agent: apply config backend/model when switching agents via /agent

pkg/agent/commands.go

@@ -207,6 +207,19 @@ func (s *agent) handleCommand(ctx context.Context, input string, handler EventHa
 			}
 			d := s.newDispatcher()
 			env := BuildAgentEnv(cfg, d, s.cwd)
+			if env.Backend != "" {
+				newBe, err := s.newBackend(env.Backend)
+				if err != nil {
+					handler(infoEvent(fmt.Sprintf("error: backend %q: %v", env.Backend, err)))
+					return
+				}
+				if env.Model != "" {
+					newBe.SetModel(env.Model)
+				}
+				s.cfg.Backend = newBe
+			} else if env.Model != "" {
+				s.cfg.Backend.SetModel(env.Model)
+			}
 			s.dispatcher = env.dispatcher
 			s.hooks = env.Hooks
 			s.cfg.preamble = env.preamble

pkg/agent/core.go

@@ -38,6 +38,8 @@ type AgentEnv struct {
 	preamble     string
 	genParams    backend.GenerationParams
 	maxSteps     int
+	Backend      string // from config; empty means no override
+	Model        string // from config; empty means no override
 	Messages     []string
 }
 
@@ -136,6 +138,12 @@ func BuildAgentEnv(cfg *config.Config, d tools.Dispatcher, cwd string) AgentEnv
 		}
 	}
 
+	var backendName, modelName string
+	if cfg != nil {
+		backendName = cfg.Backend
+		modelName = cfg.Model
+	}
+
 	return AgentEnv{
 		dispatcher:   d,
 		tools:        allTools,
@@ -145,6 +153,8 @@ func BuildAgentEnv(cfg *config.Config, d tools.Dispatcher, cwd string) AgentEnv
 		preamble:     preamble,
 		genParams:    genParams,
 		maxSteps:     maxSteps,
+		Backend:      backendName,
+		Model:        modelName,
 		Messages:     messages,
 	}
 }