Clicking "New chat" (the brand/welcome navigation path) left the previous
session's unsent draft in the composer (issue #1343). The direct model-picker
path (createDirectChat) already cleared it, but the welcome path did not.
Clear `#message` in chatRenderer.showWelcomeScreen() — the shared entry point
for that state — resetting its autosized height and dispatching an `input` event
so the send button / autosize listeners update. Switching between existing
sessions loads them directly and does not call showWelcomeScreen, so genuine
drafts are not erased.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
