Kitty graphics: app-placed images grey — 45MB frames dropped by 32MB cap, small images silently not painted

[milimat0810]

Summary

Images placed by a TUI app (opencode) render as grey boxes in herdr panes, while the same files render fine in bare Ghostty. There are two distinct failure modes:

1. Large images: frame dropped by the 32MB cap. opencode's fullscreen viewer transmits ~45MB per frame; herdr logs dropping oversized graphics payload ... graphics_bytes=45360361 max=33554432 and the image never reaches the host terminal. This retried ~15x/sec (114 drops in ~7 min), so the viewer just sits grey.
2. Small images: silently not painted. A 2KB 400x300 PNG opened fullscreen in the same viewer produces no dropping oversized line and no other WARN/ERROR/GRAPHICS line at all — yet stays grey.

Environment

• herdr 0.8.2, stable channel, server + client same version
• macOS, Ghostty outer terminal (Kitty-graphics capable)
• ~/.config/herdr/config.toml contains [experimental] kitty_graphics = true; server fully restarted (herdr server stop + start) after setting it
• Plain herdr pane: chafa -f kitty <file> renders fine, so the flag is active and dumb-blast transport works
• Same opencode build + same files in bare Ghostty (no herdr): fullscreen viewer renders correctly

Repro

1. Enable [experimental] kitty_graphics = true, restart the herdr server.
2. In a herdr pane, run opencode, attach any PNG, open it fullscreen.
3. 4K image: grey box; ~/.config/herdr/herdr-server.log fills with herdr::server::headless: dropping oversized graphics payload for client frame ... graphics_bytes=45360361 max=33554432.
4. 2KB image: grey box; no related log output whatsoever.

Notes / suspected causes

• opencode ships the fullscreen image as raw RGBA-ish base64 (~45MB for 3840x2160) per repaint instead of downscaling to the actual cell area — wasteful on its side, but herdr turns it into a silent grey box: the drop is WARN-logged only, nothing surfaces in the UI.
• The small-image case matches the existing placeholder/paint failure class (kitty_graphics: images don't render inside Neovim panes (blank box), though kitten icat works in a shell pane #494, Kitty graphics leaves blank space for Snacks image placeholders #732, kitty_graphics: virtual-placeholder images stop painting after in-session image replacement/eviction (regression of #732; tmux + bare Ghostty unaffected) #1167, #4145): transmit accepted, placement never paints, no error anywhere.
• Related: kitty_graphics: images don't render inside Neovim panes (blank box), though kitten icat works in a shell pane #494 (blank box from app panes while shell-pane icat works), kitty_graphics: virtual-placeholder images stop painting after in-session image replacement/eviction (regression of #732; tmux + bare Ghostty unaffected) #1167 (repaint/eviction), #4145 (image not visible inside herdr), Kitty Image keeps reloading in Herdr + Ghostty (but works fine in Ghostty alone) #1628 (agent image display).

Expected

• Don't silently drop: chunk oversized graphics across frames (the kitty_graphics.rs continuation machinery suggests this was anticipated), or at minimum surface a visible "image too large" state instead of grey.
• Small forwarded placements should paint (same as shell-pane icat path).