fix: use PowerShell $env: syntax for Windows hook paths (#26)

On Windows the lifecycle hooks run via PowerShell, which does not expand
cmd.exe-style %CLAUDE_PLUGIN_ROOT%. The path was passed literally, so the hook
launcher could not find the script and both SessionStart and UserPromptSubmit
failed with exit code 1 (issue #19). Switch the two commandWindows entries to
$env:CLAUDE_PLUGIN_ROOT, keeping the working node + .js invocation.

Add a regression test that rejects cmd.exe %VAR% syntax in commandWindows and
asserts every hook command points at a script that actually ships in hooks/.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/hooks-windows.test.js

@@ -0,0 +1,48 @@
+#!/usr/bin/env node
+// Regression test for issue #19: on Windows the lifecycle hooks run via
+// PowerShell, which does NOT expand cmd.exe-style %VAR% — it needs $env:VAR.
+// The hook also has to point at a script that actually ships in hooks/.
+// This guards both failure modes: the original %CLAUDE_PLUGIN_ROOT% bug, and
+// the "switch to a .ps1 that doesn't exist" mistake.
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('fs');
+const path = require('path');
+
+const root = path.join(__dirname, '..');
+const HOOKS_JSON = 'hooks/hooks.json';
+// cmd.exe variable syntax (%FOO%); PowerShell leaves it literal, breaking the path.
+const CMD_VAR_SYNTAX = /%[A-Za-z_][A-Za-z0-9_]*%/;
+// Pull the hooks/<script> a command launches, so we can check it exists.
+const HOOK_SCRIPT = /hooks[\\/]([\w.-]+\.(?:js|mjs|cjs|ps1|sh))/;
+
+// Read inside each case so a missing/malformed file fails as a clean assertion,
+// not a load-time crash.
+function commandHooks() {
+  const config = JSON.parse(fs.readFileSync(path.join(root, HOOKS_JSON), 'utf8'));
+  return Object.values(config.hooks)
+    .flat()
+    .flatMap((entry) => entry.hooks);
+}
+
+test('every commandWindows uses PowerShell $env: syntax, not cmd.exe %VAR%', () => {
+  const windowsCommands = commandHooks()
+    .map((h) => h.commandWindows)
+    .filter(Boolean);
+  assert.ok(windowsCommands.length > 0, 'expected at least one commandWindows entry');
+  for (const cmd of windowsCommands) {
+    assert.doesNotMatch(cmd, CMD_VAR_SYNTAX, `commandWindows uses cmd.exe %VAR% (breaks under PowerShell): ${cmd}`);
+  }
+});
+
+test('every hook command points at a script that ships in hooks/', () => {
+  for (const hook of commandHooks()) {
+    for (const cmd of [hook.command, hook.commandWindows].filter(Boolean)) {
+      const match = cmd.match(HOOK_SCRIPT);
+      assert.ok(match, `cannot find a hooks/ script in command: ${cmd}`);
+      const script = path.join(root, 'hooks', match[1]);
+      assert.ok(fs.existsSync(script), `command references a missing hook script: ${match[1]}`);
+    }
+  }
+});