diff --git a/src/cliproxy/executor/__tests__/claude-launcher.test.ts b/src/cliproxy/executor/__tests__/claude-launcher.test.ts
index e6111e50..3e587ca9 100644
--- a/src/cliproxy/executor/__tests__/claude-launcher.test.ts
+++ b/src/cliproxy/executor/__tests__/claude-launcher.test.ts
@@ -87,6 +87,16 @@ mock.module('../../quota/quota-manager', () => ({
   stopQuotaMonitor: jest.fn(),
 }));
 
+const mockCleanupLaunchSettings = jest.fn();
+const mockPrepareLaunchSettings = jest.fn().mockReturnValue({
+  settingsPath: '/tmp/fake-settings-overlay.json',
+  cleanup: mockCleanupLaunchSettings,
+});
+
+mock.module('../launch-settings', () => ({
+  prepareLaunchSettings: mockPrepareLaunchSettings,
+}));
+
 // ── Subject under test ────────────────────────────────────────────────────────
 
 import { launchClaude } from '../claude-launcher';
@@ -131,6 +141,12 @@ describe('launchClaude', () => {
     mockSpawn.mockClear();
     mockSetupCleanupHandlers.mockClear();
     mockEscapeShellArg.mockClear();
+    mockCleanupLaunchSettings.mockClear();
+    mockPrepareLaunchSettings.mockClear();
+    mockPrepareLaunchSettings.mockReturnValue({
+      settingsPath: '/tmp/fake-settings-overlay.json',
+      cleanup: mockCleanupLaunchSettings,
+    });
   });
 
   it('calls spawn with claudeCli and includes --settings arg', async () => {
@@ -189,6 +205,16 @@ describe('launchClaude', () => {
     expect(result).toBe(mockSpawnResult);
   });
 
+  it('calls cleanup and rethrows when spawn throws synchronously', async () => {
+    const spawnErr = new Error('ERR_INVALID_ARG_VALUE');
+    mockSpawn.mockImplementationOnce(() => {
+      throw spawnErr;
+    });
+
+    await expect(launchClaude(baseContext())).rejects.toThrow('ERR_INVALID_ARG_VALUE');
+    expect(mockCleanupLaunchSettings).toHaveBeenCalledTimes(1);
+  });
+
   describe('Windows shell escaping', () => {
     const originalPlatform = process.platform;
 
diff --git a/src/cliproxy/executor/claude-launcher.ts b/src/cliproxy/executor/claude-launcher.ts
index ca539971..ff189bbf 100644
--- a/src/cliproxy/executor/claude-launcher.ts
+++ b/src/cliproxy/executor/claude-launcher.ts
@@ -144,20 +144,28 @@ export async function launchClaude(context: ClaudeLaunchContext): Promise<ChildP
 
   // Spawn: Windows .cmd/.bat/.ps1 need shell escaping; all others spawn directly
   let claude: ChildProcess;
-  if (needsShell) {
-    const cmdString = [claudeCli, ...launchArgs].map(escapeShellArg).join(' ');
-    claude = spawn(cmdString, {
-      stdio: 'inherit',
-      windowsHide: true,
-      shell: getWindowsEscapedCommandShell(),
-      env: tracedEnv,
-    });
-  } else {
-    claude = spawn(claudeCli, launchArgs, {
-      stdio: 'inherit',
-      windowsHide: true,
-      env: tracedEnv,
-    });
+  try {
+    if (needsShell) {
+      const cmdString = [claudeCli, ...launchArgs].map(escapeShellArg).join(' ');
+      claude = spawn(cmdString, {
+        stdio: 'inherit',
+        windowsHide: true,
+        shell: getWindowsEscapedCommandShell(),
+        env: tracedEnv,
+      });
+    } else {
+      claude = spawn(claudeCli, launchArgs, {
+        stdio: 'inherit',
+        windowsHide: true,
+        env: tracedEnv,
+      });
+    }
+  } catch (spawnError) {
+    // spawn() can throw synchronously (e.g. invalid arg/env). Remove the
+    // runtime settings overlay before propagating so the secret-bearing temp
+    // file is not orphaned. cleanup is idempotent.
+    cleanupLaunchSettings();
+    throw spawnError;
   }
 
   // Remove the runtime settings overlay once Claude has read it and exited.