xt-debugging

name: xt-debugging description: Complete debugging workflow — error analysis, log interpretation, performance profiling, and GitNexus call-chain tracing. Use when investigating bugs, errors, crashes, or performance issues.

xt-debugging

Systematic debugging using the GitNexus knowledge graph for call-chain tracing, combined with error analysis, log interpretation, and performance profiling.

When to Use

• "Why is this function failing?"
• "Trace where this error comes from"
• "This endpoint returns 500"
• Investigating crashes, unexpected behavior, or regressions
• Performance issues
• Reading logs or stack traces

Prerequisites

GitNexus must be indexed before starting. If you see "index is stale" or no results:

npx gitnexus analyze   # re-index the repo (run this, then retry)
npx gitnexus status    # verify freshness

Phase 1 — Triage

Understand the symptom before touching any code.

1. Read the full error message and stack trace
2. Identify the suspect symbol (function, class, endpoint)
3. Check for regressions — what changed recently?

   gitnexus_detect_changes({scope: "compare", base_ref: "main"})
   

Phase 2 — Knowledge Graph Investigation

1. gitnexus_query({query: "<error text or symptom>"})   → Related execution flows + symbols
2. gitnexus_context({name: "<suspect>"})                → Callers, callees, process participation
3. READ gitnexus://repo/{name}/process/{processName}    → Full step-by-step execution trace
4. gitnexus_cypher({...})                               → Custom call chain if needed

Patterns by Symptom

Example — "Payment endpoint returns 500 intermittently"

1. gitnexus_query({query: "payment error handling"})
   → Processes: CheckoutFlow, ErrorHandling
   → Symbols: validatePayment, handlePaymentError

2. gitnexus_context({name: "validatePayment"})
   → Outgoing calls: verifyCard, fetchRates (external API!)

3. READ gitnexus://repo/my-app/process/CheckoutFlow
   → Step 3: validatePayment → calls fetchRates (external, no timeout)

4. Root cause: fetchRates has no timeout → intermittent failures under load

Phase 3 — Root Cause Analysis

1. Reproduce — Identify minimal reproduction steps
2. Trace data flow — Follow the value/control flow from input to error
3. Isolate — Narrow to the smallest failing unit
4. Hypothesize — Form explicit hypothesis before reading more code
5. Confirm — Verify hypothesis against source, not just symptoms

Common root cause categories:

• Null/undefined — missing guard, wrong assumption about data shape
• Race condition — async ordering, missing await, shared mutable state
• External dependency — timeout, API contract change, env difference
• Type mismatch — serialization, casting, implicit coercion
• Configuration — env var missing, wrong default, deployment drift

Phase 4 — Log Analysis

1. Read the full log output (not just the last line)
2. Identify: timestamps, error levels, request IDs, correlation tokens
3. Correlate events across log lines to build timeline
4. Look for: first occurrence, frequency, affected subset, preceding events
5. Summarize: what happened, when, why, and what was affected

Phase 5 — Performance Profiling

1. Measure baseline — Never optimize blind

   time <command>
   

2. Profile — Language-appropriate tools:
   • Node.js: --prof, clinic.js, 0x
   • Python: cProfile, py-spy, line_profiler
   • Go: pprof
3. Identify hotspot — Usually 1–2 functions account for >80% of time; use gitnexus_context to confirm call frequency
4. Fix the bottleneck — Minimal targeted change
5. Verify — Measure again, compare against baseline

Phase 6 — Remediation

1. Fix — Minimal change that addresses the confirmed root cause
2. Verify — Run the failing case to confirm fix
3. Regression test — Add a test that would have caught this bug
4. Check blast radius — gitnexus_impact({target: "fixedSymbol", direction: "upstream"})
5. Pre-commit scope check — gitnexus_detect_changes({scope: "staged"})

Checklist

- [ ] Read full error / stack trace
- [ ] Identify suspect symbol
- [ ] gitnexus_detect_changes to check for regressions
- [ ] gitnexus_query for error text or symptom
- [ ] gitnexus_context on suspect (callers, callees, processes)
- [ ] Trace execution flow via process resource
- [ ] Read source files to confirm root cause
- [ ] Form explicit hypothesis before fixing
- [ ] Verify fix against failing reproduction
- [ ] Add regression test
- [ ] gitnexus_detect_changes() before committing