Authentication profiles: durable login state across restarts

[SarthakWade]

Problem

Normal sessions share browser state, but persistence is not equivalent across engines. WKWebView uses persistent website storage, while Linux places Chromium's profile under the runtime directory. Linux login state therefore lacks a durable cross-reboot contract.

Proposed contract

Define a normal-profile storage location and lifecycle for both engines. Cookies and storage should survive host and machine restarts until the user clears them, logs out, or chooses a nonpersistent context.

Linux should use an XDG data location with a private directory, atomic setup, migration from the current runtime profile where safe, single-owner locking, and corruption recovery. macOS behavior should be made explicit and tested rather than relying on an implicit default.

Boundaries

Profile directories remain per-user and inaccessible to other users. No cookie import or unrestricted profile-path option is introduced. Sensitive diagnostics remain double-gated. Private contexts are handled by #35 and must never inherit normal profile state.

This changes persistence behavior and requires an architecture-decision entry.

Acceptance criteria

• The persistence and cleanup contract is documented for both engines.
• Linux profile permissions, locking, migration, and failure modes are tested.
• Login cookies survive controlled host restart tests on macOS and Linux.
• Logout and explicit clear operations remove the expected state.
• Concurrent hosts cannot silently corrupt or share one profile.
• Existing session-sharing documentation is corrected and E2E suites pass.

[yashranaway]

No Apple account needed. Do this first.

Linux currently loses login cookies when the host dies. WKWebView already persists, but that isn't a tested contract. Make cookies and storage survive restart on both engines, with logout/clear, single-owner locking, and no cookie-import back door.

Private contexts stay isolated per #35. This ticket does not wait on Developer ID or on #166.

[yashranaway]

Unblocked by decision 24 in #171. This is the first implementation ticket.

Linux: private XDG data dir, 0700, lock, safe migration off the runtime profile. macOS: keep persistent WKWebView storage and add restart tests. No cookie import. Private contexts still isolated per #35.