feat: serialize autonomous release runs (#335)

src/release_engine.py

@@ -2,12 +2,16 @@
 from __future__ import annotations
 
 import argparse
+import errno
+import fcntl
 import json
 import os
 import re
 import signal
 import shlex
 import subprocess
+import tempfile
+import time
 from dataclasses import asdict, dataclass
 from pathlib import Path
 from typing import Any, Iterable, Protocol
@@ -97,9 +101,71 @@ class StateStore:
 
     def save(self, state: RunState) -> None:
         self.path.parent.mkdir(parents=True, exist_ok=True)
-        tmp = self.path.with_name(self.path.name + ".tmp")
-        tmp.write_text(json.dumps(asdict(state), indent=2) + "\n")
-        tmp.replace(self.path)
+        temporary_path = None
+        try:
+            with tempfile.NamedTemporaryFile(
+                mode="w",
+                encoding="utf-8",
+                dir=self.path.parent,
+                prefix=self.path.name + ".",
+                suffix=".tmp",
+                delete=False,
+            ) as temporary:
+                temporary_path = Path(temporary.name)
+                temporary.write(json.dumps(asdict(state), indent=2) + "\n")
+                temporary.flush()
+                os.fsync(temporary.fileno())
+            os.replace(temporary_path, self.path)
+            directory = os.open(self.path.parent, os.O_RDONLY | os.O_DIRECTORY)
+            try:
+                os.fsync(directory)
+            finally:
+                os.close(directory)
+        finally:
+            if temporary_path is not None:
+                temporary_path.unlink(missing_ok=True)
+
+
+class RepositoryLease:
+    """Non-blocking, process-backed single-writer lease for one worktree."""
+
+    def __init__(self, repo_path: Path):
+        self.path = Path(repo_path).resolve() / ".release-engine" / "run.lock"
+        self._file = None
+
+    def __enter__(self):
+        self.path.parent.mkdir(parents=True, exist_ok=True)
+        lock_file = self.path.open("a+", encoding="utf-8")
+        try:
+            fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
+        except OSError as exc:
+            if exc.errno in (errno.EACCES, errno.EAGAIN):
+                detail = ""
+                try:
+                    lock_file.seek(0)
+                    metadata = json.loads(lock_file.read(512))
+                    owner_pid = int(metadata["pid"])
+                    acquired_at = float(metadata["acquired_at"])
+                    detail = f" (owner pid={owner_pid}, acquired_at={acquired_at:.3f})"
+                except (KeyError, TypeError, ValueError, json.JSONDecodeError):
+                    pass
+                lock_file.close()
+                raise RuntimeError(f"release run already active{detail}") from exc
+            lock_file.close()
+            raise
+        self._file = lock_file
+        lock_file.seek(0)
+        lock_file.truncate()
+        lock_file.write(json.dumps({"pid": os.getpid(), "acquired_at": time.time()}) + "\n")
+        lock_file.flush()
+        os.fsync(lock_file.fileno())
+        return self
+
+    def __exit__(self, exc_type, exc, traceback):
+        if self._file is not None:
+            fcntl.flock(self._file.fileno(), fcntl.LOCK_UN)
+            self._file.close()
+            self._file = None
 
 
 def _label_names(labels: Iterable[Any]) -> list[str]:
@@ -267,6 +333,10 @@ class ReleaseEngine:
         self.store = StateStore(config.state_path)
 
     def execute(self, issue_number: int | None = None, dry_run: bool = False) -> dict[str, Any]:
+        with RepositoryLease(self.config.repo_path):
+            return self._execute_locked(issue_number=issue_number, dry_run=dry_run)
+
+    def _execute_locked(self, issue_number: int | None = None, dry_run: bool = False) -> dict[str, Any]:
         deadlines = {
             "agent timeout seconds": self.config.agent_timeout_seconds,
             "test timeout seconds": self.config.test_timeout_seconds,