Deletion policy

• Prefer deletion over abstraction when:
• invariants can be enforced without an extra layer
• an extension seam is unused across releases
• a feature is undocumented or not backed by specs/tests
• Any new abstraction must list the invariant it enforces; otherwise delete or inline.
• Deprecations: mark in docs/spec/identity.md and remove in next minor unless ecosystem-bound.
• Freeze rule: dead code or unused flags are removed before tagging; no “maybe later” retention.