Function loadWasmBackend

Remarks

Concurrent calls share a single module compile (per chosen bridge) via modulePromiseByBridge.

This IS the authoritative Rust engine, and it was not until causl/causl-wasm-ts#279 slice S12a. From Phase 1 (iasbuilt/causl#1065) until that slice the WasmBackend this returns wrapped a pure-TypeScript Graph as its #graph and answered nine of its twelve BackendEngine members off it, which is why the paragraph that stood here said the opposite and told the reader never to route the real engine through this function. S12a deleted the wrap: instantiateBackend compiles the artefact, attaches the exports and enables the authoritative engine, so getAuthoritativeEngine() answers and __graph is gone. test/wasm-backend-engine-backed-279.test.ts pins all three claims, including behaviourally: a value committed through this backend is read back out of the engine that accepted the commit.

It remains a BackendEngine, which is a twelve-member surface with no derived registration on it, and it remains the shape the cross-backend determinism gate (#685) and the snapshot/hydrate round-trip (#687) drive. What changed is which implementation answers, not what the surface is.

An adopter still wants preloadCauslWasm() + createCauslWasmSync() rather than this: those return a Graph, the seven-method surface the package documents, and they stamp the per-graph engine identity. #122 retired the createCausl({ backend: 'auto' }) auto-migration that used to "migrate" onto this loader, and 'auto' is now a documented alias for the registry FLIP (wasm-when-preloaded), so this loader is on no adopter engine-selection path.

The WasmBackendUnavailableError class is retained for the narrow case where the loader is asked for a bridge id whose host preconditions are not met.

import { loadWasmBackend } from '@causl/causl-wasm-ts/wasm'

// The determinism-gate surface, over the Rust engine.
const backend = await loadWasmBackend()
const commit = backend.commit('intent', new Map([['x', 1]]))
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