weichen
e63a9f38dd
Why: acceptance clause 1 requires the anthropic preset to complete a tool-call round against recorded HTTP fixtures; audit N4's root cause was an offline body builder the real client never used, with no tool_use/thinking support on the wire. Evidence: GOWORK=off go vet + go test -count=1 ./... green; TestAnthropicPresetToolRound drives the preset through tools request → tool_use → tool_result → final text with thinking-signature round-trip against byte-recorded SSE fixtures; TestAnthropicBodyShape pins block forms and cache_control; legacy OpenAI path untouched (Client.Protocol zero value). Impact: the anthropic preset now means the native Messages API (the compat shim remains reachable via models.json custom providers); audit N4 closes. BuildBody shares anthropicBody with the live client. Refs: Agent-System-Documents#42 (N2 plan WP2), audit N4