fix(e2e): inherit PATHEXT on Windows for executable lookup

When using native bash with env_clear(), the child process loses
PATHEXT which is needed by the which crate to find executables
with extensions like .exe and .cmd on Windows.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: branchseer

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdin-passthrough/package.json

@@ -1,6 +1,6 @@
 {
   "name": "stdin-passthrough",
   "scripts": {
-    "echo-stdin": "cat"
+    "echo-stdin": "node -e \"process.stdin.pipe(process.stdout)\""
   }
 }

crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdin-passthrough/snapshots/stdin passthrough to single task.snap

@@ -1,11 +1,11 @@
 ---
 source: crates/vite_task_bin/tests/e2e_snapshots/main.rs
-assertion_line: 166
+assertion_line: 203
 expression: e2e_outputs
 input_file: crates/vite_task_bin/tests/e2e_snapshots/fixtures/stdin-passthrough
 ---
 > vite run echo-stdin
-$ cat
+$ node -e "process.stdin.pipe(process.stdout)"
 hello from stdin
 
 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
@@ -17,6 +17,6 @@ Performance:  0% cache hit rate
 
 Task Details:
 ────────────────────────────────────────────────
-  [1] stdin-passthrough#echo-stdin: $ cat ✓
+  [1] stdin-passthrough#echo-stdin: $ node -e "process.stdin.pipe(process.stdout)" ✓
       → Cache miss: no previous cache entry found
 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

crates/vite_task_bin/tests/e2e_snapshots/main.rs

@@ -168,6 +168,13 @@ fn run_case_inner(tmpdir: &AbsolutePath, fixture_path: &Path, fixture_name: &str
                 .env("NO_COLOR", "1")
                 .current_dir(e2e_stage_path.join(&e2e.cwd));
 
+            // On Windows, inherit PATHEXT for executable lookup
+            if cfg!(windows) {
+                if let Ok(pathext) = std::env::var("PATHEXT") {
+                    cmd.env("PATHEXT", pathext);
+                }
+            }
+
             let output = if let Some(stdin_content) = step.stdin() {
                 cmd.stdin(Stdio::piped());
                 cmd.stdout(Stdio::piped());