[BUG] Desktop Browser pane (macOS): no Passwords app / iCloud Keychain autofill and no passkey support

Problem

On macOS, the desktop app's built-in Browser pane cannot use the system's credentials at all:

• No Passwords app / iCloud Keychain autofill. Saved passwords from the macOS Passwords app are not offered in the pane, and there is no way to sync or pick them. Every sign-in means switching to the Passwords app, copying, and pasting by hand.
• Passkeys do not work. WebAuthn / platform authenticator (Touch ID, iCloud Keychain passkeys) is simply unsupported, so any site that is passkey-only or passkey-first is a dead end inside the pane.

Together this makes the in-app browser frustrating for Mac users on any site that needs a login, which is most of the admin consoles people want the agent to help with (developer consoles, store consoles, ad dashboards). The practical outcome is that users give up on the pane and fall back to Claude in Chrome, which defeats the point of a built-in browser.

What I'd expect

• Autofill from the macOS Passwords app / iCloud Keychain in the Browser pane (the same AutoFill integration Safari and other WebKit/Chromium apps get), with the user approving each fill.
• Passkey support via the platform authenticator (Touch ID), including iCloud Keychain passkeys and phone-as-authenticator (QR / hybrid).
• If either cannot be supported, a clear "open this sign-in in my default browser and bring the session back" path instead of a silent failure.

Related

• #77473 (built-in browser does not support passkeys on macOS)
• #100140 (support the Bitwarden extension in the Browser pane)

Environment

• Claude desktop app 2.31226.1, Claude Code 2.1.296
• macOS 27.0.1