diff --git a/apps/desktop/package.json b/apps/desktop/package.json
index 56a7374eeef..6d0ca01f33f 100644
--- a/apps/desktop/package.json
+++ b/apps/desktop/package.json
@@ -81,11 +81,13 @@
     "clsx": "^2.1.1",
     "cmdk": "^1.1.1",
     "dnd-core": "^14.0.1",
+    "dompurify": "^3.4.11",
     "hast-util-from-html-isomorphic": "^2.0.0",
     "hast-util-to-text": "^4.0.2",
     "ignore": "^7.0.5",
     "katex": "^0.16.45",
     "leva": "^0.10.1",
+    "mermaid": "^11.15.0",
     "motion": "^12.38.0",
     "nanostores": "^1.3.0",
     "node-pty": "1.1.0",
diff --git a/apps/desktop/src/components/assistant-ui/embeds/embed-size.ts b/apps/desktop/src/components/assistant-ui/embeds/embed-size.ts
new file mode 100644
index 00000000000..3f3da9fb30f
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/embed-size.ts
@@ -0,0 +1,4 @@
+// Shared height cap for inline embeds. Ratio embeds cap their width off this in
+// UrlEmbed so height follows the aspect ratio; fenced renderers (mermaid, svg)
+// reuse it directly. Pure CSS — no measuring.
+export const EMBED_MAX_H = '33dvh'
diff --git a/apps/desktop/src/components/assistant-ui/embeds/escape-html.ts b/apps/desktop/src/components/assistant-ui/embeds/escape-html.ts
new file mode 100644
index 00000000000..c8545bca52e
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/escape-html.ts
@@ -0,0 +1,3 @@
+export function escapeHtml(value: string): string {
+  return value.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;').replace(/"/g, '&quot;')
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/fail.tsx b/apps/desktop/src/components/assistant-ui/embeds/fail.tsx
new file mode 100644
index 00000000000..833f67f8390
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/fail.tsx
@@ -0,0 +1,7 @@
+export function EmbedFail({ label }: { label: string }) {
+  return (
+    <span className="grid min-h-32 w-full place-items-center p-4">
+      <span className="text-xs font-medium text-(--ui-red)">Failed to load {label} embed</span>
+    </span>
+  )
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/detect.test.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/detect.test.ts
new file mode 100644
index 00000000000..74be1caa14d
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/detect.test.ts
@@ -0,0 +1,133 @@
+import { describe, expect, it } from 'vitest'
+
+import type { FrameEmbed, TweetEmbed } from './types'
+
+import { detectEmbed, isEmbeddableUrl } from './index'
+
+function frame(url: string): FrameEmbed {
+  const descriptor = detectEmbed(url)
+
+  if (!descriptor || descriptor.renderer !== 'frame') {
+    throw new Error(`expected a frame embed for ${url}`)
+  }
+
+  return descriptor
+}
+
+describe('detectEmbed — YouTube', () => {
+  it.each([
+    'https://www.youtube.com/watch?v=dQw4w9WgXcQ',
+    'https://youtu.be/dQw4w9WgXcQ',
+    'https://www.youtube.com/shorts/dQw4w9WgXcQ',
+    'https://m.youtube.com/watch?v=dQw4w9WgXcQ',
+    'https://www.youtube.com/embed/dQw4w9WgXcQ',
+    'https://www.youtube.com/live/dQw4w9WgXcQ'
+  ])('resolves %s to the privacy-enhanced embed of the same id', url => {
+    const embed = frame(url)
+
+    expect(embed.provider).toBe('youtube')
+    expect(embed.id).toBe('youtube:dQw4w9WgXcQ')
+    expect(embed.embedUrl).toContain('youtube-nocookie.com/embed/dQw4w9WgXcQ')
+  })
+
+  it('carries a start time from t/start through to the embed', () => {
+    expect(frame('https://youtu.be/dQw4w9WgXcQ?t=90').embedUrl).toContain('start=90')
+    expect(frame('https://youtu.be/dQw4w9WgXcQ?t=1m30s').embedUrl).toContain('start=90')
+  })
+
+  it('rejects ids that are not 11 chars', () => {
+    expect(detectEmbed('https://www.youtube.com/watch?v=short')).toBeNull()
+  })
+})
+
+describe('detectEmbed — other frame providers', () => {
+  it('resolves Vimeo numeric ids across path shapes', () => {
+    expect(frame('https://vimeo.com/76979871').embedUrl).toBe('https://player.vimeo.com/video/76979871')
+    expect(frame('https://vimeo.com/channels/staffpicks/76979871').id).toBe('vimeo:76979871')
+  })
+
+  it('resolves Instagram posts and reels', () => {
+    expect(frame('https://www.instagram.com/p/CabcDEF123/').embedUrl).toBe(
+      'https://www.instagram.com/p/CabcDEF123/embed'
+    )
+    expect(frame('https://www.instagram.com/reel/CabcDEF123/').embedUrl).toContain('/reel/CabcDEF123/embed')
+    expect(frame('https://www.instagram.com/reels/CabcDEF123/').embedUrl).toContain('/reel/CabcDEF123/embed')
+  })
+
+  it('resolves Pinterest pins across locale hosts', () => {
+    expect(frame('https://www.pinterest.com/pin/1234567890/').embedUrl).toBe(
+      'https://assets.pinterest.com/ext/embed.html?id=1234567890'
+    )
+    expect(frame('https://fr.pinterest.com/pin/1234567890/').provider).toBe('pinterest')
+  })
+
+  it('resolves TikTok videos to the official player', () => {
+    expect(frame('https://www.tiktok.com/@user/video/7212345678901234567').embedUrl).toBe(
+      'https://www.tiktok.com/player/v1/7212345678901234567'
+    )
+  })
+
+  it('resolves Spotify tracks, collections, and locale-prefixed urls', () => {
+    expect(frame('https://open.spotify.com/track/4cOdK2wGLETKBW3PvgPWqT').embedUrl).toBe(
+      'https://open.spotify.com/embed/track/4cOdK2wGLETKBW3PvgPWqT'
+    )
+    expect(frame('https://open.spotify.com/playlist/37i9dQZF1DXcBWIGoYBM5M').provider).toBe('spotify')
+    expect(frame('https://open.spotify.com/intl-de/album/1DFixLWuPkv3KT3TnV35m3').id).toBe(
+      'spotify:album:1DFixLWuPkv3KT3TnV35m3'
+    )
+    expect(detectEmbed('https://open.spotify.com/track/')).toBeNull()
+  })
+})
+
+describe('detectEmbed — maps', () => {
+  it('resolves Google Maps coordinates with zoom', () => {
+    const embed = frame('https://www.google.com/maps/@40.7128,-74.0060,12z')
+
+    expect(embed.provider).toBe('googlemaps')
+    expect(embed.embedUrl).toContain('output=embed')
+    expect(embed.embedUrl).toContain('q=40.7128%2C-74.006')
+    expect(embed.embedUrl).toContain('z=12')
+  })
+
+  it('resolves a Google Maps place name', () => {
+    expect(frame('https://www.google.com/maps/place/Eiffel+Tower/').embedUrl).toContain('q=Eiffel+Tower')
+  })
+
+  it('resolves OpenStreetMap fragment state to a bbox embed', () => {
+    const embed = frame('https://www.openstreetmap.org/#map=12/40.7128/-74.0060')
+
+    expect(embed.provider).toBe('openstreetmap')
+    expect(embed.embedUrl).toContain('export/embed.html')
+    expect(embed.embedUrl).toContain('marker=40.7128%2C-74.006')
+    expect(embed.embedUrl).toContain('bbox=')
+  })
+})
+
+describe('detectEmbed — Twitter/X', () => {
+  it('resolves twitter.com and x.com status urls to a tweet descriptor', () => {
+    for (const url of ['https://twitter.com/jack/status/20', 'https://x.com/jack/status/20']) {
+      const descriptor = detectEmbed(url)
+
+      expect(descriptor?.renderer).toBe('tweet')
+      expect((descriptor as TweetEmbed).tweetId).toBe('20')
+    }
+  })
+})
+
+describe('detectEmbed — non-matches', () => {
+  it.each([
+    'https://example.com/watch?v=dQw4w9WgXcQ',
+    'https://github.com/NousResearch/hermes',
+    'not-a-url',
+    'ftp://youtube.com/watch?v=dQw4w9WgXcQ',
+    'mailto:someone@youtube.com'
+  ])('returns null for %s', url => {
+    expect(detectEmbed(url)).toBeNull()
+    expect(isEmbeddableUrl(url)).toBe(false)
+  })
+
+  it('handles empty input without throwing', () => {
+    expect(detectEmbed(undefined)).toBeNull()
+    expect(detectEmbed('')).toBeNull()
+  })
+})
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/index.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/index.ts
new file mode 100644
index 00000000000..b45983ada0d
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/index.ts
@@ -0,0 +1,54 @@
+import { instagram } from './instagram'
+import { maps } from './maps'
+import { pinterest } from './pinterest'
+import { spotify } from './spotify'
+import { tiktok } from './tiktok'
+import { twitter } from './twitter'
+import type { EmbedDescriptor, EmbedMatcher } from './types'
+import { vimeo } from './vimeo'
+import { youtube } from './youtube'
+
+export type { EmbedDescriptor, EmbedProvider, EmbedRenderer, FrameEmbed, TweetEmbed } from './types'
+
+// All provider hosts are disjoint, so order is irrelevant — first match wins.
+const MATCHERS: EmbedMatcher[] = [youtube, vimeo, instagram, pinterest, tiktok, twitter, spotify, maps]
+
+function parseUrl(raw: string): URL | null {
+  try {
+    const url = new URL(raw)
+
+    return url.protocol === 'http:' || url.protocol === 'https:' ? url : null
+  } catch {
+    return null
+  }
+}
+
+/**
+ * Resolve a URL to a rich-embed descriptor, or null when no provider matches.
+ * Pure and synchronous — safe to call during render.
+ */
+export function detectEmbed(rawUrl: string | null | undefined): EmbedDescriptor | null {
+  if (!rawUrl) {
+    return null
+  }
+
+  const url = parseUrl(rawUrl)
+
+  if (!url) {
+    return null
+  }
+
+  for (const match of MATCHERS) {
+    const descriptor = match(url)
+
+    if (descriptor) {
+      return descriptor
+    }
+  }
+
+  return null
+}
+
+export function isEmbeddableUrl(rawUrl: string | null | undefined): boolean {
+  return detectEmbed(rawUrl) !== null
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/instagram.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/instagram.ts
new file mode 100644
index 00000000000..3d45577a396
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/instagram.ts
@@ -0,0 +1,26 @@
+import { bareHost, type EmbedMatcher } from './types'
+
+export const instagram: EmbedMatcher = url => {
+  if (bareHost(url.hostname) !== 'instagram.com') {
+    return null
+  }
+
+  const [typeRaw, code] = url.pathname.split('/').filter(Boolean)
+  const type = typeRaw === 'reels' ? 'reel' : typeRaw
+
+  if (!code || !['p', 'reel', 'tv'].includes(type || '') || !/^[A-Za-z0-9_-]+$/.test(code)) {
+    return null
+  }
+
+  return {
+    embedUrl: `https://www.instagram.com/${type}/${code}/embed`,
+    // Placeholder height for content-visibility; embed.js self-sizes in-document.
+    height: 450,
+    id: `instagram:${code}`,
+    label: 'Instagram',
+    maxWidth: 400,
+    provider: 'instagram',
+    renderer: 'frame',
+    sourceUrl: url.toString()
+  }
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/maps.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/maps.ts
new file mode 100644
index 00000000000..2aa8e615c95
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/maps.ts
@@ -0,0 +1,95 @@
+import { bareHost, type EmbedMatcher, type FrameEmbed } from './types'
+
+// `@lat,lng` (optionally `,<zoom>z`) as it appears in Google Maps URLs.
+const LATLNG_RE = /@(-?\d+(?:\.\d+)?),(-?\d+(?:\.\d+)?)(?:,(\d+(?:\.\d+)?)z)?/
+
+function googleMapsEmbed(url: URL): FrameEmbed | null {
+  const host = bareHost(url.hostname)
+
+  if (host !== 'google.com' && host !== 'maps.google.com' && !host.startsWith('google.')) {
+    return null
+  }
+
+  const isMapsPath = host.startsWith('maps.') || url.pathname.startsWith('/maps')
+
+  if (!isMapsPath) {
+    return null
+  }
+
+  // Prefer explicit coordinates; then a `q=` query; then a `/place/<name>`.
+  const coords = url.pathname.match(LATLNG_RE)
+  const placeName = url.pathname.match(/\/place\/([^/@]+)/)
+  const query = url.searchParams.get('q') || url.searchParams.get('query')
+  let q = ''
+  let zoom = ''
+
+  if (coords) {
+    q = `${coords[1]},${coords[2]}`
+    zoom = coords[3] ? String(Math.round(Number(coords[3]))) : ''
+  } else if (query) {
+    q = query
+  } else if (placeName) {
+    q = decodeURIComponent(placeName[1].replace(/\+/g, ' '))
+  }
+
+  if (!q) {
+    return null
+  }
+
+  // `output=embed` is the long-standing keyless Maps embed surface.
+  const params = new URLSearchParams({ output: 'embed', q })
+
+  if (zoom) {
+    params.set('z', zoom)
+  }
+
+  return {
+    aspectRatio: 16 / 10,
+    embedUrl: `https://maps.google.com/maps?${params.toString()}`,
+    id: `googlemaps:${q}${zoom ? `@${zoom}` : ''}`,
+    label: 'Google Maps',
+    maxWidth: 640,
+    provider: 'googlemaps',
+    renderer: 'frame',
+    sourceUrl: url.toString()
+  }
+}
+
+function openStreetMapEmbed(url: URL): FrameEmbed | null {
+  if (bareHost(url.hostname) !== 'openstreetmap.org') {
+    return null
+  }
+
+  // State lives in the fragment: `#map=<zoom>/<lat>/<lng>`.
+  const match = url.hash.match(/map=(\d+(?:\.\d+)?)\/(-?\d+(?:\.\d+)?)\/(-?\d+(?:\.\d+)?)/)
+
+  if (!match) {
+    return null
+  }
+
+  const zoom = Number(match[1])
+  const lat = Number(match[2])
+  const lng = Number(match[3])
+  // Degrees spanned at this zoom; halved for the bbox half-extent.
+  const lonDelta = 360 / 2 ** zoom
+  const latDelta = lonDelta / 2
+
+  const bbox = [lng - lonDelta / 2, lat - latDelta / 2, lng + lonDelta / 2, lat + latDelta / 2]
+    .map(value => value.toFixed(5))
+    .join(',')
+
+  const params = new URLSearchParams({ bbox, layer: 'mapnik', marker: `${lat},${lng}` })
+
+  return {
+    aspectRatio: 16 / 10,
+    embedUrl: `https://www.openstreetmap.org/export/embed.html?${params.toString()}`,
+    id: `openstreetmap:${lat},${lng}@${zoom}`,
+    label: 'OpenStreetMap',
+    maxWidth: 640,
+    provider: 'openstreetmap',
+    renderer: 'frame',
+    sourceUrl: url.toString()
+  }
+}
+
+export const maps: EmbedMatcher = url => googleMapsEmbed(url) || openStreetMapEmbed(url)
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/pinterest.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/pinterest.ts
new file mode 100644
index 00000000000..f1928247eb4
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/pinterest.ts
@@ -0,0 +1,28 @@
+import { bareHost, type EmbedMatcher } from './types'
+
+export const pinterest: EmbedMatcher = url => {
+  // Pinterest runs many locale TLDs (pinterest.co.uk, fr.pinterest.com, ...).
+  if (!bareHost(url.hostname).includes('pinterest.')) {
+    return null
+  }
+
+  const segments = url.pathname.split('/').filter(Boolean)
+
+  if (segments[0] !== 'pin' || !/^\d+$/.test(segments[1] || '')) {
+    return null
+  }
+
+  const id = segments[1]
+
+  return {
+    embedUrl: `https://assets.pinterest.com/ext/embed.html?id=${id}`,
+    // Pinterest's "small" pin size — the default card is too dominant inline.
+    height: 380,
+    id: `pinterest:${id}`,
+    label: 'Pinterest',
+    maxWidth: 236,
+    provider: 'pinterest',
+    renderer: 'frame',
+    sourceUrl: url.toString()
+  }
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/spotify.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/spotify.ts
new file mode 100644
index 00000000000..526bcdc4949
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/spotify.ts
@@ -0,0 +1,34 @@
+import { bareHost, type EmbedMatcher } from './types'
+
+// Spotify's embed has only two layouts: compact (≤152) and full (352). Any
+// in-between height renders the compact player and pads the rest with grey, so
+// we snap to the compact size for every type — tight, no dead space.
+const COMPACT_HEIGHT = 152
+const EMBED_TYPES = new Set(['album', 'artist', 'episode', 'playlist', 'show', 'track'])
+
+export const spotify: EmbedMatcher = url => {
+  if (bareHost(url.hostname) !== 'open.spotify.com') {
+    return null
+  }
+
+  // Drop an optional locale prefix (`/intl-de/track/...`).
+  const segments = url.pathname.split('/').filter(Boolean)
+  const start = segments[0]?.startsWith('intl-') ? 1 : 0
+  const type = segments[start] || ''
+  const id = segments[start + 1] || ''
+
+  if (!EMBED_TYPES.has(type) || !/^[A-Za-z0-9]+$/.test(id)) {
+    return null
+  }
+
+  return {
+    embedUrl: `https://open.spotify.com/embed/${type}/${id}`,
+    height: COMPACT_HEIGHT,
+    id: `spotify:${type}:${id}`,
+    label: 'Spotify',
+    maxWidth: 480,
+    provider: 'spotify',
+    renderer: 'frame',
+    sourceUrl: url.toString()
+  }
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/tiktok.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/tiktok.ts
new file mode 100644
index 00000000000..a6ea3179ac5
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/tiktok.ts
@@ -0,0 +1,28 @@
+import { bareHost, type EmbedMatcher } from './types'
+
+export const tiktok: EmbedMatcher = url => {
+  if (bareHost(url.hostname) !== 'tiktok.com') {
+    return null
+  }
+
+  const segments = url.pathname.split('/').filter(Boolean)
+  const videoIndex = segments.indexOf('video')
+  const id = videoIndex >= 0 ? segments[videoIndex + 1] : ''
+
+  if (!/^\d+$/.test(id || '')) {
+    return null
+  }
+
+  return {
+    // The official player is a clean dark video iframe (no white blockquote
+    // chrome), so it goes through the plain-iframe frame path, sized 9:16.
+    aspectRatio: 9 / 16,
+    embedUrl: `https://www.tiktok.com/player/v1/${id}`,
+    id: `tiktok:${id}`,
+    label: 'TikTok',
+    maxWidth: 365,
+    provider: 'tiktok',
+    renderer: 'frame',
+    sourceUrl: url.toString()
+  }
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/twitter.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/twitter.ts
new file mode 100644
index 00000000000..938c1a021b7
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/twitter.ts
@@ -0,0 +1,27 @@
+import { bareHost, type EmbedMatcher } from './types'
+
+export const twitter: EmbedMatcher = url => {
+  const host = bareHost(url.hostname)
+
+  if (host !== 'twitter.com' && host !== 'x.com') {
+    return null
+  }
+
+  const segments = url.pathname.split('/').filter(Boolean)
+  const statusIndex = segments.indexOf('status')
+  const id = statusIndex >= 0 ? segments[statusIndex + 1] : ''
+
+  if (!/^\d+$/.test(id || '')) {
+    return null
+  }
+
+  return {
+    id: `twitter:${id}`,
+    label: 'X',
+    maxWidth: 480,
+    provider: 'twitter',
+    renderer: 'tweet',
+    sourceUrl: url.toString(),
+    tweetId: id
+  }
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/types.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/types.ts
new file mode 100644
index 00000000000..e9f4ce381d3
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/types.ts
@@ -0,0 +1,60 @@
+// Embed provider model. Detection is pure, synchronous, and dependency-free so
+// it is safe to run during render and trivial to unit-test. Rendering lives in
+// the lazy renderers (see ../registry.tsx) keyed off `renderer`.
+
+export type EmbedProvider =
+  | 'googlemaps'
+  | 'instagram'
+  | 'openstreetmap'
+  | 'pinterest'
+  | 'spotify'
+  | 'tiktok'
+  | 'twitter'
+  | 'vimeo'
+  | 'youtube'
+
+/** Which lazy renderer materialises the descriptor. */
+export type EmbedRenderer = 'frame' | 'tweet'
+
+interface EmbedLayout {
+  /** Frame aspect ratio (width / height). For video/maps. */
+  aspectRatio?: number
+  /** Fixed pixel height for non-ratio embeds (Instagram, Pinterest, Spotify). */
+  height?: number
+  /** Max rendered width in px; falls back to the conversation column. */
+  maxWidth?: number
+}
+
+interface BaseEmbed extends EmbedLayout {
+  /** Stable id for React keys / dedupe. */
+  id: string
+  /** Human-facing provider name (e.g. "YouTube"). */
+  label: string
+  provider: EmbedProvider
+  renderer: EmbedRenderer
+  /** Canonical URL opened in the system browser from the card. */
+  sourceUrl: string
+}
+
+/** A provider whose embed is a single iframe URL (video, post, map, ...). */
+export interface FrameEmbed extends BaseEmbed {
+  /** URL loaded inside the iframe. */
+  embedUrl: string
+  renderer: 'frame'
+}
+
+/** Twitter/X ships no iframe URL — only a widget script (see social-embed.tsx). */
+export interface TweetEmbed extends BaseEmbed {
+  renderer: 'tweet'
+  tweetId: string
+}
+
+export type EmbedDescriptor = FrameEmbed | TweetEmbed
+
+/** A provider matcher. Receives a parsed http(s) URL; returns null if unmatched. */
+export type EmbedMatcher = (url: URL) => EmbedDescriptor | null
+
+/** Strip a leading `www.`/`m.`/`mobile.` so host checks read cleanly. */
+export function bareHost(host: string): string {
+  return host.replace(/^(?:www|m|mobile)\./i, '').toLowerCase()
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/vimeo.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/vimeo.ts
new file mode 100644
index 00000000000..1ef73ff78e6
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/vimeo.ts
@@ -0,0 +1,32 @@
+import { bareHost, type EmbedMatcher } from './types'
+
+export const vimeo: EmbedMatcher = url => {
+  const host = bareHost(url.hostname)
+
+  if (host !== 'vimeo.com' && host !== 'player.vimeo.com') {
+    return null
+  }
+
+  // The clip id is the last all-digits segment, covering vimeo.com/123,
+  // /channels/x/123, /groups/x/videos/123, and player/video/123.
+  const id = url.pathname
+    .split('/')
+    .filter(Boolean)
+    .reverse()
+    .find(segment => /^\d+$/.test(segment))
+
+  if (!id) {
+    return null
+  }
+
+  return {
+    aspectRatio: 16 / 9,
+    embedUrl: `https://player.vimeo.com/video/${id}`,
+    id: `vimeo:${id}`,
+    label: 'Vimeo',
+    maxWidth: 640,
+    provider: 'vimeo',
+    renderer: 'frame',
+    sourceUrl: url.toString()
+  }
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/providers/youtube.ts b/apps/desktop/src/components/assistant-ui/embeds/providers/youtube.ts
new file mode 100644
index 00000000000..40444540e89
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/providers/youtube.ts
@@ -0,0 +1,65 @@
+import { bareHost, type EmbedMatcher } from './types'
+
+const YOUTUBE_ID_RE = /^[A-Za-z0-9_-]{11}$/
+
+// `t`/`start` accept either raw seconds ("90") or the "1m30s" form.
+function startSeconds(value: string | null): number | undefined {
+  if (!value) {
+    return undefined
+  }
+
+  if (/^\d+$/.test(value)) {
+    return Number(value)
+  }
+
+  const match = value.match(/^(?:(\d+)h)?(?:(\d+)m)?(?:(\d+)s)?$/)
+
+  if (!match || !match[0]) {
+    return undefined
+  }
+
+  const seconds = Number(match[1] || 0) * 3600 + Number(match[2] || 0) * 60 + Number(match[3] || 0)
+
+  return seconds > 0 ? seconds : undefined
+}
+
+export const youtube: EmbedMatcher = url => {
+  const host = bareHost(url.hostname)
+  const segments = url.pathname.split('/').filter(Boolean)
+  let id = ''
+
+  if (host === 'youtu.be') {
+    id = segments[0] || ''
+  } else if (host === 'youtube.com' || host === 'youtube-nocookie.com') {
+    if (segments[0] === 'watch') {
+      id = url.searchParams.get('v') || ''
+    } else if (['embed', 'shorts', 'live', 'v'].includes(segments[0] || '')) {
+      id = segments[1] || ''
+    }
+  } else {
+    return null
+  }
+
+  if (!YOUTUBE_ID_RE.test(id)) {
+    return null
+  }
+
+  const params = new URLSearchParams({ modestbranding: '1', rel: '0' })
+
+  const start = startSeconds(url.searchParams.get('t') || url.searchParams.get('start'))
+
+  if (start) {
+    params.set('start', String(start))
+  }
+
+  return {
+    aspectRatio: 16 / 9,
+    embedUrl: `https://www.youtube-nocookie.com/embed/${id}?${params.toString()}`,
+    id: `youtube:${id}`,
+    label: 'YouTube',
+    maxWidth: 640,
+    provider: 'youtube',
+    renderer: 'frame',
+    sourceUrl: url.toString()
+  }
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/rich-boundary.tsx b/apps/desktop/src/components/assistant-ui/embeds/rich-boundary.tsx
new file mode 100644
index 00000000000..ee5c5b313a9
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/rich-boundary.tsx
@@ -0,0 +1,34 @@
+import { Component, type ReactNode } from 'react'
+
+interface Props {
+  children: ReactNode
+  /** Rendered in place of the subtree when a render throws. */
+  fallback: ReactNode
+  /** Changing this clears a caught error (e.g. new source for a re-parse). */
+  resetKey?: string
+}
+
+/**
+ * Local boundary for rich renderers (Mermaid parse throws, malformed SVG, a
+ * provider widget blowing up). A failed embed must never blank the transcript —
+ * we show the `fallback` (typically the raw source) and recover when `resetKey`
+ * changes. Unlike MessageRenderBoundary this swallows ALL render errors, because
+ * the blast radius is one self-contained block, not the message tree.
+ */
+export class RichBoundary extends Component<Props, { failed: boolean }> {
+  state = { failed: false }
+
+  static getDerivedStateFromError() {
+    return { failed: true }
+  }
+
+  componentDidUpdate(prev: Props) {
+    if (this.state.failed && prev.resetKey !== this.props.resetKey) {
+      this.setState({ failed: false })
+    }
+  }
+
+  render() {
+    return this.state.failed ? this.props.fallback : this.props.children
+  }
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/types.ts b/apps/desktop/src/components/assistant-ui/embeds/types.ts
new file mode 100644
index 00000000000..7457bcd9e21
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/types.ts
@@ -0,0 +1,8 @@
+// Shared prop contract for fenced-block renderers (mermaid, svg). Kept in its
+// own module so renderers and the registry can both import it without a cycle.
+export interface RichFenceProps {
+  code: string
+  /** True while the surrounding message is still streaming. Renderers that can
+   *  throw on partial input (e.g. mermaid) defer until this is false. */
+  streaming?: boolean
+}
diff --git a/apps/desktop/src/components/assistant-ui/embeds/use-is-dark.ts b/apps/desktop/src/components/assistant-ui/embeds/use-is-dark.ts
new file mode 100644
index 00000000000..178a0c0fd5c
--- /dev/null
+++ b/apps/desktop/src/components/assistant-ui/embeds/use-is-dark.ts
@@ -0,0 +1,24 @@
+import { useEffect, useState } from 'react'
+
+// Tracks the app's dark/light mode off the `dark` class on <html> (set by
+// themes/context.tsx). Embeds that theme their own content (tweets) read this.
+export function useIsDark(): boolean {
+  const [dark, setDark] = useState(
+    () => typeof document !== 'undefined' && document.documentElement.classList.contains('dark')
+  )
+
+  useEffect(() => {
+    if (typeof document === 'undefined') {
+      return
+    }
+
+    const root = document.documentElement
+    const observer = new MutationObserver(() => setDark(root.classList.contains('dark')))
+
+    observer.observe(root, { attributeFilter: ['class'], attributes: true })
+
+    return () => observer.disconnect()
+  }, [])
+
+  return dark
+}
diff --git a/package-lock.json b/package-lock.json
index 070ed298f99..85e5679784d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -95,11 +95,13 @@
         "clsx": "^2.1.1",
         "cmdk": "^1.1.1",
         "dnd-core": "^14.0.1",
+        "dompurify": "^3.4.11",
         "hast-util-from-html-isomorphic": "^2.0.0",
         "hast-util-to-text": "^4.0.2",
         "ignore": "^7.0.5",
         "katex": "^0.16.45",
         "leva": "^0.10.1",
+        "mermaid": "^11.15.0",
         "motion": "^12.38.0",
         "nanostores": "^1.3.0",
         "node-pty": "1.1.0",