andreaswasita/copilot-agents-dojo/autonomous-bug-fix

Autonomous Bug Fix Skill

Walks the agent through the full reproduce → diagnose → fix → verify cycle on its own, without asking the user for navigation help, log-reading instructions, or test commands. Does NOT cover net-new feature work — for that use plan-before-code and executing-plans.

When to Use

• User reports a bug, regression, or unexpected behavior.
• CI is red on a branch you own.
• An error or warning appears in logs.
• A previously working feature stopped working.
• The user says "this is broken," "it doesn't work," or similar.

Prerequisites

• Read access to the failing component (use glob / grep to locate it).
• The powershell tool to run tests, git, and reproduction commands.
• A clean working tree on a feature branch (use using-git-worktrees if needed).
• verify-before-done skill loaded — you'll invoke it at the end.

How to Run

1. Reproduce  → locate the code, run the failing path, confirm with evidence.
2. Diagnose   → trace from symptom to root cause; check recent changes.
3. Fix        → minimal change at the root cause + a regression test.
4. Verify     → re-run reproduction + full suite via `verify-before-done`.

Quick Reference

Procedure

Step 1: Reproduce

Find the relevant code yourself — grep for the symbol, glob for the path. Do not ask the user "which file is this in?"

Run the failing path via the powershell tool. If no failing test exists, write a minimal one that captures the bug. Confirm reproduction with concrete evidence (stack trace, exit code, log line).

If you can't reproduce:

• Check for environment-specific behavior (OS, Node/Python version).
• Look for race conditions or state-dependent paths.
• Ask the user for clarification only as a last resort, and only with specific questions.

Step 2: Diagnose Root Cause

Read the error message and stack trace before doing anything else — they exist for a reason. Trace from the user-visible symptom back to the root cause:

# via the `powershell` tool
git log -20 --oneline
git blame path/to/suspect.ts
git diff HEAD~5 -- path/to/suspect.ts

Stop at the root cause, not the first thing that looks suspicious. "Why did this break?" — not "what broke?"

Step 3: Fix at the Root

Edit with precision via the edit tool:

• Change only what needs to change. Bigger diffs hide bigger bugs.
• Fix the root cause, never the symptom. Swallowing an exception is not a fix.
• Add a regression test that fails without the fix and passes with it.
• Check whether the same root cause exists elsewhere (grep for the pattern). If yes, fix those too or log them in tasks/lessons.md for follow-up.

Step 4: Verify

Hand off to the verify-before-done skill:

• Re-run the reproduction. The error must be gone.
• Run the full test suite. No regressions.
• Record evidence in tasks/todo.md under the task.

Step 5: Rollback If Verification Fails

If verification fails after your fix:

1. Reset the working tree (git checkout -- . or git stash via powershell).
2. Log the failed attempt in tasks/lessons.md with the root-cause analysis you had.
3. Re-plan with a different approach via plan-before-code.
4. Never push broken code hoping someone catches it later.

Pitfalls

• DO NOT ask the user "which file is it in?" or "how do I run the tests?" Use grep/glob/view/powershell to discover it.
• DO NOT apply a band-aid (catch-and-swallow, ignore the warning). Fix the root cause.
• DO NOT fix the symptom. A login button that fails because of a missing provider is a provider bug, not a button bug.
• DO NOT skip the regression test. Without one, the bug comes back in 3 months.
• DO NOT push without verification. An unverified fix is often worse than no fix.
• DO NOT abandon failed attempts silently. Log them in tasks/lessons.md.

Verification

• [ ] Reproduction was confirmed with concrete evidence before any fix.
• [ ] Root cause is identified in writing (in commit message or tasks/todo.md).
• [ ] Regression test added that fails on main and passes on the branch.
• [ ] verify-before-done checklist passed.
• [ ] If similar patterns exist elsewhere, they are fixed or logged.