Sonnet model returns 'Rate limit reached' despite 0% usage

Bug Description

Sonnet model (claude-sonnet-4-6) immediately returns Rate limit reached error when spawning a subagent via Claude Code Agent tool, despite usage dashboard showing 0% Sonnet usage.

This issue has been persistent since the morning of 2026-03-18 (over 24 hours).

Environment

• Claude Code running inside VS Code extension (Dev Container)
• Platform: Linux (WSL2)
• Opus 4.6 and Haiku 4.5 work normally in the same session

Steps to Reproduce

1. Open Claude Code in VS Code
2. Spawn a subagent with model: "sonnet"
3. Agent immediately fails (221ms) with Rate limit reached
4. Check usage dashboard — shows 0% Sonnet usage, 4% All models

Expected Behavior

Sonnet subagent should execute normally when usage is at 0%.

Actual Behavior

• Instant rejection (221ms response time — no actual API call attempted)
• Error: API Error: Rate limit reached
• Haiku and Opus agents work fine in the same session

Dashboard at time of report

• Current session: 6% used
• Weekly — All models: 4% used
• Weekly — Sonnet only: 0% used