C consumers cannot subscribe to the existing SIGWINCH dispatcher, leaving terminals without in-band resize notifications dependent on separate signal handling or polling. Expose callback registration and removal through the C API, with owned callback storage and documented threading and lifetime requirements. Reinstall SIGWINCH handling when a subscriber registers after the last handler was removed. Add a headless pseudo-terminal integration test covering delivery, removal, duplicate registrations, capacity, re-registration, and cleanup. Fixes: #365 Co-authored-by: Tim Culverhouse <tfc@ampcode.com>