Error handling audit: Document 10 critical error boundaries issues

[Copilot]

Audited AsyncMux for error handling gaps. Library silently swallows exceptions, lacks error propagation API, and has unbounded memory growth with slow consumers.

Issues Documented

High Priority (4)

• Input generator exceptions silently fail—no try-catch, no error callbacks, inputCount never decremented
• Output generator promise rejections unhandled—can crash Node.js process
• Memory leak: no backpressure mechanism, queues grow unbounded with slow/absent consumers
• Zero error propagation—no callbacks, no events, no error state inspection

Medium Priority (3)

• Race condition: multiple inputs calling stop() on inputCount==0 pushes duplicate StopSymbols
• stop() not idempotent—multiple calls push multiple StopSymbols to all queues
• No per-input cleanup—in() returns void, can't remove specific inputs

Low Priority (3)

• queue.shift() cast without undefined check
• No parameter validation, cryptic errors
• Queue cleanup only on normal completion, not on exception

Deliverables

Six markdown files (~49KB):

• DOCUMENTATION_INDEX.md - Navigation
• ERROR_HANDLING_ISSUES.md - Technical analysis with code examples
• ISSUES_TO_CREATE.md - Copy-paste GitHub issue templates
• AUDIT_SUMMARY.md - Executive summary
• QUICK_REFERENCE.md - Implementation guide, timeline (3-4 weeks)
• TASK_COMPLETE.md - Overview

Example Problem

async function* faultyGenerator() {
  yield 1;
  throw new Error('Database connection failed'); // Silent failure
  yield 2;
}

const mux = new AsyncMux<number>();
mux.in(faultyGenerator()); // Error completely invisible
// inputCount never decremented, stop() may never fire

No code changes made per issue requirements—documentation only.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Error / exception handling</issue_title>
<issue_description>This code needs to be audited significantly on its error boundaries and how to correctly ensure errors go where they should go.

I rapidly released this code to solve a problem in one of my other projects, and am starting a new job soon, so I don't have enough bandwidth triple check error handling and failure behavior.</issue_description>

<agent_instructions>Can you go through this code base and raise issues for poorly handled error boundaries?
This is a library to be used by other code. Assume the AsyncMux code is being driven externally and any inputs are possible. Exceptions could get thrown in weird places. To make this production-grade, those need to be eliminated OR made more obvious and easier to handle.

Don't do coding, just raise issues if you're capable of that.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Error / exception handling #2

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