Elamur Groupantsmodelcheck-syntax-decode-memo
The groupant beside tools/modelcheck/src/syntax.rs in the Mova repository: what the code computes, what it never does, how to go back from its outputs, its invariants, cost and checks.
Facts
Implementation material. A Mova code model describes this code at one source revision: partial models, finite checks and their stated scope. It is not a reviewed general exposition, and its labels are shown as written, never raised.
Components
| component | label | where |
|---|---|---|
| approximant | partial | Forward |
| ast | partial | ../syntax.json |
| cost | partial | Cost |
| descriptant | partial | Descriptant |
| invariant | partial | Invariant |
| tests | partial | Tests |
Obernants
The typed relations around the forward model: the behaviour complement (what the code never does), the reverse reconstruction (every input compatible with an output) and specialised views.
| id | type | label | where |
|---|---|---|---|
behavior_complement | behavior_complement | partial relational specification | behavior_complement |
reverse_reconstruction | reverse_reconstruction | partial relational specification | reverse_reconstruction |
byte_identity_over_metadata | byte_identity_over_metadata | partial relational specification | byte_identity_over_metadata |
error_preserves_slot | error_preserves_slot | partial relational specification | error_preserves_slot |
capacity_transition | capacity_transition | partial relational specification | capacity_transition |
validation_independence | validation_independence | partial relational specification | validation_independence |
Model text
Subject: current manifest source SHA and exact UTF-8 range [21794,22989). The observation is one completed scoped call with adequate resources; source-derived relations are partial specifications. Filesystem checks describe sequential reads, not an atomic snapshot.
Forward
Read artifact bytes on every call. In memo mode return the immutable saved Value only on full byte equality. Otherwise decode with serde_json; on success retain one entry only at <=8 MiB, clearing on oversized/reference success. Read or parse errors propagate without replacing the slot. New reads in reference mode always decode.
Invariant
Returned Value equals decoding the just-read bytes; no validation result or filesystem metadata is cached. One source-tree reader is dropped after traversal. Byte cap bounds serialized retention, not serde Value allocator overhead.
Cost
For m equal B-byte references, one O(B+N) parse plus O(mB) reads/equality and O(1) Rc clones replaces m JSON decodes. Full source/node validation still runs O(m(S+N)); a miss can temporarily retain old and new trees. Retained byte cap is 8 MiB.
Descriptant
Wave34, 2026-10-31: deeper scope retained under its existing parent without replacing historical views. Decode reuse was proposed before edits and checked against actual reference decoding; behavioral controls and repeated native receipts remain finite evidence. No numerical surrogate is justified for categorical validation outcomes; no percentage accuracy or complete semantic proof is claimed.
Tests
Exact native test: syntax::wave34_tests::artifact_decode_memo_matches_reference_and_observes_file_changes. Parent tests additionally exercise integration and failure order. Current evidence is in ../wave34-evidence.md; old evidence remains explicitly historical in wave33-evidence.md at the source root.
behavior_complement
Exclude returning saved JSON for unequal bytes, missing files, read errors or malformed fresh JSON. Exclude retaining oversized successful input; a saved valid slot cannot convert a failed read into success.
Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: syntax::wave34_tests::artifact_decode_memo_matches_reference_and_observes_file_changes. Finite observations do not establish universal completeness.
reverse_reconstruction
For returned Value v, compatible just-read bytes are all serde_json encodings decoding to v. A hit further constrains bytes to saved bytes; a miss does not uniquely identify previous slot. Whitespace/object spelling can differ within the decoded fiber.
Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: syntax::wave34_tests::artifact_decode_memo_matches_reference_and_observes_file_changes. Finite observations do not establish universal completeness.
byte_identity_over_metadata
Cache identity is full Vec byte equality, with no path/mtime/length-only shortcut. Same-size edited JSON must decode anew. Equal bytes from different paths are safe only because each caller still confines and rereads its path.
Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: syntax::wave34_tests::artifact_decode_memo_matches_reference_and_observes_file_changes. Finite observations do not establish universal completeness.
error_preserves_slot
A read or decode failure leaves previous memo state unchanged but returns error. A later exact restoration can hit; the error itself is never memoized or suppressed.
Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: syntax::wave34_tests::artifact_decode_memo_matches_reference_and_observes_file_changes. Finite observations do not establish universal completeness.
capacity_transition
For a successful miss with B<=8388608 retain (bytes,Rc<Value>); for B>8388608 clear. Reference mode also clears and cannot hit. This is a retention policy, not a maximum admitted artifact size.
Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: syntax::wave34_tests::artifact_decode_memo_matches_reference_and_observes_file_changes. Finite observations do not establish universal completeness.
validation_independence
Consumers call validate_artifact after every read, including hits. Fresh source hash and all node guards remain active, so a source edit with unchanged artifact JSON still rejects. Across source-tree calls no memo is reused.
Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: syntax::wave34_tests::artifact_decode_memo_matches_reference_and_observes_file_changes. Finite observations do not establish universal completeness.
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