code-blast-radius

Load mahou:basics first. Then read `.mahou/code-blast-radius.md` if present. # Code blast radius Answers one question about a change that already exists: what else does it touch, and does any of it break. This is not a review. It says nothing about whether the change is good and does not hunt for bugs inside the diff. ## Step 0: Load what the tracing needs Load mahou:changeset for the repositories, the base, and the diff. Read the project's `CLAUDE.md` and the layout it describes, so you know which layers a change can travel through and which other repositories it can reach. ## Step 1: Inventory the changed elements List every element the change alters that something else can depend on: - function and method signatures, including defaults and the types behind them - return types, raised exceptions, and error codes - endpoint paths, request payloads, response shapes, status codes - exported types and shared components - database models and columns - test factories and fixtures, which reach every test in the suite Skip anything nothing can depend on. A renamed local has no users. ## Step 2: Trace each element Dispatch one `mahou:usage-tracer` per element, all in a single message so they run together. Give each one the element, the absolute path of the repository it lives in, the base, and the absolute paths of the other repositories in scope. Spawn them as plain subagents. Do not name them. A named agent becomes a teammate, its report arrives through the message channel, and long reports get truncated there. ## Step 3: Merge what comes back Tracer findings arrive unverified. Drop any that fails to name a user and what that user does differently. Check the rest against the code yourself before they reach the report. Collapse findings that different tracers raised about the same user, and keep the attribution each tracer gave: introduced by this change, pre-existing, or pre-existing and made reachable more often by this change. A pre-existing problem goes in the report only in the third case. ## Step 4: Report State the base and the diff composition in one line. Then the findings, ordered by reach, with the ones outside the change's own feature first. Give each one its file and line, what changes for whom, and its attribution. Do not list everything the change touched, and do not pad the report with the users you cleared. When nothing changes for anyone, say so in one line.