words/engine: table factory seeds block cells, not inline nodes

Root cause of the column-insert crash + "can't edit any cell". Since P5m,
`TableCell.children` holds WordsBlock[], but the slash-menu "Table" factory still
seeded cells with bare `emptyText()` (inline `text` nodes). `normalizeBlock` has
no case for `'text'` and returns undefined, so `normalizeTableCells` stored
`[undefined]` — which then crashed `getActiveMarksForSelection`'s walk and left
the cell with no real block to edit.

- built-ins.ts: wrap each seeded cell in a paragraph block (matches the demo doc,
  the callout factory, and `createTableCell`).
- normalize.ts: `normalizeTableCells` now drops children that fail to normalize
  and re-seeds an empty paragraph when none remain — self-heals any document that
  already got a malformed table from the old factory.

Pairs with the defensive guard in selection-walkers (76b0d1c8). Engine tests
430/430 pass; changed files type-check clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/uix/soma/components/words/engine/blocks/built-ins.ts

@@ -361,9 +361,23 @@ const tableSpec: WordsBlockSpec = {
 			group: 'structure',
 			create: () => ({
 				type: 'table',
+				// Cells hold BLOCKS (P5m), not inlines: seed each with an empty
+				// paragraph. Passing bare `emptyText()` (inline nodes) here makes
+				// `normalizeBlock` return undefined for the unrecognized 'text'
+				// type, corrupting the cell (crashes the mark-walk, breaks editing).
 				rows: [
-					{ cells: [{ children: emptyText() }, { children: emptyText() }] },
+					{
-					{ cells: [{ children: emptyText() }, { children: emptyText() }] }
+						cells: [
+							{ children: [{ type: 'paragraph', children: emptyText() }] },
+							{ children: [{ type: 'paragraph', children: emptyText() }] }
+						]
+					},
+					{
+						cells: [
+							{ children: [{ type: 'paragraph', children: emptyText() }] },
+							{ children: [{ type: 'paragraph', children: emptyText() }] }
+						]
+					}
 				]
 			})
 		}

src/uix/soma/components/words/engine/operations/normalize.ts

@@ -207,12 +207,16 @@ function normalizeTableCells(
 	}
 	let mutated = false;
 	const next = cells.map((cell) => {
-		// Cells hold blocks (like callout): normalize each child block; seed
+		// Cells hold blocks (like callout): normalize each child block, then
-		// an empty paragraph when the cell has none.
+		// DROP any that failed to normalize. A stray inline slot — e.g. a cell
-		const children =
+		// seeded with bare `emptyText()` by the pre-fix table factory — makes
-			cell.children.length > 0
+		// `normalizeBlock` return undefined; keeping it would crash the
-				? cell.children.map((child) => normalizeBlock(child, idGen))
+		// mark-walk and break cell editing. Re-seed an empty paragraph when
-				: seedCellChildren(idGen);
+		// nothing valid remains, so a cell always holds at least one block.
+		const mapped = cell.children
+			.map((child) => normalizeBlock(child, idGen))
+			.filter((b) => b != null);
+		const children = mapped.length > 0 ? mapped : seedCellChildren(idGen);
 		const cellId = cell.id ?? idGen();
 		const childrenChanged =
 			children.length !== cell.children.length || children.some((c, i) => c !== cell.children[i]);