fix: add PATH to restricted hook env, protect HOME/CLAUDE_PROJECT_DIR from allowlist override, reset plugin hooks state in tests

- P1: When allowedEnvVars is provided, PATH was missing from the base
  restricted env, causing non-builtin commands to fail at exec time
- P2: Allowlisted HOME/CLAUDE_PROJECT_DIR could overwrite normalized
  values from getHomeDirectory()/cwd with ambient process.env values
- P2: Test suite mutated shared pluginHooksState singleton without
  resetting it in afterEach, causing cross-test state leaks

src/shared/command-executor/execute-hook-command.ts

@@ -56,12 +56,20 @@ export async function executeHookCommand(
 
     const isWin32 = process.platform === "win32";
 
+    // Keys that are always set from normalized sources and must not be
+    // overwritten by ambient process.env values during the allowlist merge.
+    const PROTECTED_ENV_KEYS = new Set(["HOME", "CLAUDE_PROJECT_DIR"]);
+
     let env: Record<string, string | undefined>;
     if (options?.allowedEnvVars) {
       const allowedSet = new Set(options.allowedEnvVars);
-      env = { HOME: home, CLAUDE_PROJECT_DIR: cwd };
+      env = {
+        HOME: home,
+        CLAUDE_PROJECT_DIR: cwd,
+        PATH: process.env.PATH,
+      };
       for (const key of Object.keys(process.env)) {
-        if (allowedSet.has(key)) {
+        if (allowedSet.has(key) && !PROTECTED_ENV_KEYS.has(key)) {
           env[key] = process.env[key];
         }
       }