By name: tzlint-abi-stability description: AstCoreV1 is permanently frozen; extend via additive tables; untrusted boundaries use checked rkyv::access.
Rule. AstCoreV1 (kind, span, parent, first_child, next_sibling) is
permanently frozen. Endianness is pinned little-endian; OptionNodeId is a
u32::MAX sentinel newtype (not Option<NodeId>). New data (morphology, readings) goes
into separate additive archived tables with their own interface version — never new
fields on the frozen core. Untrusted boundary reads (plugin output, cache, cross-version)
use checked rkyv::access (bytecheck); access_unchecked only for host-written
data read back immediately (e.g. a plugin reading the host-written AST), with a comment.
Why. rkyv has no inherent schema compatibility — the archived layout is bound to the
type. A frozen core + additive tables + checked access is what makes adding data safe for
old rules and turns schema mismatch into Err instead of UB.
How to apply. Want to add AST data? Add a new table + interface version; do not modify
AstCoreV1. The AstCoreV1 golden-bytes test must not change; if it does, you broke the
ABI. Confirm the encoding choice against the M0 spike before relying on it.