For agents, on top of README.md, which they read first.

• No host vocabulary. Nothing here may name a product, a character, a picture format or a runtime. A host's characters are its own MouthSpec values; the tests use specs of their own for that reason.
• Rectangles in the host's grid units, nothing drawn. No I/O, no clock, no dependencies: it must build for wasm and be readable from any shell.
• A new style is a variant of Style with its shapes for all four levels in rects, an exhaustive match: a style cannot be added without drawing every level.
• The syllable timing is a pure function over what the host has read (the vowel, whether a hop to the next syllable is under way, how far through the gap it is). Reading the text is the host's.