[codex] Hold Codex repaints through grid resize

[forketyfork]

Summary

• Reuse a populated same-mode render cache while a Codex output hold is active, even if the grid animation changes the cell's pixel size.
• Keep terminal resize holds alive until GridResizing finishes, so Codex cannot repaint live through the intermediate animated widths.
• Drop the per-cell DEC 2026 sweep overlay before publishing because short holds looked like flicker. The existing quit overlay stays as it was.

Root cause

The new-terminal path already started resize holds, but those holds could expire while the grid resize animation was still running. Once the hold expired, Codex could enter DEC 2026 with resize_hold_active=false, and the renderer refreshed live at a sequence of animated cell widths. That was the scroll-through-history window.

Validation

• nix develop -c zig build --summary all
• nix develop -c zig build test --summary all
• nix develop -c just lint
• Checked the latest Architect log: hold release now happens after grid-debug resize-complete, and cache refreshes happen at stable final cell sizes.

[Copilot]

Pull request overview

This PR updates the rendering and runtime hold logic so Codex output holds can continue to reuse an already-populated render cache through grid resize animations (where a cell’s pixel size changes over time), preventing live repaints during intermediate animated widths.

Changes:

• Relax the held-cache reuse check to depend on “same render mode + populated texture” rather than exact pixel dimensions.
• Prevent terminal resize holds from expiring while the UI is in GridResizing, so holds survive the full resize animation.
• Update architecture documentation to reflect same-mode cache reuse across pixel-size changes during holds.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/render/renderer.zig	Allows held cached textures to be reused across rect size changes (same render mode), and updates the related unit test.
src/app/runtime.zig	Skips expiring terminal resize holds during GridResizing to avoid holds dropping mid-animation.
docs/ARCHITECTURE.md	Documents the updated hold/cache behavior during resize/grid animations.

Comments suppressed due to low confidence (1)

src/render/renderer.zig:957

• shouldHoldSessionCacheRefresh no longer checks that the cached texture dimensions match rect, which allows held rendering during grid resize. However, when wave_effect is non-null the hold path calls renderWaveStrips(renderer, tex, rect, ...), and renderWaveStrips uses rect.w/h to build the source rectangles (e.g. src_rect.w = tile_w, src_rect.y = src_y). If the cached texture size differs from rect (now allowed), the source rects can extend past the texture bounds, producing incorrect/partial rendering during a hold.

Suggested fix: either (a) make the hold path disable wave strips when the cache texture size != rect (fall back to renderCachedTexture), or (b) update renderWaveStrips to query the texture size (e.g. SDL_GetTextureSize) and map strip source coordinates proportionally to the texture dimensions.

    const tex = cache_entry.texture orelse return false;
    if (wave_effect) |wave| {
        renderWaveStrips(renderer, tex, rect, wave.elapsed_ms, wave.amplitude, wave.total_ms);
    } else {
        renderCachedTexture(renderer, tex, rect);

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