Cross-repo blast radius

Blast radius answers a single question: if I change this service, what downstream services and repos break? It walks the system graph against its edge direction (a consumer → provider edge means changing the provider impacts the consumer) and returns every reachable service ranked by an impact score.

Structural vs behavioral impact

Two edge classes are weighted and labelled distinctly:

• Structural edges (http, grpc, event, package) assert a real dependency, a contract or an import. They propagate impact at full weight and surface as will break.
• Behavioral co-change edges only assert that two files historically changed together. That is correlation, not a call, so they propagate at half weight and surface as may drift.

Each impacted service carries its distance (hops from the change) and score (0-1, with distance decay and the behavioral weighting baked in). Nearer, structural impact ranks highest.

Three ways to use it

REST

GET /api/workspace/blast-radius?target=<node-id-or-repo>&max_depth=3&include_behavioral=true

target is a node id (repo or repo::service/path) or a repo alias (which expands to all of its services).

MCP

The get_blast_radius tool (workspace mode) gives an agent the impacted set before it touches a high-fan-out provider. The get_risk PR-mode directive also gains will_break_consumers and missing_cross_repo_cochanges, so a diff in one repo flags its cross-repo fallout.

System Map

Pick a service in the Blast radius control above the Live System Map. The reachable set ripples (highlighted, the rest dimmed, with badges grading intensity), and a side panel lists the impacted services. Click any impacted service to walk the impact outward from there.