blast-radius-check

Blast Radius Check

A strict pre-flight check mandated by the Karpathy Guidelines ("Surgical Changes"). Before you change the behavior or signature of an existing symbol, you must know exactly what else will explode if you get it wrong.

When to use this skill

• Before changing the arguments or return type of a function/method.
• Before refactoring a shared utility.
• Before modifying a database model or schema.
• When deleting seemingly "dead" code.

The Protocol

1. Locate the Target

Identify the exact symbol you are about to change. Use find_symbol if needed to get its exact name_path.

2. Map the Radius

Run a comprehensive search for all code that depends on this symbol.

• Use the mcp__serena__find_referencing_symbols tool to get all structural references.
• If it's an API route, string constant, or dynamic event, use mcp__serena__search_for_pattern to catch loose text references.

3. Document the Impact

Before writing any code, list the affected files. If you are delegating to a subagent via session-distiller, this list MUST be included in the ⚠️ Assumptions, Risks & Blockers section of the Context Checkpoint.

Example Checkpoint Addition:

### ⚠️ Assumptions, Risks & Blockers
- **Blast Radius**: Modifying `verifyToken()` will impact:
  - `src/middleware/auth.ts`
  - `src/routes/userProfile.ts`
  - `src/services/paymentService.ts`
- **Constraint**: You MUST update all 3 files in the same commit to prevent build failures.

Anti-Patterns (What NOT to do)

• ❌ Guessing: "I think this is only used in this one file."
• ❌ Blindly trusting the IDE: Forgetting to check if a frontend component depends on the backend payload structure.
• ❌ Changing the core function and leaving the downstream updates "for later."