fix(codegen): emit valid, bindable WIT — kebab idents + defined types (#254)

[avrabe]

Fixes #254 — spar codegen --format wit emitted WIT that wasm-tools / wit-bindgen reject, so the generated interface couldn't be bound (broke the spar-generates-WIT workflow on the wohl Matter seam).

Root causes

1. Invalid identifiers. The WIT generator reused sanitize_ident, which produces Rust snake_case — but WIT is kebab-case. Package wohl_matter:matter was the first hard error; funcs like on-message_in mix a hyphen prefix with an underscore (doubly invalid).
2. Undefined types. Ports referenced types (mattermessage, monotonictime, …) that were never defined, and emitted bytes, which isn't a WIT primitive.

Fix

• New wit_ident(): kebab-case WIT identifiers — separators → hyphens, leading-digit words letter-prefixed (WIT words must start with a letter), WIT keywords %-escaped. Used for package / interface / world / func / type / export names.
• Emit type <name> = list<u8>; for every data type a port references so the interface resolves; untyped ports use list<u8> (valid primitive) instead of non-primitive bytes.
• Regression guard: a test parses the generated WIT with wit-parser (Resolve::push_str errors on bad idents or undefined types), plus wit_ident unit tests covering the exact codegen --format wit emits unbindable WIT: invalid identifiers (underscores) + undefined types #254 identifiers.

Before → after (same model)

// before (rejected)            // after (valid)
package wohl_matter:matter;     package wohl-matter:bridge;
on-message_in: func() ...       type mattermessage = list<u8>;
... mattermessage (undefined)   on-message-in: func() -> option<mattermessage>;

Verification

• cargo test -p spar-codegen — 46 lib + 21 golden, 0 failures; new generated_wit_is_valid_and_bindable + wit_ident_kebab_cases pass.
• End-to-end: wasm-tools 1.243.0 component wit (exact tool/version from codegen --format wit emits unbindable WIT: invalid identifiers (underscores) + undefined types #254) now round-trips the generated file — the invalid character in identifier '_' error is gone.

Follow-up (noted, out of scope)

Per-type scalar-size fidelity (8-byte Data_Size → u64, etc., rather than list<u8> for everything) needs scope access threaded into the generator; tracked for a later change. This PR makes the output valid and bindable, which is the blocking issue.

🤖 Generated with Claude Code

[github-actions]

Rivet verification gate

✅ 20/20 passed

	count
Passed	20
Failed	0
Skipped (no steps)	0

Filter: (and (= type "feature") (or (has-tag "v093") (has-tag "v0100")))

Failed artifacts

(none)

_{Updated automatically by tools/post_verification_comment.py. Source of truth: artifacts/verification.yaml.}

[codecov]

Codecov Report

❌ Patch coverage is 98.80952% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/spar-codegen/src/wit_gen.rs	98.80%	1 Missing ⚠️

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