ci: restore the Claude Code workflow and .mcp.json, lost in the v2 tree swap (#1869)

* ci: restore the Claude Code workflow, lost in the v2 tree swap

Closes #1850.

Restored byte-for-byte from ac3c1a12 (sha256
1c44f2d9d51c936adb40c9acefd4b44628fe7810360e2f8196034347f9d2602d,
3592 bytes). No content changes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YAt8rqxysNbhYWLhoRm3fU

* ci: restore .mcp.json, which claude.yml's --mcp-config points at

The restored workflow runs with `--mcp-config .mcp.json` and
`--allowedTools "Bash,mcp__mcp-docs"`, so without this file the mcp-docs
server never registers and those tools do not resolve.

Lost in the same tree swap: .mcp.json survives only on v1/main, and is
absent from both main and v2/main. Restored byte-for-byte from 47f92841
(sha256 b0f0b8ea0d6c6e4bd9d19270db8c4ed13a951c6a7d8fa9a7b76d0d12ddd2491f,
123 bytes). No content changes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YAt8rqxysNbhYWLhoRm3fU

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/claude.yml

@@ -0,0 +1,93 @@
+name: Claude Code
+
+on:
+  issue_comment:
+    types: [created]
+  pull_request_review_comment:
+    types: [created]
+  issues:
+    types: [opened, assigned]
+  pull_request_review:
+    types: [submitted]
+
+jobs:
+  claude:
+    if: |
+      (
+        (github.event_name == 'issue_comment' &&
+          contains(github.event.comment.body, '@claude') &&
+          contains(fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'), github.event.comment.author_association)) ||
+        (github.event_name == 'pull_request_review_comment' &&
+          contains(github.event.comment.body, '@claude') &&
+          contains(fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'), github.event.comment.author_association)) ||
+        (github.event_name == 'pull_request_review' &&
+          contains(github.event.review.body, '@claude') &&
+          contains(fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'), github.event.review.author_association)) ||
+        (github.event_name == 'issues' &&
+          (contains(github.event.issue.body, '@claude') || contains(github.event.issue.title, '@claude')) &&
+          contains(fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'), github.event.issue.author_association))
+      )
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: read
+      issues: read
+      id-token: write
+      actions: read
+    steps:
+      - name: Get PR details
+        if: |
+          (github.event_name == 'issue_comment' && github.event.issue.pull_request) ||
+          github.event_name == 'pull_request_review_comment' ||
+          github.event_name == 'pull_request_review'
+        id: pr
+        uses: actions/github-script@v8
+        with:
+          script: |
+            let prNumber;
+            if (context.eventName === 'issue_comment') {
+              prNumber = context.issue.number;
+            } else {
+              prNumber = context.payload.pull_request.number;
+            }
+
+            const pr = await github.rest.pulls.get({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: prNumber
+            });
+
+            core.setOutput('sha', pr.data.head.sha);
+            core.setOutput('repo', pr.data.head.repo.full_name);
+
+      - name: Checkout PR branch
+        if: steps.pr.outcome == 'success'
+        uses: actions/checkout@v6
+        with:
+          ref: ${{ steps.pr.outputs.sha }}
+          repository: ${{ steps.pr.outputs.repo }}
+          fetch-depth: 0
+
+      - name: Checkout repository
+        if: steps.pr.outcome != 'success'
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Run Claude Code
+        id: claude
+        uses: anthropics/claude-code-action@v1
+        with:
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+
+          # Allow Claude to read CI results on PRs
+          additional_permissions: |
+            actions: read
+
+          # Trigger when assigned to an issue
+          assignee_trigger: "claude"
+
+          claude_args: |
+            --mcp-config .mcp.json
+            --allowedTools "Bash,mcp__mcp-docs"
+            --append-system-prompt "If posting a comment to GitHub, give a concise summary of the comment at the top and put all the details in a <details> block. When working on MCP-related code or reviewing MCP-related changes, use the mcp-docs MCP server to look up the latest protocol documentation. For schema details, reference https://github.com/modelcontextprotocol/modelcontextprotocol/tree/main/schema which contains versioned schemas in JSON (schema.json) and TypeScript (schema.ts) formats."

.mcp.json

@@ -0,0 +1,8 @@
+{
+  "mcpServers": {
+    "mcp-docs": {
+      "type": "http",
+      "url": "https://modelcontextprotocol.io/mcp"
+    }
+  }
+}