fix: Add SIGHUP handler and stdin close detection to prevent orphaned processes

[shahabzohaib]

Summary

• Add SIGHUP signal handler for terminal hangup (closing terminal window)
• Add stdin end event listener to detect parent process death

Problem

MCP server processes become orphaned when Claude sessions end through:

• Closing terminal window (sends SIGHUP, not SIGTERM)
• Claude crashes (no signal sent)
• kill -9 on Claude process (no signal sent)

Over time, users accumulate dozens of orphaned mcp-server.js processes consuming memory.

Root Cause

The wrapper only handled SIGTERM and SIGINT:

process.on('SIGTERM', () => child.kill('SIGTERM'));
process.on('SIGINT', () => child.kill('SIGINT'));

Solution

Add two additional cleanup mechanisms:

// Handle terminal hangup
process.on('SIGHUP', () => child.kill('SIGHUP'));

// Detect parent death via stdin close
process.stdin.on('end', () => {
  child.kill();
  process.exit(0);
});

The stdin detection is particularly important because it catches all abnormal parent exits, including crashes and SIGKILL.

Test Plan

• Verify normal /exit still works (SIGTERM path)
• Verify closing terminal tab kills child process (SIGHUP path)
• Verify kill -9 on Claude kills child process (stdin close path)
• Verify no orphaned processes after multiple session starts/stops

Fixes #53

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved application stability through enhanced process management and parent process death detection
  • Better signal handling to ensure reliable cleanup of child processes during shutdown

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

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR adds signal forwarding and parent process death detection to the MCP server wrapper to prevent child processes from becoming orphaned when Claude sessions terminate unexpectedly or abnormally.

Changes

Cohort / File(s)	Summary
MCP Wrapper Signal Handling cli/mcp-server-wrapper.js	Added SIGHUP handler to forward terminal hangup signals to child process. Added stdin close detection to identify parent process death and trigger child termination and wrapper exit.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A wrapper's embrace, now complete and true,
SIGHUP forwarded, stdin watched through,
No more orphans wandering the process tree—
When Claude departs, the child goes free! 🎉

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately summarizes the main changes: adding SIGHUP handler and stdin close detection to prevent orphaned processes, which matches the code changes.
Linked Issues check	✅ Passed	The code changes fully address the primary requirements from issue #53: SIGHUP handler [#53], stdin close detection [#53], and child process termination [#53].
Out of Scope Changes check	✅ Passed	All changes in cli/mcp-server-wrapper.js are directly within scope—adding SIGHUP and stdin handlers as required by issue #53 with no extraneous modifications.

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

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@cli/mcp-server-wrapper.js`:
- Around line 89-94: The 'end' listener on process.stdin won't fire because
stdin is paused by default; call process.stdin.resume() before attaching the
'end' handler so the stream enters flowing mode and the parent-death detection
works. Update the block that sets process.stdin.on('end', ...) (where
child.kill() and process.exit(0) are invoked) to call process.stdin.resume()
first; ensure this doesn't conflict with other code reading stdin (or gate it
behind a flag) and optionally add an 'error' listener to handle stream errors
gracefully.

[coderabbitai]

⚠️ Potential issue | 🔴 Critical

🧩 Analysis chain

🌐 Web query:

Node.js process.stdin 'end' event listener paused mode resume

💡 Result:

In Node.js, a Readable stream’s 'end' event won’t fire unless the stream is fully consumed. If process.stdin stays in paused mode (no consumption), Node won’t read to EOF, so 'end' may never emit. [2]

To make 'end' fire, you must consume or explicitly drain stdin by doing one of the following:

Option A: Switch to flowing mode (common)

Add a 'data' handler (consumes data) or call .resume() (drains data even if you ignore it):

process.stdin.resume();          // start flowing/draining
process.stdin.on('end', () => {
  console.log('stdin ended');
});

All Readable streams start in paused mode; calling resume() switches them to flowing mode. [1][4]

Option B: Use 'readable' + read() until EOF

process.stdin.on('readable', () => {
  while (process.stdin.read() !== null) {}
});
process.stdin.on('end', () => console.log('stdin ended'));

Reading until read() returns null ensures the stream is consumed so 'end' can emit. [2]

Note about process.stdin and “old mode”

Node docs note that process.stdin.resume() can switch stdin into the legacy (“old streams”) mode; in that mode stdin is paused by default unless resumed. [3]

Sources:
[1] Node.js Stream docs (paused vs flowing; resume()) (r2.nodejs.org)
[2] Node.js Stream docs ('end' requires complete consumption) (r2.nodejs.org)
[3] Node.js Process docs (process.stdin, old mode note) (nodejs.org)
[4] Readable.resume() behavior/example (bun.com)

Citations:

• 1: https://r2.nodejs.org/docs/v24.0.1/api/stream.html?utm_source=openai
• 2: https://r2.nodejs.org/docs/v0.12.3/api/stream.html?utm_source=openai
• 3: https://nodejs.org/api/process.html?utm_source=openai
• 4: https://bun.com/reference/node/stream/default/Readable/resume?utm_source=openai

---

process.stdin.resume() is required for the 'end' event to fire.

In Node.js, process.stdin (like all Readable streams) starts in paused mode. The 'end' event only fires when the stream is fully consumed. Simply attaching an 'end' listener does not enable flowing mode, so this handler will never trigger. Without calling process.stdin.resume(), the parent process death detection won't work.

🐛 Proposed fix

   // Detect parent process death via stdin close
   // When Claude exits (normally or abnormally), stdin will close
+  process.stdin.resume();
   process.stdin.on('end', () => {
     child.kill();
     process.exit(0);
   });

📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change

	// Detect parent process death via stdin close
	// When Claude exits (normally or abnormally), stdin will close
	process.stdin.on('end', () => {
	child.kill();
	process.exit(0);
	});
	// Detect parent process death via stdin close
	// When Claude exits (normally or abnormally), stdin will close
	process.stdin.resume();
	process.stdin.on('end', () => {
	child.kill();
	process.exit(0);
	});

🤖 Prompt for AI Agents

In `@cli/mcp-server-wrapper.js` around lines 89 - 94, The 'end' listener on
process.stdin won't fire because stdin is paused by default; call
process.stdin.resume() before attaching the 'end' handler so the stream enters
flowing mode and the parent-death detection works. Update the block that sets
process.stdin.on('end', ...) (where child.kill() and process.exit(0) are
invoked) to call process.stdin.resume() first; ensure this doesn't conflict with
other code reading stdin (or gate it behind a flag) and optionally add an
'error' listener to handle stream errors gracefully.