Bug Analyzer

bug-analyzer

When to use

Reactive mode: User reports a bug, shares a Sentry issue, or asks to investigate an error. Proactive mode: User asks to audit code for hidden bugs, edge cases, or risky patterns.

Do NOT use when:

• Feature development — route to feature-planning
• Code style or refactoring — route to code-refactoring
• Performance issues — route to performance-analysis
• Security vulnerabilities — route to security-audit
• You need to trace how one data element flows through the code — route to data-flow-mapper
• You need to enumerate every call site / consumer affected by a planned fix — route to blast-radius-analyzer

Input sources

Bugs can come from multiple sources — gather as many as available:

Branch ticket detection

Always check the current branch for ticket IDs:

git branch --show-current

Pattern matching:

• fix/DEV-1234/description → extract DEV-1234
• fix/PROJ-567-some-bug → extract PROJ-567
• hotfix/DEV-999 → extract DEV-999
• Regex: [A-Z]+-[0-9]+

If found, auto-fetch the ticket and confirm with the user.

The Iron Law

NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST

If you haven't completed Phase 1, you cannot propose fixes. Random fixes waste time and create new bugs. Quick patches mask underlying issues.

Red flags — STOP immediately

• "Quick fix for now, investigate later"
• "Just try changing X and see if it works"
• "It's probably X, let me fix that"
• Proposing solutions before tracing data flow
• "One more fix attempt" (when already tried 2+)

Procedure: Analyze a bug

1. Inspect inputs and reproducers — Pull every source named in Input sources (branch, Jira, Sentry, error string, user description) before forming a hypothesis.
2. Investigate root cause — Run Phase 1 below; gather evidence, walk the stacktrace, consult engineering memory.
3. Find the pattern — Run Phase 2; check for similar bugs elsewhere in the codebase.
4. Form and test a hypothesis — Run Phase 3; write a failing test that reproduces the bug.
5. Fix and verify — Run Phase 4; apply the minimal change, re-run the failing test plus the wider suite.

Phase 1: Root Cause Investigation

Gather all available evidence before forming any hypothesis:

• Sentry URL → use get_issue_details to fetch stacktrace, tags, environments, frequency.
• Sentry issue → use get_issue_tag_values for browser, URL, environment distribution.
• Jira ticket → fetch via Jira API, read description, comments, linked issues.
• Error message → search the codebase for the message string.
• Branch name → auto-detect ticket ID, fetch if found.
• Stacktrace → start from top frame (crash site), trace down to entry point.
• Use codebase-retrieval to find the relevant code.
• Read each file in the call chain to understand the data flow.
• Check existing context docs (agents/settings/contexts/) for the affected area.
• Consult engineering memory. Via memory-access call retrieve(types=["historical-patterns", "incident-learnings"], keys=[<error class>, <affected file paths>], limit=3). A prior matching pattern or incident is the single most reliable accelerator for root-cause analysis. Cite id and path verbatim so the user can verify the precedent.

Multi-component diagnostics

When the system has multiple layers (Controller → Service → Repository → DB, or multi-tenant DB switching), add diagnostic instrumentation before proposing fixes:

For EACH component boundary:
  - Log what data enters the component
  - Log what data exits the component
  - Verify environment/config propagation (e.g. DB connection, tenant context)
  - Check state at each layer

Run once → gather evidence → identify WHICH layer breaks → investigate that layer.

This is especially important for:

• Multi-tenant database switching (wrong DB selected)
• Queue jobs that lose tenant context
• API → Service → Repository chains with data transformation
• External service integrations (ProBauS, GPS, etc.)

Phase 2: Pattern Analysis

• Find working examples of similar code paths in the codebase.
• Compare the broken path against the working reference.
• Identify the specific difference that causes the failure.
• Check if the issue is isolated or part of a broader pattern.

Phase 3: Hypothesis and Testing

• Form a single hypothesis based on evidence from Phase 1 and 2.
• Test the hypothesis minimally — don't change multiple things at once.
• If the hypothesis is wrong, go back to Phase 1 with new evidence.
• 3-Strikes Rule: If 3+ fix attempts fail, STOP. This signals an architectural problem, not a bug. Discuss with the user before attempting more fixes. Signs:
  • Each fix reveals new shared state or coupling in a different place.
  • Fixes require "massive refactoring" to implement.
  • Each fix creates new symptoms elsewhere.
• Common root causes in this project:
  • Missing validation on external sync data (CSV, XML, JSON imports).
  • Null values from optional DB columns not handled.
  • Type mismatches between legacy DB columns and PHP code.
  • Race conditions in multi-tenant database switching.
  • Missing fallbacks when external services are unavailable.

Phase 4: Implementation

• Present the root cause and proposed fix before implementing.
• Create a failing test that reproduces the bug.
• Implement a single, focused fix — not multiple changes.
• Consider side effects — does the fix affect other code paths?
• Check if similar patterns exist elsewhere that need the same fix — run the variant analysis below before closing the bug.

Variant analysis — one bug found, find its siblings

Once the root cause is confirmed, sweep for variants before closing:

1. Extract the signature — the minimal code shape that makes the bug (e.g. "optional relation accessed without null check after first()").
2. Sweep — grep/codebase-retrieval for the shape, not the symptom: the same API misuse, the same copy-pasted block, the same missing guard.
3. Verify each hit through the false-positive gate (§ 4 proactive mode) — a matching shape whose inputs cannot reach the bad state is a rejected candidate, not a variant.
4. Report — confirmed variants join the fix (same commit if within minimal-safe-diff's remediation carve-out) or land as a noted follow-up.

Worked example: root cause $order->customer->email crashes when the customer was soft-deleted. Signature: ->customer-> after an unguarded relation. Sweep finds 3 more sites; 2 are variants (same nullable relation), 1 is rejected (eager-loaded with whereHas, cannot be null there).

• Add validation/monitoring (e.g. MonitoringHelper::captureException()) for data quality issues.
• Verify the fix with the test from step 1.

Proactive mode (bug hunting)

When asked to audit code for hidden bugs, use this workflow instead of the 4 phases above:

1. Execution tracing

Trace the actual code path step by step:

• Follow data through each function call
• Track state mutations and side effects
• Note where exceptions are caught or swallowed
• Identify where assumptions are made but not validated

2. Edge case analysis

For each code path, test these scenarios mentally:

3. Known bug patterns

→ PHP/Laravel bug-pattern catalogue: see php-debugging.

4. False-positive gate (proactive mode)

Before a candidate enters the report, restate it as one falsifiable sentence: the concrete input or state that triggers it, and the observable wrong behavior that follows. A candidate whose trigger you cannot name is not a finding — trace further or drop it with a one-line reason.

Route verification by severity: a Low/Medium finding with a traced trigger reports normally (Standard); a High/Critical finding gets a devil's-advocate pass first (Deep) — actively try to refute it (guard clause upstream? framework default? unreachable input?) and report only what survives. List killed candidates one-line under Rejected candidates so the triage is auditable.

5. Output format (proactive mode)

For each bug found: Bug → Location → Severity → Root Cause → Trigger → Fix → Confidence

Close with Rejected candidates — one line per looks-broken-but-benign pattern the gate killed, with the traced reason.

Commands

Project awareness

Read AGENTS.md and ./agents/ for project-specific architecture, business rules, and domain docs. Detect the project from the repo name (see rules/architecture.md). Check for existing contexts in agents/settings/contexts/ or module agents/settings/contexts/.

Adversarial review

Before implementing a fix, run the adversarial-review skill. Focus on the "Bug fixes" attack questions: Is this the root cause or a symptom? Will the fix break something else?

Auto-trigger keywords

• bug investigation
• error analysis
• Sentry error
• stacktrace
• root cause

Rationalization prevention

Output format

1. Root cause analysis with evidence trail
2. Fix implementation or fix plan with specific files and changes
3. Regression test covering the failure scenario

Verification examples

• Backend bug: reproduce with curl against the failing route (or an actingAs() HTTP test) before and after the fix; assert the new response shape with assertJsonPath.
• Runtime bug: place a xdebug breakpoint at the suspect frame, step through, and inspect the stack trace; for log-only repros, dump the failing variable with dd( once, then remove.
• Regression test: add a test that reproduces the original failure first (red), then makes it green — never write the test post-fix from memory.

Gotcha

• Don't assume the stacktrace shows the root cause — it often shows the symptom. Trace backwards.
• Sentry groups similar errors — check if the "latest event" is actually representative of the issue.
• The model tends to suggest fixes without verifying the fix doesn't break other code paths.

Do NOT

• Do NOT start fixing before understanding the root cause.
• Do NOT commit or push without permission.
• Do NOT ignore Sentry data if available — it provides real-world context.
• Do NOT fix only the symptom — trace to the root cause.
• Do NOT attempt fix #4 without discussing the architecture with the user.

References

• Chain-of-Verification (CoVe) — arxiv.org/abs/2309.11495 Generate candidate answers, then verify each with follow-up questions. This skill adapts CoVe by verifying stacktrace-derived hypotheses against Sentry data and surrounding code before fixing.