diff --git a/parallel_orchestrator.py b/parallel_orchestrator.py
index 09f4e22c..98778c11 100644
--- a/parallel_orchestrator.py
+++ b/parallel_orchestrator.py
@@ -439,14 +439,20 @@ def _spawn_coding_agent(self, feature_id: int) -> tuple[bool, str]:
             cmd.append("--yolo")
 
         try:
-            proc = subprocess.Popen(
-                cmd,
-                stdout=subprocess.PIPE,
-                stderr=subprocess.STDOUT,
-                text=True,
-                cwd=str(AUTOCODER_ROOT),
-                env={**os.environ, "PYTHONUNBUFFERED": "1"},
-            )
+            # CREATE_NO_WINDOW on Windows prevents console window pop-ups
+            # stdin=DEVNULL prevents blocking on stdin reads
+            popen_kwargs = {
+                "stdin": subprocess.DEVNULL,
+                "stdout": subprocess.PIPE,
+                "stderr": subprocess.STDOUT,
+                "text": True,
+                "cwd": str(AUTOCODER_ROOT),  # Run from autocoder root for proper imports
+                "env": {**os.environ, "PYTHONUNBUFFERED": "1"},
+            }
+            if sys.platform == "win32":
+                popen_kwargs["creationflags"] = subprocess.CREATE_NO_WINDOW
+
+            proc = subprocess.Popen(cmd, **popen_kwargs)
         except Exception as e:
             # Reset in_progress on failure
             session = self.get_session()
@@ -626,6 +632,12 @@ def _read_output(
                         print(f"[Feature #{feature_id}] {line}", flush=True)
             proc.wait()
         finally:
+            # CRITICAL: Kill the process tree to clean up any child processes (e.g., Claude CLI)
+            # This prevents zombie processes from accumulating
+            try:
+                _kill_process_tree(proc, timeout=2.0)
+            except Exception as e:
+                debug_log.log("CLEANUP", f"Error killing process tree for {agent_type} agent", error=str(e))
             self._on_agent_complete(feature_id, proc.returncode, agent_type, proc)
 
     def _on_agent_complete(
diff --git a/server/services/process_manager.py b/server/services/process_manager.py
index 0c50fd3d..cd685ea1 100644
--- a/server/services/process_manager.py
+++ b/server/services/process_manager.py
@@ -354,14 +354,20 @@ async def start(
         try:
             # Start subprocess with piped stdout/stderr
             # Use project_dir as cwd so Claude SDK sandbox allows access to project files
-            # IMPORTANT: Set PYTHONUNBUFFERED to ensure output isn't delayed
-            self.process = subprocess.Popen(
-                cmd,
-                stdout=subprocess.PIPE,
-                stderr=subprocess.STDOUT,
-                cwd=str(self.project_dir),
-                env={**os.environ, "PYTHONUNBUFFERED": "1"},
-            )
+            # stdin=DEVNULL prevents blocking if Claude CLI or child process tries to read stdin
+            # CREATE_NO_WINDOW on Windows prevents console window pop-ups
+            # PYTHONUNBUFFERED ensures output isn't delayed
+            popen_kwargs = {
+                "stdin": subprocess.DEVNULL,
+                "stdout": subprocess.PIPE,
+                "stderr": subprocess.STDOUT,
+                "cwd": str(self.project_dir),
+                "env": {**os.environ, "PYTHONUNBUFFERED": "1"},
+            }
+            if sys.platform == "win32":
+                popen_kwargs["creationflags"] = subprocess.CREATE_NO_WINDOW
+
+            self.process = subprocess.Popen(cmd, **popen_kwargs)
 
             # Atomic lock creation - if it fails, another process beat us
             if not self._create_lock():
diff --git a/start_ui.bat b/start_ui.bat
index 2c597539..c8ad646a 100644
--- a/start_ui.bat
+++ b/start_ui.bat
@@ -39,5 +39,3 @@ pip install -r requirements.txt --quiet
 
 REM Run the Python launcher
 python "%~dp0start_ui.py" %*
-
-pause