# Systematic Debugging

> Use when encountering any bug, test failure, or unexpected behavior, before proposing fixes

- **Type:** Skill
- **Install:** `agentstack add skill-flydev-fr-mormot2-superpowers-systematic-debugging`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [flydev-fr](https://agentstack.voostack.com/s/flydev-fr)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [flydev-fr](https://github.com/flydev-fr)
- **Source:** https://github.com/flydev-fr/mormot2-superpowers/tree/main/skills/systematic-debugging

## Install

```sh
agentstack add skill-flydev-fr-mormot2-superpowers-systematic-debugging
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Systematic Debugging

## Overview

Random fixes waste time and create new bugs. Quick patches mask underlying issues.

**Core principle:** ALWAYS find root cause before attempting fixes. Symptom fixes are failure.

**Violating the letter of this process is violating the spirit of debugging.**

## The Iron Law

```
NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST
```

If you haven't completed Phase 1, you cannot propose fixes.

## When to Use

Use for ANY technical issue:
- Test failures
- Bugs in production
- Unexpected behavior
- Performance problems
- Build failures
- Integration issues

**Use this ESPECIALLY when:**
- Under time pressure (emergencies make guessing tempting)
- "Just one quick fix" seems obvious
- You've already tried multiple fixes
- Previous fix didn't work
- You don't fully understand the issue

**Don't skip when:**
- Issue seems simple (simple bugs have root causes too)
- You're in a hurry (rushing guarantees rework)
- Manager wants it fixed NOW (systematic is faster than thrashing)

## The Four Phases

You MUST complete each phase before proceeding to the next.

### Phase 1: Root Cause Investigation

**BEFORE attempting ANY fix:**

1. **Read Error Messages Carefully**
   - Don't skip past errors or warnings
   - They often contain the exact solution
   - Read stack traces completely
   - Note line numbers, file paths, error codes

2. **Reproduce Consistently**
   - Can you trigger it reliably?
   - What are the exact steps?
   - Does it happen every time?
   - If not reproducible → gather more data, don't guess

3. **Check Recent Changes**
   - What changed that could cause this?
   - Git diff, recent commits
   - New dependencies, config changes
   - Environmental differences

4. **Gather Evidence in Multi-Component Systems**

   **WHEN system has multiple components (CI → build → signing, API → service → database):**

   **BEFORE proposing fixes, add diagnostic instrumentation:**
   ```
   For EACH component boundary:
     - Log what data enters component
     - Log what data exits component
     - Verify environment/config propagation
     - Check state at each layer

   Run once to gather evidence showing WHERE it breaks
   THEN analyze evidence to identify failing component
   THEN investigate that specific component
   ```

   **Example (multi-layer system):**
   ```bash
   # Layer 1: Workflow
   echo "=== Secrets available in workflow: ==="
   echo "IDENTITY: ${IDENTITY:+SET}${IDENTITY:-UNSET}"

   # Layer 2: Build script
   echo "=== Env vars in build script: ==="
   env | grep IDENTITY || echo "IDENTITY not in environment"

   # Layer 3: Signing script
   echo "=== Keychain state: ==="
   security list-keychains
   security find-identity -v

   # Layer 4: Actual signing
   codesign --sign "$IDENTITY" --verbose=4 "$APP"
   ```

   **This reveals:** Which layer fails (secrets → workflow ✓, workflow → build ✗)

5. **Trace Data Flow**

   **WHEN error is deep in call stack:**

   See `root-cause-tracing.md` in this directory for the complete backward tracing technique.

   **Quick version:**
   - Where does bad value originate?
   - What called this with bad value?
   - Keep tracing up until you find the source
   - Fix at source, not at symptom

### Phase 2: Pattern Analysis

**Find the pattern before fixing:**

1. **Find Working Examples**
   - Locate similar working code in same codebase
   - What works that's similar to what's broken?

2. **Compare Against References**
   - If implementing pattern, read reference implementation COMPLETELY
   - Don't skim - read every line
   - Understand the pattern fully before applying

3. **Identify Differences**
   - What's different between working and broken?
   - List every difference, however small
   - Don't assume "that can't matter"

4. **Understand Dependencies**
   - What other components does this need?
   - What settings, config, environment?
   - What assumptions does it make?

### Phase 3: Hypothesis and Testing

**Scientific method:**

1. **Form Single Hypothesis**
   - State clearly: "I think X is the root cause because Y"
   - Write it down
   - Be specific, not vague

2. **Test Minimally**
   - Make the SMALLEST possible change to test hypothesis
   - One variable at a time
   - Don't fix multiple things at once

3. **Verify Before Continuing**
   - Did it work? Yes → Phase 4
   - Didn't work? Form NEW hypothesis
   - DON'T add more fixes on top

4. **When You Don't Know**
   - Say "I don't understand X"
   - Don't pretend to know
   - Ask for help
   - Research more

### Phase 4: Implementation

**Fix the root cause, not the symptom:**

1. **Create Failing Test Case**
   - Simplest possible reproduction
   - Automated test if possible
   - One-off test script if no framework
   - MUST have before fixing
   - Use the `superpowers:test-driven-development` skill for writing proper failing tests

2. **Implement Single Fix**
   - Address the root cause identified
   - ONE change at a time
   - No "while I'm here" improvements
   - No bundled refactoring

3. **Verify Fix**
   - Test passes now?
   - No other tests broken?
   - Issue actually resolved?

4. **If Fix Doesn't Work**
   - STOP
   - Count: How many fixes have you tried?
   - If  **When this section applies:** the session is operating on a Pascal project (the
> `PASCAL_PROJECT=1` env was exported by the mormot2-superpowers session-start hook).
> If `PASCAL_PROJECT` is unset, ignore this section.

The 4-phase root-cause method applies as-is. Pascal-specific signals to use during Phase 1 (reproduce + observe):

### TSynLog as a structured observation log

`TSynLog` writes one entry per significant event with millisecond timestamps and (when configured) a stack trace per error. To enable on a target session, before reproducing the bug:

```pascal
with TSynLog.Family do begin
  Level := LOG_VERBOSE;        // sllInfo + sllDebug + sllTrace + sllError + ...
  PerThreadLog := ptIdentifiedInOneFile;
  HighResolutionTimestamp := true;
  AutoFlushTimeOut := 5;
end;
```

Logs land under the project's working directory, named after the executable. Read them before forming a hypothesis. Don't speculate without the log line that triggered the bug.

### FastMM4 leak reports (Delphi)

When a unit-test or shutdown reports a leak, the FastMM4 report identifies the allocation site by call stack. Match the stack against `.map`/DWARF (cross-link `pascal-debugging-logging`) to land on the source line. Common false positives: dynamic packages, RTL caches kept across processes.

### EAccessViolation, EAssertionFailed

Always read the address. If the project ships with `.map` (Delphi `-GD`) or DWARF symbols (FPC `-gw3 -gl`), `TSynLog` resolves the address to a source line in the log. Without symbols, use `addr2line` (FPC) or the `.map`+`mORMot2-MapDownload` flow (Delphi) before guessing.

### Pitfalls

- "It only happens in Release builds" usually means uninitialized stack (build with `-Or` on FPC to catch it) or RTL patches disabled (`NOPATCHRTL` set unintentionally).
- "It only happens with the SQLite static lib" - see `mormot2-deploy` for static-lib link flags.
- Never debug threading bugs without `PerThreadLog := ptIdentifiedInOneFile`.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [flydev-fr](https://github.com/flydev-fr)
- **Source:** [flydev-fr/mormot2-superpowers](https://github.com/flydev-fr/mormot2-superpowers)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-flydev-fr-mormot2-superpowers-systematic-debugging
- Seller: https://agentstack.voostack.com/s/flydev-fr
- Browse the marketplace: https://agentstack.voostack.com/browse

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