Table handles assume any hovered TD/TH belongs to a table block — crashes on custom blocks that render a real <table> #2964

Summary

TableHandlesView.mouseMoveHandler decides a block is a table from the DOM alone, then checks only that the schema contains a table block — never that the hovered block is one. Any custom block that renders a real <table> therefore ends up on the table path, and reading its content throws.

Still present in 0.53.0 (found on 0.51.4, verified the same code in the latest).

Where

packages/core/src/extensions/TableHandles/TableHandles.ts

// L212 — the block is decided by walking up the DOM to a TD/TH
const target = domCellAround(event.target);
…
// L262
if (!pmNodeInfo) throw new Error(`Block with ID ${blockEl.id} not found`);
…
// L274 — asks whether the *schema* has a table, not whether *this block* is one
if (editorHasBlockWithType(this.editor, "table")) {
  this.tablePos = …;
  tableBlock = block;
}
…
// L339
colIndex === tableBlock.content.rows[0].cells.length - 1,

domCellAround returns {type: "cell"} for any TD/TH. Its .ProseMirror bail-out never runs when the event target already is a cell, so nothing an integrator puts on an ancestor can opt out.

Two ways this fires

1. A custom block with content: "none" that renders a table → block.content is undefined:

Uncaught TypeError: Cannot read properties of undefined (reading 'rows')

Merely moving the mouse across the cells is enough — no click, no edit. In our app (an embedded database view drawn inside a document) this filled the console with one error per mouse move.

2. A table inside a nested editor (our synced-block feature embeds a second BlockNote editor in a custom block). The cell belongs to the inner editor, but the outer editor's handler still matches it because this.pmView.dom.contains(event.target) is true, and the id is unknown to the outer document:

Uncaught Error: Block with ID <id> not found

Minimal reproduction

1. Add a custom block spec with content: "none" whose render function returns a plain <table><tbody><tr><td>x</td></tr></tbody></table>.
2. Insert it into a document.
3. Move the mouse over the cell.

Suggested fix

After resolving the hovered block, check the block itself rather than the schema — e.g. block.type === "table" (or checkBlockIsDefaultType("table", block, this.editor)) — and return early otherwise. The same early return would cover the nested-editor case if the id lookup fails instead of throwing.

Workaround we are using

We wrap mouseMoveHandler and, when the cell is not a real table cell of this editor, call the original with the event's target proxied to the editor root: domCellAround then stops at .ProseMirror and reports "no table", which is the path that hides the handles. Swallowing the event instead is not viable — column resizing listens on window, so stopPropagation breaks it.

Related: #1411 (the colIndex variant, closed without a reproduction).