feat(ir): drop Function.synchronous, add Function.parameters, KindValue::Unit

[Kinflou]

Three of the four core ↔ target IR changes (docs Design §4.4). The fourth — throws: Vec<String> → Vec<u16> with schema-global error ordinals (incl. cross-schema use) — is a separate follow-up PR.

Function.synchronous removed

Conflated three things — a wire fact (does the call reply), a binding choice (block vs .await), server scheduling config. Only the first belongs in the schema and _return already carries it. It was always frozen true and read nowhere.

Function.parameters: Vec<FrozenUnit> added

Same shape Protocol / Struct already carry — @key = value function annotations (@timeout_ms, @idempotent, …) frozen as Property { name, expression } via the existing annotation_units(). The AST already parsed function annotations; they were dropped at freeze. Open namespace — a consumer acts on the keys it knows.

KindValue::Unit + a () type in the grammar

function commit() -> (); now freezes as _return: Some(KindValue::Unit) — a reply that carries no value (an empty ack) — distinct from function commit(); (no ->), which freezes as _return: None — no reply at all (one-way). Without the variant, "ack, no value" was inexpressible without inventing an empty struct per call.

• New rust_sitter node UnitType (( )); parser regenerates at build time, no ambiguity in the Type position.
• type_to_string / build_kind_value map it; exhaustive KindValue matches updated in diff.rs, validator.rs, kind_search.rs.

Tests

Parser + IR coverage for -> () vs no return (test_protocol_unit_return, test_protocol_unit_return_ir). Full core suite green — 241 passed, 0 failed. No frozen-unit hash goldens broke.

Downstream

FrozenUnit shape change → every comline-<lang> / generation / cli that pins comline-core needs a coordinated rev-bump when this lands (they only pattern-match Function with .., so it's a rev-bump, not code changes).