fix: render sixel and iTerm2 inline images (imgcat) again

[cantona]

Fixes #1591 — imgcat, icat, viu, chafa -f iterm and sixel tools parsed fine but nothing ever rendered.

Root cause

Since the kitty overlay rewrite, atlas graphics (sixel / iTerm2 OSC 1337) are parsed and uploaded into sugarloaf.graphics — a store no draw path reads (Renderer::prepare receives it as _graphics), and the per-cell GraphicCell references aren't consumed anywhere either. Only kitty images render, via image_data + GraphicOverlays.

Fix (3 commits)

1. crosswords: make per-cell graphics state survive large inline images — every covered cell used to allocate its own slot in the u16-indexed extras table, so ~a dozen screen-sized images exhausted the id space (images then rendered partially or not at all until restart). One shared slot per image row + a mark-and-sweep of unreferenced slots (which also reclaims images dropped off scrollback), plus two snapshot-freshness fixes.
2. deps: enable TIFF decode — chafa's iTerm2 renderer transmits TIFF; same change as Enable TIFF decode for iTerm2 images #1428.
3. rioterm: render sixel and iTerm2 graphics through the image overlay pipeline — upload atlas pixels into the per-image texture store under a namespaced key (high bit keeps sequential GraphicIds out of the kitty protocol id space) and build overlays per frame by scanning visible rows for graphic cells, mirroring the kitty Unicode-placeholder pass. Row-runs coalesce into one overlay with a normalized source-rect slice, so partial overwrites hide exactly the erased region and images scroll with the grid. Also marks the panel dirty when UpdateGraphics arrives so the pixels aren't invisible until the next unrelated repaint.

Tested (Linux/Wayland, Vulkan)

• imgcat (PNG), chafa -f iterm (TIFF), chafa -f sixels, viu — all render; chafa -f kitty unaffected.
• Repeated large (1600×900) images well past the old ~14-image exhaustion point; scrollback, clear, and partial overwrite behave.
• cargo fmt, clippy, and the full test suite pass; new behavior covered by updated graphics tests.

[cantona]

Hi @raphamorim 👋

First off — thanks for rio, it's become my daily driver. I've been scratching my own itches over the past weeks and have accumulated a batch of PRs. No rush at all, but when you find time, here's a suggested order to make reviewing painless:

Bug fix for a known issue:

• fix: render sixel and iTerm2 inline images (imgcat) again #1703 — sixel/iTerm2 inline images never render (fixes iTerm2 image protocol broken on 0.4.2 & 0.4.3 #1591). Root cause was graphics being uploaded to a store no draw path reads.

Small, low-risk fixes (each a focused diff, quick to review):

• fix: hot-reload key bindings on config update #1678, fix: copy selection to primary buffer for middle-click paste #1679, fix: pixel-snap UI text glyphs for crisp rendering on HiDPI #1680, fix: pixel-snap tab-bar border lines so they don't randomly disappear #1682, fix: hot-reload window.decorations without restart #1684, fix: recompute grid rows when the tab bar appears/disappears #1687, fix: repaint immediately when a tab closes on shell exit #1688, fix: parse function-key and enter bindings in config [bindings] #1689 — hot-reload, pixel-snapping, tab-bar and bindings fixes

Small features:

• feat: configurable tab title font size via navigation.tab-font-size #1681, feat: configurable tab bar height via navigation.tab-bar-height #1683 (tab bar font-size/height config), feat: add bindable togglemaximized action #1690 (togglemaximized action)

Bigger features (understand if these need more discussion — happy to adjust scope, split them up, or rework anything to fit your vision for rio):

• feat: terminal triggers (iTerm2-style regex → action rules) #1694 — terminal triggers (iTerm2-style regex → action rules)
• feat: session save/restore — tabs, splits, working dirs, scrollback #1704 — session save/restore (tabs, splits, CWDs, scrollback)

All are green on fmt/clippy/tests and rebased on current main. If any conflict by the time you get to them, ping me and I'll rebase same-day. And if some don't fit the project direction, no hard feelings — just close them.

Thanks for all the work you put into this project! 🙏