agentHost: avoid persisting ephemeral connections

[Aaron Munger (amunger)]

What changed

• persist managed WebSocket hosts in chat.remoteAgentHosts
• persist managed SSH hosts only in application storage
• keep WSL, tunnel, and cloud sandbox connection registration runtime-only because their owning services handle discovery/cache state or use short-lived credentials
• use an exhaustive per-connection-type switch that documents each persistence boundary
• add regression coverage for WebSocket settings writes, SSH storage without settings writes, and ephemeral registration without central persistence

Why

Registering a dev tunnel rewrote settings.json even though tunnel entries are filtered from persisted configuration. On Windows, an existing file lock could make the atomic settings-file rename fail and incorrectly surface an otherwise successful tunnel connection as failed.

Separating the persistence paths also avoids the same redundant settings rewrite for SSH connections, whose durable metadata belongs in application storage rather than user settings.

Validation

• npm run typecheck-client
• scripts\test.bat --run src\vs\platform\agentHost\test\electron-browser\remoteAgentHostService.test.ts (32 passing)
• npm run valid-layers-check
• changed-file hygiene

[Copilot]

Pull request overview

Prevents ephemeral managed agent-host connections from rewriting user settings while preserving durable WebSocket and SSH persistence.

Changes:

• Limits persistence to WebSocket and SSH connections.
• Adds regression coverage for tunnel, WSL, and cloud sandbox connections.

Show a summary per file

File	Description
remoteAgentHostServiceImpl.ts	Gates managed-connection persistence by durable connection type.
remoteAgentHostService.test.ts	Verifies ephemeral registration causes no configuration writes.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Balanced