newspaper_wedding/.aidlc/knowledge/aidlc-shared/brownfield.md

Brownfield Safeguards

For any stage that modifies existing code or infrastructure, these safeguards apply.

Safeguard Matrix

Safeguard	What It Does	When Applied
Blast Radius Analysis	Identifies affected files/components and their downstream dependents	Before code generation (stage code-generation, 3.5)
Diff Preview	Shows exact proposed changes before applying	Before any file modification
Test Baseline	Runs existing tests BEFORE changes to establish baseline	Before code generation (stage code-generation, 3.5)
Test Validation	Runs existing tests AFTER changes to confirm nothing broke	After code generation (stage build-and-test, 3.6)
Impact Analysis	Documents affected APIs, components, and dependencies	During reverse engineering (stage reverse-engineering, 2.1) and code generation (3.5)
Rollback Plan	Documents how to undo changes if needed	Before deployment (stage deployment-execution, 4.3)

Blast Radius Analysis Template

Before modifying existing code:

1. List all files that will be changed
2. For each file, identify: imports/consumers, test files, configuration references
3. Classify impact: low (isolated change), medium (affects 2-3 dependents), high (cross-cutting)
4. Present impact summary to user before proceeding

Test Baseline Protocol

1. Run full test suite before ANY code changes
2. Record: total tests, passing, failing, skipped, coverage %
3. After code generation, re-run full test suite
4. Compare: new failures = regressions introduced by changes
5. If regressions found, fix before proceeding