[FEATURE] Add automatic authentication failover between Pro Plan and API

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Claude Code Pro plan users face interruptions when they hit their usage limits during a billing period. Currently, there's no way to automatically fall back to API key billing when Pro plan quota is exhausted, then switch back
when the quota resets.

Proposed Solution

Add automatic authentication failover with the following behavior:

1. Primary: Use Pro plan quota by default
2. Failover: When Pro plan quota is exhausted (rate limit/usage block), automatically switch to API key billing
3. Recovery: When Pro plan quota resets (timer resets), automatically switch back to Pro plan

{
"authentication": {
"primary": "claude_pro",
"fallback": {
"enabled": true,
"method": "api_key",
"apiKey": "${ANTHROPIC_API_KEY}"
},
"autoRecover": true
}
}

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

Configuration and settings

Use Case Example

_No response_

Additional Context

• Pro plan users already have both entitlements (included quota + ability to use API keys)
• Similar fallback patterns exist in other services (AWS, Google Cloud)
• Would make Claude Code more suitable for high-volume professional use