Elamur Groupantsworld-school-student-state-retained-codec
The groupant beside world/src/school.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 source model | forward |
| ast | partial | ../../syntax.json |
| composition | partial source model | composition |
| cost | partial source model | cost |
| descriptant | partial source model | epoch-memory |
| invariant | partial source model | invariant |
| tests | partial source model | checks |
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 |
|---|---|---|---|
world-school-student-state-retained-codec-behavior-complement | behavior_complement | partial source model | behavior-complement |
world-school-student-state-retained-codec-reverse-reconstruction | reverse_reconstruction | partial source model | reverse-reconstruction |
world-school-student-state-retained-codec-accumulator_activation | state_transition | partial source model | accumulator_activation |
world-school-student-state-retained-codec-duplicate_width | order_relation | partial source model | duplicate_width |
world-school-student-state-retained-codec-canonical_projection | identity_relation | partial source model | canonical_projection |
world-school-student-state-retained-codec-row_order | observation_relation | partial source model | row_order |
Model text
Wave34, 2026-10-31. Source-bound helper model; no universal proof or approximation-error certificate. Historical parent epoch remains intact.
forward
Decode lines in order: ignore # and widths below five; parse four current columns with invalid numbers mapped to zero; widths >=9 also replace accumulator columns. A later five-column duplicate replaces w but leaves an earlier acc row. Encode sorted union keys; emit nonzero w or any explicit acc, and only emit accumulator columns when present.
invariant
For format-safe keys (no tab/newline and no leading #), numeric table selection survives canonical encoding. Current-only zero rows disappear; orphan acc rows gain a zero current row. This is projection, not arbitrary map identity.
cost
R rows, K keys, B bytes: decoding O(B+R log K), encoding O(K log K+B), O(K) maps and O(B) output.
composition
Student load invokes this decoder; save creates a directory then calls write_atomic with this encoder. The parent selects acc globally when nonempty. Presence is therefore a control bit shared with selection, not merely a numeric zero. Filesystem publication and global paths are unexecuted.
behavior-complement
In the supplied TSV/map universe, exclude decoding a short duplicate as deletion of an existing accumulator; exclude encoding explicit zero acc as absent; exclude invented nonzero values for omitted or malformed numeric cells. Unsafe key strings are outside the roundtrip relation.
reverse-reconstruction
Given decoded maps, antecedents are all ordered TSV rows whose last >=5-column occurrence sets each w and whose last >=9-column occurrence sets each acc; comments, malformed zero spellings and overridden rows remain free. Given encoded bytes, compatible input maps may additionally contain omitted current-only zero keys.
accumulator_activation
The observation acc.is_empty after decode/encode equals its input value for format-safe maps, including explicit zero rows; w-only state and zero-acc state can choose different operations.
duplicate_width
Two rows of the same key commute only if their effective current replacements agree and accumulator writes do not conflict. A five-column row cannot undo a prior nine-column accumulator.
canonical_projection
Encode(decode(encode(s)))=encode(s) for format-safe representable rows. Decoding may insert zero w for orphan acc; equality is byte-canonical, not every original key-set identity.
row_order
Encoder key union is a BTreeSet: output is lexical key order regardless of insertion order. Within a row current coordinates precede accumulator coordinates in Add/Sub/Mul/Div order.
checks
Exact world library selections: school::wave12_models::retained_student_format_is_ordered_and_legacy_tolerant, school::wave12_models::legacy_retention_does_not_change_answer_table, school::wave12_models::zero_accumulator_activation_survives_retention. Current repeated debug/release outcomes and compiled controls are in the root sidecar wave34-evidence.md. Only these supplied-input tests are current evidence; older parent module-wide receipts are historical. Macro bodies remain opaque.
epoch-memory
Prospective model saved before edits. This epoch deepens one existing node rather than renaming it. Production implementation unchanged; tests add helper-boundary observations where stated. No live lessons, frozen suites, model loading, teacher or network. Read-only symbolic relations are broader than the finite native domain.
This page in Markdown → https://md.groupants.elamur.ai/free/en/mova/world/src/school.rs.groupant/student-state.groupant/retained-codec.groupant/