Build errors and limits

Required exports

Export	Type	Notes
`gameConfig`	`GameStateConfigFn`	Returns the initial config. Called once.
`getSelectableItems`	`GetSelectableItemsFn`	Returns the viewer-visible click targets.
`applyActions`	`ApplyActionsFn`	Mutates `state` in place.
`getPlayerScores`	`GetPlayerScoresFn`	Returns `Scores` map.
`isGameOver`	`IsGameOverFn`	Returns a boolean.

Every value in pieces / spaces MUST be a PieceDef / SpaceDef instance. Raw object literals are rejected.
A kind used only at runtime (via state.addPiece(id, new Foo())) MUST also appear in pieceDefs or spaceDefs, otherwise addPiece throws "PieceDef kind ... is not registered".
Imports resolve only to other /src files (relative or absolute /src path) and the "boardweaver" runtime. There's no node_modules, so a bare import like import x from "pieces/Foo" fails the build : use "./pieces/Foo" or "/src/pieces/Foo".

Style validation is .strict(): an unknown style property (e.g. transform typoed as tranform, or background shorthand) is REJECTED, not silently dropped.
No CSS shorthand parsing anywhere : border, background, font, transition, animation etc. are absent by design.
A piece's render() MUST NOT return a Pieces node (or contain one in its children) : piece-side BWSS rejects it.
A space's render() MUST return exactly one Pieces node for piece children to appear (zero → no pieces + warning; multiple → fallback to default container + warning).
Image.src is a GameImageKey string : unknown keys render nothing. See images.
Svg.paths[*].d is character-class restricted: digits, MLHVCSQTAZmlhvcsqtaz, whitespace, +-.eE, only. URLs, parens, and quote marks throw.
Text inside a Box is a plain string child : there's no Text node. To style text, set typography style fields on the enclosing Box.