feat(mcp): MCP/HTTP affected tool (Phase 2)

[SutuSebastian]

Summary

• Adds MCP/HTTP affected tool with { paths?, changed_since?, test_glob?, max_depth? } — same preprocessor as codemap affected → affected-tests recipe.
• Extracts shared logic to src/application/affected-engine.ts (CLI + transports).
• Documents in mcp-instructions + skill; registers in CODEMAP_MCP_TOOLS allowlist.

Follow-up to #132 (Phase 2 optional from agent-surface plan).

Test plan

• bun test src/application/affected-engine.test.ts
• bun test src/application/mcp-server.test.ts (affected + allowlist)
• bun test src/application/http-server.test.ts (affected)
• bun test src/cli/cmd-affected.test.ts
• bun run typecheck

Summary by CodeRabbit

• New Features

  • Added "affected" tool to automatically identify tests impacted by file changes. Supports explicit path specification or git-based change detection with configurable depth limits and test matching options.

• Documentation

  • Updated guidance on using the affected tool in agent workflows and CLI commands with example usage patterns.

[changeset-bot]

🦋 Changeset detected

Latest commit: bff97fd

The changes in this PR will be included in the next version bump.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7ee50c4f-eac9-4bd7-ab79-39f42652a111

📥 Commits

Reviewing files that changed from the base of the PR and between 7ad7dd8 and bff97fd.

📒 Files selected for processing (19)

• .codemap/.gitignore
• docs/architecture.md
• docs/glossary.md
• docs/plans/affected-tests-recipe.md
• docs/plans/agent-surface-delivery.md
• docs/roadmap.md
• src/application/affected-engine.test.ts
• src/application/affected-engine.ts
• src/application/http-server.test.ts
• src/application/mcp-server.test.ts
• src/application/mcp-server.ts
• src/application/recipe-params.test.ts
• src/application/recipe-params.ts
• src/application/recipe-recency.ts
• src/application/tool-handlers.ts
• src/cli/cmd-affected.test.ts
• src/cli/cmd-affected.ts
• templates/agent-content/skill/10-recipes-context.md
• templates/recipes/affected-tests.md

📝 Walkthrough

Walkthrough

This PR introduces a new MCP/HTTP affected tool that identifies test dependencies from changed file paths. The change extracts shared logic into a reusable affected-engine module, refactors the existing CLI to delegate to it, wires the tool through both MCP and HTTP dispatch layers, and updates planning and documentation to reflect the new Phase 2 delivery.

Changes

MCP/HTTP Affected Tool Implementation

Layer / File(s)	Summary
Shared affected-engine module src/application/affected-engine.ts, src/application/affected-engine.test.ts	New module exports path normalization (normalizeChangedPathList, joinChangedPaths), change resolution (resolveAffectedChangedPaths using git or explicit paths), and recipe execution (executeAffectedTests via the affected-tests recipe). Comprehensive unit tests validate path deduplication, git-based change detection, and transitive test discovery with action metadata.
CLI refactoring to shared engine src/cli/cmd-affected.ts	Delegates path normalization, change resolution, and test execution to the affected-engine module. Removes inline recipe parameter building and SQL query logic; re-exports CHANGED_PATH_DELIM and joinChangedPaths from the engine. Error handling and output formatting preserved for CLI clients.
Affected tool handler and schema src/application/tool-handlers.ts	Implements handleAffected that composes resolveAffectedChangedPaths and executeAffectedTests from the shared engine. Exports affectedArgsSchema and AffectedArgs for request validation; converts engine failures and exceptions into ToolResult errors with appropriate status codes.
MCP server registration and integration tests src/application/mcp-server.ts, src/application/mcp-server.test.ts	Registers affected as an MCP tool via registerAffectedTool, wrapping the handler with wrapToolResult. Tests verify tool listing, request/response payload structure with run-affected-tests actions, and allowlist-based gating via CODEMAP_MCP_TOOLS.
HTTP server dispatch and integration tests src/application/http-server.ts, src/application/http-server.test.ts	Extends dispatchTool to route POST /tool/affected requests; adds affected to the TOOL_NAMES catalog. Tests verify tool response envelope and HTTP 400 validation errors for malformed inputs like non-integer max_depth.
Allowlist registration and documentation src/application/mcp-tool-allowlist.ts, .changeset/mcp-affected-tool.md, docs/plans/*.md, templates/agent-content/*.md	Adds "affected" to recognized MCP tool names. Updates planning documents to mark PR 5 as merged and the MCP affected tool as shipped Phase 2 delivery. Updates agent guidance with affected tool contract, parameter semantics, and calling examples for both CLI and MCP/HTTP forms.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• stainless-code/codemap#35: Both PRs extend the MCP server/tooling scaffolding, with the main PR adding a new MCP affected tool wired into src/application/mcp-server.ts and tool-handlers.ts (in the same MCP transport/registry layer introduced by PR #35).

• stainless-code/codemap#44: Both PRs extend the HTTP tool-dispatch layer—main PR adds the new affected tool to src/application/http-server.ts's TOOL_NAMES catalog and dispatchTool routing (via affectedArgsSchema/handleAffected), building on the HTTP API server infrastructure introduced in PR #44).

Poem

🐰 Hops with glee through paths aflame,
A new tool born—the "affected" name!
Shared engine sings, from CLI to MCP's call,
One module feeds them all! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 27.27% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding an MCP/HTTP affected tool as a Phase 2 follow-up. It is concise, specific, and clearly reflects the primary feature introduced across the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/mcp-affected-tool

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