testing/cross_backend/provided_context.ts

The vitest ProvidedContext keys the cross-backend global setups provide, and the helpers a *.cross.test.ts file reads them with.

create_cross_backend_global_setup provides one backend's handle as backend_handle; create_dual_spawn_global_setup provides two, as parity_handle_a / parity_handle_b by default. This module augments vitest's ProvidedContext with those keys, so a test file that imports inject_backend_handle (or inject_parity_handles) gets the typed inject with no augmentation of its own. A project providing other keys — a dual spawn under its own provide_keys, a probe result — augments ProvidedContext for those in its own module, beside this one.

vitest refuses a value that isn't serializable, so the handles cross as SerializableBootstrappedBackendHandle; the helpers rebuild a usable handle with reconstruct_bootstrapped_handle.