Desktop app browser has no system password manager integration (Apple Passwords autofill unavailable on macOS)

## Summary

There is no way to use the system password manager from the desktop app's built-in browser. On macOS this means Apple Passwords autofill is unavailable, so every login requires switching to the Passwords app, finding the entry, copying, switching back, and pasting - per field, per site.

## Environment

- Claude Code 2.1.235
- macOS 26.6.1 (build 25G76), arm64, Darwin 25.6.0
- Claude Code desktop app (ClaudeCode.app)
- Password manager: Apple Passwords (the system one, used via Safari and native apps)

## What happens

Open any login form in the app's browser. No autofill is offered. There is no way to invoke the system credential provider, and no way to open or query Apple Passwords from inside the app. The only path is manual copy and paste from a separate application.

## Expected

At minimum one of:

1. Support the macOS AutoFill credential provider API, so Apple Passwords (and any other registered provider) can fill credentials the way Safari and native apps do.
2. Failing that, an explicit "open system password manager" affordance.
3. At an absolute minimum, guarantee that paste into password fields is never blocked or intercepted, so the manual workaround stays viable.

## Why this matters

The premise of a password manager is that credentials are long, unique, and not memorized. An embedded browser with no autofill path does not just add friction, it pushes users toward reusing memorable passwords, which is a security regression rather than an inconvenience.

## Related

#79976 covers 1Password's credential-request failing in Claude in Chrome. That is the extension path in a real Chrome profile; this report is about the desktop app's own embedded browser and the macOS system provider, so I do not believe a fix for one covers the other. Flagging in case they share a root cause.

The report names no repository files, tests, or entry points. Begin by locating the desktop app's embedded-browser implementation and any macOS credential integration boundary, then determine the supported approach. Done means system password-provider autofill works, or the documented fallback and unrestricted password-field paste behavior are implemented.

索引モデルが issue の本文から書いたものです。