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Deep Debugging & Root-Cause1 / 3

1 min lesson

Minimal repro is the deliverable

Describe what "Strip the scenario to the smallest steps that still trigger the bug" changes in practice.

Step 1 of 3

Minimal repro is the deliverablethe step everyone wants to skip

Strip the scenario to the smallest steps that still trigger the bug. A solid minimal repro converts a vague "agent keeps breaking my file" into "on this 3-file repo, with this prompt and Auto model, the agent overwrites unrelated functions 4 runs out of 5." That sentence is most of the diagnosis and it's the artifact an engineer can act on without re-deriving your work.

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Advanced table

One variable at a time

One variable at a timebisect, don't shotgun

Shotgun debugging - changing five things and seeing if the bug goes away - hides which factor mattered even when it "works." Cut the space in half along whatever axis is cheapest to flip and change only that.

Axis to bisect
Version
How to flip it
Roll back to a prior Cursor build, rerun
What it rules in or out
A regression an update introduced
Axis to bisect
Model
How to flip it
Swap the selected model, same prompt
What it rules in or out
Model-specific quality or a backend regression
Axis to bisect
Extensions
How to flip it
Disable all, re-enable in halves
What it rules in or out
Third-party extension conflict
Axis to bisect
Workspace
How to flip it
Reproduce in a fresh minimal repo
What it rules in or out
Project size, .cursor rules or local config
Axis to bisect
Network
How to flip it
Try a different network or disable a proxy
What it rules in or out
Corporate proxy, firewall or transit issue

Flip exactly one row per test or the result tells you nothing.

Interview move

Announce your loop in the first 30 seconds: "I'll reproduce first, then isolate one variable at a time, then form a hypothesis I can test." It signals method before you've found anything and buys you patience while you dig. Narrate the dead ends too - a discarded hypothesis is evidence of reasoning, not failure.

Watch out

Timebox the investigation out loud. Senior quality work isn't infinite digging - it's saying "I've spent 20 minutes, here's what I know, here's what I'd try next and here's the point where I'd escalate." Bottomless rabbit-holing reads as poor judgment, not thoroughness.