Databricks App MCP servers fail silently in `ucode configure mcp`

[zjacobson1016]

Summary

Selecting a Databricks App MCP server in ucode configure mcp appears to succeed (no error shown), but the server is not registered with coding agents and may not be saved to ucode state.

Expected behavior

When a user selects a discovered Databricks App MCP server (apps whose name starts with mcp-), ucode should register it with configured MCP clients (Claude, Codex, etc.) and persist it in ~/.ucode/state.json.

Actual behavior

• User toggles an App MCP server in the picker and presses Enter
• No error is displayed
• Server is not added to agent MCP config (e.g. ~/.claude.json for Claude Code)
• Server may be missing from mcp_servers in ucode state

Suspected cause

In configure_mcp_command(), when _resolve_mcp_selection() returns None for an app selection, the code currently continues without surfacing a warning or error:

resolved = _resolve_mcp_selection(selection, workspace, available_app_mcp_servers)
if resolved is None:
    continue

App MCP resolution depends on matching the selection prefix against entries in available_app_mcp_servers keyed as databricks-app-{app_name}. Any mismatch between picker values and discovered app metadata causes a silent skip.

Reproduction

1. Deploy a Databricks App with MCP enabled (app name prefixed with mcp-)
2. Run ucode configure for at least one MCP-capable agent
3. Run ucode configure mcp
4. Select the App MCP server from the picker
5. Observe no error, but server not registered

Suggested fix

• Print a warning/error when _resolve_mcp_selection() fails instead of silently continuing
• Verify app name / URL resolution logic in _resolve_mcp_selection() and build_mcp_picker_choices() for Databricks Apps
• Add test coverage for app MCP registration in configure_mcp_command()

Environment

• ucode (latest)
• Databricks workspace with Databricks Apps MCP
• MCP clients: Claude Code, Codex, etc.

[rohita5l]

cc @AarushiShah-db

[Baijack-star]

I took a quick source-level pass on current main. One useful narrowing point: the happy path for App MCP registration looks covered and currently passes.

What I checked:

• app_mcp_servers() turns an app named mcp-my-app into server name databricks-app-mcp-my-app and URL <app-url>/mcp.
• build_mcp_picker_choices() emits the unchecked picker value +app:mcp-my-app for that server.
• _resolve_mcp_selection("app:mcp-my-app", ..., available_app_mcp_servers) resolves back to ("databricks-app-mcp-my-app", "<app-url>/mcp").
• tests/test_mcp.py::TestConfigureMcpCommand::test_registers_discovered_app_mcp_server passes on current main.

That suggests the bug is likely one of these:

1. the released package differs from current main;
2. the real databricks apps list --output json payload does not contain the name/url shape assumed by app_mcp_servers();
3. a selection can become stale or malformed, and the command silently drops it.

The last part is definitely a UX/test gap. In configure_mcp_command():

resolved = _resolve_mcp_selection(selection, workspace, available_app_mcp_servers)
if resolved is None:
    continue

If any selected app:* value cannot resolve, the command exits cleanly with no warning, no failed status, and no saved MCP server. A small regression test would make this visible:

• patch choices to return +app:mcp-my-app;
• patch discover_app_mcp_servers() to return either [], a server without url, or a mismatched name;
• assert the command prints a warning containing the selected app value and discovered app server names;
• assert no client config is written and state is not silently presented as successful.

I would also add one real-payload fixture test around _extract_apps_payload() + app_mcp_servers() using captured databricks apps list --output json from a workspace with an MCP app. That will confirm whether the field mismatch is upstream of the picker or only in selection resolution.

If useful, I can package a small PR with the negative tests and warning/error behavior; for a paid follow-up, the clean scope would be: add the failing fixture, add the no-silent-skip guard, and verify Claude/Codex config writes stay unchanged on unresolved selections. Contact: jackshao1981@gmail.com.