fix: prevent agent subprocess blocking on Windows

[mmereu]

Summary

• Add stdin=subprocess.DEVNULL to prevent blocking on stdin reads
• Add CREATE_NO_WINDOW flag on Windows to prevent console pop-ups
• Remove trailing pause from start_ui.bat
• Add PYTHONUNBUFFERED env var for immediate output

Problem

On Windows, the agent subprocess would block with "Press any key to continue" message, requiring manual restart.

Test plan

• Tested on Windows - agent runs without blocking
• Server continues responding while agent is running

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Suppressed unexpected console windows on Windows and added stronger cleanup of background processes to avoid lingering/zombie processes.
  • Ensured feature state is reset when a background agent fails to start so it can be retried.

• Improvements

  • Improved background process I/O for real‑time, unbuffered output and more robust input handling.
  • Streamlined UI startup by removing an unnecessary pause after launch.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

Replaces direct subprocess Popen calls with explicit popen_kwargs, adds stdin=DEVNULL and Windows CREATE_NO_WINDOW handling, ensures unbuffered Python output, introduces child-process-tree cleanup and feature in_progress reset on spawn failure, and removes a final pause from the UI batch script. (50 words)

Changes

Cohort / File(s)	Summary
Parallel orchestrator changes parallel_orchestrator.py	Use popen_kwargs for Popen (stdin=DEVNULL, stdout/stderr preserved, text, cwd, env); on win32 include creationflags=CREATE_NO_WINDOW; add child-process cleanup (_kill_process_tree(proc, timeout=2.0)) in _read_output finally block; reset feature in_progress flag on spawn failure and commit.
Process manager updates server/services/process_manager.py	Replace direct Popen with subprocess.Popen(cmd, **popen_kwargs) using stdin=DEVNULL, stdout=PIPE, stderr=STDOUT, cwd, and set PYTHONUNBUFFERED=1 in env; add win32 creationflags=CREATE_NO_WINDOW.
Batch script start_ui.bat	Removed final pause so the script exits immediately after launching the Python process.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 I nudged spawns to sleep, then swept the mess away,
No windows popping up to shout throughout the day.
Outputs flow unbuffered, children gently end,
The batch script hops off—no pause to apprehend. 🥕

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main objective of the PR: preventing Windows subprocess blocking through stdin and console window handling.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

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[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (2)

parallel_orchestrator.py (2)

519-527: Inconsistent: Missing Windows subprocess handling in testing agent spawner.

This Popen call lacks stdin=subprocess.DEVNULL and the Windows CREATE_NO_WINDOW flag that were added to _spawn_coding_agent. Testing agents could still block on stdin or show console pop-ups on Windows.

🔧 Proposed fix to align with _spawn_coding_agent

         try:
-            proc = subprocess.Popen(
-                cmd,
-                stdout=subprocess.PIPE,
-                stderr=subprocess.STDOUT,
-                text=True,
-                cwd=str(AUTOCODER_ROOT),
-                env={**os.environ, "PYTHONUNBUFFERED": "1"},
-            )
+            popen_kwargs = {
+                "stdin": subprocess.DEVNULL,
+                "stdout": subprocess.PIPE,
+                "stderr": subprocess.STDOUT,
+                "text": True,
+                "cwd": str(AUTOCODER_ROOT),
+                "env": {**os.environ, "PYTHONUNBUFFERED": "1"},
+            }
+            if sys.platform == "win32":
+                popen_kwargs["creationflags"] = subprocess.CREATE_NO_WINDOW
+
+            proc = subprocess.Popen(cmd, **popen_kwargs)

---

570-577: Inconsistent: Missing Windows subprocess handling in initializer.

Same issue as _spawn_testing_agent — this Popen call is missing stdin=subprocess.DEVNULL and the Windows CREATE_NO_WINDOW flag.

🔧 Proposed fix to align with _spawn_coding_agent

-        proc = subprocess.Popen(
-            cmd,
-            stdout=subprocess.PIPE,
-            stderr=subprocess.STDOUT,
-            text=True,
-            cwd=str(AUTOCODER_ROOT),
-            env={**os.environ, "PYTHONUNBUFFERED": "1"},
-        )
+        popen_kwargs = {
+            "stdin": subprocess.DEVNULL,
+            "stdout": subprocess.PIPE,
+            "stderr": subprocess.STDOUT,
+            "text": True,
+            "cwd": str(AUTOCODER_ROOT),
+            "env": {**os.environ, "PYTHONUNBUFFERED": "1"},
+        }
+        if sys.platform == "win32":
+            popen_kwargs["creationflags"] = subprocess.CREATE_NO_WINDOW
+
+        proc = subprocess.Popen(cmd, **popen_kwargs)