fix(windows): align escaped wrapper shell handling

Use ComSpec-aware shell selection for escaped wrapper launches.

Apply it to the remaining Windows Claude launch paths.

Rewrite the Codex exec regression test to use scoped spies so the full suite stays isolated.

src/utils/claude-spawner.ts

@@ -6,7 +6,11 @@
  */
 
 import { spawn, ChildProcess, SpawnOptions } from 'child_process';
-import { escapeShellArg, stripClaudeCodeEnv } from './shell-executor';
+import {
+  escapeShellArg,
+  getWindowsEscapedCommandShell,
+  stripClaudeCodeEnv,
+} from './shell-executor';
 import { getClaudeCliInfo } from './claude-detector';
 import { ErrorManager } from './error-manager';
 
@@ -56,7 +60,7 @@ export function spawnClaude(options: SpawnClaudeOptions = {}): SpawnClaudeResult
     child = spawn(cmdString, {
       stdio,
       windowsHide: true,
-      shell: true,
+      shell: getWindowsEscapedCommandShell(),
       env: mergedEnv,
       cwd,
     });