diff --git a/core-web/libs/block-editor/src/lib/shared/utils/parser.utils.spec.ts b/core-web/libs/block-editor/src/lib/shared/utils/parser.utils.spec.ts
new file mode 100644
index 000000000000..27de53b4778f
--- /dev/null
+++ b/core-web/libs/block-editor/src/lib/shared/utils/parser.utils.spec.ts
@@ -0,0 +1,166 @@
+import { JSONContent } from '@tiptap/core';
+
+import { getBlockMap, purifyNodeTree, removeInvalidNodes } from './parser.utils';
+
+describe('parser.utils', () => {
+    describe('getBlockMap', () => {
+        it('should always include the basic nodes (paragraph, text, doc, hardBreak)', () => {
+            const map = getBlockMap(['heading']);
+
+            expect(map.paragraph).toBe(true);
+            expect(map.text).toBe(true);
+            expect(map.doc).toBe(true);
+            expect(map.hardBreak).toBe(true);
+        });
+
+        it('should expand related content dependencies (e.g. table)', () => {
+            const map = getBlockMap(['table']);
+
+            expect(map.table).toBe(true);
+            expect(map.tableRow).toBe(true);
+            expect(map.tableHeader).toBe(true);
+            expect(map.tableCell).toBe(true);
+        });
+
+        it('should add plain allowed blocks as-is', () => {
+            const map = getBlockMap(['heading', 'blockquote']);
+
+            expect(map.heading).toBe(true);
+            expect(map.blockquote).toBe(true);
+        });
+    });
+
+    describe('purifyNodeTree', () => {
+        it('should drop nodes whose type is not in the block map', () => {
+            const content: JSONContent[] = [
+                { type: 'paragraph', content: [{ type: 'text', text: 'keep' }] },
+                { type: 'blockquote', content: [{ type: 'text', text: 'drop' }] }
+            ];
+
+            const result = purifyNodeTree(content, getBlockMap(['paragraph']));
+
+            expect(result).toHaveLength(1);
+            expect(result[0].type).toBe('paragraph');
+        });
+
+        it('should preserve hardBreak nodes nested inside a paragraph', () => {
+            const content: JSONContent[] = [
+                {
+                    type: 'paragraph',
+                    content: [
+                        { type: 'text', text: 'line 1' },
+                        { type: 'hardBreak' },
+                        { type: 'text', text: 'line 2' }
+                    ]
+                }
+            ];
+
+            const result = purifyNodeTree(content, getBlockMap(['paragraph']));
+
+            expect(result[0].content).toHaveLength(3);
+            expect(result[0].content[1].type).toBe('hardBreak');
+        });
+
+        it('should keep a heading whose composite level key is allowed', () => {
+            const content: JSONContent[] = [
+                { type: 'heading', attrs: { level: 2 }, content: [{ type: 'text', text: 'title' }] }
+            ];
+
+            const result = purifyNodeTree(content, getBlockMap(['heading2']));
+
+            expect(result).toHaveLength(1);
+            expect(result[0].type).toBe('heading');
+        });
+
+        it('should strip a heading whose level is not in the allowed composite keys', () => {
+            const content: JSONContent[] = [
+                { type: 'heading', attrs: { level: 3 }, content: [{ type: 'text', text: 'title' }] }
+            ];
+
+            const result = purifyNodeTree(content, getBlockMap(['heading2']));
+
+            expect(result).toHaveLength(0);
+        });
+    });
+
+    describe('removeInvalidNodes', () => {
+        // Regression for #35985: hard breaks were stripped when re-opening
+        // content for editing on a Block Editor field with allowed-block
+        // restrictions (allowedBlocks.length > 1).
+        it('should keep hardBreak nodes on a restricted-blocks field', () => {
+            const allowedBlocks = ['heading', 'paragraph', 'orderedList'];
+            const content: JSONContent = {
+                type: 'doc',
+                content: [
+                    {
+                        type: 'paragraph',
+                        content: [
+                            { type: 'text', text: '123 Main St' },
+                            { type: 'hardBreak' },
+                            { type: 'text', text: 'Suite 100' },
+                            { type: 'hardBreak' },
+                            { type: 'text', text: 'Springfield' }
+                        ]
+                    }
+                ]
+            };
+
+            const result = removeInvalidNodes(content, allowedBlocks);
+
+            const paragraph = result[0];
+            expect(paragraph.type).toBe('paragraph');
+
+            const hardBreaks = paragraph.content.filter((node) => node.type === 'hardBreak');
+            expect(hardBreaks).toHaveLength(2);
+        });
+
+        it('should accept a bare JSONContent array as input (not just a doc node)', () => {
+            const allowedBlocks = ['heading', 'paragraph'];
+            const content: JSONContent[] = [
+                {
+                    type: 'paragraph',
+                    content: [
+                        { type: 'text', text: 'line 1' },
+                        { type: 'hardBreak' },
+                        { type: 'text', text: 'line 2' }
+                    ]
+                }
+            ];
+
+            const result = removeInvalidNodes(content, allowedBlocks);
+
+            expect(result).toHaveLength(1);
+            expect(result[0].type).toBe('paragraph');
+            expect(result[0].content.filter((node) => node.type === 'hardBreak')).toHaveLength(1);
+        });
+
+        it('should keep paragraph nodes via the basic-node fallback even when not in allowedBlocks', () => {
+            const allowedBlocks = ['heading', 'orderedList'];
+            const content: JSONContent = {
+                type: 'doc',
+                content: [{ type: 'paragraph', content: [{ type: 'text', text: 'plain text' }] }]
+            };
+
+            const result = removeInvalidNodes(content, allowedBlocks);
+
+            expect(result).toHaveLength(1);
+            expect(result[0].type).toBe('paragraph');
+        });
+
+        it('should still strip nodes that are neither basic nor allowed', () => {
+            const allowedBlocks = ['heading', 'paragraph'];
+            const content: JSONContent = {
+                type: 'doc',
+                content: [
+                    { type: 'paragraph', content: [{ type: 'text', text: 'keep' }] },
+                    { type: 'codeBlock', content: [{ type: 'text', text: 'drop' }] }
+                ]
+            };
+
+            const result = removeInvalidNodes(content, allowedBlocks);
+
+            expect(result).toHaveLength(1);
+            expect(result[0].type).toBe('paragraph');
+        });
+    });
+});
diff --git a/core-web/libs/block-editor/src/lib/shared/utils/parser.utils.ts b/core-web/libs/block-editor/src/lib/shared/utils/parser.utils.ts
index 1cff0e148c02..dd76e469075c 100644
--- a/core-web/libs/block-editor/src/lib/shared/utils/parser.utils.ts
+++ b/core-web/libs/block-editor/src/lib/shared/utils/parser.utils.ts
@@ -1,5 +1,7 @@
 import { Content, JSONContent } from '@tiptap/core';
 
+import { NodeTypes } from './constants.utils';
+
 interface BlockMap {
     [key: string]: boolean;
 }
@@ -32,7 +34,16 @@ const video: BlockMap = {
     youtube: true
 };
 
-const basicNodes: BlockMap = { paragrah: true, text: true, doc: true };
+// Nodes that are always allowed regardless of the field's allowed-block
+// restrictions. `hardBreak` (Shift+Enter line break) must live here so
+// `purifyNodeTree`/`removeInvalidNodes` never strips it when content is
+// re-opened for editing on a restricted field.
+const basicNodes: BlockMap = {
+    [NodeTypes.PARAGRAPH]: true,
+    [NodeTypes.TEXT]: true,
+    [NodeTypes.DOC]: true,
+    [NodeTypes.HARD_BREAK]: true
+};
 
 const gridContent: BlockMap = {
     gridBlock: true,