/brownfield-blast

/brownfield-blast — Blast Radius Report

Purpose

Generate a detailed blast radius report showing all files affected if you change a given file.

Trigger

• "Show me the blast radius of this file"
• "What happens if I change X?"
• "Who depends on this module?"

Type: `/brownfield-blast <file-path>`

---

Steps

1. Resolve the target file

If `$ARGUMENTS` is empty, use the currently open file. Resolve relative paths to project root. Verify the file exists in the graph.

2. Load blast radius from DB

const queries = require('./.claude/query-helpers.js');
const blastData = queries.getBlastRadius(targetFilePath);

Returns:

• count (total transitive dependents)
• direct (files that directly import this)
• transitive (all affected files at all depths)
• files (array with distances/hops)
• crossLang (cross-language dependencies)

3. Load file summary for context

const summary = queries.getFileSummary(targetFilePath);

Provides:

• summary (1-line module purpose)
• primaryRole (Util, Logic, Infra, etc.)
• importedByCount (fan-in)
• riskScore, band
• dangerReason

4. Build the report

**Format:**

# Blast Radius — <file-path>

## File Summary
[Summary from dep-graph]

**Role:** <role>  
**Risk Score:** <score>/100  
**Bug Fixes:** <count>  

---

## Direct Dependents
<N> files directly import this:
- <file 1>
- <file 2>
- ...

---

## Transitive Dependents
<N> files would be affected if this changes:
- <file 1> (distance: 1 hop)
- <file 2> (distance: 1 hop)
- <file 3> (distance: 2 hops)
- ...
[Show up to 20; note if more exist]

---

## Cross-Language Hits
[If any]
- <swift file> imports this JS file (iOS build may break)
- <go file> depends on exported JSON schema

---

## Recommended Action

[If transitive dependents < 5]
✓ Safe to change. Low blast radius. Run tests in dependent files.

[If transitive dependents 5-20]
⚠ Moderate impact. Affects <N> files. Ensure tests pass for:
  • <top 3 dependent files>

[If transitive dependents > 20]
🛑 CRITICAL impact. <N> files depend on this.
Before changing:
  1. Ensure changes are backwards compatible
  2. Update all dependent imports
  3. Run full test suite
  4. Notify team (@owner)

5. If cross-language hits exist

Flag them prominently — changing a JS file that's imported by Swift code can break the iOS build.

6. Note if any dependents are in danger zone

If any transitive dependent has risk score > 60, flag it: > "⚠ Dependent `auth.js` is high-risk (score: 78). Changes here cascade through auth, which is already fragile."

---

Fallback (if DB query fails)

If the graph.db query fails, the codebase must be mapped first:

wednesday-skills map --full

Once mapped, the DB will be populated and queries will work. If DB is locked, kill any running processes:

pkill -f 'wednesday-skills'

---

Error Handling

| Situation | Action | |-----------|--------| | File not in graph | "File not yet mapped. Run `wednesday-skills map --full`." | | File exists but has 0 dependents | "✓ This file is not imported by anything. Safe to delete or change freely." | | Blast radius > 50% of codebase | "⚠ This is a core infrastructure file. Changes affect the entire system." | | Cross-language hits detected | "⚠ WARNING: This file is imported by non-JS code (Swift/Go). Mobile build may break." |

---

Success Criteria

• [ ] Report shows all dependents, not capped at a threshold
• [ ] Cross-language dependencies are flagged
• [ ] Recommended action matches impact level
• [ ] Works without blast-radius.json (fallback compute)
• [ ] Execution time < 2 seconds
• [ ] Developer can see the full picture in under 30 seconds