feat(layouts): toggle-delete when clicking same brush-piece

Clicking a square with the palette's currently-selected piece now
deletes that piece instead of re-placing it. Makes tap-to-delete a
natural single-gesture operation without switching to the Erase
brush. A different brush-piece still replaces (unchanged behaviour).

packages/chess/e2e/layouts.spec.ts

@@ -157,6 +157,51 @@ test.describe('LayoutEditor modal', () => {
     ).toHaveCount(0);
   });
 
+  test('clicking a square with the same brush-piece toggles it off (delete)', async ({
+    page,
+  }) => {
+    // Place a white king on e1 using the palette brush.
+    await page.getByTestId('palette-white-king').click();
+    await page.getByTestId('editor-square-4').click();
+    await expect(
+      page.getByTestId('editor-square-4').locator('img'),
+    ).toBeVisible();
+
+    // Same brush still selected — clicking the same square should
+    // TOGGLE the piece off instead of no-op / re-place.
+    await page.getByTestId('editor-square-4').click();
+    await expect(
+      page.getByTestId('editor-square-4').locator('img'),
+    ).toHaveCount(0);
+
+    // Clicking a 3rd time with the same brush re-adds the piece.
+    await page.getByTestId('editor-square-4').click();
+    await expect(
+      page.getByTestId('editor-square-4').locator('img'),
+    ).toBeVisible();
+  });
+
+  test('clicking a square with a DIFFERENT brush-piece replaces (does NOT delete)', async ({
+    page,
+  }) => {
+    // Place a white king on e1.
+    await page.getByTestId('palette-white-king').click();
+    await page.getByTestId('editor-square-4').click();
+
+    // Switch brush to black queen and click the same square — piece
+    // should be REPLACED, not deleted (only same-piece clicks toggle).
+    await page.getByTestId('palette-black-queen').click();
+    await page.getByTestId('editor-square-4').click();
+    await expect(
+      page.getByTestId('editor-square-4').locator('img'),
+    ).toBeVisible();
+    // Alt text reflects the new piece (black queen), proving a
+    // replacement happened rather than a same-piece toggle.
+    await expect(
+      page.getByTestId('editor-square-4').locator('img'),
+    ).toHaveAttribute('alt', 'black queen');
+  });
+
   test('FEN Load replaces the board', async ({ page }) => {
     const fen = '8/8/8/8/8/8/8/4K2k'; // white king e1, black king h1 (not a realistic position but valid)
     await page.getByTestId('editor-fen').fill(fen);

packages/chess/src/ui/LayoutEditor.tsx

@@ -147,8 +147,21 @@ export function LayoutEditor({
   function placeAt(square: number) {
     if (brush.type === 'none') return;
     setPlacements((prev) => {
+      const existing = prev.find((p) => p.square === square);
       const filtered = prev.filter((p) => p.square !== square);
       if (brush.type === 'erase') return filtered;
+      // Toggle-delete: clicking a square that already holds the
+      // exact piece the brush would place acts as an erase. This
+      // lets users tap-to-delete with the palette selection without
+      // first switching to the Erase brush — the same gesture that
+      // placed a piece undoes it.
+      if (
+        existing !== undefined &&
+        existing.type === brush.piece.type &&
+        existing.color === brush.piece.color
+      ) {
+        return filtered;
+      }
       return [
         ...filtered,
         { type: brush.piece.type, color: brush.piece.color, square },