fix: preserve stack below when deleting a top stack block

src/context_menu_items.ts

@@ -34,9 +34,7 @@ export function registerDeleteBlock() {
       if (!scope.block) {
         return
       }
-      Blockly.Events.setGroup(true)
-      scope.block.dispose(true, true)
-      Blockly.Events.setGroup(false)
+      deleteBlock(scope.block)
     },
     scopeType: Blockly.ContextMenuRegistry.ScopeType.BLOCK,
     id: 'blockDelete',
@@ -45,6 +43,28 @@ export function registerDeleteBlock() {
   Blockly.ContextMenuRegistry.registry.register(deleteOption)
 }
 
+export function deleteBlock(block: Blockly.Block) {
+  if (block.workspace.isFlyout) return
+
+  const priorGroup = Blockly.Events.getGroup()
+  Blockly.Events.setGroup(true)
+  try {
+    if (!block.outputConnection && !block.previousConnection?.isConnected()) {
+      block.nextConnection?.disconnect()
+    }
+    if (block.workspace instanceof Blockly.WorkspaceSvg) {
+      block.workspace.hideChaff()
+    }
+    if (block instanceof Blockly.BlockSvg) {
+      block.dispose(!block.outputConnection, true)
+    } else {
+      block.dispose(!block.outputConnection)
+    }
+  } finally {
+    Blockly.Events.setGroup(priorGroup)
+  }
+}
+
 function getDeletableBlocksInStack(block: Blockly.Block): Blockly.Block[] {
   let descendants = block.getDescendants(false).filter(isDeletable)
   const nextBlock = block.getNextBlock()

src/index.ts

@@ -189,6 +189,9 @@ if (!blockCommentMenuItem) {
 }
 Blockly.ContextMenuRegistry.registry.unregister('blockDelete')
 contextMenuItems.registerDeleteBlock()
+Blockly.BlockSvg.prototype.checkAndDelete = function () {
+  contextMenuItems.deleteBlock(this)
+}
 contextMenuItems.registerDuplicateBlock()
 contextMenuItems.registerCopyShortcut()
 contextMenuItems.registerCutShortcut()

tests/unit/context_menu_items.test.ts

@@ -4,7 +4,7 @@
  */
 import * as Blockly from 'blockly/core'
 import { afterAll, afterEach, assert, beforeAll, beforeEach, describe, expect, it } from 'vitest'
-import { registerDeleteBlock } from '../../src/context_menu_items'
+import { deleteBlock, registerDeleteBlock } from '../../src/context_menu_items'
 
 // Tests for the scratch-specific delete context menu override (registerDeleteBlock).
 // The copy/cut/paste override (registerDuplicateBlock, issue #3470) is tested
@@ -171,4 +171,48 @@ describe('registerDeleteBlock', () => {
       delete Blockly.Blocks.test_output_block
     }
   })
+
+  it('callback deletes only a top stack block and preserves its next block', () => {
+    const first = workspace.newBlock('test_stack_block')
+    const second = workspace.newBlock('test_stack_block')
+    const nextConn = first.nextConnection
+    const prevConn = second.previousConnection
+    assert(nextConn, 'Expected next connection')
+    assert(prevConn, 'Expected previous connection')
+    nextConn.connect(prevConn)
+
+    const item = Blockly.ContextMenuRegistry.registry.getItem('blockDelete')
+    assert(item, 'Expected blockDelete item to be registered')
+    const callback = item.callback as (scope: Blockly.ContextMenuRegistry.Scope) => void
+    callback({ block: asBlockSvg(first) })
+
+    expect(workspace.getAllBlocks(false)).toEqual([second])
+    expect(second.getParent()).toBeNull()
+  })
+
+  it('checkAndDelete override routes through deleteBlock and preserves next block', () => {
+    const first = workspace.newBlock('test_stack_block')
+    const second = workspace.newBlock('test_stack_block')
+    const nextConn = first.nextConnection
+    const prevConn = second.previousConnection
+    assert(nextConn, 'Expected next connection')
+    assert(prevConn, 'Expected previous connection')
+    nextConn.connect(prevConn)
+
+    // Mirror the wiring in src/index.ts so we cover the keyboard-delete path.
+    // Tests use plain Workspace (not WorkspaceSvg), so blocks aren't BlockSvg
+    // instances — invoke the override via prototype to simulate the call site.
+    const originalCheckAndDelete = Blockly.BlockSvg.prototype.checkAndDelete
+    Blockly.BlockSvg.prototype.checkAndDelete = function () {
+      deleteBlock(this)
+    }
+    try {
+      Blockly.BlockSvg.prototype.checkAndDelete.call(first)
+    } finally {
+      Blockly.BlockSvg.prototype.checkAndDelete = originalCheckAndDelete
+    }
+
+    expect(workspace.getAllBlocks(false)).toEqual([second])
+    expect(second.getParent()).toBeNull()
+  })
 })