diff --git a/packages/core/src/services/shellExecutionService.ts b/packages/core/src/services/shellExecutionService.ts
index a9ad273b..e501e6ec 100644
--- a/packages/core/src/services/shellExecutionService.ts
+++ b/packages/core/src/services/shellExecutionService.ts
@@ -108,47 +108,38 @@ export class ShellExecutionService {
   private static activePtys = new Map<number, ActivePty>();
   private static activeChildProcesses = new Set<number>();
 
-  static {
-    const cleanup = () => {
-      // Cleanup PTYs
-      for (const [pid, pty] of this.activePtys) {
-        try {
-          if (os.platform() === 'win32') {
-            pty.ptyProcess.kill();
-          } else {
-            process.kill(-pid, 'SIGKILL');
-          }
-        } catch {
-          // ignore
+  static cleanup() {
+    // Cleanup PTYs
+    for (const [pid, pty] of this.activePtys) {
+      try {
+        if (os.platform() === 'win32') {
+          pty.ptyProcess.kill();
+        } else {
+          process.kill(-pid, 'SIGKILL');
         }
+      } catch {
+        // ignore
       }
-
-      // Cleanup child processes
-      for (const pid of this.activeChildProcesses) {
-        try {
-          if (os.platform() === 'win32') {
-            spawnSync('taskkill', ['/pid', pid.toString(), '/f', '/t']);
-          } else {
-            process.kill(-pid, 'SIGKILL');
-          }
-        } catch {
-          // ignore
-        }
-      }
-    };
-
-    process.on('exit', cleanup);
-
-    // Ensure cleanup happens on SIGINT/SIGTERM
-    const signalHandler = () => {
-      process.exit();
-    };
-
-    // We only attach these if we are in a node environment where we can control the process
-    if (typeof process !== 'undefined' && process.on) {
-      process.on('SIGINT', signalHandler);
-      process.on('SIGTERM', signalHandler);
     }
+
+    // Cleanup child processes
+    for (const pid of this.activeChildProcesses) {
+      try {
+        if (os.platform() === 'win32') {
+          spawnSync('taskkill', ['/pid', pid.toString(), '/f', '/t']);
+        } else {
+          process.kill(-pid, 'SIGKILL');
+        }
+      } catch {
+        // ignore
+      }
+    }
+  }
+
+  static {
+    process.on('exit', () => {
+      ShellExecutionService.cleanup();
+    });
   }
 
   /**
diff --git a/packages/core/src/tools/shell.test.ts b/packages/core/src/tools/shell.test.ts
index bde50837..b431f494 100644
--- a/packages/core/src/tools/shell.test.ts
+++ b/packages/core/src/tools/shell.test.ts
@@ -831,4 +831,33 @@ describe('ShellTool', () => {
       expect(shellTool.description).toMatchSnapshot();
     });
   });
+
+  describe('Windows background execution', () => {
+    it('should detect immediate failure in Windows background task', async () => {
+      vi.mocked(os.platform).mockReturnValue('win32');
+      const mockAbortSignal = new AbortController().signal;
+
+      const invocation = shellTool.build({
+        command: 'invalid_command',
+        is_background: true,
+      });
+
+      const promise = invocation.execute(mockAbortSignal);
+
+      // Wait a tick to ensure mockShellOutputCallback is assigned
+      await new Promise((resolve) => setTimeout(resolve, 0));
+
+      if (mockShellOutputCallback) {
+        mockShellOutputCallback({
+          type: 'data',
+          chunk:
+            "'invalid_command' is not recognized as an internal or external command,\r\noperable program or batch file.\r\n",
+        });
+      }
+
+      const result = await promise;
+      expect(result.error).toBeDefined();
+      expect(result.llmContent).toContain('Command failed to start');
+    });
+  });
 });
diff --git a/packages/core/src/tools/shell.ts b/packages/core/src/tools/shell.ts
index b303b0fa..4ee7e79c 100644
--- a/packages/core/src/tools/shell.ts
+++ b/packages/core/src/tools/shell.ts
@@ -194,16 +194,16 @@ export class ShellToolInvocation extends BaseToolInvocation<
           commandToExecute,
           cwd,
           (event: ShellOutputEvent) => {
-            if (!updateOutput) {
-              return;
-            }
-
             let shouldUpdate = false;
 
             switch (event.type) {
               case 'data':
                 if (isBinaryStream) break;
-                cumulativeOutput = event.chunk;
+                if (typeof cumulativeOutput === 'string') {
+                  cumulativeOutput += event.chunk;
+                } else {
+                  cumulativeOutput = event.chunk;
+                }
                 shouldUpdate = true;
                 break;
               case 'binary_detected':
@@ -226,7 +226,7 @@ export class ShellToolInvocation extends BaseToolInvocation<
               }
             }
 
-            if (shouldUpdate) {
+            if (shouldUpdate && updateOutput) {
               updateOutput(
                 typeof cumulativeOutput === 'string'
                   ? cumulativeOutput
@@ -258,6 +258,32 @@ export class ShellToolInvocation extends BaseToolInvocation<
 
         if (raceResult === null) {
           // Timeout reached, process is still running.
+          // throw new Error(`DEBUG: raceResult is null. Output: ${JSON.stringify(cumulativeOutput)}`);
+
+          // Check for common Windows error messages in the output
+          const outputStr =
+            typeof cumulativeOutput === 'string'
+              ? cumulativeOutput
+              : JSON.stringify(cumulativeOutput);
+          console.log('DEBUG: outputStr:', outputStr);
+          const errorPatterns = [
+            'is not recognized as an internal or external command',
+            'The system cannot find the path specified',
+            'Access is denied',
+          ];
+
+          if (errorPatterns.some((pattern) => outputStr.includes(pattern))) {
+            abortController.abort();
+            return {
+              llmContent: `Command failed to start: ${outputStr}`,
+              returnDisplay: `Command failed to start: ${outputStr}`,
+              error: {
+                type: ToolErrorType.EXECUTION_FAILED,
+                message: `Command failed to start: ${outputStr}`,
+              },
+            };
+          }
+
           const pidMsg = pid ? ` PID: ${pid}` : '';
           const winHint = isWindows
             ? ' (Note: Use taskkill /F /T /PID <pid> to stop)'