Remote agent host sessions often fail to open in Insiders 1.143 ("Couldn't load this conversation", and re-opening doesn't retry) #341828

Telemetry (agents/sessionOpen, Insiders, last 3 days) shows a jump on 1.143 builds in remote agent host opens that never bind the chat. Those opens end as timeout or cancelled, with no model bound:

By build, for remote: 16d22415b6 is normal, 4c6cba1504 is at 24–64%, and 9ebdca5c15 is at 71%. Older builds stay normal over the same hours, so this is client-side, not a service change.

Likely cause: f9eda24 (#340702). It's the only commit in 16d22415b6..4c6cba1504 that changes how the Agents window loads chats.

1. Failed loads stay stuck.
   • The error path of ChatView._loadChat now keeps _currentChatResource and shows "Couldn't load this conversation. / Retry".
   • Before, it cleared _currentChatResource, so the next setChat reloaded the chat and recovered. That next setChat came from re-clicking the session, or from ChatGroupView re-running its autorun.
   • Now every later setChat for that chat takes the !chatChanged early return and never reloads.
2. Replacing a provider cancels loads in progress.
   • Disposing a chat session content provider registration now cancels any content resolution in progress.
   • Remote agent hosts dispose and re-register their provider when the connection's clientId changes, for example on reconnect.
   • So a load that is waiting on the remote subscription rejects with a CancellationError that did not come from the view's own token. It then ends up stuck as in (1).
   • This part is reasoned from the code, not reproduced.

Local hosts register their provider once, which would explain why only remote is affected.

Suggested fix:

• When the user re-opens a chat whose load failed (a setChat on a chat left unbound after the failure), retry the load.
• Treat a CancellationError that isn't from the view's own token (the provider was replaced) as a reason to retry, not as a failure.
• Optionally, report modelBindFailed instead of letting the open time out.

I can share the dashboard queries if useful.