feat(model): LLM 多供应商适配（Adapter/OpenAI 非流式+SSE 流式/per-role 路由/主备降级/多模态检测/调用记录）

internal/runtime/model/router.go

@@ -0,0 +1,70 @@
+package model
+
+// Router maps roles to model names. An unknown role resolves to the configured
+// default model. When a request carries image content and a vision model is
+// configured, the request routes to the vision model.
+type Router struct {
+	defaultModel string
+	byRole       map[Role]string
+	visionModel  string
+}
+
+// RouterOption configures a Router.
+type RouterOption func(*Router)
+
+// WithRoleModel binds a model to a role.
+func WithRoleModel(role Role, model string) RouterOption {
+	return func(r *Router) { r.byRole[role] = model }
+}
+
+// WithVisionModel configures the dedicated vision model.
+func WithVisionModel(model string) RouterOption {
+	return func(r *Router) { r.visionModel = model }
+}
+
+// NewRouter builds a Router with a default model applied to any role that has
+// no explicit binding.
+func NewRouter(defaultModel string, opts ...RouterOption) *Router {
+	r := &Router{defaultModel: defaultModel, byRole: map[Role]string{}}
+	for _, o := range opts {
+		o(r)
+	}
+	return r
+}
+
+// Route returns the model for a role, falling back to the default model.
+func (r *Router) Route(role Role) string {
+	if m, ok := r.byRole[role]; ok && m != "" {
+		return m
+	}
+	return r.defaultModel
+}
+
+// RouteRequest picks the model for a request and reports whether the request
+// needs a vision model. When the request carries image content and a vision
+// model is configured, the vision model is returned with needsVision set to
+// true. Otherwise the role of the last message drives routing (user by
+// default).
+func (r *Router) RouteRequest(req Request) (model string, needsVision bool) {
+	role := RoleUser
+	if n := len(req.Messages); n > 0 {
+		role = req.Messages[n-1].Role
+	}
+	needsVision = HasImage(req.Messages)
+	if needsVision && r.visionModel != "" {
+		return r.visionModel, true
+	}
+	return r.Route(role), needsVision
+}
+
+// HasImage reports whether any message carries an image content part.
+func HasImage(msgs []Message) bool {
+	for _, m := range msgs {
+		for _, part := range m.Content {
+			if part.Type == ContentTypeImage {
+				return true
+			}
+		}
+	}
+	return false
+}