[alvinwin]

Summary

• add the standard COSMIC sub-page back control after selecting one of multiple Bluetooth adapters
• return directly to the adapter chooser by clearing the selected adapter
• recompute the Bluetooth status heading when entering or leaving an adapter
• add regression coverage for chooser, selected-adapter, and return states

Root cause

The multi-adapter chooser stores the selected adapter as in-page state. Bluetooth is registered as a top-level settings page, so it did not receive the automatic back header used by separately registered sub-pages even though SelectAdapter(None) already provided the correct state transition.

Fixes pop-os/pop#3931.

Validation

• cargo fmt --all --check
• cargo clippy --all-features
• cargo test --all-features (42 passed)
• manually launched cosmic-settings bluetooth with two adapters, selected an adapter, and used the new back control to return to the chooser

Manual result

The existing mouse-button-4 behavior is outside this patch; this change addresses the missing visible navigation control reported in the issue.

[jklgrasso]

Since the Bluetooth page was the only change, I didn't do the full checklist.

Bluetooth

• Bluetooth device connects.
• Paired device can be disconnected & reconnected.
• Paired device can be forgotten & connecting again works.

This change works as expected :)