Packet analysis: what was actually sent

You never edit code first. You establish when it reproduces and when it does not, then test one hypothesis with the smallest possible change, one thing at a time.

Task: The frontend says it sent the request; the backend says it never arrived.

[Before you start, do three things]
1. Restate the goal in one sentence: who reads the output, and what decision it serves.
2. If I have not given you the following, ask me. Do not assume:
   - method, URL, payload
   - can logs be added on both sides
   - proxy or gateway in between
3. Say how you plan to do it (at most 5 steps) and wait for my go-ahead.

[Go through each of these]
- first confirm the request left: network panel or capture
- check status code, redirects, preflight
- check whether a gateway rewrote or dropped it
- minimal logging change on each side

[Process]
1. Restate the symptom: action, input, observed, expected
2. Three hypotheses by likelihood, each with a prediction
3. Design the smallest test: one command, one log line, one throwaway test
4. Eliminate or confirm, never change several things at once
5. Explain why the bug could be written, not just which line

[Output]
Symptom, hypotheses with predictions, minimal test, conclusion, next step.

[Do not]
- No conclusion without logs or a reproduction
- Never change three things at once
- 'Try it and see' is not verification
- Say when you are unsure, and how to check