docs(proposals/0001): annotate v0 producer surface — flag reserved codepoints (#101)

## Summary

Adds `=== v0 producer surface` subsection to
`docs/proposals/0001-multi-producer-carrier-section.adoc`, recording
what no producer at v0 exercises and explicitly flagging those
codepoints as **reserved** (forward-compatible).

Doc-only — no spec wire-format change, no verifier code change.

## Source of the finding

Evidence-based per-producer surface measurements from the 2026-05-30
paired-review of ephapax#165 + affinescript#402:

- **affinescript** (`lib/wasm.ml`, `lib/codegen.ml:180-190`): emits only
`{I32, I64, F32, F64}`; WBool lowered to i32.
- **ephapax** (`src/ephapax-syntax/src/lib.rs:49`,
`src/ephapax-wasm/src/lib.rs:1290+`): emits only `BaseTy { Unit, Bool,
I32, I64, F32, F64 }`; collapses borrow distinctions to
`Linear`/`Unrestricted` before codegen.

Cross-cutting result: **5 of 11 WasmType variants used**, **2-of-4
PtrKind variants from ephapax**, **cardinality≡1 from both**, **zero
producers for typedwasm.capabilities** at v0.

## Policy stated

Consumers MUST accept reserved codepoints (lenient-reader contract
applies) and MUST NOT reject v0 modules that omit them. Producers
introducing them in v1.x trigger either:
1. **Additive** version bump if wire shape extends, or
2. **Breaking** version bump if existing-codepoint semantics change.

Verifier implementations should NOT preallocate handling for reserved
codepoints at v0.

## Test plan

- [ ] doc-render check (asciidoctor) on the modified proposal — no
syntax errors.
- [ ] visual sanity: subsection inserts cleanly between `L15-C` deferral
note and `=== Versioning policy`.

Closes #93
Refs #34
Refs #76
Refs hyperpolymath/ephapax#165
Refs hyperpolymath/affinescript#402

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: hyperpolymath

docs/proposals/0001-multi-producer-carrier-section.adoc

@@ -145,6 +145,45 @@ Mapping to `ResourceCapabilities.idr`:
   v1.4.x** (per LEVEL-STATUS) and needs a separate per-call-site grant
   record; out of scope for v1.
 
+=== v0 producer surface
+
+As of v0 (proposal acceptance), no shipping producer exercises the full
+wire surface defined above.  Concretely:
+
+* `wasm_ty` codepoints `0`–`5` (`U8, U16, U32, U64, I8, I16`) — no
+  producer language surfaces narrow integer types at the type-system
+  level.  AffineScript emits `{I32, I64, F32, F64}` only (`lib/wasm.ml`);
+  Ephapax exposes `BaseTy { Unit, Bool, I32, I64, F32, F64 }` only
+  (`src/ephapax-syntax/`).  `WBool` (codepoint `10`) is emitted by
+  both producers but lowered to `i32` on the wire.
+* `kind` codepoints `1`–`3` (`PtrOwning, PtrBorrow, PtrExclusive`) are
+  exercised only by AffineScript.  Ephapax codegen erases the borrow
+  distinction (`SharedBorrow`/`ExclBorrow`) before wasm emission and
+  collapses to `Linear`/`Unrestricted` only, so an ephapax-emitted
+  `typedwasm.regions` section would carry `kind ∈ {0, 1}` exclusively.
+* `cardinality` values other than `1` — variable-cardinality fields
+  require array-as-field support, which no producer ships at v0.
+  AffineScript arrays are length-prefixed runtime objects;  Ephapax
+  uses runtime list handles.  Neither emits fixed-array struct fields.
+* The `typedwasm.capabilities` section as a whole — L15 has **no
+  producer at v0**.  The wire format is specified for forward
+  compatibility, but no current producer emits this section.
+
+These codepoints are **reserved** (forward-compatible): consumers
+MUST accept them when they appear (the lenient-reader contract
+applies) and MUST NOT reject a v0 module that omits them.  A producer
+that begins emitting a reserved codepoint in v1.x triggers either:
+
+. an **additive** version bump if only the wire shape extends, or
+. a **breaking** version bump if the semantics of an existing codepoint
+  change.
+
+Implementations of `crates/typed-wasm-verify/` should NOT preallocate
+handling for reserved codepoints at v0; hitting one in a v0 module
+signals either a future-version producer (reject with
+`UnsupportedCarrierVersion`) or a producer bug (reject with the
+appropriate `OwnershipError` variant).
+
 === Versioning policy
 
 Both new sections start with `u16le version = 1`.  Future versions: