feat(ci): comment-triggered PR fix-ups via @claude

Commenting '@claude <instruction>' on a PR runs headless Claude Code on the
PR branch (subscription auth), pushes the resulting commit — re-running the
PR checks — and replies with a summary. Owner-only trigger; runs unsandboxed
inside the ephemeral runner container per explicit maintainer sign-off.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PqGhF93UrpDNvXBLMjJENL

scripts/ci/ai_fixup.py

@@ -0,0 +1,106 @@
+#!/usr/bin/env python3
+"""Comment-triggered PR fix-ups, powered by Claude Code.
+
+Runs when a maintainer comments `@claude <instruction>` on a pull request.
+Checks out the PR head branch, hands the instruction to headless Claude Code
+(subscription OAuth auth — no API billing), commits and pushes whatever it
+changed (which re-runs the PR checks), and replies on the PR with a summary.
+
+Uses only the Python standard library plus the `claude` CLI.
+
+Required environment:
+    CLAUDE_CODE_OAUTH_TOKEN  token from `claude setup-token`
+    GITEA_TOKEN              run-scoped token (checkout auth handles the push)
+    GITEA_SERVER_URL         e.g. https://privaterepo.sitaru.org
+    GITEA_REPOSITORY         owner/repo
+    PR_NUMBER                pull request index
+    COMMENT_BODY             the triggering comment text
+"""
+
+import json
+import os
+import subprocess
+import sys
+import urllib.request
+
+TRIGGER = "@claude"
+CLAUDE_TIMEOUT_S = 2400  # 40 min ceiling for one fix-up session
+
+
+def api(path: str, payload: dict | None = None) -> dict:
+    server = os.environ["GITEA_SERVER_URL"].rstrip("/")
+    repo = os.environ["GITEA_REPOSITORY"]
+    req = urllib.request.Request(
+        f"{server}/api/v1/repos/{repo}{path}",
+        data=json.dumps(payload).encode() if payload is not None else None,
+        headers={
+            "Authorization": f"token {os.environ['GITEA_TOKEN']}",
+            "Content-Type": "application/json",
+        },
+        method="POST" if payload is not None else "GET",
+    )
+    with urllib.request.urlopen(req, timeout=30) as resp:
+        return json.loads(resp.read())
+
+
+def run(*cmd: str, **kwargs) -> subprocess.CompletedProcess:
+    return subprocess.run(cmd, check=True, capture_output=True, text=True, **kwargs)
+
+
+def main() -> int:
+    pr_number = os.environ["PR_NUMBER"]
+    instruction = os.environ["COMMENT_BODY"].strip()
+    if instruction.lower().startswith(TRIGGER):
+        instruction = instruction[len(TRIGGER):].strip()
+    if not instruction:
+        print("Empty instruction after trigger word; nothing to do")
+        return 0
+
+    pr = api(f"/pulls/{pr_number}")
+    head_ref = pr["head"]["ref"]
+    base_ref = pr["base"]["ref"]
+
+    run("git", "fetch", "origin", head_ref, base_ref)
+    run("git", "checkout", head_ref)
+
+    prompt = f"""You are working on pull request #{pr_number} ("{pr['title']}")
+in the SchoolCompare repository. The PR branch is checked out; its base is
+{base_ref}. A maintainer left this instruction on the PR:
+
+{instruction}
+
+Implement exactly what was asked, following the conventions in CLAUDE.md.
+Run any relevant tests or typechecks you can. Do NOT commit or push — the
+harness handles that. When done, summarise in a few sentences what you
+changed and how you verified it."""
+
+    proc = subprocess.run(
+        ["claude", "-p", prompt, "--dangerously-skip-permissions", "--output-format", "json"],
+        capture_output=True,
+        text=True,
+        timeout=CLAUDE_TIMEOUT_S,
+    )
+    if proc.returncode != 0:
+        raise RuntimeError(f"claude CLI failed:\n{proc.stderr[-2000:]}")
+    summary = json.loads(proc.stdout)["result"].strip()
+
+    changed = run("git", "status", "--porcelain").stdout.strip()
+    if changed:
+        run("git", "config", "user.name", "Claude (CI)")
+        run("git", "config", "user.email", "noreply@anthropic.com")
+        run("git", "add", "-A")
+        title = instruction.splitlines()[0][:60]
+        run("git", "commit", "-m", f"ai: {title}\n\nRequested via PR comment; applied by Claude Code in CI.")
+        run("git", "push", "origin", head_ref)
+        sha = run("git", "rev-parse", "--short", "HEAD").stdout.strip()
+        reply = f"## 🤖 Claude fix-up applied (`{sha}`)\n\n{summary}\n\n_PR checks re-run automatically on the new commit._"
+    else:
+        reply = f"## 🤖 Claude fix-up — no changes made\n\n{summary}"
+
+    api(f"/issues/{pr_number}/comments", {"body": reply})
+    print(reply)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())