diff --git a/core/http/react-ui/e2e/chats-send-snap.spec.js b/core/http/react-ui/e2e/chats-send-snap.spec.js
new file mode 100644
index 0000000000..28d441c1c8
--- /dev/null
+++ b/core/http/react-ui/e2e/chats-send-snap.spec.js
@@ -0,0 +1,77 @@
+import { test, expect } from './coverage-fixtures.js'
+import { mockChat } from './chat-fixtures.js'
+
+// Sending a message snaps the thread to the bottom, also when the reader had
+// scrolled up, so the new message is in view. Scrolling up while an answer
+// streams still stays where the reader put it.
+
+const AT = '2026-10-25T10:00:00Z'
+const LONG = 'A long line of history that fills the thread so that it needs to scroll. '.repeat(6)
+const HISTORY = Array.from({ length: 40 }, (_, i) => ({ seq: i + 1, turn: Math.floor(i / 2) + 1, role: i % 2 ? 'assistant' : 'user', text: `Message ${i + 1}. ${LONG}`, at: AT }))
+
+async function open(page) {
+  await page.addInitScript(() => {
+    window.__sources = []
+    window.EventSource = class {
+      constructor(url) { this.url = url; this.l = {}; window.__sources.push(this); setTimeout(() => this.onopen && this.onopen(), 0) }
+      addEventListener(kind, fn) { (this.l[kind] = this.l[kind] || []).push(fn) }
+      close() { this.closed = true }
+    }
+    window.__emit = (kind, payload) => {
+      const src = window.__sources.filter((x) => x.url.includes('/api/chats/c1/events') && !x.closed).pop()
+      for (const fn of (src && src.l[kind]) || []) fn({ data: JSON.stringify(payload) })
+    }
+  })
+  await mockChat(page)
+  const detail = { id: 'c1', title: 'Quotes', model: 'qwen3-8b', kind: 'chat', created: AT, updated: AT, running: false, last_turn: 'done', pending: [] }
+  let messages = HISTORY
+  await page.route(/\/api\/chats\/c1\/messages(\?.*)?$/, route => {
+    if (route.request().method() === 'POST') {
+      const text = route.request().postDataJSON().text
+      messages = [...messages, { seq: messages.length + 1, turn: 99, role: 'user', text, at: AT }]
+      return route.fulfill({ json: { started: true } })
+    }
+    return route.fulfill({ json: { messages } })
+  })
+  await page.route('**/api/chats/c1', route => route.fulfill({ json: detail }))
+  await page.route(/\/api\/chats(\?.*)?$/, route => route.fulfill({ json: { conversations: [{ ...detail, pending: undefined }], persistent: true, files: true } }))
+  await page.route('**/api/chats/agents*', route => route.fulfill({ json: { agents: [] } }))
+  await page.setViewportSize({ width: 1280, height: 720 })
+  await page.goto('/app/chats/c1')
+  await expect(page.getByTestId('chat-foot')).toBeVisible()
+}
+
+const body = (page) => page.locator('.cx-body')
+const gap = (page) => body(page).evaluate(el => el.scrollHeight - el.scrollTop - el.clientHeight)
+
+test.describe('Chat scroll on send', () => {
+  test('sending a message snaps to the bottom after the reader scrolled up', async ({ page }) => {
+    await open(page)
+    await expect(page.getByTestId('chat-thread')).toContainText('Message 40.')
+    await expect.poll(() => gap(page)).toBeLessThan(5)
+    await body(page).evaluate(el => { el.scrollTop = 0 })
+    await expect.poll(() => gap(page)).toBeGreaterThan(500)
+    await page.getByTestId('chat-input').fill('the new question')
+    await page.getByTestId('chat-input').press('Enter')
+    await expect(page.getByTestId('chat-thread')).toContainText('the new question')
+    await expect.poll(() => gap(page), { timeout: 5000 }).toBeLessThan(5)
+    await expect(page.getByTestId('chat-thread').getByText('the new question')).toBeInViewport()
+    // The answer that streams in after it stays in view too.
+    await page.evaluate(() => window.__emit('turn_start', {}))
+    for (let i = 0; i < 6; i++) {
+      await page.evaluate(() => window.__emit('text', { text: 'The answer keeps coming in, line after line of it.\n\n'.repeat(6) }))
+      await page.waitForTimeout(150)
+    }
+    await expect.poll(() => gap(page), { timeout: 5000 }).toBeLessThan(5)
+  })
+
+  test('scrolling up while an answer streams is not undone', async ({ page }) => {
+    await open(page)
+    await expect.poll(() => gap(page)).toBeLessThan(5)
+    await body(page).evaluate(el => { el.scrollTop = 0 })
+    await expect.poll(() => gap(page)).toBeGreaterThan(500)
+    await page.evaluate(() => window.__emit('message', { seq: 41, turn: 100, role: 'assistant', text: 'streaming answer '.repeat(80), at: '2026-10-25T10:00:00Z' }))
+    await page.waitForTimeout(500)
+    expect(await body(page).evaluate(el => el.scrollTop)).toBeLessThan(5)
+  })
+})
diff --git a/core/http/react-ui/src/pages/Chat.jsx b/core/http/react-ui/src/pages/Chat.jsx
index 46e04576ff..fefb626044 100644
--- a/core/http/react-ui/src/pages/Chat.jsx
+++ b/core/http/react-ui/src/pages/Chat.jsx
@@ -300,9 +300,16 @@ function ChatPage() {
   useEffect(() => {
     const el = messagesRef.current
     if (!el) return undefined
+    let last = el.scrollTop
     const onScroll = () => {
       const distanceFromBottom = el.scrollHeight - el.scrollTop - el.clientHeight
-      stickToBottomRef.current = distanceFromBottom < 80
+      // Only a move up unpins the thread. Our own smooth scroll to the bottom
+      // moves down and reports a distance above the threshold on its way, which
+      // must not unpin it: the send and the streamed answer would stop following.
+      const up = el.scrollTop < last
+      last = el.scrollTop
+      if (distanceFromBottom < 80) stickToBottomRef.current = true
+      else if (up) stickToBottomRef.current = false
       setScrolledUp(distanceFromBottom > 160)
     }
     el.addEventListener('scroll', onScroll, { passive: true })