Enable agentic commit reviewer on Windows

The agentic reviewer is silently no-op on Windows today. SessionStart
bootstrap (ensure_agent_sdk.py) short-circuits with SKIP_WIN32 because
the consumer glob in llm.py only matches POSIX venv layout
(lib/pythonX.Y/site-packages). On Windows, venvs use Lib/site-packages
(capital L, no pythonX.Y subdir), so even if a venv got built the
glob wouldn't find its contents.

Result: Windows users on default installs (no system-wide
claude_agent_sdk) get layer 1 (pattern warnings) and layer 2 (single-
shot LLM diff review) but not layer 3 — the cross-file agentic review
that catches IDOR, auth-bypass, cross-file SSRF, and other things that
need to read related files. Plugin description claims layer 3 but it
silently doesn't run.

Three changes:

1. llm.py — extend the consumer glob (2 sites: 3P SDK fallback at
   ~L297, agentic_review fallback at ~L1090) to also match the Windows
   Lib/site-packages layout, so a venv built on Windows is actually
   discoverable.

2. ensure_agent_sdk.py — remove the sys.platform == 'win32' early-exit
   so the SessionStart bootstrap builds the venv on Windows too.
   Outcome code 4 (formerly SKIP_WIN32) is retired but not reused so
   pre-fix telemetry rows still decode correctly.

3. ensure_agent_sdk.py — venv_py path now branches on sys.platform:
   Windows venvs put the interpreter at Scripts\python.exe; POSIX
   uses bin/python. Previously assumed POSIX, so even with the glob
   fix, the post-build SDK-importability probe would fail on Windows.

Verified locally on macOS:
- glob test: both layouts now match (POSIX venv detected, simulated
  Windows venv also detected via the new Lib/site-packages branch)
- both files pass py_compile
- POSIX path unchanged (sys.platform != 'win32' so old branch runs)

Not verified on Windows in this commit — needs an actual Windows
runner to confirm the venv build + SDK import + subprocess plumbing
all work end-to-end. The SDK spawns a child claude.exe; Windows
process plumbing has its own quirks (shell semantics, path escaping)
that may surface separately. Worth a controlled rollout (one-week
soak under env-var opt-in before flipping default).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugins/security-guidance/hooks/ensure_agent_sdk.py

@@ -28,7 +28,9 @@ NOOP_SYSTEM = 0      # claude_agent_sdk already importable in system python
 NOOP_VENV = 1        # venv already built and SDK imports from it
 BUILT = 2            # venv created + SDK pip-installed this run
 BUILD_FAILED = 3     # venv create or pip install raised/timed out
-SKIP_WIN32 = 4       # Windows; consumer glob doesn't handle Lib/ layout
+# Outcome 4 was previously SKIP_WIN32; retired now that the consumer glob in
+# llm.py also matches Windows venv layout (Lib/site-packages). Don't reuse the
+# value — telemetry rows from older plugin builds still emit 4.
 SKIP_SENTINEL = 5    # another SessionStart is currently building
 
 
@@ -60,13 +62,6 @@ def main() -> tuple[int, str, str]:
     err_phase / err_kind are non-empty only on BUILD_FAILED — they let
     telemetry split bootstrap failures by root cause.
     """
-    # Windows venv layout (Lib/site-packages, no python* subdir) isn't
-    # handled by the consumer's glob in security_reminder_hook.py; skip the
-    # bootstrap entirely rather than build a venv that's never read.
-    if sys.platform == "win32":
-        return SKIP_WIN32, "", ""
-
-
     if _sdk_on_syspath():
         return NOOP_SYSTEM, "", ""
 
@@ -75,7 +70,11 @@ def main() -> tuple[int, str, str]:
         or os.path.expanduser("~/.claude/security")
     )
     venv = state_dir / "agent-sdk-venv"
-    venv_py = venv / "bin" / "python"
+    # Windows venvs put the interpreter at Scripts\python.exe; POSIX uses bin/python.
+    if sys.platform == "win32":
+        venv_py = venv / "Scripts" / "python.exe"
+    else:
+        venv_py = venv / "bin" / "python"
 
     # Another SessionStart (concurrent CC instance, same plugin) may already
     # be building. The sentinel lives NEXT TO the venv, not inside it —

plugins/security-guidance/hooks/llm.py

@@ -298,9 +298,12 @@ def _call_claude_via_sdk(prompt, output_schema, *, max_tokens=16000, model=None)
             "SECURITY_WARNINGS_STATE_DIR",
             os.path.expanduser("~/.claude/security"),
         )
-        for _sp in glob.glob(
-            os.path.join(_state_dir, "agent-sdk-venv", "lib",
-                         "python*", "site-packages")
+        # POSIX venv: lib/pythonX.Y/site-packages
+        # Windows venv: Lib/site-packages  (capital L, no pythonX.Y subdir)
+        _venv_root = os.path.join(_state_dir, "agent-sdk-venv")
+        for _sp in (
+            glob.glob(os.path.join(_venv_root, "lib", "python*", "site-packages"))
+            + glob.glob(os.path.join(_venv_root, "Lib", "site-packages"))
         ):
             if os.path.isdir(_sp) and _sp not in sys.path:
                 sys.path.insert(0, _sp)
@@ -1094,9 +1097,12 @@ def agentic_review(
             "SECURITY_WARNINGS_STATE_DIR",
             os.path.expanduser("~/.claude/security"),
         )
-        for _sp in glob.glob(
-            os.path.join(_state_dir, "agent-sdk-venv", "lib",
-                         "python*", "site-packages")
+        # POSIX venv: lib/pythonX.Y/site-packages
+        # Windows venv: Lib/site-packages  (capital L, no pythonX.Y subdir)
+        _venv_root = os.path.join(_state_dir, "agent-sdk-venv")
+        for _sp in (
+            glob.glob(os.path.join(_venv_root, "lib", "python*", "site-packages"))
+            + glob.glob(os.path.join(_venv_root, "Lib", "site-packages"))
         ):
             if os.path.isdir(_sp) and _sp not in sys.path:
                 sys.path.insert(0, _sp)