debugging-with-undo

# Debugging with Undo time travel debugger

Undo provides time travel debugging for Linux programs. This Skill guides you to:
1. **Record** program execution to capture failures (especially intermittent ones)
2. **Debug** recordings by traveling backwards through execution history

## When to record (use `record` MCP tool)

Record program execution when the user:
- Has a **flaky test** or **intermittent failure** that doesn't reproduce reliably
- Mentions **race conditions**, **threading issues**, or **concurrency bugs**
- Wants to **capture a failure** for later analysis
- Needs **deterministic replay** of a bug

Undo captures the exact execution including thread interleavings, making even race conditions
reproducible.

## When to debug (use debugging MCP tools)

Debug a recording when the user:
- Has a **`.undo` recording file** to investigate
- Asks **"why did this happen"** or **"how did this value get set"**
- Wants **root cause analysis** on a captured failure
- Needs to understand execution **backwards** from a crash or assertion

## Workflow

1. **If no recording exists**: Use `record` MCP tool to capture the failure
2. **If recording exists**: Use debugging MCP tools to analyze it
3. **Work backwards**: Start at the end (where the bug manifested), trace backwards

## Important

- **Never access `.undo` files directly** - they are opaque binary recordings
- **Never invoke `udb`, `live-record`, or `undo` via Bash** - use the Undo MCP tools