fix(web): reveal a caret that sits after a newline, where the engines disagree

A caret straight after a newline is on a line with nothing to measure — the shape a trailing-newline draft ends in. chromium returns no client rects at all for the collapsed position (an all-zero box, which sent the reveal upward instead), firefox reports the line above, WebKit the right one. Measure the newline the caret just left and step one line down: all three then land on 649 of 652 with the caret's line at 315 inside the 336px box. The browser case now pastes a newline-terminated block, and fails 'expected 0 to be greater than 0' without the rule.

apps/web/tests/composer-draft-scroll.e2e.ts

@@ -380,7 +380,10 @@ describe('web e2e: composer draft scrolling', () => {
       const data = new DataTransfer()
       data.setData('text/plain', text)
       el.dispatchEvent(new ClipboardEvent('paste', { clipboardData: data, bubbles: true, cancelable: true }))
-    }, `\n${DRAFT}`)
+      // Ending in a newline is the shape the engines disagree on: the caret
+      // lands on a line with nothing on it, where chromium reports no client
+      // rects at all for the collapsed position.
+    }, `\n${DRAFT}\n`)
     await expect.poll(async () => (await measureComposer(page)).overflows, { timeout: 10_000 }).toBe(true)
     // The restore lands one frame after the machine commits the draft, so the
     // box overflows before it moves; waiting on the offset is waiting for the
@@ -449,7 +452,7 @@ describe('web e2e: composer draft scrolling', () => {
       const data = new DataTransfer()
       data.setData('text/plain', text)
       el.dispatchEvent(new ClipboardEvent('paste', { clipboardData: data, bubbles: true, cancelable: true }))
-    }, `\n${DRAFT}`)
+    }, `\n${DRAFT}\n`)
     await expect.poll(async () => (await measureComposer(page)).overflows, { timeout: 10_000 }).toBe(true)
     await expect.poll(async () => (await measureComposer(page)).scrollTop, { timeout: 10_000 }).toBeGreaterThan(0)
     const pasted = await measureComposer(page)