ucode configure skills: MCP-connection mode (add/remove/replace) + status

[xsh310]

Stacked on databricks#235 (draft). Base branch is skills-refactor-setup-helpers (PR 0's branch), not main, so this PR's diff shows only PR 1's changes. Merge databricks#235 first. (Opened on the fork because PR 0's branch lives on the fork, not on databricks/ucode.)

What this delivers

MCP mode end-to-end for ucode configure skills. Download mode lands in a follow-up PR.

Single multi-schema connection

• Exactly one skills MCP entry: name databricks-skill-registry, kind: "skills", rebuilt on every run (single-connection invariant — _resolve_skills_mcp_servers drops any prior kind=="skills" entry and any entry with that name, keeps everything else, appends one rebuilt entry, and merges prior clients).
• skill_locations: list[str] is the source of truth. The URL is always derived from it via build_skills_mcp_url ({ws}/ai-gateway/skills/?schema=a&schema=b; empty list -> bare {ws}/ai-gateway/skills/), never parsed back.
• The skills entry rides alwaysLoad=True into build_mcp_http_entry (Claude-only; other clients get URL only).

CLI surface

• ucode configure skills --location <list> (required, comma-separated).
• --mcp mutates the connection; --remove / --replace refine the set mutation (add = union, remove = difference, replace = deduped requested); all order-stable.
• Guards mirror configure_mcp (RuntimeError -> exit 1): --remove+--replace together; --remove/--replace without --mcp; --path with --mcp.
• Bare default (no --mcp): registers the connection for the given schemas — the useful interim behavior until download mode ships.
• Soft-warn (still writes) when the resulting set exceeds 10 schemas.

Download-only flags in this PR

Download mode does not exist yet, so rather than silently ignore download-only affordances, the bare default raises a clear "download mode is not available yet; use --mcp" error if --path, --yes, or a 3-part <catalog>.<schema>.<skill> location is supplied. A 3-part location with --mcp is also rejected (it names a single skill, which is download-only).

status

New top-level "Skills" section (peer of Coding Agents / Tracing): Connection, Mode (mcp if skill_locations non-empty else download), Locations (comma-joined, or none — utility tools only), Configured (agent display names). Renders "not configured" when no skills entry exists. The skills entry is also excluded from each agent's per-client MCP-servers line so it isn't double-listed.

Tests added

• test_databricks.py: build_skills_mcp_url for empty / one / two locations (order preserved).
• test_mcp.py: resolve_skill_location_set (add/remove/replace/empty, dedupe, order); _resolve_skills_mcp_servers (canonical entry, single-entry rebuild while an mcp-service entry survives, drops stale/old-named entries, URL derives from list not a stale url, bare route on empty); configure_skills_mcp_command flows (add-to-empty with alwaysLoad, add-second, remove, replace, remove-last -> [] + bare URL + entry kept, mcp-service entries preserved, soft-warn over cap); configure_skills_command bare default.
• test_cli.py: two-mode dispatch (default/--mcp/--mcp --remove/--mcp --replace), comma --location, mutual-exclusion and download-only guards -> exit 1, malformed -> exit 1 naming --location, missing --location -> exit 2; status Skills renderings (not-configured/mcp/download) and skills entry absent from per-client MCP lines.

How verified

uv run ruff check ., uv run ruff format --check, and the full suite run with FORCE_COLOR unset (that env var otherwise injects ANSI into CliRunner buffers and flakes 3 unrelated CLI color tests locally). Result: 1 failed, 932 passed, 39 skipped. The single failure is the pre-existing test_e2e_user_agent.py case (the local claude binary is Claude Code, not the Anthropic CLI) — unrelated to this change.

This pull request and its description were written by Isaac.

[xsh310]

Superseded by databricks#236 (folded into a single PR against databricks/ucode:main).