C API

foldback-sys is a full C ABI over foldback-core — session lifecycle, Level 1/2/3 hashing (foldback_hash_tick/foldback_hash_entity/foldback_hash_field and their peer-recording counterparts), schema-drift’s foldback_record_schema, pending-hash draining, divergence checking, and error reporting. It’s what bindings/unity and bindings/unreal are both built on (Godot calls foldback-core directly through gdext instead — see Architecture).

The generated header is the actual reference, not this page — see crates/foldback-sys/include/foldback.h (cbindgen-generated, never hand-edited — see RFC-0002 for why generation is the source of truth), per the project’s “link out, don’t duplicate” rule for generated references. Regenerate it after any change to the crate’s #[no_mangle] extern "C" surface: cbindgen --config crates/foldback-sys/cbindgen.toml --crate foldback-sys --output crates/foldback-sys/include/foldback.h.

Wire format the C ABI’s data ultimately feeds into: Protocol Spec §1. Live-mode transport (also C-ABI-adjacent, since it streams the same frame types): Protocol Spec §2.