fix(library): keep floating editor surfaces visible in fullscreen

[FelixTJDietrich]

Summary

Route editor-owned floating surfaces through an editor-local portal root when element-level fullscreen excludes the document body. This keeps popovers, selects, tooltips, color controls, and palette drag previews visible and interactive in subtree fullscreen without a global shared root or host-specific z-index workarounds.

Release note

Popovers, selects, tooltips, color pickers, and drag previews remain visible and interactive when an embedded editor enters fullscreen.

Implementation notes

• Each editor declaratively owns one lifecycle-bound, layout-neutral portal root.
• Surfaces continue to portal to document.body whenever body remains in the fullscreen subtree, preserving normal embedding and host dialog layering.
• Subtree fullscreen uses the editor-local root only when body is excluded by the browser's fullscreen top layer.
• The fullscreen subscription re-portals already-open surfaces when the Fullscreen API state changes.
• Multiple editors remain isolated: only the editor contained by document.fullscreenElement uses its local root.
• The shared UI tooltip now accepts Base UI's native portal container option instead of adding a parallel portal implementation.

Steps for testing

1. Run pnpm lint && pnpm format:check && pnpm build && pnpm test.
2. Run pnpm exec playwright test standalone/webapp/tests/e2e/fullscreen-portals.spec.ts.
3. In the local editor, fullscreen the editor subtree, edit a node, hover a chrome control, and drag a palette item; confirm the popover, tooltip, and drag preview stay visible.
4. Exit fullscreen and confirm floating surfaces return to the document portal.

Screenshots / screencasts

Not attached: this fixes top-layer behavior rather than static appearance. The added Playwright test exercises the behavior in a real browser.

Checklist

• Linked to a related issue (not applicable)
• Added a changeset whose summary is written in the user's voice
• PR title's Conventional Commit type matches the kind of change
• Tests added or updated
• Ran pnpm lint && pnpm format:check && pnpm build && pnpm test locally — green
• Documentation updated (not applicable)
• Screenshots or screencasts attached (behavior covered by Playwright)

[Claudia-Anthropica]

@FelixTJDietrich The editor-local portal routing is coherent for ordinary document-tree embeds, and the new coverage exercises those transitions. However, the containment check breaks when the embeddable editor is mounted inside a shadow root: fullscreen state is retargeted to the shadow host, so surfaces still portal outside the fullscreen subtree. Please resolve fullscreen state from the portal root's own tree and add shadow-DOM coverage.

[Claudia-Anthropica]

@FelixTJDietrich [medium] This check fails for editors mounted inside a shadow root. When the inner .apollon-editor enters fullscreen, document.fullscreenElement is retargeted to the shadow host, but host.contains(portalContainer) is false because shadow descendants belong to a separate node tree. The hook consequently returns document.body, leaving all floating surfaces outside the fullscreen subtree. Resolve the fullscreen element from the portal container's own getRootNode()—handling both Document and ShadowRoot—and add a shadow-root regression test.

🤖 Prompt for AI agents

In library/lib/components/ui/portalContainer.tsx, fullscreen containment is checked only against document.fullscreenElement, which is retargeted across shadow boundaries and leaves shadow-DOM editors portaling to document.body. Resolve the fullscreen element from the portal container's own root (Document or ShadowRoot) and cover a shadow-root mount in tests.

[Claudia-Anthropica]

@FelixTJDietrich The current head still resolves fullscreen exclusively through document.fullscreenElement. For an editor mounted in a shadow root, that value is retargeted to the shadow host, whose contains(portalContainer) check fails, so the prior medium finding remains unresolved and requires shadow-root-aware lookup plus regression coverage.

[Claudia-Anthropica]

@FelixTJDietrich The exact head still resolves fullscreen solely through document.fullscreenElement. For a shadow-DOM embed, that value is retargeted to the shadow host, whose contains(portalContainer) check fails, leaving floating surfaces outside the fullscreen subtree. Please use the portal container's Document or ShadowRoot fullscreen state and add shadow-root regression coverage.

[FelixTJDietrich]

Superseded by #841, which carries this work plus the rest of the fixes the Artemis integration needs on a single branch off main. Splitting the integration across two branches meant neither could be reviewed or released on its own. Closing in favour of that one.