Here is a list of all documented files with brief descriptions:

include
operator_sdk
abi
mode_api.h	The Operator function table a mode calls into, plus the mode export signatures and the input gesture ABI
mode_param.h	Declarative parameter schema embedded in a .opm mode binary
draw.h	Convenience wrappers over the display draw API (opt-in, header-only)
held_notes.h	Held-note registry for modes that rewrite note pitch (opt-in, header-only)
log.h	Ergonomic logging: op::log(...) wrappers over the raw ABI log entry
math.h	Value-mapping helpers (opt-in, header-only)
midi.h	MIDI helper library (scales, chords, CC constants)
params.h	Declarative parameter-table DSL for Operator SDK modes
storage.h	Saving a whole file in one call with op::write_file(...)
text.h	Text-layout helpers for Operator modes (opt-in, header-only)
timing.h	Musical subdivision helpers + clock interpolation (opt-in, header-only)
operator_sdk.h	Public ABI umbrella header for Operator SDK modes
sim
include
operator_sdk_sim.h	The mock device a mode is tested against