feat(stdlib): WasmValue + wasm_export_call typed wasm-exports binding (closes #455)

[hyperpolymath]

Summary

Tier 1 #5 of the AS bindings top-50 roadmap (#446). Owner's #455-decided Option B: generic `wasm_export_call(exports, name, args: [WasmValue]) -> WasmValue` with `WasmValue` as a tagged scalar carrier covering all four wasm numeric kinds (i32, i64, f32, f64).

Encoding decision

`WasmValue` lands as an OPAQUE `pub extern type` rather than a true AS sum type. Rationale: the JS interop boundary needs a hand-written marshaller pairing `wv_i32(42) -> { kind: "i32", v: 42 }` with the export-call dispatch `__as_wasm_export_call(exports, name, args)`. Mirrors the existing `WasmExports` opaque pattern.

A true sum-type variant on top of this opaque base ships in a follow-up once `json.affine`-style tagged-variant codegen lands for the Deno-ESM backend. Per #455 "weaker static safety acknowledged trade-off; typed wrappers will land as a follow-up sub-issue once usage patterns crystallise."

What this PR ships

`stdlib/Deno.affine` (+87 lines)

• `pub extern type WasmValue`
• Constructors: `wv_i32` / `wv_i64` / `wv_f32` / `wv_f64`
• Accessors: `wv_as_int` / `wv_as_float` / `wv_kind`
• `wasm_export_call(exports, name, args: [WasmValue]) -> WasmValue`
• Worked example: `addI32ViaWasm(bytes, a, b)` in the docstring

`lib/codegen_deno.ml` (+47 lines)

• JS prelude: 8 `_as_wv*` / `__as_wasm_export_call` helpers
• `deno_builtins` dispatch table: 8 entries
• BigInt for i64 (preserves precision beyond 2^53); `Math.fround` for f32
• Return wraps as f64 by default (lossless for any numeric); i64 returns detected via `typeof result === "bigint"` and wrapped as i64

What's deferred (per #455 implementation-scope breakdown)

Each independently shippable now that the Deno.affine surface is in place; will file follow-up tracking issues after merge:

• Zig FFI implementation for the native backend
• Idris2 ABI pattern doc (Zig=APIs/FFIs, Idris2=ABIs convention)
• `examples/wasm-exports-demo.affine` end-to-end demo
• Smoke-test through the Zig FFI

Owner-directive compliance

• Adds 8 externs in the WebAssembly section adjacent to existing `wasmCall`.
• Adds 8 codegen dispatch entries in the existing `let () = ...` block.
• Pure additive change; no existing surface modified.
• Owner Option B confirmed in [#446 Tier 1 #5] WASM-exports calling pattern (recommended kickoff) #455 comment 2026-05-30 13:18Z.

Test plan

• CI build job (`opam exec -- dune build`) green
• CI `dune runtest` green
• CI `tools/run_codegen_deno_tests.sh` green (existing wasm tests stay unaffected)
• Manual smoke: load a tiny wasm module emitting an `add(i32, i32) -> i32` export; call via `wasm_export_call` with `[wv_i32(2), wv_i32(3)]`; verify `wv_as_int(result)` returns 5. Defer to follow-up PR with example file + harness.

Refs

• closes [#446 Tier 1 #5] WASM-exports calling pattern (recommended kickoff) #455 (Tier 1 ci: Bump actions/github-script from 7.0.1 to 8.0.0 #5, scope: Deno.affine + JS codegen)
• [campaign] AffineScript top-50 framework bindings roadmap (UMBRELLA) #446 — AS bindings top-50 umbrella
• `stdlib/Deno.affine:155-176` — existing `wasmCall` / `wasmInstance` surface for context

🤖 Generated with Claude Code

[github-actions]

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Findings: 83 issues detected

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🟠 High	11
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