fix(opencode): add input token limit for Claude Opus 4.6

[okhsunrog]

Summary

Adds input = 200_000 to the opencode provider's Claude Opus 4.6 model definition.

Context

Related to anomalyco/opencode#12342 (comment)

Claude Opus 4.6 has a 1M context window, but without the context-1m-2025-08-07 beta header the Anthropic API enforces a 200k input token limit. The opencode provider uses OAuth, which doesn't support this beta header, so the effective input limit is 200k.

This is different from models with a 200k context window (like Haiku 4.5), where 200k is the total budget for input + output combined. For Opus 4.6, the 200k only gates input tokens — output and thinking tokens live in the larger 1M context window space.

Without this field, opencode's compaction logic (compaction.ts:37) falls back to context - output (1M - 128k = ~872k) as the compaction threshold, which is far too high. The API rejects requests at 200k input tokens long before compaction triggers.

The model.limit.input field is already supported in opencode's compaction check — it just wasn't populated for this model.

[okhsunrog]

Looks like I was wrong about this, closing it