[lexical-table][lexical-playground] Feature: $setTableRowIsHeader and $setTableColumnIsHeader utilities

[mayrang]

Description

Adds two public utility functions to @lexical/table for setting row-level and column-level header state: $setTableRowIsHeader(tableNode, rowIndex, isHeader) and $setTableColumnIsHeader(tableNode, colIndex, isHeader).

The playground's table action menu contained ~56 lines of inline header toggle logic — iterating the table map, deduplicating merged cells, and applying header bitmask operations. This PR extracts that logic into reusable library functions. The playground now calls these utilities in ~22 lines, and any consumer can use the same API for header manipulation without reimplementing the map iteration and merged-cell deduplication.

Both functions use $computeTableMapSkipCellCheck to build the rectangular grid map (handling colSpan/rowSpan), iterate the target row or column, deduplicate merged cells via Set<TableCellNode>, and call setHeaderStyles(state, mask) — which preserves the orthogonal header bit (e.g., setting ROW header on a COLUMN-header cell keeps the COLUMN bit intact).

Design notes

Index-based API — The functions take a numeric row/column index rather than a cell node. This matches $moveTableColumn(tableNode, colIndex, ...) and directly serves the two main use cases: toggling from a context menu (index available via $getTableRowIndexFromTableCellNode) and restoring headers after row/column insertion (index known from the insertion point). A cell-based convenience is trivial to add on top if needed.

set over toggle — The isHeader: boolean parameter explicitly sets state rather than toggling. This avoids ambiguity with merged cells spanning header/non-header rows and is safer for post-insertion restoration where the caller knows the desired state. Toggle is a one-liner at the call site: $setTableRowIsHeader(table, row, !cell.hasHeaderState(TableCellHeaderStates.ROW)).

Closes #8812

Test plan

• 14 new unit tests covering: set/clear header, preserve orthogonal bits, colSpan, rowSpan, middle row/column, out-of-range invariant, BOTH→clear single bit
• npm run test-unit — 3697 passed (211 test files)
• E2E gate — 768 passed (chromium)
• Manual playground (Chrome, Firefox, Safari):
  • Toggle row/column header on/off via context menu
  • Merged cells across header boundaries update correctly
  • Toggling one axis preserves the other axis's header state

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Project	Deployment	Actions	Updated (UTC)
lexical	Ready	Preview	Jul 8, 2026 2:09pm
lexical-playground	Ready	Preview	Jul 8, 2026 2:09pm