Trait MigrationSection 

pub trait MigrationSection {
    // Required methods
    fn record(
        &mut self,
        id: &str,
    ) -> Result<Option<MigrationRecord>, WritePlaneError>;
    fn data_checksum(
        &mut self,
        id: &str,
    ) -> Result<Option<String>, WritePlaneError>;
    fn adopt_checksums(
        &mut self,
        id: &str,
        opaque: Option<&str>,
        content: &str,
    ) -> Result<(), WritePlaneError>;
    fn resolve_run_id_cursor(
        &mut self,
        run_id: &str,
    ) -> Result<Option<String>, WritePlaneError>;
    fn apply(
        &mut self,
        id: &str,
        supplied_checksum: &str,
        content_checksum: &str,
        normalized: &[String],
        identity_json: &str,
    ) -> Result<String, WritePlaneError>;
}

The migration-store view OneShotBackend::with_migration_barrier passes to its closure. Reads carry NO decisions — the replay/adopt matrix over them is execute_public_migration’s, the same compiled code on every host; every op executes under the barrier’s exclusion span.

Required Methods

fn record( &mut self, id: &str, ) -> Result<Option<MigrationRecord>, WritePlaneError>

Read the migrations-journal row for id, if the tag was already applied.

fn data_checksum(&mut self, id: &str) -> Result<Option<String>, WritePlaneError>

The recorded checksum of a DATA migration under id, if any — the kind-collision probe behind MIGRATION_KIND_MISMATCH.

fn adopt_checksums( &mut self, id: &str, opaque: Option<&str>, content: &str, ) -> Result<(), WritePlaneError>

Backfill id’s stored checksums — the opaque one when the coordinator adopted it, and the canonical content checksum — WITHOUT overwriting a present value (COALESCE semantics). The barrier serializes same-tag racers, so plain COALESCE carries the value; the coordinator’s matrix already carried the decision.

fn resolve_run_id_cursor( &mut self, run_id: &str, ) -> Result<Option<String>, WritePlaneError>

The legacy run_id → commit-cursor journal scan — the same scan OneShotBackend::resolve_public_run_id_cursor wraps, run inside the section. The C4 resolver spine drives it, with record as the GC-race re-read leg.

fn apply( &mut self, id: &str, supplied_checksum: &str, content_checksum: &str, normalized: &[String], identity_json: &str, ) -> Result<String, WritePlaneError>

Apply one fresh public DDL migration as its own atomic unit and return the committed cursor. supplied_checksum is journaled as the opaque checksum; content_checksum is coordinator-computed identity the host stores VERBATIM and never recomputes; identity_json is the recorded statement vector (the caller’s original slots).

Contract (same as OneShotBackend::apply_public_ddl): every validation runs INSIDE the transaction — the zero-capture MIGRATION_DDL_ONLY refusal, the destructive-DDL (227) guards, schema-registry validation, the broken-foreign-keys refusal — before the co-transactional journal insert and the commit.

Implementors