Rotator base exposes the four lifecycle methods as abstract; subclasses
register at compile time via 'register_as :kind' macro. REGISTRY is
populated as soon as the rotator file is required - drop a new file in
src/cre/rotators/ and the orchestrator can dispatch to it.
EnvFileRotator implements the simplest rotation:
- generate: 32 random bytes -> base64-urlsafe (no padding)
- apply: write to PATH.pending atomically (in-place line replace, 0600)
- verify: parse pending file, confirm key=value present and non-empty
- commit: rename PATH.pending -> PATH (atomic on POSIX)
- rollback_apply: unlink PATH.pending
RotationOrchestrator runs the 4-step contract with full event publishing,
state machine transitions in DB (generating -> applying -> verifying ->
committing -> completed | failed), and rollback_apply on apply/verify
failure. 8 specs cover happy path + raised-during-apply + rollback verification.