[Feature Request] Per-model usage credits restriction to prevent overage on plan-included models

Bug Description
Title: Allow restricting usage credits to specific models (e.g. Fable only)

Problem
I use Opus as my main model in Claude Code with Fable as the
advisor (/advisor fable). On my plan, Fable bills to usage credits, so
credits must stay enabled. But usage credits are a single pool: once I
hit my plan limits, the main model silently continues on credits too.
I want to pay credits for Fable advisor calls only, never for models
already included in my plan.

Current workarounds (all inadequate)

• A low spend cap or small prepaid balance: limits the damage, but

spillover from the main model still drains the budget meant for Fable.

• Watching /usage and stopping manually: easy to miss, especially in

long or background sessions.

Requested behavior
A per-model control over usage credits, for example:

• an account setting "Allow usage credits for: [Fable only / all models]"
• or a Claude Code setting such as "usageCreditsModels": ["fable"]

When plan limits are reached with this set, non-allowed models should
stop with the normal limit message instead of billing to credits, while
Fable advisor calls keep working.

Environment
Plan: Pro
Claude Code version: 2.1.291
OS: Windows

Environment Info

• Platform: win32
• Terminal: null
• Version: 2.1.291
• Feedback ID: 5f1df8a0-98c9-4db8-90c6-7a363f65db97