- config.go: LLMConfig.FallbackMaxTokens(LLM_FALLBACK_MAX_TOKENS, 默认8192) - runtimeconfig/models.go: Group.MaxTokens(models.json每模型独立预算, 负值拒绝) - model/fallback.go: Chain.WithTokenBudget + applyBudget; runtime.go buildSnapshot接入(active.MaxTokens, env.FallbackMaxTokens) - 优先级: 显式Request.MaxTokens > 组maxTokens > 仅多步链末端的LLM_FALLBACK_MAX_TOKENS > 适配器默认8192; 单步链不动env兜底(避免OpenAI主模型行为回归) - gateway admin: AdminLlmProvider.MaxTokens 透传/回显/负值400 - .env.example + .env(LLM_FALLBACK_MAX_TOKENS=8192); Docs/api-client v0.27 + api-reference + design/04 - 新增测试(config/runtimeconfig/budget_test/admin_write), build/vet/test绿+3平台交叉编译