[#446 Tier 1 #5] WASM-exports calling pattern (recommended kickoff) #455

Part of #446 — Tier 1 item 5. Recommended kickoff per roadmap memory.

Goal

Ship the WASM-exports calling pattern as the first concrete binding from the top-50 roadmap. Lowest scope, highest leverage:

• ~30 extern fns OR one generic wasm_export_call (design decision)
• < 1 day estimated
• Unlocks idaptik vm/wasm AND every future WASM-host integration

Background

stdlib/Deno.affine has WasmExports type + wasmInstance. What it lacks is the calling pattern for the exports of a loaded wasm instance — i.e., once you've loaded mywasm.wasm, how do you call mywasm.exports.add(1, 2) from AffineScript?

Two design options:

Option A: extern fns per type signature

Generate ~30 extern fns covering common signatures:

• wasm_call_0args_returns_i32
• wasm_call_1arg_i32_returns_i32
• wasm_call_2args_i32_i32_returns_i32
• ... etc.

Pros: type-safe; AS typechecker knows what's allowed.
Cons: bloats Deno.affine; doesn't cover unusual signatures.

Option B: single generic wasm_export_call

extern fn wasm_export_call(
  exports: WasmExports,
  name: String,
  args: Array<WasmValue>
): WasmValue

Where WasmValue is a sum of I32 | I64 | F32 | F64.

Pros: single binding; covers any signature.
Cons: weaker type-safety at the AS call-site (user must marshal manually).

Owner decision needed in PR review — recommendation: ship Option B first (smaller, covers everything), then add Option A overloads as Deno.affine mature.

Acceptance

• Deno.affine exports a wasm_export_call (or per-signature variants)
• Idris2 ABI pattern documented (per estate convention: Zig=APIs/FFIs, Idris2=ABIs)
• Zig FFI implementation lives in affinescript-stdlib/ffi/zig/ (or wherever current pattern dictates)
• At least one consumer-side example: e.g., examples/wasm-exports-demo.affine that loads a tiny wasm and invokes an export

Test plan

• Build green: dune build (or whatever the AS build command is — confirm at start)
• Example runs end-to-end with deno run -A examples/wasm-exports-demo.ts (or AS equivalent)
• Idaptik vm/wasm consumer team verifies the binding shape works for their use case

Sequencing

• BLOCKED ON: nothing — this is the kickoff.
• BLOCKS: every future Tier 1 item that needs to interact with loaded wasm modules (idaptik vm/wasm, Phoenix WebSocket framing if it composes a wasm marshalling step, etc.)

Cross-references

• Memory: project_affinescript_bindings_top50_roadmap.md — "Highest-leverage starting points" §1
• Umbrella: [campaign] AffineScript top-50 framework bindings roadmap (UMBRELLA) #446