Before you edit

Before you edit

Check blast radius and test impact before changing unfamiliar code.

Know what depends on a file — and which tests cover it — before you touch it. For a whole task (pack, reuse, House Style), start with Prepare a change.

prism blast src/auth/session.ts
prism test-impact src/auth/session.ts
prism blast src/auth/session.ts --fail-on high

What you get back

Direct and transitive dependents — files that would notice a change.
Affected tests and features — what to run and what user-facing area moves.
Risk band — Low / Moderate / High from a 0–100 score. Higher means more risk. See risk bands.

Static analysis is a floor, not a complete call graph: dynamic imports and runtime DI are invisible.

When this is wrong

Path outside the workspace is refused (not clamped).
Underestimate when coupling is string-keyed or reflective — treat the band as a lower bound.
Blast radius does not know if your edit is breaking; identical radius for adding an optional param vs deleting an export.

Prepare a change · Guard a session · Delete safely · Review a PR

Prepare a change

One call before you edit: the files to open, helpers to reuse, House Style, notes, and a work order — never file bodies.

Guard a session

Rank the dirty files that can actually hurt, so you read the 3% first.