fix(cache): make shared cache state survive a second instance

Installing a second LoRA Manager instance (standalone or a second
ComfyUI install) that shares the settings directory puts two processes
on the same cache databases. Three things made that unsafe.

- The updater preserved cache/ and model_cache/ but not a legacy
  recipe_cache/ directory, so a portable install predating the cache/
  move lost its recipe database on a git-based update. Add it to
  _PRESERVE_DIRS and to .gitignore.
- Cache connections used the sqlite3 default 5s timeout, which a
  scanning instance can exceed, turning a concurrent write into
  "database is locked". Route every shared cache connection through
  connect_cache_db(), which raises the timeout to 30s and sets
  busy_timeout + synchronous=NORMAL to match the existing WAL mode.
  App-private databases (download queue, update history) are unchanged.
- A full-table cache replace is a read-modify-write that SQLite cannot
  make atomic across processes, so two instances could interleave and
  one snapshot could overwrite the other. Guard the recipe and model
  save_cache paths with a cross-process advisory lock (flock on POSIX,
  msvcrt on Windows). Locking is best-effort: if it is unavailable the
  call proceeds and the SQLite busy timeout is the fallback.

The lock file is a hidden sibling of the database and is deliberately
never unlinked, so a second process cannot lock a fresh inode.

.gitignore

@@ -15,6 +15,7 @@ node_modules/
 coverage/
 .coverage
 model_cache/
+recipe_cache/
 
 # agent / dev tooling
 .opencode/

py/routes/update_routes.py

@@ -21,7 +21,20 @@ NETWORK_EXCEPTIONS = (ClientError, OSError, asyncio.TimeoutError)
 # otherwise delete them because they are untracked and, in released tags,
 # not listed in ``.gitignore``. ``-e`` excludes a path from cleaning
 # regardless of whether it is ignored.
-_PRESERVE_DIRS = ('settings.json', 'civitai', 'wildcards', 'backups', 'stats', 'logs', 'cache', 'model_cache')
+# ``cache`` covers the resolved cache tree (cache/model, cache/recipe,
+# cache/fts, ...); the legacy ``recipe_cache`` / ``model_cache`` directories
+# are listed too because a portable install can predate the cache/ move.
+_PRESERVE_DIRS = (
+    'settings.json',
+    'civitai',
+    'wildcards',
+    'backups',
+    'stats',
+    'logs',
+    'cache',
+    'model_cache',
+    'recipe_cache',
+)
 
 
 def _clean_excludes() -> List[str]:

py/services/persistent_model_cache.py

@@ -6,7 +6,9 @@ import threading
 from dataclasses import dataclass, field
 from typing import Any, Dict, List, Mapping, Optional, Sequence, Tuple
 
+from ..utils.cache_db import connect_cache_db
 from ..utils.cache_paths import CacheType, resolve_cache_path_with_migration
+from ..utils.file_lock import exclusive_lock
 from .model_sources import normalize_metadata_source
 
 logger = logging.getLogger(__name__)
@@ -257,6 +259,10 @@ class PersistentModelCache:
             return
         try:
             with self._db_lock:
+                # Cross-process serialization: another LoRA Manager instance may
+                # share this settings directory, and the read-merge-write below
+                # spans several statements.
+                with exclusive_lock(self._db_path):
                     conn = self._connect()
                     try:
                         conn.execute("PRAGMA foreign_keys = ON")
@@ -650,16 +656,14 @@ class PersistentModelCache:
                 conn.execute(f"ALTER TABLE models ADD COLUMN {column} {definition}")
 
     def _connect(self, readonly: bool = False) -> sqlite3.Connection:
-        uri = False
-        path = self._db_path
-        if readonly:
-            if not os.path.exists(path):
-                raise FileNotFoundError(path)
-            path = f"file:{path}?mode=ro"
-            uri = True
-        conn = sqlite3.connect(path, check_same_thread=False, uri=uri, detect_types=sqlite3.PARSE_DECLTYPES)
-        conn.row_factory = sqlite3.Row
-        return conn
+        if readonly and not os.path.exists(self._db_path):
+            raise FileNotFoundError(self._db_path)
+        return connect_cache_db(
+            self._db_path,
+            readonly=readonly,
+            detect_types=sqlite3.PARSE_DECLTYPES,
+            row_factory=sqlite3.Row,
+        )
 
     def _prepare_model_row(self, model_type: str, item: Dict[str, Any]) -> Tuple[Any, ...]:
         # Keep `source_*` and the legacy `hf_url` alias consistent no matter

py/services/persistent_recipe_cache.py

@@ -19,7 +19,9 @@ import threading
 from dataclasses import dataclass, field
 from typing import Any, Dict, List, Optional, Set, Tuple
 
+from ..utils.cache_db import connect_cache_db
 from ..utils.cache_paths import CacheType, resolve_cache_path_with_migration
+from ..utils.file_lock import exclusive_lock
 
 logger = logging.getLogger(__name__)
 
@@ -197,6 +199,10 @@ class PersistentRecipeCache:
 
         try:
             with self._db_lock:
+                # Cross-process serialization: another LoRA Manager instance may
+                # share this settings directory, and a full-table replace is a
+                # read-modify-write that SQLite alone cannot make atomic.
+                with exclusive_lock(self._db_path):
                     conn = self._connect()
                     try:
                         conn.execute("PRAGMA foreign_keys = ON")
@@ -515,16 +521,14 @@ class PersistentRecipeCache:
                 logger.warning("Failed to initialize persistent recipe cache schema: %s", exc)
 
     def _connect(self, readonly: bool = False) -> sqlite3.Connection:
-        uri = False
-        path = self._db_path
-        if readonly:
-            if not os.path.exists(path):
-                raise FileNotFoundError(path)
-            path = f"file:{path}?mode=ro"
-            uri = True
-        conn = sqlite3.connect(path, check_same_thread=False, uri=uri, detect_types=sqlite3.PARSE_DECLTYPES)
-        conn.row_factory = sqlite3.Row
-        return conn
+        if readonly and not os.path.exists(self._db_path):
+            raise FileNotFoundError(self._db_path)
+        return connect_cache_db(
+            self._db_path,
+            readonly=readonly,
+            detect_types=sqlite3.PARSE_DECLTYPES,
+            row_factory=sqlite3.Row,
+        )
 
     def _prepare_recipe_row(self, recipe: Dict[str, Any], json_path: str) -> Tuple[Any, ...]:
         """Convert a recipe dict to a row tuple for SQLite insertion."""

py/services/recipe_fts_index.py

@@ -16,6 +16,7 @@ import threading
 import time
 from typing import Any, Dict, List, Optional, Set, Tuple
 
+from ..utils.cache_db import connect_cache_db
 from ..utils.cache_paths import CacheType, resolve_cache_path_with_migration
 
 logger = logging.getLogger(__name__)
@@ -633,16 +634,13 @@ class RecipeFTSIndex:
 
     def _connect(self, readonly: bool = False) -> sqlite3.Connection:
         """Create a database connection."""
-        uri = False
-        path = self._db_path
-        if readonly:
-            if not os.path.exists(path):
-                raise FileNotFoundError(path)
-            path = f"file:{path}?mode=ro"
-            uri = True
-        conn = sqlite3.connect(path, check_same_thread=False, uri=uri)
-        conn.row_factory = sqlite3.Row
-        return conn
+        if readonly and not os.path.exists(self._db_path):
+            raise FileNotFoundError(self._db_path)
+        return connect_cache_db(
+            self._db_path,
+            readonly=readonly,
+            row_factory=sqlite3.Row,
+        )
 
     def _remove_recipe_locked(self, conn: sqlite3.Connection, recipe_id: str) -> None:
         """Remove a recipe entry. Caller must hold the lock."""

py/services/recipe_scanner.py

@@ -2729,6 +2729,10 @@ class RecipeScanner:
                     try:
                         # Invalidate persistent cache so the sync path does a
                         # full directory scan instead of reconciling stale data.
+                        # This is the deliberate escape hatch from the
+                        # all-missing prune guard: an explicit user rebuild is
+                        # allowed to clear the stored cache, while an implicit
+                        # startup scan is not.
                         if self._persistent_cache:
                             self._persistent_cache.save_cache([], {})
                         self._json_path_map = {}

py/services/tag_fts_index.py

@@ -20,6 +20,7 @@ import time
 from pathlib import Path
 from typing import Any, Dict, List, Optional, Set
 
+from ..utils.cache_db import connect_cache_db
 from ..utils.cache_paths import CacheType, resolve_cache_path_with_migration
 
 logger = logging.getLogger(__name__)
@@ -677,16 +678,13 @@ class TagFTSIndex:
 
     def _connect(self, readonly: bool = False) -> sqlite3.Connection:
         """Create a database connection."""
-        uri = False
-        path = self._db_path
-        if readonly:
-            if not os.path.exists(path):
-                raise FileNotFoundError(path)
-            path = f"file:{path}?mode=ro"
-            uri = True
-        conn = sqlite3.connect(path, check_same_thread=False, uri=uri)
-        conn.row_factory = sqlite3.Row
-        return conn
+        if readonly and not os.path.exists(self._db_path):
+            raise FileNotFoundError(self._db_path)
+        return connect_cache_db(
+            self._db_path,
+            readonly=readonly,
+            row_factory=sqlite3.Row,
+        )
 
     def _build_fts_query(self, query: str) -> str:
         """Build an FTS5 query string with prefix matching.

py/utils/cache_db.py

@@ -0,0 +1,81 @@
+"""Shared SQLite connection setup for LoRA Manager cache databases.
+
+Cache databases live under the settings directory (``cache/model/<library>.sqlite``,
+``cache/recipe/<library>.sqlite``, ``cache/fts/*.sqlite``). With portable mode or a
+pinned ``LORA_MANAGER_SETTINGS_DIR`` off, that directory is shared by every ComfyUI
+instance on the machine, so two processes can open the same cache file at once.
+
+SQLite serializes writers, but the default ``timeout`` is 5 seconds: a second
+instance that writes while the first is mid-transaction fails with "database is
+locked". These settings make concurrent access wait instead of failing, and keep
+the write path in WAL so readers are never blocked by a writer.
+"""
+
+from __future__ import annotations
+
+import sqlite3
+from typing import Any
+
+# How long a connection waits for a competing writer before raising.
+CONCURRENT_TIMEOUT_SECONDS = 30.0
+
+# PRAGMAs applied to every cache connection.
+#
+# ``busy_timeout`` mirrors the connection timeout so a busy database is retried
+# inside SQLite rather than surfacing as an immediate error. ``synchronous=NORMAL``
+# is the documented companion of WAL: still crash-safe, far fewer fsyncs.
+_TUNING_PRAGMAS = (
+    "PRAGMA busy_timeout = 30000",
+    "PRAGMA synchronous = NORMAL",
+)
+
+
+def connect_cache_db(
+    path: str,
+    *,
+    readonly: bool = False,
+    uri: bool = False,
+    detect_types: int = 0,
+    row_factory: Any = None,
+) -> sqlite3.Connection:
+    """Open a cache database with multi-instance-friendly settings.
+
+    Args:
+        path: Database path, or a ``file:`` URI when *uri* is True.
+        readonly: Open through a read-only URI. Callers still pass the
+            plain path; the ``mode=ro`` suffix is added here. The
+            write-oriented tuning pragmas are skipped in that case so a
+            read-only connection never attempts to change the file.
+        uri: Treat *path* as a SQLite URI.
+        detect_types: Forwarded to :func:`sqlite3.connect`.
+        row_factory: Optional ``row_factory`` for the connection.
+
+    Returns:
+        A configured :class:`sqlite3.Connection`.
+    """
+    if readonly:
+        if not uri and not path.startswith("file:"):
+            path = f"file:{path}?mode=ro"
+            uri = True
+
+    conn = sqlite3.connect(
+        path,
+        check_same_thread=False,
+        uri=uri,
+        detect_types=detect_types,
+        timeout=CONCURRENT_TIMEOUT_SECONDS,
+    )
+    if row_factory is not None:
+        conn.row_factory = row_factory
+
+    try:
+        for pragma in _TUNING_PRAGMAS:
+            # A read-only connection may reject write PRAGMAs; they are not
+            # needed there anyway.
+            conn.execute(pragma)
+    except sqlite3.Error:
+        # Tuning is best-effort: a connection that cannot set pragmas still
+        # works, just without the concurrency headroom.
+        pass
+
+    return conn

py/utils/file_lock.py

@@ -0,0 +1,146 @@
+"""Cross-process advisory locking for shared LoRA Manager state.
+
+Two LoRA Manager processes (the ComfyUI plugin and a standalone server, or two
+ComfyUI installs pointed at the same settings directory) can open the same cache
+database. SQLite serializes individual statements, but it cannot make a
+read-modify-write *sequence* atomic across processes: two full-table cache
+replacements can interleave so that one process's snapshot overwrites the
+other's.
+
+This module provides a small advisory file lock for those sequences. It is
+deliberately non-fatal: if locking is unavailable or the wait times out, callers
+keep working with SQLite's own ``busy_timeout`` as the fallback.
+"""
+
+from __future__ import annotations
+
+import logging
+import os
+import time
+
+logger = logging.getLogger(__name__)
+
+# How long to wait for another process to release the lock before giving up.
+DEFAULT_LOCK_TIMEOUT_SECONDS = 30.0
+_POLL_INTERVAL_SECONDS = 0.05
+
+# Windows byte-range locks; fcntl.flock on POSIX.
+try:  # pragma: no cover - platform dependent
+    import fcntl
+except ImportError:  # pragma: no cover - Windows
+    fcntl = None  # type: ignore[assignment]
+
+try:  # pragma: no cover - Windows only
+    import msvcrt
+except ImportError:  # pragma: no cover - POSIX
+    msvcrt = None  # type: ignore[assignment]
+
+
+class FileLockUnavailable(RuntimeError):
+    """Raised when the lock could not be acquired within the timeout."""
+
+
+def lock_path_for(db_path: str) -> str:
+    """Return the sibling lock file path used for *db_path*."""
+    absolute = os.path.abspath(db_path)
+    directory = os.path.dirname(absolute)
+    if not directory:
+        raise ValueError(f"Cannot derive a lock directory from {db_path!r}")
+    return os.path.join(directory, f".{os.path.basename(absolute)}.lock")
+
+
+class CrossProcessLock:
+    """A best-effort advisory lock backed by a lock file.
+
+    The lock file is a sibling of the guarded resource and is never deleted:
+    unlinking it would let a second process create a fresh inode and lock that
+    instead, defeating mutual exclusion.
+    """
+
+    def __init__(self, path: str, timeout: float = DEFAULT_LOCK_TIMEOUT_SECONDS):
+        self.path = path
+        self.timeout = timeout
+        self._handle = None
+
+    def acquire(self) -> bool:
+        """Try to take the lock, waiting up to ``timeout`` seconds.
+
+        Returns:
+            True when the lock is held (including when another lock is already
+            held by *this* process — the calls are not reentrant, so callers must
+            not nest them). False when locking is unsupported or timed out; the
+            caller should proceed and rely on the SQLite busy timeout instead.
+        """
+        if fcntl is None and msvcrt is None:  # pragma: no cover - exotic platform
+            return False
+
+        os.makedirs(os.path.dirname(self.path), exist_ok=True)
+        try:
+            handle = open(self.path, "a+b")
+        except OSError as exc:
+            logger.debug("Could not open lock file %s: %s", self.path, exc)
+            return False
+
+        deadline = time.monotonic() + max(0.0, self.timeout)
+        while True:
+            if self._try_lock(handle):
+                self._handle = handle
+                return True
+            if time.monotonic() >= deadline:
+                handle.close()
+                return False
+            time.sleep(_POLL_INTERVAL_SECONDS)
+
+    def release(self) -> None:
+        """Release the lock if held. Safe to call more than once."""
+        handle = self._handle
+        if handle is None:
+            return
+        self._handle = None
+        try:
+            self._unlock(handle)
+        except OSError as exc:  # pragma: no cover - defensive
+            logger.debug("Failed to release lock %s: %s", self.path, exc)
+        finally:
+            try:
+                handle.close()
+            except OSError:  # pragma: no cover - defensive
+                pass
+
+    def __enter__(self) -> "CrossProcessLock":
+        self.acquire()
+        return self
+
+    def __exit__(self, *_exc_info: object) -> None:
+        self.release()
+
+    # -- platform primitives -------------------------------------------------
+
+    def _try_lock(self, handle) -> bool:
+        if fcntl is not None:
+            try:
+                fcntl.flock(handle.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
+                return True
+            except OSError:
+                return False
+        if msvcrt is not None:  # pragma: no cover - Windows
+            try:
+                handle.seek(0)
+                msvcrt.locking(handle.fileno(), msvcrt.LK_NBLCK, 1)
+                return True
+            except OSError:
+                return False
+        return False
+
+    def _unlock(self, handle) -> None:
+        if fcntl is not None:
+            fcntl.flock(handle.fileno(), fcntl.LOCK_UN)
+            return
+        if msvcrt is not None:  # pragma: no cover - Windows
+            handle.seek(0)
+            msvcrt.locking(handle.fileno(), msvcrt.LK_UNLCK, 1)
+
+
+def exclusive_lock(db_path: str, timeout: float = DEFAULT_LOCK_TIMEOUT_SECONDS):
+    """Return a :class:`CrossProcessLock` for the database at *db_path*."""
+    return CrossProcessLock(lock_path_for(db_path), timeout=timeout)

tests/utils/test_cache_db.py

@@ -0,0 +1,107 @@
+"""Tests for the shared cache SQLite connection settings (:mod:`py.utils.cache_db`).
+
+Two LoRA Manager processes can share one settings directory, so cache
+connections must tolerate a competing writer instead of failing immediately
+with "database is locked".
+"""
+
+from __future__ import annotations
+
+import sqlite3
+import threading
+import time
+
+from py.utils.cache_db import CONCURRENT_TIMEOUT_SECONDS, connect_cache_db
+
+
+def test_busy_timeout_pragma_is_applied(tmp_path):
+    """The connection must retry inside SQLite, not just at connect() time."""
+    conn = connect_cache_db(str(tmp_path / "cache.sqlite"))
+    try:
+        value = conn.execute("PRAGMA busy_timeout").fetchone()[0]
+    finally:
+        conn.close()
+    assert value == int(CONCURRENT_TIMEOUT_SECONDS * 1000)
+
+
+def test_waiting_writer_succeeds_after_competing_writer_commits(tmp_path):
+    """A blocked writer waits for the lock instead of raising."""
+    db_path = str(tmp_path / "cache.sqlite")
+
+    holder = connect_cache_db(db_path)
+    holder.execute("CREATE TABLE t (v INTEGER)")
+    holder.commit()
+    holder.execute("BEGIN IMMEDIATE")
+
+    def release_after_delay() -> None:
+        time.sleep(0.5)
+        holder.commit()
+
+    releaser = threading.Thread(target=release_after_delay)
+    releaser.start()
+    try:
+        waiter = connect_cache_db(db_path)
+        try:
+            # Under the old 5s default this still worked, but an immediate
+            # failure is what low-timeout connections produced; assert the
+            # write lands rather than propagating "database is locked".
+            waiter.execute("INSERT INTO t VALUES (1)")
+            waiter.commit()
+        finally:
+            waiter.close()
+    finally:
+        releaser.join()
+        holder.close()
+
+    check = connect_cache_db(db_path)
+    try:
+        assert check.execute("SELECT COUNT(*) FROM t").fetchone()[0] == 1
+    finally:
+        check.close()
+
+
+def test_readwrite_connection_uses_row_factory(tmp_path):
+    conn = connect_cache_db(str(tmp_path / "cache.sqlite"), row_factory=sqlite3.Row)
+    try:
+        conn.execute("CREATE TABLE t (v INTEGER)")
+        conn.execute("INSERT INTO t VALUES (7)")
+        conn.commit()
+        row = conn.execute("SELECT v FROM t").fetchone()
+        assert row["v"] == 7
+    finally:
+        conn.close()
+
+
+def test_readonly_connection_reads_without_writing(tmp_path):
+    db_path = str(tmp_path / "cache.sqlite")
+    writer = connect_cache_db(db_path)
+    writer.execute("CREATE TABLE t (v INTEGER)")
+    writer.execute("INSERT INTO t VALUES (1)")
+    writer.commit()
+    writer.close()
+
+    conn = connect_cache_db(db_path, readonly=True)
+    try:
+        assert conn.execute("SELECT v FROM t").fetchone()[0] == 1
+    finally:
+        conn.close()
+
+
+def test_readonly_connection_rejects_writes(tmp_path):
+    db_path = str(tmp_path / "cache.sqlite")
+    writer = connect_cache_db(db_path)
+    writer.execute("CREATE TABLE t (v INTEGER)")
+    writer.commit()
+    writer.close()
+
+    conn = connect_cache_db(db_path, readonly=True)
+    try:
+        try:
+            conn.execute("INSERT INTO t VALUES (1)")
+            conn.commit()
+        except sqlite3.OperationalError:
+            pass
+        else:  # pragma: no cover - would mean mode=ro was not applied
+            raise AssertionError("read-only connection accepted a write")
+    finally:
+        conn.close()

tests/utils/test_file_lock.py

@@ -0,0 +1,118 @@
+"""Tests for the cross-process advisory lock (:mod:`py.utils.file_lock`)."""
+
+from __future__ import annotations
+
+import os
+import time
+
+import pytest
+
+from py.utils.file_lock import (
+    CrossProcessLock,
+    FileLockUnavailable,
+    exclusive_lock,
+    lock_path_for,
+)
+
+
+def test_lock_path_is_a_sibling_of_the_resource(tmp_path):
+    db_path = str(tmp_path / "recipe" / "default.sqlite")
+    lock_path = lock_path_for(db_path)
+
+    assert os.path.dirname(lock_path) == os.path.dirname(db_path)
+    assert os.path.basename(lock_path) == ".default.sqlite.lock"
+
+
+def test_acquire_and_release_round_trip(tmp_path):
+    lock = exclusive_lock(str(tmp_path / "cache.sqlite"))
+
+    assert lock.acquire() is True
+    lock.release()
+    # Releasing twice must be safe.
+    lock.release()
+    # ...and the lock is reusable afterwards.
+    assert lock.acquire() is True
+    lock.release()
+
+
+def test_second_lock_holder_waits_until_release(tmp_path):
+    """A held lock blocks a competing holder for the same resource."""
+    db_path = str(tmp_path / "cache.sqlite")
+    first = exclusive_lock(db_path)
+    second = CrossProcessLock(lock_path_for(db_path), timeout=0.2)
+
+    assert first.acquire() is True
+    try:
+        started = time.monotonic()
+        assert second.acquire() is False
+        # It must have waited for the timeout rather than failing instantly.
+        assert time.monotonic() - started >= 0.15
+    finally:
+        first.release()
+
+    # Once released, the contender gets the lock.
+    assert second.acquire() is True
+    second.release()
+
+
+def test_context_manager_releases_on_exception(tmp_path):
+    lock = exclusive_lock(str(tmp_path / "cache.sqlite"))
+    contender = CrossProcessLock(lock.path, timeout=0.2)
+
+    with pytest.raises(RuntimeError):
+        with lock:
+            raise RuntimeError("boom")
+
+    assert contender.acquire() is True
+    contender.release()
+
+
+def test_lock_file_is_not_deleted(tmp_path):
+    """Deleting the lock file would let a second process lock a fresh inode."""
+    lock = exclusive_lock(str(tmp_path / "cache.sqlite"))
+    assert lock.acquire() is True
+    lock.release()
+
+    assert os.path.exists(lock.path)
+
+
+def test_unsupported_platform_degrades_gracefully(tmp_path, monkeypatch):
+    """Without a platform primitive the lock reports failure instead of raising."""
+    import py.utils.file_lock as file_lock_module
+
+    monkeypatch.setattr(file_lock_module, "fcntl", None)
+    monkeypatch.setattr(file_lock_module, "msvcrt", None)
+
+    lock = exclusive_lock(str(tmp_path / "cache.sqlite"))
+    assert lock.acquire() is False
+    # Callers use it as a context manager and continue without the lock.
+    with exclusive_lock(str(tmp_path / "cache.sqlite")):
+        pass
+
+
+def test_file_lock_unavailable_is_exported():
+    assert issubclass(FileLockUnavailable, RuntimeError)
+
+
+def test_save_cache_creates_lock_next_to_database(tmp_path):
+    """The recipe cache write path actually takes the cross-process lock."""
+    from py.services.persistent_recipe_cache import PersistentRecipeCache
+
+    db_path = tmp_path / "recipe_cache.sqlite"
+    cache = PersistentRecipeCache(db_path=str(db_path))
+    assert cache.save_cache([{"id": "r1", "title": "One"}], {"r1": "/tmp/r1.json"})
+
+    assert os.path.exists(lock_path_for(str(db_path)))
+
+
+def test_save_cache_releases_lock_after_write(tmp_path):
+    """A second writer must not be blocked once the first has finished."""
+    from py.services.persistent_recipe_cache import PersistentRecipeCache
+
+    db_path = tmp_path / "recipe_cache.sqlite"
+    cache = PersistentRecipeCache(db_path=str(db_path))
+    cache.save_cache([{"id": "r1", "title": "One"}], {"r1": "/tmp/r1.json"})
+
+    contender = CrossProcessLock(lock_path_for(str(db_path)), timeout=0.2)
+    assert contender.acquire() is True
+    contender.release()