test(web): harden live thinking tail observation

apps/web/tests/lifecycle-chrome.e2e.ts

@@ -159,7 +159,8 @@ describe('web e2e: lifecycle & chrome (workspace flow / reload / dark mode)', ()
     const settled = scaffold.whenTurnSettled()
     await input.fill(PROMPT)
     const observeTurn = async () => {
-      if (MODE !== 'record') await page.setViewportSize({ width: 640, height: 1000 })
+      const originalViewport = page.viewportSize() ?? { width: 1680, height: 1000 }
+      if (MODE !== 'record') await page.setViewportSize({ width: 480, height: 1000 })
       try {
         await input.press('Enter')
         if (MODE !== 'record') {
@@ -167,11 +168,11 @@ describe('web e2e: lifecycle & chrome (workspace flow / reload / dark mode)', ()
           await expect.poll(async () => await liveTail.evaluate(element => (
             element.scrollWidth > element.clientWidth
               && element.scrollLeft >= element.scrollWidth - element.clientWidth - 1
-          )), { timeout: 10_000 }).toBe(true)
+          )), { timeout: 10_000, interval: 10 }).toBe(true)
         }
         return await settled
       } finally {
-        if (MODE !== 'record') await page.setViewportSize({ width: 1680, height: 1000 })
+        if (MODE !== 'record') await page.setViewportSize(originalViewport)
       }
     }
     const sessionId = await observeTurn()

packages/client/ui-conversation/src/client/chat/ToolRow.tsx

@@ -5,7 +5,8 @@
 // Enter / Space, icon→chevron hover preview). The collapsed row is always
 // one line; every row with body, output, or a card material (terminal, diff,
 // read, search, web) is expandable; the summary stays inline while open,
-// except Think, whose body opens with the same first line and would repeat it.
+// except Think, where the running collapsed row follows the latest line at its
+// scroll end and the summary yields while open to avoid repeating the body.
 // The expanded body — an IN/OUT gutter-labeled card (figma 1249:35657) for
 // text input/output, the run_code program through CodeBlock, or a card
 // primitive (TerminalBlock, DiffBlock, ReadBlock, SearchBlock, WebBlock) for a