Summary

• render the authored Workspace Glyph Grid through deterministic fixed 256-root Slug pages
• retain coherent Grid frames across source, axis and structural invalidation
• keep Grid cell/row geometry fixed and shrink only oversized outlines
• cache pages in a disposable Zstd CachedAtlas with integrity checks, atomic publication, carry-forward, retry-safe staging and a one-GiB LRU
• stream cached/native page bytes with bounded backpressure and install page sets atomically
• add real Electron GPU coverage for variable replacement, distant topology, scrolling and fixed-cell fitting

Product-boundary update

Source Han TTF is no longer this PR's representative authored-workspace acceptance fixture. Direct TTF/VF preview is now tracked by #143 and will bypass authored Shift conversion and SQLite entirely.

The pushed branch still implements visible-first/background page scheduling. The local working tree contains an uncommitted candidate that replaces visibleBuild/completeBuild with one complete atlasBuild, removes Visible readiness, and performs no atlas acquisition during scrolling.

Before that scheduler is committed:

1. run release-native cold/warm complete residency on Hahmlet, Zen Kaku Gothic and M+ Kanji;
2. separate native compile, packing, cache publication, transfer, GPU upload and first-frame phases;
3. keep complete-before-present only if those representative authored fixtures pass the reviewed product gate;
4. otherwise split scheduling from the proven fixed-page/cache/atomic foundation.

Do not use the flat 65,535-glyph Source Han TTF to force scheduling policy for 5–12k-glyph authored sources.

Verification completed on pushed/current work

• Rust Slug/bridge tests and clippy
• desktop tests
• typecheck, lint and formatting
• real macOS Electron GPU Grid suite
• visual home suite with no intentional snapshot changes
• manual Source Han cache measurement: 42.84 MiB artifact, about 516 ms median all-page cache load, about 1.067 s renderer-connect to complete warm frame

Current complete-scheduler working-tree validation additionally passed desktop, focused/full GPU Grid and visual tests locally. It remains uncommitted pending authored-fixture release measurement.

Stack

Draft stacked on #171. Retarget/rebase after #171 lands.

Out of scope:

• direct TTF/VF preview (Open TTF/VF as direct read-only binary previews #143)
• foreign-source first-Save conversion (Open convertible sources lazily and materialize .shift on first Save #154)
• VARC shared geometry (Measure and preserve VARC shared-component residency #175)
• native .shift physical storage/fingerprint changes (Reuse verified .shift identity across save and reopen #174 and the native document stack)