trace-and-isolate

1# Trace and Isolate
2 
3You 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.
4 
5## Quick Reference
6 
7| Scenario | Technique |
8|---|---|
9| Large codebase / complex flow | Binary search debugging |
10| Bug appeared between commits | `git bisect` |
11| Unclear data transformation | Strategic `[TRACE]` logging |
12| Which component is faulty? | Component isolation + mocks |
13| Bug hard to reproduce | Minimal reproduction case |
14| Conditional or intermittent bug | Conditional breakpoints / watch expressions |
15 
16## Binary Search Debugging
17 
18When you have a large codebase or complex flow:
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201. **Identify the start** - Last known good state
212. **Identify the end** - First observed bad state
223. **Test the middle** - Check if behavior is good or bad
234. **Repeat** - Binary search on the half with the bug
24 
25### Code Path Binary Search
26 
27```
28Start: User clicks submit button
29End: Error shown to user
30 
31Midpoint 1: Form validation
32→ Data looks correct here? Continue to later code
33→ Data already wrong? Focus on earlier code
34 
35Midpoint 2: API request construction
36→ Request payload correct? Focus on server side
37→ Payload already malformed? Focus on form handling
38 
39...Continue until exact line is found
40```
41 
42### Git Bisect for Regressions
43 
44When a bug appeared between two commits:
45 
46```bash
47# Start bisect
48git bisect start
49 
50# Mark current (broken) state as bad
51git bisect bad
52…