Provider instances: a manual order for accounts of the same driver

[mkantautas]

Problem

I have three Claude accounts as provider instances (M, V and Claude Team) and want them used in that order. T3 has no notion of a preferred order between instances of one driver.

When the composer's instance is disabled or unavailable, it falls back to the first ready instance of the same driver. That order is alphabetical by display name: provider snapshots are sorted by driver, then display name, then instance id (providerStatusCache.ts#L46-L55), and the composer takes the first ready entry (ChatView.logic.ts#L603-L607). With M disabled, new threads land on "Claude Team", because C sorts before V, although V is the account I want next.

Today the only way to steer this is to rename the accounts so they sort in the order I want.

Proposal

A manual order for the instances of one driver, set by dragging them in Settings → Providers and stored in settings. The composer's same-driver fallback follows it. The same order could also drive the instance list in the model picker and the account columns in Usage → Limits, which #23903 asks to make stable.

Scope

• Only the order of instances within one driver. Switching accounts automatically on usage limits is a separate idea (Scheduled tasks: optional fallback provider/model when the primary hits usage limits #16512, Unified subscription and API usage with configurable fallback #19695).
• With no order set, today's order stays, so nothing changes for anyone who doesn't set one.