OpenCode Go 5-hour limit shows ~50% consumed after only ~$1.80 of usage (DeepSeek V4 Pro, 13.9M cache reads)

Bug Report

OpenCode Go 5-hour usage limit shows ~50% (≈$6 of the $12 window) consumed, but actual usage is only ~$1.80. Requests get rate-limited before the dollar limit is reached.

Actual behavior

• 5-hour limit: ~50% consumed with < $2 real usage
• Local opencode stats --days 1 --models output:
  • opencode-go/deepseek-v4-pro: 102 messages, 673.1K input, 143.6K output, 13.9M cache read, local cost $1.03
  • opencode-go/deepseek-v4-flash: 18 messages, 44.6K input, 4.6K output, 233.9K cache read, local cost $0.01
  • Total local cost: $1.83
• Suspected cause: cache-read tokens billed at full input price instead of the discounted cache price ($0.022/M for DeepSeek V4 Pro), inflating usage ~30x (13.9M x $0.66 = ~$9.2)

Expected behavior

Usage should be counted at the documented Go rates (cache read = $0.022/M off-peak for V4 Pro).

Environment

• OpenCode 1.18.18
• Plan: OpenCode Go ($10/mo)
• Model: opencode-go/deepseek-v4-pro, opencode-go/deepseek-v4-flash

Related: #38570, #24473, #38855, #26213