Explanation

Background and rationale for UndoLog's design decisions.

Document	What it explains
Safety model	Why three tiers, how the approval gate works, crash guarantees
Exactly-once semantics	BLAKE3 call signatures, advisory locks, idempotency key design
Saga pattern	LIFO compensation ordering, state machine, crash recovery protocol
MCP-native design	Why Model Context Protocol instead of framework-specific hooks
Comparison with LangGraph	Factual comparison of safety, idempotency, rollback, and approval features