The terminal sys module provides runtime-swappable function pointers
for operations that depend on external implementations (e.g. PNG
decoding). This exposes that functionality through the C API via a
ghostty_sys_set() function, modeled after the ghostty_terminal_set()
enum-based option pattern.
Embedders can install a PNG decode callback to enable Kitty Graphics
Protocol PNG support. The callback receives a userdata pointer
(set via GHOSTTY_SYS_OPT_USERDATA) and a GhosttyAllocator that must
be used to allocate the returned pixel data, since the library takes
ownership of the buffer. Passing NULL clears the callback and
disables the feature.
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