If no argument is provided, check whether design/assets/asset-manifest.md exists:

If it exists: read it, find the first context (system/level/character) with any asset at status "Needed" but no spec file written yet, and use AskUserQuestion:
- Prompt: "The next unspecced context is [target]. Generate asset specs for it?"
- Options: [A] Yes — spec [target] / [B] Pick a different target / [C] Stop here
If no manifest: fail with:

"Usage: /asset-spec system:<name> — e.g., /asset-spec system:tower-defense Or: /asset-spec level:iron-gate-fortress / /asset-spec character:frost-warden Run after your art bible and GDDs are approved."

Phase 0: Parse Arguments

Target type: system , level , or character
Target name: the name after the colon (normalize to kebab-case)
Review mode: --review [full|lean|solo] if present

Extract:

asset-spec