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Slate v2 rootless explicit selections must not inherit sibling roots

docs/solutions/runtime-errors/2026-05-23-slate-v2-rootless-explicit-selections-must-not-inherit-sibling-root.md

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Original Source

Slate v2 rootless explicit selections must not inherit sibling roots

Problem

After focusing a non-main root, clicking a later paragraph in the main root could store the main path under the previous root. A header-root marks read then tried to resolve [1,0] inside the header tree and crashed.

Symptoms

  • Runtime overlay: Cannot find a descendant at path [1,0].
  • Header then body click produced a body focus but a roots:header set_selection commit.
  • The crash stack passed through state.marks.get() in runtime-root-engine.ts.

What Didn't Work

  • Only fixing useSlateActiveRoot. That removed a selector rerender loop, but did not change how rootless explicit selection targets were rooted.
  • Treating the issue as example-owned focus repair. The bad root was created in the core runtime transaction path before the example could recover.

Solution

Keep current-selection-root fallback for implicit edits, but do not let it root an explicit rootless location on the base runtime. Rootless explicit locations on the runtime mean main; root-bound views still stamp their view root through the active operation root.

ts
const getLocationMutationRoot = (
  editor: Editor,
  location: Location
): string | undefined =>
  getExplicitLocationRoot(location) ??
  getActiveMutationRoot(editor) ??
  MAIN_ROOT_KEY

Also avoid wrapping a plain editor.update in the current selection root. The per-mutation root resolver already handles implicit operations that should follow the current selection.

Why This Works

There are two different cases:

  • Implicit mutation: tx.text.insert('x') should follow the current selection root.
  • Explicit rootless location: tx.selection.set({ path: [1, 0], offset: 0 }) on the base runtime should target main.

The bug came from collapsing both cases into "current selection root". Splitting them lets main-root DOM selection imports replace a previous header selection instead of storing a main path under header ownership.

Prevention

  • Add a core runtime/view contract before patching React symptoms.
  • Test the exact root transition: header selection first, then rootless explicit runtime selection at a main-only path.
  • Assert both the public selection shape and view marks reads; marks catch the stale-root/path mismatch that focus checks miss.