Select the next independent Rust semantic category

[swernerx]

Parent

• [Epic] Attach TypeScript semantic facts to OXC nodes #4
• [Epic] Prove the TS7 to internal OXC/Rust vertical slice #5

What to build

Use the completed primitive/literal evidence and the resolved rollout blockers to choose and specify the next semantic category for an independent Rust/OXC implementation. The decision must be evidence-driven and preserve the category-by-category migration boundary.

Candidate categories may include the next composite type structures, union/intersection expansion beyond the current literal slice, or another narrowly bounded category exposed by the existing protocol. The issue produces the decision and implementation contract; it does not switch production authority.

Acceptance criteria

• Current primitive/literal evidence and all unresolved blockers are summarized.
• At least two candidate categories are compared by semantic scope, OXC inputs, graph dependencies, corpus coverage, and expected risk.
• One category is selected with explicit non-goals, versioned structured output, fixtures, and differential-gate requirements.
• A successor ADR or RFC update records the decision and replacement checklist.
• A follow-up implementation issue is created with precise acceptance criteria.
• Go remains semantic authority and production fallback.

Blocked by

• Resolve primitive/literal rollout blockers #52
• Exercise production-equivalent fallback and comparable measurements #53