Write API surface change guardrail

[jdelfino]

Write the API surface change detection guardrail check.

File

.github/workflows/guardrail-api-surface.yml

What

• Trigger: PR opened or synchronized
• Detect changes to exported functions, public interfaces, API endpoints
• Language-aware heuristics (export keyword changes, route definitions)
• If API surface changes: action_required with annotations
• Check for non-stale PR approval override

Note

Most complex guardrail — start with simple heuristics and iterate.

Reference

• docs/design.md: API Surface Change Detection (Layer 4)