The Belief Ledger — the single source of truth for everything a startup believes. Sorts every claim into verifiable FACTS (with sources), ASSUMPTIONS (with validation plans and evidence grades E0–E4), and UNKNOWNS (with research steps), each with a stable ID that all other frameworks reference. Use FIRST before any other startup framework, when someone says "we know our customers want this", or whenever a plan is being built on unverified beliefs.
