio",
     "command": "npx",
     "args": ["-y", "@playwright/mcp@latest", "--browser", "msedge"]
   }

2. In a separate repo, define the same server name in ./.mcp.json with different args (e.g., no --browser flag, so it defaults to chrome).
3. Launch copilot from inside that repo.
4. Run /mcp. Observe that the playwright entry appears in the user-level section showing the user-level args.
5. Trigger any playwright tool call. Observe that the launched process uses the project-level args (looking for chrome instead of msedge).

Expected behavior

Either:

1. The /mcp UI should display whichever config is actually in effect, with a clear annotation when there's a naming conflict ("shadowed by ./.mcp.json" or similar), OR
2. A naming conflict should be surfaced as a warning/error at startup with guidance, OR
3. Configs should be merged with a documented precedence (and /mcp should display the merged result with provenance per field).

In all cases, the displayed metadata and the actually-launched process must match.

Additional context

• OS: Windows 11 (PowerShell 7).
• This isn't just a UI bug; it actively breaks debugging. I spent significant time troubleshooting why playwright was looking for chrome when the only config I could see said msedge. The fix turned out to be "realise the project's .mcp.json is shadowing the user config you're looking at."
• Related: there's no easy way to ignore the project-level configs short of editing/deleting .mcp.json in the repo (which can't be committed because it's a shared file). See the related feature request for a --disable-repo-mcps flag.