[FEATURE] Expose enterprise spending limit data via /api/oauth/usage

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

I'm building a Claude Code statusline extension that displays real-time usage information. For subscription plans, the /api/oauth/usage endpoint provides five_hour and seven_day utilization data, which works great for showing usage limits with reset timers.

However, for enterprise plans, this endpoint returns no usage data at all. Enterprise users have per-user monthly spending limits visible in the Console UI (Settings > Usage), but there's no programmatic way to access this information. The statusline can only show rough session cost estimates, while subscription users get a much richer experience with actual limit tracking.

This makes it impossible to build tools that help enterprise users monitor their budget consumption in real time.

Proposed Solution

The /api/oauth/usage endpoint should return spending limit data for enterprise plans, similar to how it already returns five_hour/seven_day data for subscription plans:

{
  "spending_limit": {
    "limit_usd": 1000.00,
    "used_usd": 133.49,
    "utilization": 13.35,
    "resets_at": "2025-05-01T00:00:00Z"
  }
}

This keeps the response structure consistent — enterprise users get a spending_limit object, subscription users get five_hour/seven_day objects. Tools consuming this API can handle both plan types uniformly.

Alternative Solutions

• Console UI: Manually checking Settings > Usage in the browser — not programmatic, breaks workflow.
• Session cost estimation: Calculating approximate cost from token counts per model — inaccurate and doesn't reflect the actual spending limit or cumulative usage.

Priority

Nice to have — Enterprise users can still work without this, but it would significantly improve the developer experience and enable better tooling.

Feature Category

API / CLI behavior

Use Case Example

1. An enterprise user starts a Claude Code session with a $1,000/month spending limit
2. They've used $800 so far this month and want to be mindful of remaining budget
3. Their statusline currently shows: Opus 4.6 | v1.0.80 | main | 120k/1.0M | $2.35 (only session cost)
4. With this feature, the statusline could show: Opus 4.6 | v1.0.80 | main | 120k/1.0M | 80% (5d12h) — showing 80% of monthly limit used with reset timer, just like subscription plans show their 5h/7d limits
5. This helps users pace their usage and avoid hitting the limit unexpectedly

Additional Context

• The subscription plan response structure (five_hour.utilization, five_hour.resets_at) is a great pattern to follow
• The proposed spending_limit object mirrors the same shape for consistency
• This would enable the community to build richer statusline extensions and monitoring tools for enterprise environments