[BUG] VSCode extension: Unsent prompt text lost when new session is opened

Extension version: 2.1.294 · macOS

What happened: I spent a long time writing a detailed prompt in a session's input box, but hadn't yet finished or sent it. I pressed Cmd+N to open a new untitled file, but because the Claude panel where I'd been typing was focused, the extension caught the shortcut and opened a new Claude session instead. When I went back to the original session, the input box was empty and the draft was gone.

Expected: Unsent drafts survive switching between sessions, ideally saved per session to webview state or extension storage so they also survive a panel reload. At minimum, a session with a non-empty draft shouldn't be dropped without a warning.

Investigation: I asked Claude for help, and it checked the extension's globalState and workspaceState, the webview's localStorage and sessionStorage, and ~/.claude. It didn't find anything, so it appears it only existed in the webview's memory and can't be recovered.

Secondary issue, though much less important if the main issue is fixed: Taking over Cmd+N, a core VSCode shortcut, is surprising. Consider not binding it by default.

Related: #63975 (same data loss on iOS)