Banner for remote server disconnect

[kevinyang372]

Summary

When a remote SSH session disconnects while a code editor or file notebook pane is open, the pane silently becomes stale — save fails, auto-reload stops, and there is no visual indication. This PR adds a disconnection banner and save guard.

Changes

• Disconnection banner — Shows "Remote host disconnected. You will not be able to see updates and save changes." above the editor/notebook content when the remote host loses connection. The banner auto-dismisses on reconnection.
• Save guard — save_local() immediately returns ImmediateSaveError::RemoteDisconnected when the host is disconnected, with a specific toast message ("Cannot save — remote session disconnected.").
• On-the-fly state derivation — No stored boolean; is_remote_disconnected() checks RemoteServerManager::client_for_host() each render, so it is always in sync.
• File notebook support — FileNotebookView subscribes to HostDisconnected/HostConnected events to trigger re-renders.
• Loaded-only gating — Banner only appears if the file was successfully loaded; error/loading states handle the "never loaded" case.

Files Changed

• app/src/code/mod.rs — Added ImmediateSaveError::RemoteDisconnected variant
• app/src/code/local_code_editor.rs — is_remote_disconnected(), save guard, render banner, render_remote_disconnected_banner()
• app/src/code/view.rs — Specific toast + error handling for RemoteDisconnected
• app/src/notebooks/file/mod.rs — is_remote_disconnected(), render banner, subscribe to RemoteServerManager events

Conversation

https://staging.warp.dev/conversation/bab4762c-633a-40a3-9258-4a0752b608e1

Plan

https://staging.warp.dev/drive/notebook/VqsXi9GmQ7EW1TnCJ9jlOp

Demo

https://www.loom.com/share/f0bab2f11c4047609bf1b318827af0ec

[kevinyang372]

• Banner for remote server disconnect #11565 👈 (View in Graphite)
• master

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@kevinyang372

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[oz-for-oss]

Overview

This PR adds remote-disconnect detection, a banner, and a save failure toast for remote code editor and file notebook panes.

Concerns

• The file notebook change contains a Rust move-out-of-borrow compile error in the new loaded-state check.
• The code editor banner is derived at render time, but the view is not subscribed to remote host connection events, so the banner may not appear or disappear when the remote connection state changes.
• No security findings. No approved spec context was available for this PR.

Verdict

Found: 1 critical, 1 important, 0 suggestions

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