[wieslawsoltes]

Problem and resulting behavior

Code OSS creates Markdown Preview overlays after the workbench loads and assigns top, left, width, and height through JavaScript style named setters. In the exact signed AppScene package, the editor anchors measure 792×857 and 396×822, but the overlay and iframe remain 0×0. WebScene retained these anchor functions from stylesheets and setProperty(), but lost them through named setters and again when a detached element was attached and recascaded. This change retains the six inset/size functions and restores only authored inline anchor functions during recascade. Ordinary nodes avoid the extra authored-style lookups.

The product-neutral contract creates an anchor and fixed overlay through CSSOM, then checks resize, movement, replacement/restoration, right/bottom insets, and 64 panel moves. No Code OSS source change is needed. This is the focused engine fix for #903; keep #903 open until the exact rebuilt SDK/CLI app paints Markdown and passes visual, lifecycle, and idle-CPU acceptance.

Validation

• Chrome headless dynamic CSSOM contract: 9/9 assertions pass.
• Native V8 Release before fix: 2/9 pass; after fix: 9/9 pass.
• Existing native anchor geometry contract: 9/9 pass.
• Both native and Chrome dynamic contracts keep 64 move cycles below the 500 ms fixture budget.
• Native engine Release dylib rebuilt successfully.

Details: docs/validation/css-anchor-cssom-903-20260922.md.