Rotate across Claude accounts when one hits its usage limit, including running agents

[andripeetso]

Idea
I have three Claude subscriptions set up as provider instances (A, B, C via CLAUDE_CONFIG_DIR). When the active one hits its 5-hour limit, I want T3 to move the work to the next account that still has headroom and keep going: A → B → C → back to A once A has reset.

That should cover everything running on the limited account, not just the thread I'm looking at: other threads, lineage and delegated child agents, scheduled wakes and queued messages.

Today
On usage_limit the thread only waits for that account's reset (auto-resume or snooze, always on the same instance). Every thread and child agent on that account stops. Switching means picking another instance in each thread's model picker by hand. Lineage agents can't be switched like that, and I'm usually AFK when it happens.

Proposal

• A rotation order of Claude instances, set in provider settings.
• When an instance reports usage_limit, everything running on it continues on the next instance that isn't limited (T3 already tracks each instance's limit windows from rate_limit_event). Each thread shows a "Switched A → B" notice.
• Queued and pending messages move to the new account too. Otherwise queue pinning ([Bug]: Queued agent messages silently switch a thread back to an account the user explicitly left #22457) switches them straight back to the limited one.
• If every account is limited, auto-resume on whichever resets first.
• An off switch per thread or project.

Related: #21705, #22457