Black Shapes

burnBacking is the one operation that destroys value on purpose. It is available only to the owner of an apex Complete Shape: 100 ETH, index 8, carrying all 10000 origins.

function burnBacking(uint256 tokenId) external;

function isBlackShape(uint256 tokenId) external view returns (bool);
function blackShapeCount() external view returns (uint256);
function burnedBacking() external view returns (uint256);

Rules

The caller owns the token, it is live, and it is not already Black.
denomIndexOf(tokenId) == 8 and originCountOf(tokenId) == 10000, else NotApexComplete(tokenId). A 100 ETH Shape minted directly has one origin and does not qualify; only one assembled from 10000 direct mints does.
One way. There is no reverse.

Effect

Exactly 100 ETH leaves the reserve to 0x000000000000000000000000000000000000dEaD. redeemableBacking drops by 100 ETH, burnedBacking rises by 100 ETH, blackShapeCount rises by one. The token keeps its id, owner, seed, origins, denomination index 8 and modules, and is marked Black.

A Black Shape:

Read or action	Result
`valueOf`, `backingOf`	0
`denomIndexOf`	8
`formationOf`	4 (`Black`)
`isComplete`	false
`tokenURI`	The same geometry, inverted: light field, dark marks
`transferFrom`, `safeTransferFrom`	Allowed
`burn`	Allowed; destroys it for zero, lowers `blackShapeCount`
`redeem*`	`TokenIsBlack`
`compose` as survivor or input, `decompose`, `split`, `burnBacking`	`TokenIsBlack`

burnedBacking is monotonic. Burning a Black Shape for zero does not change it, because that ETH already left at burnBacking.

Events

Event	Count
`BlackShapeCreated(tokenId, burnedWei)`	Once, `burnedWei` = 100 ETH
`MetadataUpdate(tokenId)` (ERC-4906)	Once

No Transfer is emitted; the token does not move. A Black Shape that is later burned emits Transfer to zero and ShapeRedeemed with amountWei == 0.