trace-and-isolate

# Trace and Isolate You are using systematic tracing and isolation techniques to narrow down where a bug originates. The goal is to find the exact location in code where behavior diverges from expectation. ## Quick Reference | Scenario | Technique | |---|---| | Large codebase / complex flow | Binary search debugging | | Bug appeared between commits | `git bisect` | | Unclear data transformation | Strategic `[TRACE]` logging | | Which component is faulty? | Component isolation + mocks | | Bug hard to reproduce | Minimal reproduction case | | Conditional or intermittent bug | Conditional breakpoints / watch expressions | ## Binary Search Debugging When you have a large codebase or complex flow: 1. **Identify the start** - Last known good state 2. **Identify the end** - First observed bad state 3. **Test the middle** - Check if behavior is good or bad 4. **Repeat** - Binary search on the half with the bug ### Code Path Binary Search ``` Start: User clicks submit button End: Error shown to user Midpoint 1: Form validation → Data looks correct here? Continue to later code → Data already wrong? Focus on earlier code Midpoint 2: API request construction → Request payload correct? Focus on server side → Payload already malformed? Focus on form handling ...Continue until exact line is found ``` ### Git Bisect for Regressions When a bug appeared between two commits: ```bash # Start bisect git bisect start # Mark current (broken) state as bad git bisect bad # Mark last k...