roundtrip-derived-piece-codec-line-script

The groupant beside tools/roundtrip/src/blocks/site_code.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	approximant
ast	partial	`../syntax.json`
cost	symbolic source derived	invariant-and-cost
descriptant	present	descriptant
invariant	partial	invariant-and-cost
tests	executed bounded checks	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 source derived model	behavior_complement
`reverse_reconstruction`	reverse_reconstruction	partial source derived model	reverse_reconstruction
`newline_units`	newline_units	partial source derived model	newline_units
`insertion_tie`	insertion_tie	partial source derived model	insertion_tie
`drop_coordinates`	drop_coordinates	partial source derived model	drop_coordinates
`cost_domain`	cost_domain	partial source derived model	cost_domain

Model text

descriptant

Description and epoch memory

Bottom-up LCS lengths feed greedy keep/insert/drop. apply removes indexed source lines then inserts stored lines at output positions; script_bits charges drop positions plus stored-line bytes/positions.

Epoch 2026-10-31

Prospective model retained externally before edits. Existing production bytes preserved; only bounded inline tests appended to six owned files. Models distinguish byte reconstruction with residual from semantic understanding and persistent learning. Finite tests and compiled mutants support selected boundaries only. Source inspection identified noninjective projections and explicit admissibility restrictions; no bug repair or performance claim.

Combiner input is this source snapshot, syntax projection, models, costs and retained receipts. Proposed next epoch: target the stated unexecuted branches with bounded witnesses before expanding any claim. AST remains partial, macros opaque; no name resolution or proof.

approximant

Forward relation

Domain: Same model/lexicon/environment at encode/decode; valid references and 10-column patches; LCS dimensions/counts fit usize/u32 and memory. Tests execute pure scripts/tree validation/reference/damage, not model-backed encoder.

No executable percentage surrogate is supplied: these categorical codec/effect observations have no justified lossy metric. Future caps are 1/2/5/10% only after defining metric, zero behavior and differential reference.

catalog

Source-bound typed models

Each section is a partial source-derived relation on the bound snapshot and declared domain; finite checks are falsification evidence, not a universal proof. Observation horizon is one call unless history is explicitly named.

behavior_complement

Generated script never reorders retained lines; equal-match path keeps before edit; ties prefer insertion.

Domain and held state: Same model/lexicon/environment at encode/decode; valid references and 10-column patches; LCS dimensions/counts fit usize/u32 and memory. Tests execute pure scripts/tree validation/reference/damage, not model-backed encoder.