diff --git a/pyproject.toml b/pyproject.toml
index b9578f3fc53e..5509e7aafc71 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -115,6 +115,11 @@ dependencies = [
   # imports win32security/win32file/etc. directly — declare pywin32 rather than
   # relying on the concurrent-log-handler → portalocker transitive chain.
   "pywin32>=306,<312; sys_platform == 'win32'",
+  # Host-projected plugins use cross-process locks on every platform. Keep
+  # portalocker direct: its existing lockfile entries are otherwise reachable
+  # only through platform/optional transitive dependencies, so a fresh lean
+  # Linux install can load the plugin but fail closed on its first lock.
+  "portalocker>=2.8.0,<4",
   # Image resize recovery for the vision tools. Pillow shrinks oversized images
   # (>5 MB or >8000px) at embed time; without it the byte AND pixel-dimension
   # shrink paths no-op, so an oversized image bakes into immutable history and
diff --git a/tests/test_packaging_metadata.py b/tests/test_packaging_metadata.py
index f646e05a19cb..464d283b7133 100644
--- a/tests/test_packaging_metadata.py
+++ b/tests/test_packaging_metadata.py
@@ -46,6 +46,22 @@ def test_packaging_declared_as_core_dependency():
     )
 
 
+def test_portalocker_declared_as_core_dependency():
+    """Host-projected plugins must not depend on incidental lock packages.
+
+    ``portalocker`` was present in ``uv.lock`` only through Windows and optional
+    dependency chains. A fresh lean Linux sync therefore omitted it, allowing
+    lock-using plugins to load before failing closed on their first operation.
+    """
+    data = tomllib.loads((REPO_ROOT / "pyproject.toml").read_text(encoding="utf-8"))
+    core = data["project"]["dependencies"]
+    names = {_distribution_name(dep) for dep in core}
+    assert "portalocker" in names, (
+        "portalocker is required by host-projected runtime plugins and must be "
+        "a declared core dependency, not an optional or platform-only transitive"
+    )
+
+
 def test_faster_whisper_is_not_a_base_dependency():
     data = tomllib.loads((REPO_ROOT / "pyproject.toml").read_text(encoding="utf-8"))
     deps = data["project"]["dependencies"]
diff --git a/uv.lock b/uv.lock
index 592d5db2612f..05be0013772c 100644
--- a/uv.lock
+++ b/uv.lock
@@ -1576,6 +1576,7 @@ dependencies = [
     { name = "packaging" },
     { name = "pathspec" },
     { name = "pillow" },
+    { name = "portalocker" },
     { name = "prompt-toolkit" },
     { name = "psutil" },
     { name = "ptyprocess", marker = "sys_platform != 'win32'" },
@@ -1887,6 +1888,7 @@ requires-dist = [
     { name = "parallel-web", marker = "extra == 'parallel-web'", specifier = "==0.4.2" },
     { name = "pathspec", specifier = "==1.1.1" },
     { name = "pillow", specifier = "==12.3.0" },
+    { name = "portalocker", specifier = ">=2.8.0,<4" },
     { name = "prompt-toolkit", specifier = "==3.0.52" },
     { name = "psutil", specifier = "==7.2.2" },
     { name = "ptyprocess", marker = "sys_platform != 'win32'", specifier = ">=0.7.0,<1" },