diff --git a/apps/frontend/src/__tests__/integration/subprocess-spawn.test.ts b/apps/frontend/src/__tests__/integration/subprocess-spawn.test.ts
index cf03c5136e..e73f60ea54 100644
--- a/apps/frontend/src/__tests__/integration/subprocess-spawn.test.ts
+++ b/apps/frontend/src/__tests__/integration/subprocess-spawn.test.ts
@@ -58,6 +58,16 @@ vi.mock('../../main/python-detector', async (importOriginal) => {
   };
 });
 
+// Mock python-env-manager for ensurePythonEnvReady (ACS-254)
+vi.mock('../../main/python-env-manager', () => ({
+  pythonEnvManager: {
+    isEnvReady: vi.fn(() => true),
+    initialize: vi.fn(() => Promise.resolve({ ready: true })),
+    getPythonEnv: vi.fn(() => ({}))
+  },
+  getConfiguredPythonPath: vi.fn(() => DETECTED_PYTHON_CMD)
+}));
+
 // Auto-claude source path (for getAutoBuildSourcePath to find)
 const AUTO_CLAUDE_SOURCE = path.join(TEST_DIR, 'auto-claude-source');
 
diff --git a/apps/frontend/src/main/agent/agent-manager.ts b/apps/frontend/src/main/agent/agent-manager.ts
index 400ba21cdb..7ce8790954 100644
--- a/apps/frontend/src/main/agent/agent-manager.ts
+++ b/apps/frontend/src/main/agent/agent-manager.ts
@@ -110,6 +110,13 @@ export class AgentManager extends EventEmitter {
       return;
     }
 
+    // Ensure Python environment is ready before spawning process (prevents exit code 127 race condition)
+    const pythonStatus = await this.processManager.ensurePythonEnvReady('AgentManager');
+    if (!pythonStatus.ready) {
+      this.emit('error', taskId, `Python environment not ready: ${pythonStatus.error || 'initialization failed'}`);
+      return;
+    }
+
     const autoBuildSource = this.processManager.getAutoBuildSourcePath();
 
     if (!autoBuildSource) {
@@ -196,6 +203,13 @@ export class AgentManager extends EventEmitter {
       return;
     }
 
+    // Ensure Python environment is ready before spawning process (prevents exit code 127 race condition)
+    const pythonStatus = await this.processManager.ensurePythonEnvReady('AgentManager');
+    if (!pythonStatus.ready) {
+      this.emit('error', taskId, `Python environment not ready: ${pythonStatus.error || 'initialization failed'}`);
+      return;
+    }
+
     const autoBuildSource = this.processManager.getAutoBuildSourcePath();
 
     if (!autoBuildSource) {
@@ -250,6 +264,13 @@ export class AgentManager extends EventEmitter {
     projectPath: string,
     specId: string
   ): Promise<void> {
+    // Ensure Python environment is ready before spawning process (prevents exit code 127 race condition)
+    const pythonStatus = await this.processManager.ensurePythonEnvReady('AgentManager');
+    if (!pythonStatus.ready) {
+      this.emit('error', taskId, `Python environment not ready: ${pythonStatus.error || 'initialization failed'}`);
+      return;
+    }
+
     const autoBuildSource = this.processManager.getAutoBuildSourcePath();
 
     if (!autoBuildSource) {
diff --git a/apps/frontend/src/main/agent/agent-process.test.ts b/apps/frontend/src/main/agent/agent-process.test.ts
index c06b8f6824..b6897acd95 100644
--- a/apps/frontend/src/main/agent/agent-process.test.ts
+++ b/apps/frontend/src/main/agent/agent-process.test.ts
@@ -95,18 +95,46 @@ vi.mock('../python-detector', () => ({
   parsePythonCommand: vi.fn(() => ['python', []])
 }));
 
+// Mock python-env-manager for ensurePythonEnvReady tests
+vi.mock('../python-env-manager', () => ({
+  pythonEnvManager: {
+    isEnvReady: vi.fn(() => true),
+    initialize: vi.fn(() => Promise.resolve({ ready: true })),
+    getPythonEnv: vi.fn(() => ({}))
+  },
+  getConfiguredPythonPath: vi.fn(() => 'python3')
+}));
+
 vi.mock('electron', () => ({
   app: {
     getAppPath: vi.fn(() => '/fake/app/path')
   }
 }));
 
+// Mock fs.existsSync for getAutoBuildSourcePath path validation
+vi.mock('fs', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('fs')>();
+  return {
+    ...actual,
+    existsSync: vi.fn((path: string) => {
+      // Return true for the fake auto-build path and its expected files
+      if (path === '/fake/auto-build' ||
+          path === '/fake/auto-build/runners' ||
+          path === '/fake/auto-build/runners/spec_runner.py') {
+        return true;
+      }
+      return false;
+    })
+  };
+});
+
 // Import AFTER all mocks are set up
 import { AgentProcessManager } from './agent-process';
 import { AgentState } from './agent-state';
 import { AgentEvents } from './agent-events';
 import * as profileService from '../services/profile';
 import * as rateLimitDetector from '../rate-limit-detector';
+import { pythonEnvManager } from '../python-env-manager';
 
 describe('AgentProcessManager - API Profile Env Injection (Story 2.3)', () => {
   let processManager: AgentProcessManager;
@@ -491,4 +519,105 @@ describe('AgentProcessManager - API Profile Env Injection (Story 2.3)', () => {
       expect(envArg.ANTHROPIC_BASE_URL).toBe('');
     });
   });
+
+  describe('ensurePythonEnvReady - Python Environment Readiness (ACS-254)', () => {
+    let testProcessManager: AgentProcessManager;
+
+    beforeEach(() => {
+      // Reset all mocks
+      vi.clearAllMocks();
+      spawnCalls.length = 0;
+
+      // Create fresh process manager for these tests
+      state = new AgentState();
+      events = new AgentEvents();
+      emitter = new EventEmitter();
+      testProcessManager = new AgentProcessManager(state, events, emitter);
+    });
+
+    it('should return ready: true when Python environment is already ready', async () => {
+      vi.mocked(pythonEnvManager.isEnvReady).mockReturnValue(true);
+
+      // Configure with valid autoBuildSource
+      testProcessManager.configure(undefined, '/fake/auto-build');
+
+      const result = await testProcessManager.ensurePythonEnvReady('TestContext');
+
+      expect(result.ready).toBe(true);
+      expect(result.error).toBeUndefined();
+      expect(pythonEnvManager.initialize).not.toHaveBeenCalled();
+    });
+
+    it('should initialize Python environment when not ready', async () => {
+      vi.mocked(pythonEnvManager.isEnvReady).mockReturnValue(false);
+      vi.mocked(pythonEnvManager.initialize).mockResolvedValue({
+        ready: true,
+        pythonPath: '/fake/python',
+        sitePackagesPath: '/fake/site-packages',
+        venvExists: true,
+        depsInstalled: true,
+        usingBundledPackages: false
+      });
+
+      testProcessManager.configure(undefined, '/fake/auto-build');
+
+      const result = await testProcessManager.ensurePythonEnvReady('TestContext');
+
+      expect(result.ready).toBe(true);
+      expect(result.error).toBeUndefined();
+      expect(pythonEnvManager.initialize).toHaveBeenCalledWith('/fake/auto-build');
+    });
+
+    it('should return error when autoBuildSource is not found', async () => {
+      vi.mocked(pythonEnvManager.isEnvReady).mockReturnValue(false);
+
+      // Don't configure - autoBuildSource will be null
+      const result = await testProcessManager.ensurePythonEnvReady('TestContext');
+
+      expect(result.ready).toBe(false);
+      expect(result.error).toBe('auto-build source not found');
+      expect(pythonEnvManager.initialize).not.toHaveBeenCalled();
+    });
+
+    it('should return error when Python initialization fails', async () => {
+      vi.mocked(pythonEnvManager.isEnvReady).mockReturnValue(false);
+      vi.mocked(pythonEnvManager.initialize).mockResolvedValue({
+        ready: false,
+        pythonPath: null,
+        sitePackagesPath: null,
+        venvExists: false,
+        depsInstalled: false,
+        usingBundledPackages: false,
+        error: 'Failed to create venv: permission denied'
+      });
+
+      testProcessManager.configure(undefined, '/fake/auto-build');
+
+      const result = await testProcessManager.ensurePythonEnvReady('TestContext');
+
+      expect(result.ready).toBe(false);
+      expect(result.error).toBe('Failed to create venv: permission denied');
+    });
+
+    it('should return error when Python initialization fails without message', async () => {
+      vi.mocked(pythonEnvManager.isEnvReady).mockReturnValue(false);
+      vi.mocked(pythonEnvManager.initialize).mockResolvedValue({
+        ready: false,
+        pythonPath: null,
+        sitePackagesPath: null,
+        venvExists: false,
+        depsInstalled: false,
+        usingBundledPackages: false
+        // No error field
+      });
+
+      testProcessManager.configure(undefined, '/fake/auto-build');
+
+      const result = await testProcessManager.ensurePythonEnvReady('TestContext');
+
+      expect(result.ready).toBe(false);
+      expect(result.error).toBe('initialization failed');
+      expect(pythonEnvManager.initialize).toHaveBeenCalledWith('/fake/auto-build');
+    });
+  });
 });
diff --git a/apps/frontend/src/main/agent/agent-process.ts b/apps/frontend/src/main/agent/agent-process.ts
index 6291912a4e..b94488322d 100644
--- a/apps/frontend/src/main/agent/agent-process.ts
+++ b/apps/frontend/src/main/agent/agent-process.ts
@@ -301,6 +301,38 @@ export class AgentProcessManager {
     return null;
   }
 
+  /**
+   * Ensure Python environment is ready before spawning processes.
+   * This is a shared method used by AgentManager and AgentQueueManager
+   * to prevent race conditions where tasks start before venv initialization completes.
+   *
+   * @param context - Context identifier for logging (e.g., 'AgentManager', 'AgentQueue')
+   * @returns Object with ready status and optional error message
+   */
+  async ensurePythonEnvReady(context: string): Promise<{ ready: boolean; error?: string }> {
+    if (pythonEnvManager.isEnvReady()) {
+      return { ready: true };
+    }
+
+    console.log(`[${context}] Python environment not ready, waiting for initialization...`);
+
+    const autoBuildSource = this.getAutoBuildSourcePath();
+    if (!autoBuildSource) {
+      const error = 'auto-build source not found';
+      console.error(`[${context}] Cannot initialize Python - ${error}`);
+      return { ready: false, error };
+    }
+
+    const status = await pythonEnvManager.initialize(autoBuildSource);
+    if (!status.ready) {
+      console.error(`[${context}] Python environment initialization failed:`, status.error);
+      return { ready: false, error: status.error || 'initialization failed' };
+    }
+
+    console.log(`[${context}] Python environment now ready`);
+    return { ready: true };
+  }
+
   /**
    * Get project-specific environment variables based on project settings
    */
diff --git a/apps/frontend/src/main/agent/agent-queue.ts b/apps/frontend/src/main/agent/agent-queue.ts
index 6f4220ec58..279ecc2b70 100644
--- a/apps/frontend/src/main/agent/agent-queue.ts
+++ b/apps/frontend/src/main/agent/agent-queue.ts
@@ -59,6 +59,8 @@ export class AgentQueueManager {
    * Prevents the race condition where generation starts before dependencies are installed,
    * which would cause it to fall back to system Python and fail with ModuleNotFoundError.
    *
+   * Delegates to AgentProcessManager.ensurePythonEnvReady() for the actual initialization.
+   *
    * @param projectId - The project ID for error event emission
    * @param eventType - The error event type to emit on failure
    * @returns true if environment is ready, false if initialization failed (error already emitted)
@@ -67,23 +69,10 @@ export class AgentQueueManager {
     projectId: string,
     eventType: 'ideation-error' | 'roadmap-error'
   ): Promise<boolean> {
-    const autoBuildSource = this.processManager.getAutoBuildSourcePath();
-
-    if (!pythonEnvManager.isEnvReady()) {
-      debugLog('[Agent Queue] Python environment not ready, waiting for initialization...');
-      if (autoBuildSource) {
-        const status = await pythonEnvManager.initialize(autoBuildSource);
-        if (!status.ready) {
-          debugError('[Agent Queue] Python environment initialization failed:', status.error);
-          this.emitter.emit(eventType, projectId, `Python environment not ready: ${status.error || 'initialization failed'}`);
-          return false;
-        }
-        debugLog('[Agent Queue] Python environment now ready');
-      } else {
-        debugError('[Agent Queue] Cannot initialize Python - auto-build source not found');
-        this.emitter.emit(eventType, projectId, 'Python environment not ready: auto-build source not found');
-        return false;
-      }
+    const status = await this.processManager.ensurePythonEnvReady('AgentQueue');
+    if (!status.ready) {
+      this.emitter.emit(eventType, projectId, `Python environment not ready: ${status.error || 'initialization failed'}`);
+      return false;
     }
     return true;
   }