Stands up the schema-evolution machinery as a tested behavioral no-op, the
load-bearing one-way-door piece the later phases build on.
- SchemaVersion::V1 (bundle/ids.rs) -- infrastructure, an identity today.
- The core dispatch seam Score::decode_canonical_versioned(bytes, major)
(core/codec.rs), with the decode_v0_score / migrate_v0_score scaffold. It is
the identity at major 1's introduction (v0 layout == v1 layout), with
explicit "Phase C/D freeze this by value + default-fill the new field"
contracts baked into the doc comments so the freeze is a clean edit later.
Unit-tested by versioned_decode_is_identity_across_majors.
A first-pass review caught that the initial gate widening over-reached: it
admitted major 1 for every chunk kind, but the bundle's own op-block decoder
(block::decode_block) and manifest decoder are unversioned, so a spec-valid
major-1 op block would have passed the gate and then been mis-read rather than
migrated / opened read-only. The accept-set ran ahead of the decoders.
Corrected: the gates stay EXACT to major 0 in this phase -- the manifest gate
to Manifest::SCHEMA.major (the manifest never grows a v1 layout in this bump),
the generic-chunk gate to SUPPORTED_SCHEMA_MAJOR = 0. Admission of major 1 is
raised PER CHUNK ROLE by the phase that adds that role's versioned decode or
discard path (snapshot -> C, op block -> D, layout cache -> E), never as a
blanket accept-set ahead of a decoder that can read it. The roundtrip
seam-exercise was reverted too (it conflated the canonical-base MaterializedState
role with the acceleration-snapshot Score role); the acceleration-snapshot read
path + the first usable_* wrapper land in Phase C.
So Phase B is version infrastructure + the dispatch seam only; the gate
widening, usable_* wrappers, and ops symmetry move to the phases that exercise
them.
863 workspace tests pass; clippy -D warnings, fmt --check, rustdoc -D warnings
all clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NEs4aYiu8MXjdYdMxw8PTd
Levi Neuwirth
9f688cc592