diff --git a/lib/cypress.config.ts b/lib/cypress.config.ts
index 5db7fe24..b0334c4e 100644
--- a/lib/cypress.config.ts
+++ b/lib/cypress.config.ts
@@ -6,6 +6,6 @@ export default defineConfig({
       framework: 'react',
       bundler: 'vite',
     },
-    specPattern: ['**/**/*.cy.{ts,tsx}'],
+    specPattern: 'cypress/component/**/*.cy.{ts,tsx}',
   },
 })
diff --git a/lib/cypress/component/TipTap/Hashtag.cy.tsx b/lib/cypress/component/TipTap/Hashtag.cy.tsx
new file mode 100644
index 00000000..83753c07
--- /dev/null
+++ b/lib/cypress/component/TipTap/Hashtag.cy.tsx
@@ -0,0 +1,172 @@
+/// <reference types="cypress" />
+import { mount } from 'cypress/react'
+
+import { TestEditorWithRouter, createTestTag } from './TestEditor'
+
+import type { Editor } from '@tiptap/core'
+
+describe('Hashtag Extension', () => {
+  describe('Hashtag Parsing', () => {
+    it('parses simple hashtag in markdown', () => {
+      const content = 'Hello #world'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.hashtag').should('exist')
+      cy.get('.hashtag').should('contain.text', '#world')
+    })
+
+    it('parses multiple hashtags', () => {
+      const content = '#one #two #three'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.hashtag').should('have.length', 3)
+    })
+
+    it('parses hashtag with numbers', () => {
+      const content = 'Check out #tag123'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.hashtag').should('contain.text', '#tag123')
+    })
+
+    // Note: The regex in Hashtag.tsx includes underscores: /^#([a-zA-Z0-9À-ÖØ-öø-ʸ_-]+)/
+    it('parses hashtag with underscore', () => {
+      const content = 'See #my_tag here'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      // decodeTag() converts underscores to non-breaking spaces (\u00A0) for display
+      cy.get('.hashtag').should('exist')
+      cy.get('.hashtag').should('contain.text', '#my\u00A0tag')
+    })
+
+    it('parses hashtag with hyphen', () => {
+      const content = 'Find #my-tag'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.hashtag').should('contain.text', '#my-tag')
+    })
+
+    it('parses unicode hashtag (German umlauts)', () => {
+      const content = 'Visit #München'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.hashtag').should('contain.text', '#München')
+    })
+  })
+
+  describe('Hashtag Styling', () => {
+    it('applies color from known tag', () => {
+      const tags = [createTestTag('nature', '#22C55E')]
+      const content = 'Love #nature'
+
+      mount(<TestEditorWithRouter content={content} tags={tags} />)
+
+      cy.get('.hashtag')
+        .should('have.css', 'color')
+        .and('match', /rgb\(34, 197, 94\)|#22[cC]55[eE]/)
+    })
+
+    it('uses inherit color for unknown tag', () => {
+      const content = 'Unknown #sometag'
+
+      mount(<TestEditorWithRouter content={content} tags={[]} />)
+
+      cy.get('.hashtag').should('exist')
+      // Unknown tags should use inherit
+      cy.get('.hashtag').should('have.css', 'color')
+    })
+
+    it('has bold font weight', () => {
+      const content = '#test'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.hashtag').should('have.class', 'tw:font-bold')
+    })
+  })
+
+  describe('Hashtag Click Behavior', () => {
+    it('calls onTagClick when clicked in view mode', () => {
+      const tags = [createTestTag('clickme', '#3B82F6')]
+      const onTagClick = cy.stub().as('tagClickHandler')
+      const content = '#clickme'
+
+      mount(
+        <TestEditorWithRouter
+          content={content}
+          tags={tags}
+          onTagClick={onTagClick}
+          editable={false}
+        />,
+      )
+
+      cy.get('.hashtag').click()
+      cy.get('@tagClickHandler').should('have.been.calledOnce')
+    })
+
+    it('does NOT call onTagClick when clicked in edit mode', () => {
+      const tags = [createTestTag('clickme', '#3B82F6')]
+      const onTagClick = cy.stub().as('tagClickHandler')
+      const content = '#clickme'
+
+      mount(
+        <TestEditorWithRouter
+          content={content}
+          tags={tags}
+          onTagClick={onTagClick}
+          editable={true}
+        />,
+      )
+
+      cy.get('.hashtag').click()
+      cy.get('@tagClickHandler').should('not.have.been.called')
+    })
+
+    it('shows pointer cursor in view mode', () => {
+      const content = '#test'
+
+      mount(<TestEditorWithRouter content={content} editable={false} />)
+
+      cy.get('.hashtag').should('have.css', 'cursor', 'pointer')
+    })
+
+    it('shows text cursor in edit mode', () => {
+      const content = '#test'
+
+      mount(<TestEditorWithRouter content={content} editable={true} />)
+
+      cy.get('.hashtag').should('have.css', 'cursor', 'text')
+    })
+  })
+
+  describe('Markdown Serialization (Roundtrip)', () => {
+    it('serializes hashtag back to markdown', () => {
+      const content = 'Hello #world'
+      let editorInstance: Editor
+
+      mount(
+        <TestEditorWithRouter
+          content={content}
+          onReady={(editor) => {
+            editorInstance = editor
+          }}
+        />,
+      )
+
+      cy.get('.hashtag')
+        .should('exist')
+        .then(() => {
+          // TipTap with Markdown extension exposes getMarkdown() directly on editor
+          const markdown = editorInstance.getMarkdown()
+          expect(markdown).to.include('#world')
+          return null
+        })
+    })
+  })
+})
diff --git a/lib/cypress/component/TipTap/ItemMention.cy.tsx b/lib/cypress/component/TipTap/ItemMention.cy.tsx
new file mode 100644
index 00000000..19599b4d
--- /dev/null
+++ b/lib/cypress/component/TipTap/ItemMention.cy.tsx
@@ -0,0 +1,168 @@
+/// <reference types="cypress" />
+import { mount } from 'cypress/react'
+
+import { TestEditorWithRouter, createTestItem } from './TestEditor'
+
+import type { Editor } from '@tiptap/core'
+
+describe('ItemMention Extension', () => {
+  describe('Item Mention Parsing', () => {
+    // Note: Item IDs are UUIDs (hex format: [a-fA-F0-9-])
+    // Example real UUID: "144e379c-b719-4334-9f0e-de277d3b6d0f"
+
+    it('parses standard item mention with UUID', () => {
+      // Using realistic UUID format
+      const content = 'Thanks [@Alice](/item/144e379c-b719-4334-9f0e-de277d3b6d0f)'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.item-mention').should('exist')
+      cy.get('.item-mention').should('contain.text', '@Alice')
+    })
+
+    it('parses item mention with layer path (legacy format)', () => {
+      // The regex: /^\[@([^\]]+?)\]\(\/item\/(?:[^/]+\/)?([a-fA-F0-9-]+)\)/
+      // Captures layer name as optional non-capturing group, then hex UUID
+      const content = 'See [@Bob](/item/people/efe00aaa-8b14-47b5-a032-3e0560980c1e)'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.item-mention').should('exist')
+      cy.get('.item-mention').should('contain.text', '@Bob')
+    })
+
+    it('parses multiple item mentions', () => {
+      const content = '[@Alice](/item/aaa-111) and [@Bob](/item/bbb-222)'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.item-mention').should('have.length', 2)
+    })
+
+    it('parses item mention with spaces in label', () => {
+      const content = 'Contact [@Max Müller](/item/abc-123-def)'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.item-mention').should('contain.text', '@Max Müller')
+    })
+
+    it('parses item mention with uppercase UUID', () => {
+      // UUIDs are case-insensitive, regex uses [a-fA-F0-9-]
+      const content = '[@Name](/item/ABC-DEF-123)'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.item-mention').should('exist')
+    })
+  })
+
+  describe('Item Mention Styling', () => {
+    it('applies color from known item', () => {
+      const items = [createTestItem('abc-123', 'Alice', '#EF4444')]
+      const content = '[@Alice](/item/abc-123)'
+
+      mount(<TestEditorWithRouter content={content} items={items} />)
+
+      cy.get('.item-mention')
+        .should('have.css', 'color')
+        .and('match', /rgb\(239, 68, 68\)|#[eE][fF]4444/)
+    })
+
+    it('uses getItemColor function when provided', () => {
+      const items = [createTestItem('abc-123', 'Alice')]
+      const getItemColor = () => '#8B5CF6' // Purple
+      const content = '[@Alice](/item/abc-123)'
+
+      mount(<TestEditorWithRouter content={content} items={items} getItemColor={getItemColor} />)
+
+      cy.get('.item-mention')
+        .should('have.css', 'color')
+        .and('match', /rgb\(139, 92, 246\)|#8[bB]5[cC][fF]6/)
+    })
+
+    it('uses fallback color for unknown item', () => {
+      // UUID must be hex characters only: [a-fA-F0-9-]
+      const content = '[@Unknown](/item/aaa-bbb-ccc-111)'
+
+      mount(<TestEditorWithRouter content={content} items={[]} />)
+
+      // Should still render, using fallback color
+      cy.get('.item-mention').should('exist')
+    })
+
+    it('has bold font weight', () => {
+      const content = '[@Test](/item/123)'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.item-mention').should('have.class', 'tw:font-bold')
+    })
+  })
+
+  describe('Item Mention Click Behavior', () => {
+    it('shows pointer cursor in view mode', () => {
+      const content = '[@Alice](/item/123)'
+
+      mount(<TestEditorWithRouter content={content} editable={false} />)
+
+      cy.get('.item-mention').should('have.css', 'cursor', 'pointer')
+    })
+
+    it('shows text cursor in edit mode', () => {
+      const content = '[@Alice](/item/123)'
+
+      mount(<TestEditorWithRouter content={content} editable={true} />)
+
+      cy.get('.item-mention').should('have.css', 'cursor', 'text')
+    })
+
+    // Note: Navigation behavior uses react-router's useNavigate
+    // Full navigation testing would require more complex setup
+  })
+
+  describe('Markdown Serialization (Roundtrip)', () => {
+    it('serializes item mention back to markdown', () => {
+      const content = '[@Alice](/item/abc-123)'
+      let editorInstance: Editor
+
+      mount(
+        <TestEditorWithRouter
+          content={content}
+          onReady={(editor) => {
+            editorInstance = editor
+          }}
+        />,
+      )
+
+      cy.get('.item-mention')
+        .should('exist')
+        .then(() => {
+          const markdown = editorInstance.getMarkdown()
+          expect(markdown).to.include('[@Alice](/item/abc-123)')
+          return null
+        })
+    })
+  })
+
+  describe('Edge Cases', () => {
+    it('does not parse regular links without @', () => {
+      const content = '[Alice](/item/123)'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      // Should be a regular link, not an item mention
+      cy.get('.item-mention').should('not.exist')
+      cy.get('a').should('contain.text', 'Alice')
+    })
+
+    it('does not parse @ links to non-item paths', () => {
+      const content = '[@Alice](/profile/123)'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      // Should be a regular link, not an item mention
+      cy.get('.item-mention').should('not.exist')
+    })
+  })
+})
diff --git a/lib/cypress/component/TipTap/TestEditor.tsx b/lib/cypress/component/TipTap/TestEditor.tsx
new file mode 100644
index 00000000..391a97a5
--- /dev/null
+++ b/lib/cypress/component/TipTap/TestEditor.tsx
@@ -0,0 +1,106 @@
+import { Image } from '@tiptap/extension-image'
+import { Link } from '@tiptap/extension-link'
+import { Markdown } from '@tiptap/markdown'
+import { EditorContent, useEditor } from '@tiptap/react'
+import { StarterKit } from '@tiptap/starter-kit'
+import { useEffect } from 'react'
+import { MemoryRouter } from 'react-router-dom'
+
+import { Hashtag, ItemMention, VideoEmbed } from '#components/TipTap/extensions'
+import { createConfiguredMarked } from '#components/TipTap/utils/configureMarked'
+
+import type { Item } from '#types/Item'
+import type { Tag } from '#types/Tag'
+import type { Editor } from '@tiptap/core'
+
+const configuredMarked = createConfiguredMarked()
+
+export interface TestEditorProps {
+  content: string
+  editable?: boolean
+  tags?: Tag[]
+  onTagClick?: (tag: Tag) => void
+  items?: Item[]
+  getItemColor?: (item: Item | undefined, fallback?: string) => string
+  onReady?: (editor: Editor) => void
+  testId?: string
+}
+
+export function TestEditor({
+  content,
+  editable = false,
+  tags = [],
+  onTagClick,
+  items = [],
+  getItemColor,
+  onReady,
+  testId = 'test-editor',
+}: TestEditorProps) {
+  const editor = useEditor({
+    extensions: [
+      StarterKit.configure({
+        bulletList: { keepMarks: true, keepAttributes: false },
+        orderedList: { keepMarks: true, keepAttributes: false },
+      }),
+      Markdown.configure({
+        marked: configuredMarked,
+      }),
+      Image,
+      Link,
+      VideoEmbed,
+      Hashtag.configure({
+        tags,
+        onTagClick,
+      }),
+      ItemMention.configure({
+        items,
+        getItemColor,
+      }),
+    ],
+    content,
+    contentType: 'markdown',
+    editable,
+  })
+
+  useEffect(() => {
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition -- editor can be null initially
+    if (editor && onReady) {
+      onReady(editor)
+    }
+  }, [editor, onReady])
+
+  // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition -- editor can be null initially
+  if (!editor) {
+    return null
+  }
+
+  return (
+    <div data-testid={testId} className='test-editor-wrapper'>
+      <EditorContent editor={editor} />
+    </div>
+  )
+}
+
+export function TestEditorWithRouter(props: TestEditorProps) {
+  return (
+    <MemoryRouter>
+      <TestEditor {...props} />
+    </MemoryRouter>
+  )
+}
+
+export function createTestTag(name: string, color = '#3B82F6'): Tag {
+  return {
+    id: `tag-${name}`,
+    name,
+    color,
+  } as Tag
+}
+
+export function createTestItem(id: string, name: string, color = '#10B981'): Item {
+  return {
+    id,
+    name,
+    color,
+  } as Item
+}
diff --git a/lib/cypress/component/TipTap/VideoEmbed.cy.tsx b/lib/cypress/component/TipTap/VideoEmbed.cy.tsx
new file mode 100644
index 00000000..8f5cc05f
--- /dev/null
+++ b/lib/cypress/component/TipTap/VideoEmbed.cy.tsx
@@ -0,0 +1,288 @@
+/// <reference types="cypress" />
+import { mount } from 'cypress/react'
+
+import { TestEditorWithRouter } from './TestEditor'
+
+import type { Editor } from '@tiptap/core'
+
+describe('VideoEmbed Extension', () => {
+  describe('YouTube Video Parsing', () => {
+    it('parses YouTube standard URL autolink to video embed', () => {
+      const content = '<https://www.youtube.com/watch?v=dQw4w9WgXcQ>'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      // Should render as iframe, not as text
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('iframe.video-embed')
+        .should('have.attr', 'src')
+        .and('include', 'youtube-nocookie.com/embed/dQw4w9WgXcQ')
+    })
+
+    it('parses YouTube short URL autolink to video embed', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('iframe.video-embed')
+        .should('have.attr', 'src')
+        .and('include', 'youtube-nocookie.com/embed/dQw4w9WgXcQ')
+    })
+
+    it('handles YouTube URL with extra parameters', () => {
+      const content = '<https://www.youtube.com/watch?v=dQw4w9WgXcQ&t=120>'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('iframe.video-embed').should('have.attr', 'src').and('include', 'dQw4w9WgXcQ')
+    })
+  })
+
+  describe('Rumble Video Parsing', () => {
+    it('parses Rumble embed URL autolink to video embed', () => {
+      const content = '<https://rumble.com/embed/v1abc23>'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('iframe.video-embed')
+        .should('have.attr', 'src')
+        .and('include', 'rumble.com/embed/v1abc23')
+    })
+  })
+
+  describe('Multiple Videos', () => {
+    it('renders multiple video embeds correctly', () => {
+      const content = `<https://youtu.be/video1234567>
+
+<https://youtu.be/video7654321>`
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('iframe.video-embed').should('have.length', 2)
+    })
+  })
+
+  describe('Markdown Serialization (Roundtrip)', () => {
+    it('serializes video embed back to autolink markdown', () => {
+      const content = '<https://www.youtube.com/watch?v=dQw4w9WgXcQ>'
+      let editorInstance: Editor
+
+      mount(
+        <TestEditorWithRouter
+          content={content}
+          onReady={(editor) => {
+            editorInstance = editor
+          }}
+        />,
+      )
+
+      cy.get('iframe.video-embed')
+        .should('exist')
+        .then(() => {
+          const markdown = editorInstance.getMarkdown()
+          expect(markdown).to.include('<https://www.youtube.com/watch?v=dQw4w9WgXcQ>')
+          return null
+        })
+    })
+  })
+
+  describe('Non-Video URLs', () => {
+    it('does not convert regular URLs to video embeds', () => {
+      const content = '<https://example.com>'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('iframe.video-embed').should('not.exist')
+      // Should render as a link instead
+      cy.get('a').should('contain.text', 'example.com')
+    })
+
+    it('does not convert non-embed Rumble URLs', () => {
+      // Regular Rumble video page, not embed URL
+      const content = '<https://rumble.com/v1abc23-some-video.html>'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('iframe.video-embed').should('not.exist')
+    })
+  })
+
+  describe('Video Embed Attributes', () => {
+    it('renders with correct iframe attributes', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('iframe.video-embed').should('have.attr', 'allowfullscreen').and('exist')
+      cy.get('iframe.video-embed').should('have.attr', 'allow').and('include', 'fullscreen')
+    })
+
+    it('wraps video in container div', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+
+      mount(<TestEditorWithRouter content={content} />)
+
+      cy.get('.video-embed-wrapper').should('exist')
+      cy.get('.video-embed-wrapper').find('iframe.video-embed').should('exist')
+    })
+  })
+
+  describe('Adding Video Below Existing Video', () => {
+    it('user clicks after video and presses Enter - first video should remain', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+
+      mount(<TestEditorWithRouter content={content} editable={true} />)
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('.ProseMirror').click()
+      cy.get('.ProseMirror').type('{enter}')
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('iframe.video-embed').should('have.attr', 'src').and('include', 'dQw4w9WgXcQ')
+    })
+
+    it('user clicks after video and types some text - first video should remain', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+
+      mount(<TestEditorWithRouter content={content} editable={true} />)
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('.ProseMirror').click()
+      cy.get('.ProseMirror').type('{enter}Some text after the video')
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('iframe.video-embed').should('have.attr', 'src').and('include', 'dQw4w9WgXcQ')
+    })
+
+    it('user pastes a URL directly after video (no Enter) - first video should remain', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+
+      mount(<TestEditorWithRouter content={content} editable={true} />)
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('.ProseMirror').click()
+      cy.get('.ProseMirror').trigger('paste', {
+        clipboardData: {
+          getData: () => 'https://www.youtube.com/watch?v=abc123xyz99',
+        },
+      })
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('iframe.video-embed').first().should('have.attr', 'src').and('include', 'dQw4w9WgXcQ')
+    })
+
+    it('user presses Enter then pastes a URL - first video should remain', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+
+      mount(<TestEditorWithRouter content={content} editable={true} />)
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('.ProseMirror').click()
+      cy.get('.ProseMirror').type('{enter}')
+
+      cy.get('iframe.video-embed').should('exist')
+
+      cy.get('.ProseMirror').trigger('paste', {
+        clipboardData: {
+          getData: () => 'https://www.youtube.com/watch?v=abc123xyz99',
+        },
+      })
+
+      cy.get('iframe.video-embed').should('exist')
+      cy.get('iframe.video-embed').first().should('have.attr', 'src').and('include', 'dQw4w9WgXcQ')
+    })
+
+    it('preserves first video when setting content with two videos', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+      let editorInstance: Editor | undefined
+
+      mount(
+        <TestEditorWithRouter
+          content={content}
+          editable={true}
+          onReady={(editor) => {
+            editorInstance = editor
+          }}
+        />,
+      )
+
+      cy.get('iframe.video-embed')
+        .should('exist')
+        .should(() => expect(editorInstance).to.exist)
+        .then(() => {
+          if (!editorInstance) return null
+          const newContent = `<https://youtu.be/dQw4w9WgXcQ>
+
+<https://youtu.be/second12345>`
+          editorInstance.commands.setContent(newContent, { contentType: 'markdown' })
+          return null
+        })
+
+      cy.get('iframe.video-embed').should('have.length', 2)
+    })
+
+    it('verifies markdown roundtrip with two videos', () => {
+      const content = `<https://youtu.be/dQw4w9WgXcQ>
+
+<https://youtu.be/second12345>`
+      let editorInstance: Editor | undefined
+
+      mount(
+        <TestEditorWithRouter
+          content={content}
+          editable={true}
+          onReady={(editor) => {
+            editorInstance = editor
+          }}
+        />,
+      )
+
+      cy.get('iframe.video-embed')
+        .should('have.length', 2)
+        .should(() => expect(editorInstance).to.exist)
+        .then(() => {
+          if (!editorInstance) return null
+          const markdown = editorInstance.getMarkdown()
+          expect(markdown).to.include('dQw4w9WgXcQ')
+          expect(markdown).to.include('second12345')
+          return null
+        })
+    })
+
+    it('handles keyboard navigation: Arrow down from video creates new paragraph', () => {
+      const content = '<https://youtu.be/dQw4w9WgXcQ>'
+      let editorInstance: Editor | undefined
+
+      mount(
+        <TestEditorWithRouter
+          content={content}
+          editable={true}
+          onReady={(editor) => {
+            editorInstance = editor
+          }}
+        />,
+      )
+
+      cy.get('iframe.video-embed')
+        .should('exist')
+        .should(() => expect(editorInstance).to.exist)
+        .then(() => {
+          if (!editorInstance) return null
+          editorInstance.commands.focus('end')
+          editorInstance
+            .chain()
+            .insertContentAt(editorInstance.state.doc.content.size, {
+              type: 'paragraph',
+            })
+            .run()
+          editorInstance.commands.setVideoEmbed({ provider: 'youtube', videoId: 'newvideo1234' })
+          return null
+        })
+
+      cy.get('iframe.video-embed').should('have.length', 2)
+    })
+  })
+})
diff --git a/lib/cypress/component/TipTap/roundtrip.cy.tsx b/lib/cypress/component/TipTap/roundtrip.cy.tsx
new file mode 100644
index 00000000..4533ceb6
--- /dev/null
+++ b/lib/cypress/component/TipTap/roundtrip.cy.tsx
@@ -0,0 +1,106 @@
+/// <reference types="cypress" />
+import { mount } from 'cypress/react'
+
+import { TestEditorWithRouter } from './TestEditor'
+
+import type { Editor } from '@tiptap/core'
+
+/**
+ * Roundtrip tests verify that Markdown -> TipTap -> Markdown preserves
+ * key content elements. Note: TipTap may normalize markdown (whitespace,
+ * list markers, etc.) so we test for semantic preservation, not exact match.
+ */
+describe('Markdown Roundtrip Tests', () => {
+  function testRoundtripContains(originalMarkdown: string, expectedPatterns: string[]) {
+    let editorInstance: Editor | undefined
+
+    mount(
+      <TestEditorWithRouter
+        content={originalMarkdown}
+        onReady={(editor) => {
+          editorInstance = editor
+        }}
+      />,
+    )
+
+    cy.get('[data-testid="test-editor"]')
+      .should('exist')
+      .should(() => expect(editorInstance).to.exist)
+      .then(() => {
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        const markdown = editorInstance!.getMarkdown()
+        for (const pattern of expectedPatterns) {
+          expect(markdown).to.include(pattern)
+        }
+        return null
+      })
+  }
+
+  describe('Custom Extensions Roundtrip', () => {
+    // These are the critical tests - our custom extensions must serialize correctly
+
+    it('hashtag: #tag is preserved', () => {
+      testRoundtripContains('Hello #world', ['#world'])
+    })
+
+    it('hashtag: multiple hashtags preserved', () => {
+      testRoundtripContains('#one #two #three', ['#one', '#two', '#three'])
+    })
+
+    it('item mention: preserved with correct format', () => {
+      // Using hex UUID as required by the regex
+      testRoundtripContains('Thanks [@Alice](/item/abc-123-def)', ['[@Alice](/item/abc-123-def)'])
+    })
+
+    it('item mention: with spaces in name', () => {
+      testRoundtripContains('Contact [@Max Müller](/item/abc-123)', [
+        '[@Max Müller](/item/abc-123)',
+      ])
+    })
+
+    it('video embed: YouTube autolink preserved', () => {
+      testRoundtripContains('<https://www.youtube.com/watch?v=dQw4w9WgXcQ>', [
+        '<https://www.youtube.com/watch?v=dQw4w9WgXcQ>',
+      ])
+    })
+  })
+
+  describe('Standard Markdown Roundtrip', () => {
+    it('plain text preserved', () => {
+      testRoundtripContains('Hello, world!', ['Hello, world!'])
+    })
+
+    it('bold text preserved', () => {
+      testRoundtripContains('This is **bold** text.', ['**bold**'])
+    })
+
+    it('italic text preserved', () => {
+      testRoundtripContains('This is *italic* text.', ['*italic*'])
+    })
+
+    it('inline code preserved', () => {
+      testRoundtripContains('Use `code` here.', ['`code`'])
+    })
+
+    it('links preserved', () => {
+      testRoundtripContains('Visit [Example](https://example.com).', [
+        '[Example](https://example.com)',
+      ])
+    })
+  })
+
+  describe('Complex Content Roundtrip', () => {
+    it('mixed content with all custom extensions', () => {
+      const content = 'Hello #world! Thanks [@Alice](/item/abc-123) for helping.'
+      testRoundtripContains(content, ['#world', '[@Alice](/item/abc-123)', 'Hello', 'for helping'])
+    })
+
+    it('formatting with hashtags', () => {
+      testRoundtripContains('**Bold** text with #hashtag and *italic*.', [
+        '**Bold**',
+        '#hashtag',
+        '*italic*',
+      ])
+    })
+  })
+})
diff --git a/lib/tsconfig.json b/lib/tsconfig.json
index 001999dc..8e4ac629 100644
--- a/lib/tsconfig.json
+++ b/lib/tsconfig.json
@@ -29,7 +29,8 @@
     "setupTest.ts",
     "cypress.config.ts",
     "cypress/support/commands.ts",
-    "cypress/support/component.ts"
+    "cypress/support/component.ts",
+    "cypress/component"
   ],
   "exclude": ["node_modules", "dist", "example"],
   "typeRoots": ["./src/types", "./node_modules/@types/"]