Tracked grid references previously held a raw terminal wrapper pointer and were required to be freed before the terminal. If callers kept one past terminal destruction, later tracked-ref calls could dereference freed terminal or page-list memory before detecting that the reference was no longer meaningful. Track live C tracked-grid-ref handles from the terminal wrapper and detach them before tearing down terminal storage. Detached refs now report no value through the tracked-ref APIs and can still be freed by the caller. Update the C API docs to describe this lifetime behavior and add a regression test for using a tracked ref after terminal free. This introduces some overhead but tracked pins shouldn't be numerous and this dramatically improves safety.