---
title: "wasi-engine — Mova code model"
description: "Mova code model of wasi-host/src/lib.rs: components with their labels, obernants and the model text."
url: "https://groupants.elamur.ai/free/en/mova/wasi-host/src/lib.rs.groupant/wasi-engine.groupant/"
---
Elamur: [Mova](https://md.mova.elamur.ai/free/en/) · [Dictionary](https://md.dictionary.elamur.ai/free/en/) · [Research](https://md.research.elamur.ai/free/en/) · **Groupants**

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# wasi-engine

The groupant beside wasi-host/src/lib.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

- **kind:** groupant_fragment
- **status:** partial source bound model
- **source:** [`wasi-host/src/lib.rs`](https://github.com/ElamurAI/mova-free/blob/main/wasi-host/src/lib.rs)
- **source SHA-256:** `91213ce903810791…`
- **covers:** new configures fuel only when Some, validates Module and binds WASI. run creates Store with Ctx limits, sets optional fuel, instantiates/starts module then calls typed _start. Return success0, i32 exit preserved without trap, other error134 with text; fuel used=ceiling-remaining. (bytes 30226–33508)
- **part of:** [wasi-runtime](https://md.groupants.elamur.ai/free/en/mova/wasi-host/src/lib.rs.groupant/)
- **repository folder:** [`wasi-host/src/lib.rs.groupant/wasi-engine.groupant`](https://github.com/ElamurAI/mova-free/tree/main/wasi-host/src/lib.rs.groupant/wasi-engine.groupant)
- **repository commit:** `855da7bd4a7b`

> **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](#approximant) |
| **ast** | partial | `../syntax.json` |
| **cost** | symbolic source derived | [invariant](#invariant) |
| **descriptant** | present | [descriptant](#descriptant) |
| **invariant** | partial | [invariant](#invariant) |
| **tests** | executed bounded checks | [tests](#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](#behavior-complement) |
| `reverse_reconstruction` | reverse_reconstruction | partial source derived model | [reverse_reconstruction](#reverse-reconstruction) |
| `fresh_context` | fresh_context | partial source derived model | [fresh_context](#fresh-context) |
| `import_name_filter` | import_name_filter | partial source derived model | [import_name_filter](#import-name-filter) |
| `entry_requirement` | entry_requirement | partial source derived model | [entry_requirement](#entry-requirement) |
| `fuel_observation` | fuel_observation | partial source derived model | [fuel_observation](#fuel-observation) |

## Model text


### descriptant

#### wasi-engine

new configures fuel only when Some, validates Module and binds WASI. run creates Store with Ctx limits, sets optional fuel, instantiates/starts module then calls typed _start. Return success0, i32 exit preserved without trap, other error134 with text; fuel used=ceiling-remaining.

##### Epoch 2026-10-31

Prospective review recorded before edits. Source review found late output FAULT effects and weaker-than-capability rights metadata; these are modeled as current behavior rather than silently repaired. Only bounded new test blocks were added; production code remains unchanged. Actual finite results and exact restoration receipts live under $MOVA_DATA/runs/octopus-wave31-wasi-2026-10-31. No full mlab guest, frozen suite, GPU or corpus run. This node retains its scoped observations for future refinement.

### approximant

#### Forward relation

new configures fuel only when Some, validates Module and binds WASI. run creates Store with Ctx limits, sets optional fuel, instantiates/starts module then calls typed _start. Return success0, i32 exit preserved without trap, other error134 with text; fuel used=ceiling-remaining.

Scope: `wasi-engine`. State and transitions follow the authoritative source, including partial effects before errors. No executable approximate replacement is attached: categorical errno/effects and module execution lack a useful validated percentage metric; future numerical profiles may only use1/2/5/10% caps after domain/reference evidence.

### invariant

#### Invariant and cost

new configures fuel only when Some, validates Module and binds WASI. run creates Store with Ctx limits, sets optional fuel, instantiates/starts module then calls typed _start. Return success0, i32 exit preserved without trap, other error134 with text; fuel used=ceiling-remaining.

The invariant is conditional on the admitted transition: A non-exit engine error cannot yield trap=None; a normal return cannot yield134. Named allowed imports do not exclude signature mismatches.

Cost: Module-dependent validation and interpreter cost; optional fuel constrains instructions only, Store memory separate; per-run instance allocation.

No wall-time gain, universal resource bound or atomic rollback is inferred. External Vfs/wasmi/native-mlab work remains separately charged.

### models

## Typed model catalog

### behavior_complement

Subject: `wasi-host/src/lib.rs` at SHA-256 `91213ce9038107912c2dd707c3a6639a2d723cdfceb02981a166a6853800248e`, scope `wasi-engine`. Domain: the source transition and bounded fixtures described in approximant.md; readable valid host resources where required. Observation: returned values, byte coordinates, state/effect order, not total-system semantics. Operator/relation: A non-exit engine error cannot yield trap=None; a normal return cannot yield134. Named allowed imports do not exclude signature mismatches.

Status: partial source-derived relation; complement is a scoped exclusion hypothesis, reverse preserves all compatible antecedents described rather than a chosen inverse. Assumptions: production branch order, declared coordinate/resource premises; no completeness claim for untested inputs. Evidence: tests.md distinguishes actual execution from source review; finite observations can falsify but not prove the relation.

### reverse_reconstruction

Subject: `wasi-host/src/lib.rs` at SHA-256 `91213ce9038107912c2dd707c3a6639a2d723cdfceb02981a166a6853800248e`, scope `wasi-engine`. Domain: the source transition and bounded fixtures described in approximant.md; readable valid host resources where required. Observation: returned values, byte coordinates, state/effect order, not total-system semantics. Operator/relation: Successful exit0 can arise from normal return or proc_exit(0); trap134 admits validation-compatible modules failing at instantiate/start/call. Missing imports list cannot recover type mismatches.

Status: partial source-derived relation; complement is a scoped exclusion hypothesis, reverse preserves all compatible antecedents described rather than a chosen inverse. Assumptions: production branch order, declared coordinate/resource premises; no completeness claim for untested inputs. Evidence: tests.md distinguishes actual execution from source review; finite observations can falsify but not prove the relation.

### fresh_context

Subject: `wasi-host/src/lib.rs` at SHA-256 `91213ce9038107912c2dd707c3a6639a2d723cdfceb02981a166a6853800248e`, scope `wasi-engine`. Domain: the source transition and bounded fixtures described in approximant.md; readable valid host resources where required. Observation: returned values, byte coordinates, state/effect order, not total-system semantics. Operator/relation: Host shares compiled module/linker but each run gets fresh Store and supplied Ctx, not previous memory.

Status: partial source-derived relation; complement is a scoped exclusion hypothesis, reverse preserves all compatible antecedents described rather than a chosen inverse. Assumptions: production branch order, declared coordinate/resource premises; no completeness claim for untested inputs. Evidence: tests.md distinguishes actual execution from source review; finite observations can falsify but not prove the relation.

### import_name_filter

Subject: `wasi-host/src/lib.rs` at SHA-256 `91213ce9038107912c2dd707c3a6639a2d723cdfceb02981a166a6853800248e`, scope `wasi-engine`. Domain: the source transition and bounded fixtures described in approximant.md; readable valid host resources where required. Observation: returned values, byte coordinates, state/effect order, not total-system semantics. Operator/relation: missing_imports tests namespace/name membership only; known name with wrong signature still fails linking.

Status: partial source-derived relation; complement is a scoped exclusion hypothesis, reverse preserves all compatible antecedents described rather than a chosen inverse. Assumptions: production branch order, declared coordinate/resource premises; no completeness claim for untested inputs. Evidence: tests.md distinguishes actual execution from source review; finite observations can falsify but not prove the relation.

### entry_requirement

Subject: `wasi-host/src/lib.rs` at SHA-256 `91213ce9038107912c2dd707c3a6639a2d723cdfceb02981a166a6853800248e`, scope `wasi-engine`. Domain: the source transition and bounded fixtures described in approximant.md; readable valid host resources where required. Observation: returned values, byte coordinates, state/effect order, not total-system semantics. Operator/relation: Valid module lacking compatible exported _start becomes run error134, not Host::new error.

Status: partial source-derived relation; complement is a scoped exclusion hypothesis, reverse preserves all compatible antecedents described rather than a chosen inverse. Assumptions: production branch order, declared coordinate/resource premises; no completeness claim for untested inputs. Evidence: tests.md distinguishes actual execution from source review; finite observations can falsify but not prove the relation.

### fuel_observation

Subject: `wasi-host/src/lib.rs` at SHA-256 `91213ce9038107912c2dd707c3a6639a2d723cdfceb02981a166a6853800248e`, scope `wasi-engine`. Domain: the source transition and bounded fixtures described in approximant.md; readable valid host resources where required. Observation: returned values, byte coordinates, state/effect order, not total-system semantics. Operator/relation: None produces no fuel_used; Some reports consumed instructions even on trap, not elapsed time or all host work.

Status: partial source-derived relation; complement is a scoped exclusion hypothesis, reverse preserves all compatible antecedents described rather than a chosen inverse. Assumptions: production branch order, declared coordinate/resource premises; no completeness claim for untested inputs. Evidence: tests.md distinguishes actual execution from source review; finite observations can falsify but not prove the relation.


### tests

#### Checks and limits

Named actual-source tests run twice per debug/release; exact commands and numeric statuses retained externally. Test success is finite evidence only.

Exact names: tests::wave31_tiny_engine_outcomes.

Memory tests bypass linker ABI; tiny empty/unreachable guests exercise engine outcomes only. The CLI test uses isolated import/export/journal fixtures.

Five compiled production/helper-source controls: append offset, virtual clock advance, trap status, CLI export gate and newest-mtime max. Each compiles, fails its selected assertion, restores exact original bytes and passes again. These controls cover their target relations, not every node. No assertion-only mutants. See external source-test-map.json, native-commands.json, verify.rs and numeric/raw receipts in $MOVA_DATA/runs/octopus-wave31-wasi-2026-10-31. The example main and frozen mlab paths are never executed.