compute-blast-radius

name	compute-blast-radius
description	Given a change surface (file list) and a dependency graph, compute directly and transitively impacted tests, identify coverage gaps in the change surface, and emit blast-radius.yaml. Used by test-engineer.
user-invocable	false
model	sonnet
allowed-tools	Read, Write, Grep, Glob
deprecated	true
deprecated_note	#434 ProductOS realignment — superseded by the command model; retained for Phase E reference, not installed

compute-blast-radius

Model-invocable skill for test blast-radius computation.

Purpose

Given (a) a list of files that will change, (b) the dependency graph produced by build-dependency-graph, and (c) the test surface produced by map-test-surface, compute which tests are directly or transitively affected, which tests are at risk of false pass, and where the change surface has no test coverage at all. Emit blast-radius.yaml.

Input

Field	Required	Description
change_surface	yes	List of files expected to change
dependency_graph_path	yes	Path to dependency-graph.yaml
test_surface_path	yes	Path to test-surface.yaml
transitive_depth	optional	Max depth for transitive closure (default 3)
output_base	yes	Directory to write blast-radius.yaml

Process

1. Read inputs. Deserialize both YAML inputs. Normalize path forms (absolute vs. relative) to match the change-surface list.

2. Direct impact. For each file in change_surface, find test files whose subjects include that file (via subjects_index in test-surface).

3. Transitive impact. Walk the dependency graph out to transitive_depth. For each reachable module, collect tests covering any file in that module.

4. Coverage gaps. Files in change_surface that have ZERO direct or transitive tests — these are the gaps where specify-baseline-tests must author new tests.

5. Risk tiers. Classify affected tests:

   • high — direct subjects match
   • medium — transitive within depth 2
   • low — transitive within depth 3

6. Emit blast-radius.yaml:

   change_surface: [ ... ]
   generated_at: "{ISO-8601}"
   directly_affected_tests: [ "{test file}" ]
   transitively_affected_tests:
     - test_file: "{path}"
       via_module: "{module}"
       depth: {n}
   risk_tiers:
     high: [ ... ]
     medium: [ ... ]
     low: [ ... ]
   coverage_gaps:
     - file: "{path}"
       reason: no_direct_or_transitive_tests
   summary:
     direct: {n}
      {}
      {}
   

Output

blast_radius_path: "{output_base}/blast-radius.yaml"
direct_count: {n}
transitive_count: {n}
gap_count: {n}
status: written

Boundaries

• Read-only against the codebase.
• Transitive traversal is bounded by transitive_depth — do not exceed it (cost explosion on large graphs).
• You do not specify baseline tests for gaps — that is specify-baseline-tests's job.