diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..49168e3
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,28 @@
+name: plugin-ci
+
+on:
+  pull_request:
+  push:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  validate:
+    name: validate (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+          - windows-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      - name: Run plugin validation and lifecycle smoke
+        shell: bash
+        run: PYTHON=python bash scripts/ci-local.sh
diff --git a/README.md b/README.md
index b4bd4b6..45cb035 100644
--- a/README.md
+++ b/README.md
@@ -99,6 +99,10 @@ The validation script compiles the plugin, loads the Hermes registration
 surface, exercises the original and 0.2 methods, checks lifecycle hooks, and
 checks the public distribution surface.
 
+GitHub Actions runs this same validation on current Ubuntu and Windows runners.
+The matrix protects the POSIX `fcntl` backend used on macOS and Linux and the
+Windows `msvcrt` backend used by the installed Hermes plugin.
+
 ## Documentation
 
 - [Hermes plugin operation](docs/HERMES_PLUGIN.md)
diff --git a/aem_store.py b/aem_store.py
index 9022b78..8321907 100644
--- a/aem_store.py
+++ b/aem_store.py
@@ -64,7 +64,7 @@ def _atomic_replace_text(path: Path, text: str) -> None:
     handle, temporary_name = tempfile.mkstemp(prefix=f".{path.name}.", dir=path.parent)
     try:
         with os.fdopen(handle, "w", encoding="utf-8") as temporary:
-            if path.exists():
+            if path.exists() and hasattr(os, "fchmod"):
                 os.fchmod(temporary.fileno(), path.stat().st_mode & 0o777)
             temporary.write(text)
             temporary.flush()
diff --git a/aethermind_core.py b/aethermind_core.py
index d639691..472c6e7 100644
--- a/aethermind_core.py
+++ b/aethermind_core.py
@@ -250,13 +250,30 @@ def _layer_hash(layer: "AetherLayer") -> str:
 except ImportError:  # pragma: no cover - Windows or unsupported host
     fcntl = None  # type: ignore[assignment]
 
+try:
+    import msvcrt
+except ImportError:  # pragma: no cover - POSIX or unsupported host
+    msvcrt = None  # type: ignore[assignment]
+
 
 def _lock_backend() -> str:
-    return "fcntl" if fcntl is not None else "unavailable"
+    if fcntl is not None:
+        return "fcntl"
+    if msvcrt is not None:
+        return "msvcrt"
+    return "unavailable"
+
+
+def _locking_scope() -> str:
+    if fcntl is not None:
+        return "local-posix-advisory"
+    if msvcrt is not None:
+        return "local-windows-byte-range"
+    return "unavailable"
 
 
 def _require_lock_backend() -> None:
-    if fcntl is None:
+    if _lock_backend() == "unavailable":
         raise LockUnavailableError(
             "no safe local file locking backend is available; refusing to write"
         )
@@ -265,16 +282,55 @@ def _require_lock_backend() -> None:
 class _FileLock:
     def __init__(self, file_obj):
         self.file_obj = file_obj
+        self._windows_lock_file = None
+
+    def _windows_lock_path(self) -> Path:
+        path = Path(self.file_obj.name)
+        return path.with_name(f"{path.name}.lock")
+
+    def _lock_with_msvcrt(self) -> None:
+        """Lock a dedicated byte so ledger data files remain readable on Windows.
+
+        ``msvcrt.locking`` operates on byte ranges. Locking a sibling file keeps
+        the data ledger free of mandatory byte-range locks while serializing all
+        cooperating AetherMind writers for that ledger.
+        """
+        assert msvcrt is not None
+        lock_file = self._windows_lock_path().open("a+b")
+        self._windows_lock_file = lock_file
+        try:
+            lock_file.seek(0, io.SEEK_END)
+            if lock_file.tell() == 0:
+                lock_file.write(b"\0")
+                lock_file.flush()
+                os.fsync(lock_file.fileno())
+            lock_file.seek(0)
+            msvcrt.locking(lock_file.fileno(), msvcrt.LK_LOCK, 1)
+        except BaseException:
+            lock_file.close()
+            self._windows_lock_file = None
+            raise
 
     def __enter__(self):
         _require_lock_backend()
-        assert fcntl is not None
-        fcntl.flock(self.file_obj.fileno(), fcntl.LOCK_EX)
+        if fcntl is not None:
+            fcntl.flock(self.file_obj.fileno(), fcntl.LOCK_EX)
+        else:
+            self._lock_with_msvcrt()
         return self.file_obj
 
     def __exit__(self, _exc_type, _exc, _tb):
-        assert fcntl is not None
-        fcntl.flock(self.file_obj.fileno(), fcntl.LOCK_UN)
+        if fcntl is not None:
+            fcntl.flock(self.file_obj.fileno(), fcntl.LOCK_UN)
+            return
+        assert msvcrt is not None
+        assert self._windows_lock_file is not None
+        try:
+            self._windows_lock_file.seek(0)
+            msvcrt.locking(self._windows_lock_file.fileno(), msvcrt.LK_UNLCK, 1)
+        finally:
+            self._windows_lock_file.close()
+            self._windows_lock_file = None
 
 # --- Data Models ---
 
@@ -1830,7 +1886,7 @@ def runtime_capabilities(
         "implementation_sha256": hashlib.sha256(source_path.read_bytes()).hexdigest(),
         "safe_default_create": True,
         "lock_backend": _lock_backend(),
-        "locking_scope": "local-posix-advisory" if fcntl is not None else "unavailable",
+        "locking_scope": _locking_scope(),
         "capabilities": [
             "acknowledged-layer-append",
             "explicit-store-init",
diff --git a/plugin.yaml b/plugin.yaml
index 3937bfe..898f40f 100644
--- a/plugin.yaml
+++ b/plugin.yaml
@@ -1,6 +1,9 @@
 name: aethermind
 version: 0.2.0
 description: Project-local continuity layers for Hermes agents.
+provides_hooks:
+  - on_session_start
+  - pre_llm_call
 provides_tools:
   - aethermind_init_store
   - aethermind_write_layer
diff --git a/scripts/ci-local.sh b/scripts/ci-local.sh
index 82bb6e2..f6e85d9 100755
--- a/scripts/ci-local.sh
+++ b/scripts/ci-local.sh
@@ -53,7 +53,14 @@ for forbidden in ("src", "tests", "tools", "plugins", "pyproject.toml"):
         raise SystemExit(f"forbidden publish surface still present: {forbidden}")
 
 manifest = (root / "plugin.yaml").read_text(encoding="utf-8")
-for expected in ("name: aethermind", "aethermind_write_layer", "aethermind_reorient"):
+for expected in (
+    "name: aethermind",
+    "aethermind_write_layer",
+    "aethermind_reorient",
+    "provides_hooks:",
+    "on_session_start",
+    "pre_llm_call",
+):
     if expected not in manifest:
         raise SystemExit(f"plugin.yaml missing {expected!r}")
 
@@ -186,6 +193,8 @@ if not (
     and imported["ok"]
     and imported_report["valid"]
     and capabilities["runtime_version"] == "0.2.0"
+    and capabilities["lock_backend"] in {"fcntl", "msvcrt"}
+    and capabilities["locking_scope"] in {"local-posix-advisory", "local-windows-byte-range"}
     and len(currentness["active_heads"]) == 1
     and event["event_id"] == "0001"
     and len(events["events"]) == 1