Allow newlines in the message composer and fix loading earlier messages

[kentcdodds]

Fixes the two bugs from this Cap recording on the recipient thread page.

Newlines in the composer. Enter used to add the message to the queue, so on phones the Return key queued half-written notes and there was no obvious way to add a line break. Enter now inserts a newline on every device. Cmd/Ctrl+Enter or the "Add to Queue" button adds the message. The textarea also sets enterKeyHint="enter" so mobile keyboards label the key as a line break.

Infinite scroll. "Scroll up to load earlier messages" never loaded anything. The fetcher loaded ?cursor=… from an index route without ?index, so React Router sent the request to the parent $recipientId layout loader. That loader has no pastMessages and no searchQuery, so the merge effect returned early every time. The fetch now includes index, and earlier pages append while keeping the scroll position.

Test Plan

• New tests/e2e/recipient-thread.test.ts:
  • Typing, pressing Enter, and typing again leaves one multi-line draft with nothing queued. The button queues First line\nSecond line, and Cmd/Ctrl+Enter queues a second message.
  • With 75 sent messages, scrolling to the top with the mouse wheel loads 30, then 60, then all 75, and the "Scroll up…" hint goes away.
  • Both tests fail on main (Enter queues the message, and the thread stays at 30 messages) and pass with this change. They passed 5 repeats each.
• Full e2e suite with one worker, as in CI: 16/16 pass. bun run lint, bun run typecheck, and bun run test pass.

Checklist

• Tests updated
• Docs updated

Screenshots

Before (from the recording): the thread is stuck at "Scroll up to load earlier messages."

  

[kentcdodds]

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