Patches to the vendored libghostty-vt

D12 vendors libghostty-vt pinned by commit, "with a patches file if we ever need one". This is that file.

Patches are applied to the vendored tree in this repository, which is committed, so a normal make vendor build already has them. The .patch files here exist for provenance: they say what we changed, why, and what has to be re-applied when the vendored version is bumped. vendor/*.vendor.json lists them under patches.

Re-vendoring is therefore: drop in the new upstream tree, apply each patch in order, resolve anything that has moved, rebuild, run make test.

0001 — keep kitty images across a screen clear

Terminal.eraseDisplay called kitty_images.delete(..., .{ .all = true }) for both ED 2 and ED 3, where the true means "and free the image data for anything no longer placed".

The kitty graphics protocol separates transmitting an image (a=t, which stores it under an id) from placing it (a=p, which puts it on screen), so that a program can upload once and place many times — that is the whole point of having two verbs, and the reason the delete command distinguishes d=a (placements) from d=A (placements and data). Freeing the data on a screen clear breaks it: any full-screen program that clears and redraws loses every image it uploaded, and every later placement of that id draws nothing at all.

Found with a bouncing-DVD screensaver that transmits ten frames up front and then places one per frame. It works in kitty; under us it drew nothing, and the reason was three layers down.

The patch removes only the freeing. Placements on the cleared screen still go — clearing the screen should clear what is on it — and the image store still bounds itself the way it always did, with a 320MB limit and LRU eviction on insert, which is exactly the mechanism that makes keeping them safe.

Worth sending upstream.