A per-document-kind migrator. Receives the document's serialized source and
returns a flattened update payload (Foundry dot-path keys, e.g.
{ "system.foo": 1 }) to write, or undefined / an empty object for a no-op.
The payload is a Foundry document.update() argument, so express nested
changes as dot paths and write a whole array back rather than an element by
index (see the array-field contract in the runtime-contracts reference). A
migrator must not mutate source.
A per-document-kind migrator. Receives the document's serialized source and returns a flattened update payload (Foundry dot-path keys, e.g.
{ "system.foo": 1 }) to write, orundefined/ an empty object for a no-op.The payload is a Foundry
document.update()argument, so express nested changes as dot paths and write a whole array back rather than an element by index (see the array-field contract in the runtime-contracts reference). A migrator must not mutatesource.