diff --git a/pyproject.toml b/pyproject.toml
index 5e42e1749..922ac04ac 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -160,6 +160,12 @@ vllm-omni = "vllm_omni.entrypoints.cli.main:main"
 # only import vllm, not vllm_omni) will still pick up the omni archs.
 [project.entry-points."vllm.general_plugins"]
 vllm_omni_register_models = "vllm_omni.engine.arg_utils:register_omni_models_to_vllm"
+# [edge-infer] Host-OS compatibility for native Windows (no-op elsewhere); vLLM runs
+# general plugins in the API server, every engine-core child and every worker.
+vllm_omni_windows = "vllm_omni.windows:activate"
+
+[project.entry-points."vllm_omni.general_plugins"]
+vllm_omni_windows = "vllm_omni.windows:activate"
 
 
 [tool.setuptools.packages.find]
diff --git a/tests/windows/__init__.py b/tests/windows/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/windows/test_windows_compat.py b/tests/windows/test_windows_compat.py
new file mode 100644
index 000000000..e32d0f461
--- /dev/null
+++ b/tests/windows/test_windows_compat.py
@@ -0,0 +1,269 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""``vllm_omni.windows`` on any OS: the shim logic through injected primitives,
+the no-op contract off Windows, the report schema, and the marker/hash rules
+that decide whether a vLLM function is replaced or left alone."""
+
+from __future__ import annotations
+
+import asyncio
+import os
+import sys
+import tempfile
+
+import pytest
+
+from vllm_omni.windows import activate, is_active, is_windows, report
+from vllm_omni.windows import aio, shims, vllm_patches
+from vllm_omni.windows.paths import shm_dir, shm_path
+
+
+# ---- fcntl shim ------------------------------------------------------------
+
+
+class FakeLocking:
+    """Byte-range primitive with msvcrt.locking's contract, held state in memory."""
+
+    NBLCK, UNLCK = 2, 0
+
+    def __init__(self) -> None:
+        self.held: set[int] = set()
+        self.calls: list[tuple[int, int]] = []
+
+    def __call__(self, fd: int, mode: int, nbytes: int) -> None:
+        self.calls.append((fd, mode))
+        if mode == self.NBLCK:
+            if fd in self.held:
+                raise OSError(36, "Resource deadlock avoided")
+            self.held.add(fd)
+        elif mode == self.UNLCK:
+            self.held.discard(fd)
+
+
+@pytest.fixture
+def lock_fd():
+    fd, path = tempfile.mkstemp()
+    yield fd
+    os.close(fd)
+    os.unlink(path)
+
+
+def _shim(locking: FakeLocking, sleeps: list[float]):
+    return shims.FcntlShim(locking, FakeLocking.NBLCK, FakeLocking.UNLCK, sleep=sleeps.append, poll_interval=0.01)
+
+
+def test_flock_exclusive_then_unlock(lock_fd):
+    locking, sleeps = FakeLocking(), []
+    s = _shim(locking, sleeps)
+    s.flock(lock_fd, shims.LOCK_EX)
+    assert lock_fd in locking.held
+    s.flock(lock_fd, shims.LOCK_UN)
+    assert lock_fd not in locking.held
+    assert sleeps == []
+
+
+def test_flock_non_blocking_raises_blockingioerror_when_held(lock_fd):
+    locking, sleeps = FakeLocking(), []
+    locking.held.add(lock_fd)
+    s = _shim(locking, sleeps)
+    with pytest.raises(BlockingIOError):
+        s.flock(lock_fd, shims.LOCK_EX | shims.LOCK_NB)
+    assert sleeps == []
+
+
+def test_flock_blocking_waits_until_released(lock_fd):
+    locking = FakeLocking()
+    locking.held.add(lock_fd)
+    sleeps: list[float] = []
+
+    def sleep(dt: float) -> None:  # the other holder lets go after two polls
+        sleeps.append(dt)
+        if len(sleeps) == 2:
+            locking.held.discard(lock_fd)
+
+    s = shims.FcntlShim(locking, FakeLocking.NBLCK, FakeLocking.UNLCK, sleep=sleep, poll_interval=0.01)
+    s.flock(lock_fd, shims.LOCK_EX)
+    assert len(sleeps) == 2 and lock_fd in locking.held
+
+
+def test_shared_lock_is_served_as_exclusive_and_counted(lock_fd):
+    locking, sleeps = FakeLocking(), []
+    s = _shim(locking, sleeps)
+    s.flock(lock_fd, shims.LOCK_SH)
+    assert s.shared_served_as_exclusive == 1
+    assert lock_fd in locking.held
+
+
+def test_lock_offset_leaves_file_position_alone(lock_fd):
+    os.write(lock_fd, b"12345\n")
+    os.lseek(lock_fd, 3, os.SEEK_SET)
+    s = _shim(FakeLocking(), [])
+    s.flock(lock_fd, shims.LOCK_EX)
+    assert os.lseek(lock_fd, 0, os.SEEK_CUR) == 3
+
+
+def test_fcntl_shim_module_shape():
+    mod = _shim(FakeLocking(), []).as_module()
+    assert mod.__name__ == "fcntl" and mod.__vllm_omni_windows_shim__
+    assert (mod.LOCK_SH, mod.LOCK_EX, mod.LOCK_NB, mod.LOCK_UN) == (1, 2, 4, 8)
+    assert callable(mod.flock) and callable(mod.lockf)
+
+
+# ---- uvloop shim -----------------------------------------------------------
+
+
+def test_uvloop_shim_runs_a_coroutine():
+    mod = shims.make_uvloop_shim()
+    assert mod.__vllm_omni_windows_shim__
+
+    async def main():
+        await asyncio.sleep(0)
+        return 42
+
+    assert mod.run(main()) == 42
+    loop = mod.new_event_loop()
+    try:
+        assert isinstance(loop, asyncio.AbstractEventLoop)
+    finally:
+        loop.close()
+
+
+def test_provide_leaves_a_real_module_alone():
+    # ``os`` is always real; provide() must not touch it.
+    assert shims.provide("os", lambda: None) == "real"
+    assert sys.modules["os"] is os
+
+
+def test_provide_installs_and_then_reports_already():
+    name = "_vllm_omni_windows_test_missing_module_"
+    sys.modules.pop(name, None)
+    try:
+        assert shims.provide(name, shims.make_uvloop_shim) == "provided"
+        assert shims.provide(name, shims.make_uvloop_shim) == "already"
+        assert sys.modules[name].__vllm_omni_windows_shim__
+    finally:
+        sys.modules.pop(name, None)
+
+
+# ---- signal fallback -------------------------------------------------------
+
+
+class FakeLoop:
+    def __init__(self) -> None:
+        self.scheduled = []
+        self.__dict__["_x"] = None
+
+    def call_soon_threadsafe(self, cb, *args):
+        self.scheduled.append((cb, args))
+
+
+def test_signal_fallback_registers_and_fires_via_call_soon_threadsafe(monkeypatch):
+    import signal as _signal
+
+    installed = {}
+
+    def fake_signal(sig, handler):
+        installed[sig] = handler
+
+    monkeypatch.setattr(_signal, "signal", fake_signal)
+
+    def original_add(self, sig, cb, *args):
+        raise NotImplementedError
+
+    def original_remove(self, sig):
+        raise NotImplementedError
+
+    add, remove = aio.make_signal_fallback(original_add, original_remove)
+    loop = FakeLoop()
+    hits = []
+    add(loop, _signal.SIGINT, hits.append, "x")
+    assert _signal.SIGINT in installed
+    installed[_signal.SIGINT](_signal.SIGINT, None)  # the OS delivers the signal
+    assert loop.scheduled == [(hits.append, ("x",))]
+    assert remove(loop, _signal.SIGINT) is True
+    assert remove(loop, _signal.SIGINT) is False  # nothing left, original says NotImplemented
+
+
+def test_signal_fallback_prefers_the_native_implementation():
+    calls = []
+
+    def original_add(self, sig, cb, *args):
+        calls.append(sig)
+
+    add, _ = aio.make_signal_fallback(original_add, lambda self, sig: True)
+    add(FakeLoop(), 2, lambda: None)
+    assert calls == [2]
+
+
+# ---- vLLM patch rules ------------------------------------------------------
+
+
+def test_upstream_hashes_are_the_pinned_bodies_or_the_branch_marker():
+    """On the installed vLLM each replaceable function is either the known upstream body or already patched."""
+    vllm = pytest.importorskip("vllm")
+    from vllm.utils import network_utils, system_utils
+
+    for name, fn in (("get_open_zmq_ipc_path", network_utils.get_open_zmq_ipc_path),
+                     ("find_loaded_library", system_utils.find_loaded_library)):
+        marked = vllm_patches._has_mark(fn)
+        known = vllm_patches._src_hash(fn) in vllm_patches.KNOWN_UPSTREAM[name]
+        assert marked or known, f"{name} on vllm {vllm.__version__}: neither branch-patched nor a known upstream body"
+
+
+def test_verify_reports_wheel_required_on_an_unpatched_source(monkeypatch):
+    class Fake:
+        pass
+
+    import types
+
+    m = types.ModuleType("fake_vllm_site")
+
+    def wait_for_engine_startup():
+        return "poller.register(sentinel)"
+
+    m.wait_for_engine_startup = wait_for_engine_startup
+    monkeypatch.setitem(sys.modules, "fake_vllm_site", m)
+    import inspect
+
+    monkeypatch.setattr(inspect, "getsource", lambda obj: "poller.register(sentinel)")
+    assert vllm_patches._verify("fake_vllm_site", "wait_for_engine_startup", "_win_sentinels") == "wheel_required"
+    assert vllm_patches._verify("fake_vllm_site", "wait_for_engine_startup", "sentinel") == "already"
+
+
+# ---- paths -----------------------------------------------------------------
+
+
+def test_shm_dir_exists_and_path_joins():
+    d = shm_dir()
+    assert os.path.isdir(d)
+    assert shm_path("x.lock").startswith(d)
+    if os.path.isdir("/dev/shm"):
+        assert d == "/dev/shm"
+
+
+# ---- activation contract ---------------------------------------------------
+
+
+def test_activate_is_idempotent_and_a_noop_off_windows():
+    first = activate()
+    second = activate()
+    assert first == second
+    if not is_windows():
+        assert first == {"platform": "n/a"}
+        assert not is_active()
+    else:
+        assert is_active()
+        assert set(first) >= {"fcntl", "uvloop", "event_loop_policy", "signal_handlers", "get_open_zmq_ipc_path"}
+
+
+def test_report_schema():
+    rep = report()
+    for key in ("platform", "active", "activations", "steps", "asyncio", "zmq", "shm_dir", "vllm", "native_modules", "optional_deps"):
+        assert key in rep, key
+    assert rep["activations"] >= 1
+    assert isinstance(rep["optional_deps"], dict) and "fcntl" in rep["optional_deps"]
+    if rep["vllm"]:
+        if is_windows():
+            assert rep["vllm"]["wheel_sites"], "on Windows the wheel sites must be reported"
+        else:
+            assert rep["vllm"]["wheel_sites"] == {}
diff --git a/vllm_omni/distributed/omni_connectors/connectors/cuda_ipc_connector.py b/vllm_omni/distributed/omni_connectors/connectors/cuda_ipc_connector.py
index 73b11701e..45b51f423 100644
--- a/vllm_omni/distributed/omni_connectors/connectors/cuda_ipc_connector.py
+++ b/vllm_omni/distributed/omni_connectors/connectors/cuda_ipc_connector.py
@@ -42,7 +42,10 @@ from vllm_omni.distributed.omni_connectors.connectors.shm_connector import Share
 logger = init_logger(__name__)
 
 MARKER = "__cuda_ipc__"
-ACK_DIR = "/dev/shm"
+# [edge-infer] /dev/shm where it exists (Linux, WSL); a per-user directory on Windows.
+from vllm_omni.windows.paths import shm_dir as _shm_dir
+
+ACK_DIR = _shm_dir()
 
 
 def _ack_path(put_key: str) -> str:
diff --git a/vllm_omni/edge/local/engine.py b/vllm_omni/edge/local/engine.py
index 636fb7faf..452993134 100644
--- a/vllm_omni/edge/local/engine.py
+++ b/vllm_omni/edge/local/engine.py
@@ -114,6 +114,18 @@ def _host_kind() -> str:
     return "linux"
 
 
+def _host_compat_report() -> dict[str, Any] | None:
+    """``vllm_omni.windows.report()`` on Windows, so a record says what made the run possible."""
+    from vllm_omni.windows import is_windows, report
+
+    if not is_windows():
+        return None
+    try:
+        return report()
+    except Exception as exc:  # the audit must never take the engine down
+        return {"error": f"{type(exc).__name__}: {exc}"}
+
+
 def gpu_attribution_for_tree() -> dict[str, Any]:
     """Try to attribute GPU bytes to this process tree, and say why when it fails.
 
@@ -765,6 +777,9 @@ class LocalTextEngine:
                 "tree_rss_delta_at_load": self.load_memory.get("tree_rss_delta"),
                 **gpu_attribution_for_tree(),
             },
+            # [edge-infer] On native Windows, which compatibility layer carried this
+            # process (shims, patches, wheel-provided sites). None elsewhere.
+            "host_compat": _host_compat_report(),
         }
 
     def report_usage(self) -> dict[str, Any]:
diff --git a/vllm_omni/edge/step_stats.py b/vllm_omni/edge/step_stats.py
index 11f68dbfc..7c7838411 100644
--- a/vllm_omni/edge/step_stats.py
+++ b/vllm_omni/edge/step_stats.py
@@ -237,7 +237,9 @@ def instrument_sampler(sampler: Any) -> None:
 def shm_lockfile_age_ms(key: str, now: float | None = None) -> float | None:
     """Age of the SharedMemoryConnector lock file for ``key`` (written at put time)."""
     try:
-        st = os.stat(f"/dev/shm/shm_{key}_lockfile.lock")
+        from vllm_omni.windows.paths import shm_path
+
+        st = os.stat(shm_path(f"shm_{key}_lockfile.lock"))
     except OSError:
         return None
     return ((now if now is not None else time.time()) - st.st_mtime) * 1000.0
diff --git a/vllm_omni/patch.py b/vllm_omni/patch.py
index 045c87b38..9c8da61f2 100644
--- a/vllm_omni/patch.py
+++ b/vllm_omni/patch.py
@@ -3,6 +3,13 @@ import os
 import sys
 from functools import cached_property
 
+# [edge-infer] Host-OS compatibility must precede every vLLM import below: it
+# provides `fcntl`/`uvloop` and sets the event-loop policy on native Windows.
+# No-op on other platforms. Design: analysis/design_windows_compat_plugin_20260921.md
+from vllm_omni.windows import activate as _activate_windows_compat  # isort:skip
+
+_activate_windows_compat()
+
 import torch
 from aenum import extend_enum
 from vllm.config import ModelConfig as _OriginalModelConfig
diff --git a/vllm_omni/windows/__init__.py b/vllm_omni/windows/__init__.py
new file mode 100644
index 000000000..95d9abcf1
--- /dev/null
+++ b/vllm_omni/windows/__init__.py
@@ -0,0 +1,72 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""``vllm_omni.windows`` -- host-OS compatibility so vLLM and vLLM-Omni run on native Windows.
+
+Design: ``analysis/design_windows_compat_plugin_20260921.md`` (edge-infer). In
+one sentence: the POSIX assumptions that killed Windows runs in W0–W8 are a
+handful of classes repeated across vLLM, vLLM-Omni and model code; this
+package provides the missing modules (``fcntl``, ``uvloop``), fixes the
+process state Windows gets wrong (event loop policy, signal handlers), replaces
+whole the two vLLM functions whose entire body is platform logic, and
+*reports* the sites that must come from the Windows wheel.
+
+Three doors, all idempotent, so import order does not matter:
+
+* ``vllm_omni/patch.py`` calls :func:`activate` first thing;
+* the ``vllm.general_plugins`` entry point ``vllm_omni_windows`` -- vLLM calls
+  it in the API server, every engine-core child and every worker;
+* the ``vllm_omni.general_plugins`` entry point of the same name.
+
+Off Windows every function here is a no-op that reports ``n/a``.
+"""
+
+from __future__ import annotations
+
+import logging
+import sys
+
+from vllm_omni.windows.report import LEDGER, report
+
+logger = logging.getLogger(__name__)
+
+__all__ = ["activate", "is_active", "is_windows", "report"]
+
+
+def is_windows() -> bool:
+    return sys.platform == "win32"
+
+
+def is_active() -> bool:
+    return bool(LEDGER["active"])
+
+
+def activate() -> dict[str, str]:
+    """Apply every layer once per process. Returns the per-step outcome."""
+    LEDGER["activations"] += 1
+    if not is_windows():
+        LEDGER["steps"] = {"platform": "n/a"}
+        return LEDGER["steps"]
+    if LEDGER["active"]:
+        return LEDGER["steps"]
+
+    from vllm_omni.windows import aio, paths, shims, vllm_patches
+
+    steps: dict[str, str] = {}
+    # 1. modules that do not exist here -- before anything can import them
+    steps["fcntl"] = shims.provide("fcntl", shims.make_msvcrt_fcntl)
+    steps["uvloop"] = shims.provide("uvloop", shims.make_uvloop_shim)
+    # 2. process state
+    steps["event_loop_policy"] = aio.install_selector_policy()
+    steps["signal_handlers"] = aio.patch_signal_handlers()
+    steps["os_geteuid"] = paths.provide_geteuid()
+    # 3. vLLM functions replaced whole (only when the wheel lacks the branch patch)
+    steps["get_open_zmq_ipc_path"] = vllm_patches.patch_get_open_zmq_ipc_path()
+    steps["find_loaded_library"] = vllm_patches.patch_find_loaded_library()
+    LEDGER["steps"] = steps
+    LEDGER["active"] = True
+    logger.info("[vllm_omni.windows] active: %s", ", ".join(f"{k}={v}" for k, v in steps.items()))
+    fc = sys.modules.get("fcntl")
+    impl = getattr(fc, "_impl", None)
+    if impl is not None and getattr(impl, "shared_served_as_exclusive", 0):
+        logger.info("[vllm_omni.windows] LOCK_SH served as exclusive (msvcrt has no shared locks)")
+    return steps
diff --git a/vllm_omni/windows/__main__.py b/vllm_omni/windows/__main__.py
new file mode 100644
index 000000000..01422220b
--- /dev/null
+++ b/vllm_omni/windows/__main__.py
@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""``python -m vllm_omni.windows report`` -- print the audit as JSON (exit 1 if a wheel site is missing)."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import sys
+
+
+def main(argv: list[str] | None = None) -> int:
+    ap = argparse.ArgumentParser(prog="python -m vllm_omni.windows")
+    ap.add_argument("command", choices=["report"], nargs="?", default="report")
+    ap.add_argument("--json", dest="json_path", help="also write the report here")
+    args = ap.parse_args(argv)
+
+    from vllm_omni.windows import activate, report
+
+    activate()
+    rep = report()
+    text = json.dumps(rep, indent=2, default=str)
+    print(text)
+    if args.json_path:
+        with open(args.json_path, "w", encoding="utf-8") as fh:
+            fh.write(text + "\n")
+    sites = (rep.get("vllm") or {}).get("wheel_sites") or {}
+    missing = sorted(k for k, v in sites.items() if v in ("wheel_required", "unknown_upstream"))
+    if missing:
+        print(f"wheel_required: {', '.join(missing)}", file=sys.stderr)
+        return 1
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/vllm_omni/windows/aio.py b/vllm_omni/windows/aio.py
new file mode 100644
index 000000000..49a79ef7c
--- /dev/null
+++ b/vllm_omni/windows/aio.py
@@ -0,0 +1,97 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""asyncio on Windows: the selector loop, and signal handlers that exist.
+
+``loop.add_signal_handler`` is Unix-only; on Windows every loop raises
+``NotImplementedError``. vLLM's ``serve_http`` registers SIGINT/SIGTERM through
+it, so the API server died right after the engine came up (W8, measured). The
+fallback registers a plain ``signal.signal`` handler that hops back onto the
+loop with ``call_soon_threadsafe`` -- the same shutdown path, registered the
+only way Windows allows. Signals Windows does not have raise the original
+error, so nothing is silently ignored.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import signal
+import sys
+from collections.abc import Callable
+from typing import Any
+
+from vllm_omni.windows.shims import ensure_selector_policy
+
+_MARK = "__vllm_omni_windows_signal_fallback__"
+
+_WINDOWS_SIGNALS = {
+    getattr(signal, name) for name in ("SIGINT", "SIGTERM", "SIGBREAK", "SIGABRT") if hasattr(signal, name)
+}
+
+
+def make_signal_fallback(original_add: Callable, original_remove: Callable):
+    """Build ``add_signal_handler``/``remove_signal_handler`` replacements.
+
+    Returned functions try the loop's own implementation first (a real selector
+    loop on Unix keeps its native behaviour), and fall back to
+    ``signal.signal`` when the loop says ``NotImplementedError``.
+    """
+
+    def add_signal_handler(self, sig: int, callback: Callable, *args: Any) -> None:
+        try:
+            return original_add(self, sig, callback, *args)
+        except NotImplementedError:
+            if sig not in _WINDOWS_SIGNALS:
+                raise
+
+            def _handler(signum, frame):  # runs on the main thread, outside the loop
+                self.call_soon_threadsafe(callback, *args)
+
+            signal.signal(sig, _handler)
+            registry = self.__dict__.setdefault(_MARK, {})
+            registry[sig] = _handler
+
+    def remove_signal_handler(self, sig: int) -> bool:
+        registry = self.__dict__.get(_MARK) or {}
+        if sig in registry:
+            signal.signal(sig, signal.SIG_DFL)
+            del registry[sig]
+            return True
+        try:
+            return original_remove(self, sig)
+        except NotImplementedError:
+            return False
+
+    add_signal_handler.__vllm_omni_windows__ = True  # type: ignore[attr-defined]
+    remove_signal_handler.__vllm_omni_windows__ = True  # type: ignore[attr-defined]
+    return add_signal_handler, remove_signal_handler
+
+
+def patch_signal_handlers() -> str:
+    """Install the fallback on the loop classes Windows uses. Returns already|patched|n/a."""
+    if sys.platform != "win32":
+        return "n/a"
+    targets = [cls for cls in (getattr(asyncio, "ProactorEventLoop", None), getattr(asyncio, "SelectorEventLoop", None)) if cls]
+    if not targets:
+        return "n/a"
+    if all(getattr(cls.add_signal_handler, "__vllm_omni_windows__", False) for cls in targets):
+        return "already"
+    for cls in targets:
+        if getattr(cls.add_signal_handler, "__vllm_omni_windows__", False):
+            continue
+        add, remove = make_signal_fallback(cls.add_signal_handler, cls.remove_signal_handler)
+        cls.add_signal_handler = add  # type: ignore[method-assign]
+        cls.remove_signal_handler = remove  # type: ignore[method-assign]
+    return "patched"
+
+
+def install_selector_policy() -> str:
+    if sys.platform != "win32":
+        return "n/a"
+    return "set" if ensure_selector_policy() else "already"
+
+
+def running_loop_class() -> str | None:
+    try:
+        return type(asyncio.get_running_loop()).__name__
+    except RuntimeError:
+        return None
diff --git a/vllm_omni/windows/paths.py b/vllm_omni/windows/paths.py
new file mode 100644
index 000000000..75b16383f
--- /dev/null
+++ b/vllm_omni/windows/paths.py
@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""Filesystem places POSIX code hard-codes, and the one ``os`` function Windows lacks."""
+
+from __future__ import annotations
+
+import os
+import sys
+import tempfile
+from pathlib import Path
+
+_POSIX_SHM = "/dev/shm"
+
+
+def shm_dir() -> str:
+    """The directory for ``/dev/shm``-style lock and ack files.
+
+    ``/dev/shm`` where it exists (Linux, WSL). On Windows a per-user directory
+    under ``%LOCALAPPDATA%`` (falling back to the temp dir), created on first
+    use. Callers that used to write ``f"/dev/shm/..."`` go through this so the
+    path is the same on every platform that has one and a real one elsewhere.
+    """
+    if os.path.isdir(_POSIX_SHM):
+        return _POSIX_SHM
+    base = os.environ.get("LOCALAPPDATA") or tempfile.gettempdir()
+    path = Path(base) / "vllm_omni" / "shm"
+    path.mkdir(parents=True, exist_ok=True)
+    return str(path)
+
+
+def shm_path(name: str) -> str:
+    return os.path.join(shm_dir(), name)
+
+
+def provide_geteuid() -> str:
+    """``os.geteuid``/``os.getuid`` do not exist on Windows.
+
+    ``host_weight_runtime`` compares ``st_uid`` against ``os.geteuid()`` for a
+    "did we create this" check; Windows ``os.stat`` reports ``st_uid == 0``, so
+    returning 0 makes the comparison mean the same thing it can mean there.
+    """
+    if sys.platform != "win32":
+        return "n/a"
+    if hasattr(os, "geteuid"):
+        return "already" if getattr(os.geteuid, "__vllm_omni_windows__", False) else "real"
+
+    def geteuid() -> int:
+        return 0
+
+    geteuid.__vllm_omni_windows__ = True  # type: ignore[attr-defined]
+    os.geteuid = geteuid  # type: ignore[attr-defined]
+    if not hasattr(os, "getuid"):
+        os.getuid = geteuid  # type: ignore[attr-defined]
+    return "provided"
diff --git a/vllm_omni/windows/procs.py b/vllm_omni/windows/procs.py
new file mode 100644
index 000000000..96752d689
--- /dev/null
+++ b/vllm_omni/windows/procs.py
@@ -0,0 +1,38 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""Process helpers that work on every OS (no ``os.killpg``, no ``kill -9``)."""
+
+from __future__ import annotations
+
+import subprocess
+
+
+def kill_tree(pid: int, *, timeout: float = 30.0) -> dict[str, int]:
+    """Terminate ``pid`` and every descendant; escalate to kill after ``timeout``.
+
+    Returns counts: ``{"terminated": n, "killed": m}``. Missing processes are
+    not an error (the tree may already be gone).
+    """
+    import psutil
+
+    try:
+        parent = psutil.Process(pid)
+    except psutil.NoSuchProcess:
+        return {"terminated": 0, "killed": 0}
+    procs = [*parent.children(recursive=True), parent]
+    for p in procs:
+        try:
+            p.terminate()
+        except psutil.NoSuchProcess:
+            pass
+    _, alive = psutil.wait_procs(procs, timeout=timeout)
+    for p in alive:
+        try:
+            p.kill()
+        except psutil.NoSuchProcess:
+            pass
+    return {"terminated": len(procs) - len(alive), "killed": len(alive)}
+
+
+def kill_popen_tree(proc: subprocess.Popen, *, timeout: float = 30.0) -> dict[str, int]:
+    return kill_tree(proc.pid, timeout=timeout)
diff --git a/vllm_omni/windows/report.py b/vllm_omni/windows/report.py
new file mode 100644
index 000000000..1bbd4bb93
--- /dev/null
+++ b/vllm_omni/windows/report.py
@@ -0,0 +1,78 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""The audit: what the Windows layer did in this process, and what it could not do.
+
+Everything ``activate()`` does lands in ``LEDGER``; ``report()`` adds the
+facts a Windows record needs next to a result (zmq transport, loop policy,
+which vLLM sites came from the wheel, which native modules are present, which
+optional dependencies import). Nothing here changes state.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import importlib
+import importlib.util
+import sys
+from typing import Any
+
+LEDGER: dict[str, Any] = {"active": False, "steps": {}, "activations": 0}
+
+OPTIONAL_DEPS = ("torchaudio", "soundfile", "diffusers", "flashinfer", "pynvml", "uvloop", "fcntl")
+
+
+def _importable(name: str) -> str:
+    mod = sys.modules.get(name)
+    if mod is not None and getattr(mod, "__vllm_omni_windows_shim__", False):
+        return "shim"
+    try:
+        return "yes" if importlib.util.find_spec(name) is not None else "no"
+    except (ImportError, ValueError):
+        return "no"
+
+
+def _native_modules() -> list[str]:
+    try:
+        import vllm
+    except ImportError:
+        return []
+    from pathlib import Path
+
+    root = Path(vllm.__file__).parent
+    suffixes = (".pyd", ".so")
+    return sorted(
+        str(p.relative_to(root)).replace("\\", "/").split(".", 1)[0]
+        for p in root.rglob("*")
+        if p.suffix in suffixes and "third_party" not in p.parts
+    )
+
+
+def report() -> dict[str, Any]:
+    from vllm_omni.windows import aio, paths, vllm_patches
+
+    out: dict[str, Any] = {
+        "platform": sys.platform,
+        "active": LEDGER["active"],
+        "activations": LEDGER["activations"],
+        "steps": dict(LEDGER["steps"]),
+    }
+    out["asyncio"] = {
+        "policy": type(asyncio.get_event_loop_policy()).__name__,
+        "running_loop": aio.running_loop_class(),
+    }
+    try:
+        import zmq
+
+        out["zmq"] = {"version": zmq.zmq_version(), "has_ipc": bool(zmq.has("ipc"))}
+    except ImportError:
+        out["zmq"] = None
+    out["shm_dir"] = paths.shm_dir() if sys.platform == "win32" else None
+    try:
+        import vllm
+
+        out["vllm"] = {"version": vllm.__version__, "wheel_sites": vllm_patches.verify_wheel_sites()}
+    except ImportError:
+        out["vllm"] = None
+    out["native_modules"] = _native_modules()
+    out["optional_deps"] = {name: _importable(name) for name in OPTIONAL_DEPS}
+    return out
diff --git a/vllm_omni/windows/shims.py b/vllm_omni/windows/shims.py
new file mode 100644
index 000000000..a60b4055b
--- /dev/null
+++ b/vllm_omni/windows/shims.py
@@ -0,0 +1,191 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""Modules that do not exist on Windows, provided so ``import`` succeeds.
+
+Two of them account for most Windows import deaths measured in W0–W8:
+
+* ``fcntl`` — file locks. vLLM-Omni and model code call ``fcntl.flock`` for
+  device-init locks, weight-store locks, media caches. Windows has
+  ``msvcrt.locking`` instead: byte-range, mandatory, exclusive only.
+* ``uvloop`` — no Windows wheels. Every ``uvloop.run(...)`` entry point can run
+  on ``asyncio.run`` provided the loop is a *selector* loop (zmq.asyncio needs
+  ``add_reader``; the Windows default Proactor loop has none).
+
+Both shims are only installed when the real module is absent, and both are
+built on injectable primitives so the logic is testable on Linux.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import os
+import sys
+import time
+import types
+from collections.abc import Callable
+
+# ---------------------------------------------------------------------------
+# fcntl
+# ---------------------------------------------------------------------------
+
+# POSIX values, so code that does arithmetic on them (``LOCK_EX | LOCK_NB``)
+# behaves identically.
+LOCK_SH = 1
+LOCK_EX = 2
+LOCK_NB = 4
+LOCK_UN = 8
+
+# The locked byte lives far past any content a caller writes into a lock file
+# (PID lines and the like), so the lock never overlaps data. Same design as
+# ``vllm_omni._filelock_compat`` (W1).
+_LOCK_OFFSET = 1 << 30
+
+
+class FcntlShim:
+    """``flock``/``lockf`` on a byte-range primitive.
+
+    ``locking(fd, mode, nbytes)`` follows ``msvcrt.locking``'s contract: mode
+    ``NBLCK`` takes a non-blocking exclusive lock and raises ``OSError`` when
+    held elsewhere; ``UNLCK`` releases. Shared locks (``LOCK_SH``) are served
+    as exclusive because the primitive has none -- strictly more serialising
+    than POSIX, never less safe; this is said once per process in the log.
+    """
+
+    def __init__(
+        self,
+        locking: Callable[[int, int, int], None],
+        nblck: int,
+        unlck: int,
+        *,
+        sleep: Callable[[float], None] = time.sleep,
+        poll_interval: float = 0.01,
+    ) -> None:
+        self._locking = locking
+        self._nblck = nblck
+        self._unlck = unlck
+        self._sleep = sleep
+        self._poll_interval = poll_interval
+        self.shared_served_as_exclusive = 0
+
+    def _at_lock_offset(self, fd: int, fn: Callable[[], None]) -> None:
+        here = os.lseek(fd, 0, os.SEEK_CUR)
+        os.lseek(fd, _LOCK_OFFSET, os.SEEK_SET)
+        try:
+            fn()
+        finally:
+            os.lseek(fd, here, os.SEEK_SET)
+
+    def flock(self, fd: int, operation: int) -> None:
+        fd = fd if isinstance(fd, int) else fd.fileno()
+        if operation & LOCK_UN:
+            self._at_lock_offset(fd, lambda: self._locking(fd, self._unlck, 1))
+            return
+        if operation & LOCK_SH and not operation & LOCK_EX:
+            self.shared_served_as_exclusive += 1
+        non_blocking = bool(operation & LOCK_NB)
+        while True:
+            try:
+                self._at_lock_offset(fd, lambda: self._locking(fd, self._nblck, 1))
+                return
+            except OSError as exc:
+                if non_blocking:
+                    raise BlockingIOError(str(exc)) from exc
+                self._sleep(self._poll_interval)
+
+    def lockf(self, fd: int, cmd: int, len: int = 0, start: int = 0, whence: int = 0) -> None:  # noqa: A002
+        # POSIX lockf's F_LOCK/F_TLOCK/F_ULOCK spell the same three states.
+        self.flock(fd, cmd)
+
+    def as_module(self) -> types.ModuleType:
+        mod = types.ModuleType("fcntl")
+        mod.__doc__ = "fcntl shim from vllm_omni.windows (msvcrt.locking underneath)"
+        mod.LOCK_SH, mod.LOCK_EX, mod.LOCK_NB, mod.LOCK_UN = LOCK_SH, LOCK_EX, LOCK_NB, LOCK_UN
+        # lockf's command constants, for callers that use them by name.
+        mod.F_ULOCK, mod.F_LOCK, mod.F_TLOCK, mod.F_TEST = LOCK_UN, LOCK_EX, LOCK_EX | LOCK_NB, LOCK_NB
+        mod.flock = self.flock
+        mod.lockf = self.lockf
+        mod.__vllm_omni_windows_shim__ = True
+        mod._impl = self
+        return mod
+
+
+def make_msvcrt_fcntl() -> types.ModuleType:
+    import msvcrt  # Windows only
+
+    return FcntlShim(msvcrt.locking, msvcrt.LK_NBLCK, msvcrt.LK_UNLCK).as_module()
+
+
+# ---------------------------------------------------------------------------
+# uvloop
+# ---------------------------------------------------------------------------
+
+
+def selector_policy_class() -> type | None:
+    return getattr(asyncio, "WindowsSelectorEventLoopPolicy", None)
+
+
+def ensure_selector_policy() -> bool:
+    """Make new event loops selector loops. Returns True if it changed the policy."""
+    policy = selector_policy_class()
+    if policy is None:  # not Windows
+        return False
+    if isinstance(asyncio.get_event_loop_policy(), policy):
+        return False
+    asyncio.set_event_loop_policy(policy())
+    return True
+
+
+def make_uvloop_shim() -> types.ModuleType:
+    """A ``uvloop`` whose ``run``/``install``/``new_event_loop`` are asyncio on a selector loop."""
+    mod = types.ModuleType("uvloop")
+    mod.__doc__ = "uvloop shim from vllm_omni.windows: asyncio on a selector event loop"
+    mod.__version__ = "0.0.0+vllm_omni_windows_shim"
+
+    def install() -> None:
+        ensure_selector_policy()
+
+    def new_event_loop() -> asyncio.AbstractEventLoop:
+        ensure_selector_policy()
+        return asyncio.new_event_loop()
+
+    def run(main, **kwargs):
+        ensure_selector_policy()
+        return asyncio.run(main, **kwargs)
+
+    mod.install = install
+    mod.new_event_loop = new_event_loop
+    mod.run = run
+    mod.EventLoopPolicy = selector_policy_class() or asyncio.DefaultEventLoopPolicy
+    mod.Loop = getattr(asyncio, "SelectorEventLoop", asyncio.AbstractEventLoop)
+    mod.__vllm_omni_windows_shim__ = True
+    return mod
+
+
+# ---------------------------------------------------------------------------
+# installation
+# ---------------------------------------------------------------------------
+
+
+def _real_module_importable(name: str) -> bool:
+    if name in sys.modules:
+        return not getattr(sys.modules[name], "__vllm_omni_windows_shim__", False)
+    try:
+        __import__(name)
+        return True
+    except ImportError:
+        return False
+
+
+def provide(name: str, factory: Callable[[], types.ModuleType]) -> str:
+    """Install ``factory()`` as ``sys.modules[name]`` unless a real module exists.
+
+    Returns ``"real"`` (nothing done), ``"provided"`` (shim installed now) or
+    ``"already"`` (our shim was installed earlier in this process).
+    """
+    existing = sys.modules.get(name)
+    if existing is not None and getattr(existing, "__vllm_omni_windows_shim__", False):
+        return "already"
+    if _real_module_importable(name):
+        return "real"
+    sys.modules[name] = factory()
+    return "provided"
diff --git a/vllm_omni/windows/vllm_patches.py b/vllm_omni/windows/vllm_patches.py
new file mode 100644
index 000000000..1ec53166c
--- /dev/null
+++ b/vllm_omni/windows/vllm_patches.py
@@ -0,0 +1,180 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+"""Runtime patches of vLLM control-plane functions, and verification of the rest.
+
+The rule (design §4): a function may be replaced *whole* at runtime only when
+its entire body is platform logic and its upstream body is one we recognise by
+hash. Sites whose fix sits in the middle of a larger function (the engine
+startup sentinel poll, the sampler seed dtype) must come from the wheel -- the
+Windows branch carries them -- and are only *verified* here, so a run on an
+unpatched wheel is reported as ``wheel_required`` at the exact site instead of
+failing somewhere downstream.
+
+Every outcome string used here: ``already`` (the wheel carries the branch
+patch, marker found), ``patched`` (replaced now), ``unknown_upstream`` (no
+marker and the upstream body is not one we know -- left alone, reported),
+``wheel_required`` (verify-only site, marker absent), ``not_needed`` (another
+layer covers it), ``n/a`` (off Windows or module absent).
+"""
+
+from __future__ import annotations
+
+import hashlib
+import inspect
+import sys
+from typing import Any
+
+BRANCH_MARK = "edge-infer"  # every branch patch carries "[edge-infer W? windows patch]"
+
+# sha256[:16] of inspect.getsource() of the *upstream* function, measured on the
+# PyPI wheels vllm==0.28.0 and vllm==0.29.0 (identical bodies at both tags).
+KNOWN_UPSTREAM = {
+    "get_open_zmq_ipc_path": {"1d9aeb608d4c5dbc"},
+    "find_loaded_library": {"b7916f0a8ebae56c"},
+}
+
+
+def _src_hash(obj: Any) -> str | None:
+    try:
+        return hashlib.sha256(inspect.getsource(obj).encode()).hexdigest()[:16]
+    except (OSError, TypeError):
+        return None
+
+
+def _has_mark(obj: Any) -> bool:
+    try:
+        return BRANCH_MARK in inspect.getsource(obj)
+    except (OSError, TypeError):
+        return False
+
+
+# ---------------------------------------------------------------------------
+# replaced whole
+# ---------------------------------------------------------------------------
+
+
+def _win_get_open_zmq_ipc_path() -> str:
+    """The W0 body: libzmq on Windows has no ipc:// transport; loopback TCP is the local option.
+
+    This drops the filesystem permissions a Unix socket carries -- a loopback
+    port is reachable by any local user -- so it is a fallback conditional on
+    ipc being truly unavailable, never a preference.
+    """
+    import zmq
+
+    from vllm import envs
+    from vllm.utils.network_utils import get_open_port, get_tcp_uri
+
+    if not zmq.has("ipc"):
+        return get_tcp_uri("127.0.0.1", get_open_port())
+    from uuid import uuid4
+
+    return f"ipc://{envs.VLLM_RPC_BASE_PATH}/{uuid4()}"
+
+
+def _make_win_find_loaded_library(original):
+    def find_loaded_library(lib_name: str) -> str | None:
+        """On Windows an already-imported extension module's __file__ IS the loaded path (W0)."""
+        if sys.platform != "win32":
+            return original(lib_name)
+        for mod in list(sys.modules.values()):
+            f = getattr(mod, "__file__", None)
+            if not f:
+                continue
+            base = f.replace("\\", "/").rsplit("/", maxsplit=1)[-1]
+            if base.startswith((f"{lib_name}.", f"{lib_name}-")):
+                return f
+        return None
+
+    find_loaded_library.__vllm_omni_windows__ = True  # type: ignore[attr-defined]
+    return find_loaded_library
+
+
+def _replace(module, name: str, replacement) -> str:
+    current = getattr(module, name, None)
+    if current is None:
+        return "n/a"
+    if getattr(current, "__vllm_omni_windows__", False):
+        return "already"
+    if _has_mark(current):
+        return "already"
+    if _src_hash(current) not in KNOWN_UPSTREAM.get(name, set()):
+        return "unknown_upstream"
+    setattr(module, name, replacement)
+    return "patched"
+
+
+def patch_get_open_zmq_ipc_path() -> str:
+    if sys.platform != "win32":
+        return "n/a"
+    try:
+        from vllm.utils import network_utils
+    except ImportError:
+        return "n/a"
+    _win_get_open_zmq_ipc_path.__vllm_omni_windows__ = True  # type: ignore[attr-defined]
+    status = _replace(network_utils, "get_open_zmq_ipc_path", _win_get_open_zmq_ipc_path)
+    if status == "patched":
+        # Callers that imported the name directly (``from ... import get_open_zmq_ipc_path``)
+        # before activation keep the old binding; the ones that matter import lazily
+        # (Omni's stage_engine_startup) or after plugin load (vLLM's own engine code).
+        pass
+    return status
+
+
+def patch_find_loaded_library() -> str:
+    if sys.platform != "win32":
+        return "n/a"
+    try:
+        from vllm.utils import system_utils
+    except ImportError:
+        return "n/a"
+    current = getattr(system_utils, "find_loaded_library", None)
+    if current is None:
+        return "n/a"
+    if getattr(current, "__vllm_omni_windows__", False) or _has_mark(current):
+        return "already"
+    if _src_hash(current) not in KNOWN_UPSTREAM["find_loaded_library"]:
+        return "unknown_upstream"
+    system_utils.find_loaded_library = _make_win_find_loaded_library(current)
+    return "patched"
+
+
+# ---------------------------------------------------------------------------
+# verify only (the fix must be in the wheel)
+# ---------------------------------------------------------------------------
+
+
+def _verify(import_path: str, attr: str | None, needle: str) -> str:
+    try:
+        module = __import__(import_path, fromlist=["_"])
+    except ImportError:
+        return "n/a"
+    obj = getattr(module, attr) if attr else module
+    try:
+        src = inspect.getsource(obj)
+    except (OSError, TypeError):
+        return "n/a"
+    return "already" if needle in src else "wheel_required"
+
+
+def verify_wheel_sites() -> dict[str, str]:
+    """The sites a runtime plugin cannot fix; each must be `already` on Windows."""
+    if sys.platform != "win32":
+        return {}
+    out = {
+        # v1/engine/utils.py: zmq cannot poll a process HANDLE; 500 ms poll + exitcode checks.
+        "wait_for_engine_startup_sentinel_poll": _verify("vllm.v1.engine.utils", "wait_for_engine_startup", "_win_sentinels"),
+        # sample/states.py: numpy's default int is int32 on Windows; int64 seed bounds overflow.
+        "sampler_seed_int64": _verify("vllm.v1.worker.gpu.sample.states", None, "dtype=np.int64"),
+    }
+    # v1/utils.py binds uvloop lazily on the branch; with the uvloop shim present the
+    # module-level import would succeed anyway, so absence is "not_needed", not a failure.
+    status = _verify("vllm.v1.utils", None, "__getattr__")
+    if status == "wheel_required":
+        status = "not_needed" if "uvloop" in sys.modules else "wheel_required"
+    out["v1_utils_uvloop_lazy"] = status
+    # launcher.serve_http: the branch has a signal.signal fallback; the loop-class patch
+    # (aio.patch_signal_handlers) covers an unpatched wheel too.
+    status = _verify("vllm.entrypoints.launchers.launcher", "serve_http", "signal-handler")
+    out["serve_http_signal_fallback"] = "already" if status == "already" else ("not_needed" if status == "wheel_required" else status)
+    return out