feat(mcp): add drt_doctor tool + drt_run_sync(compute_diff=True) CLI parity

[masukai]

Summary

Two MCP tools that had been shipped on the CLI for months but weren't reachable from Claude / Cursor:

1. drt_doctor — mirrors drt doctor (v0.7.0, good first issue: add drt doctor command (environment check) #264)
2. drt_run_sync(compute_diff=True) — mirrors drt run --dry-run --diff (v0.7.1, feat: drt diff — show record-level diff in dry-run mode #413)

This closes the visible part of the MCP-vs-CLI gap. Part of the broader skill/MCP refresh sequence triggered by "skillやMCPに最新の情報が載っていないのは困ります".

What drt_doctor returns

{
  "passed": true,
  "checks": [
    {"category": "runtime", "name": "Python version", "ok": true, "message": "3.12.12 ✅"},
    {"category": "runtime", "name": "drt version", "ok": true, "message": "0.7.8"},
    {"category": "project", "name": "Project file", "ok": true, "message": "✅"},
    {"category": "project", "name": "Profile", "ok": true, "message": "✅ default"},
    {"category": "project", "name": "Syncs", "ok": true, "message": "✅ 1 sync file"},
    {"category": "extras", "name": "bigquery", "ok": false, "message": "❌ not installed (pip install drt-core[bigquery])"},
    ...
  ]
}

passed is False only when a required check fails (project file / profile / Python version); missing optional extras don't flip it. Reuses the _check_* helpers in drt/cli/doctor.py — no CLI changes, no duplicated orchestration.

What drt_run_sync adds

Two new parameters, both default False/20:

drt_run_sync(
    sync_name: str,
    dry_run: bool = False,
    compute_diff: bool = False,    # NEW
    diff_limit: int = 20,           # NEW
)

When set with dry_run=True, the response carries a structured diff field via the existing cli/output.diff_to_dict serialiser, so an LLM can preview added / updated / deleted / unchanged records for queryable destinations before committing.

Contract: compute_diff=True without dry_run=True returns a structured error rather than running against a live destination. Matches the CLI's --diff requires --dry-run contract.

Docstring + README catch-up

• Module docstring now lists 9 tools (was 7; missing run_test + get_history + new doctor)
• drt_get_history — registered in code since feat: sync execution history — drt status --history + drt_get_history MCP tool (#276) #445 but missing from the docstring — is now listed there
• README.md MCP tool table updated to 9 tools
• README.ja.md MCP tool table mirrored
• CHANGELOG [Unreleased] → Changed (Internal) entry

Tests

5 new tests in tests/unit/test_mcp.py:

Test	Coverage
test_server_lists_drt_doctor_tool	Registration check
test_run_sync_compute_diff_requires_dry_run	Contract error path (no live-dest accident)
test_doctor_returns_structured_report	Shape contract — {passed, checks} + per-check keys
test_doctor_passes_on_well_formed_project	Happy path on fixture project + fake ~/.drt/profiles.yml
test_doctor_fails_without_project_file	passed=False path

Test plan

• pytest tests/unit/test_mcp.py — 19 passed (14 existing + 5 new)
• Full unit + contracts: 1466 passed
• make lint — ruff + mypy clean
• CI green on 3.10–3.13 + CodeQL

Out of scope (deliberate)

• drt_list_connectors doesn't yet enumerate Mixpanel / Amazon S3 / Twilio / Intercom / Email SMTP / Salesforce Bulk / Staged Upload / Google Ads / Amplitude / Zendesk — a separate drift. Keeping this PR focused on the two flagged gaps.
• No new MCP tools beyond the two listed; the existing surface is preserved.

Sequence

This is the MCP leg of the skill / MCP refresh:

1. ✅ /drt-debug refresh — chore(skill): refresh /drt-debug — catch up to v0.7+ features (3-month gap) #625
2. ✅ /drt-init refresh — chore(skill): refresh /drt-init — catch up to v0.7+ sources + flows (2-month gap) #626
3. ✅ /drt-migrate refresh — chore(skill): refresh /drt-migrate — add mirror/replace modes + post-v0.7 mappings #627
4. ⏳ /drt-create-sync GCS+Azure follow-up (after feat(destinations): add Google Cloud Storage destination (csv/json/jsonl/parquet + gzip) (closes #169) #623 feat(destinations): add Azure Blob Storage destination (csv/json/jsonl/parquet + gzip) (closes #170) #624 merge)
5. ✅ This PR — MCP refresh

🤖 Generated with Claude Code

[codecov]

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