Haiku models don't support extended thinking at all. Without this
guard, claude-haiku-4-5-20251001 would receive type=enabled +
budget_tokens and return a 400 error.
Incorporates the fix from PR #1127 (by frizynn) on top of #1128's
adaptive thinking refactor.
Verified live with Claude Code OAuth:
claude-opus-4-6 → adaptive thinking ✓
claude-haiku-4-5 → no thinking params ✓
claude-sonnet-4 → enabled thinking ✓
638136e353