truefix-store — pluggable persistence of sequence numbers and sent messages.
The [MessageStore] trait abstracts the storage needed for resend (FR-G2): the next inbound
and outbound sequence numbers, and the bytes of each sent message keyed by sequence number.
Implementations: [MemoryStore], [FileStore], [CachedFileStore], [NoopStore], and a
SQL-backed store behind the sql feature.
Audit 006 additions: [MessageStore::contains] exposes duplicate-sequence detection without
changing save()'s existing overwrite-on-conflict contract (NEW-137);
[FileStoreOptions::max_body_records] bounds a file-backed store's body-log index while
preserving resend/recovery semantics (NEW-108); Mongo/SQL/MSSQL reset() is atomic across
messages and sequence numbers (NEW-116); and NoopStore tracks sequence numbers in memory for
the session lifetime (NEW-118).
Feature 012 (audit 007) additions / migration note: [StoreConfig] gained a Custom(Arc<dyn MessageStore>) variant (NEW-158), letting a caller supply a backend not on the built-in list
through the same config surface Engine::start resolves (see truefix::Engine::start_with_overrides).
This is additive to the variant set, but StoreConfig can no longer derive Debug (dyn MessageStore isn't Debug) -- it now has a hand-written Debug impl with the same output for
every pre-existing variant, so this only breaks code that exhaustively matches StoreConfig
without a _ => arm.
Design: specs/001-fix-engine-parity/, specs/012-audit-007-remediation/.