fix: resolve model selector mismatch for ACP agents (#410)

apps/backend/cmd/mock-agent/emitter.go

@@ -70,7 +70,7 @@ func (e *emitter) completeTool(id acp.ToolCallId, output any) {
 func (e *emitter) requestPermission(toolCallID acp.ToolCallId, title string, kind acp.ToolKind, input any) bool {
 	resp, err := e.conn.RequestPermission(e.ctx, acp.RequestPermissionRequest{
 		SessionId: e.sid,
-		ToolCall: acp.RequestPermissionToolCall{
+		ToolCall: acp.ToolCallUpdate{
 			ToolCallId: toolCallID,
 			Title:      acp.Ptr(title),
 			Kind:       acp.Ptr(kind),

apps/backend/cmd/mock-agent/main.go

@@ -116,6 +116,10 @@ func (a *mockAgent) SetSessionMode(_ context.Context, _ acp.SetSessionModeReques
 	return acp.SetSessionModeResponse{}, nil
 }
 
+func (a *mockAgent) SetSessionConfigOption(_ context.Context, _ acp.SetSessionConfigOptionRequest) (acp.SetSessionConfigOptionResponse, error) {
+	return acp.SetSessionConfigOptionResponse{}, nil
+}
+
 // extractPromptText concatenates text content blocks from the prompt.
 func extractPromptText(blocks []acp.ContentBlock) string {
 	var parts []string

apps/backend/go.mod

@@ -114,4 +114,4 @@ require (
 
 // Fix for ACP notification ordering race condition
 // See: https://github.com/coder/acp-go-sdk/issues/20
-replace github.com/coder/acp-go-sdk => github.com/kdlbs/acp-go-sdk v0.6.3-fix.1
+replace github.com/coder/acp-go-sdk => github.com/agentcooper/acp-go-sdk v0.0.0-20260227120930-f21f3950f56d

apps/backend/go.sum

@@ -48,6 +48,8 @@ github.com/Microsoft/go-winio v0.4.21 h1:+6mVbXh4wPzUrl1COX9A+ZCvEpYsOBZ6/+kwDnv
 github.com/Microsoft/go-winio v0.4.21/go.mod h1:JPGBdM1cNvN/6ISo+n8V5iA4v8pBzdOpzfwIujj1a84=
 github.com/UserExistsError/conpty v0.1.4 h1:+3FhJhiqhyEJa+K5qaK3/w6w+sN3Nh9O9VbJyBS02to=
 github.com/UserExistsError/conpty v0.1.4/go.mod h1:PDglKIkX3O/2xVk0MV9a6bCWxRmPVfxqZoTG/5sSd9I=
+github.com/agentcooper/acp-go-sdk v0.0.0-20260227120930-f21f3950f56d h1:9VmeQddWE4m9UksAzVg0Me8V1KhXy8fOI1nLnWn94WM=
+github.com/agentcooper/acp-go-sdk v0.0.0-20260227120930-f21f3950f56d/go.mod h1:yKzM/3R9uELp4+nBAwwtkS0aN1FOFjo11CNPy37yFko=
 github.com/bahlo/generic-list-go v0.2.0 h1:5sz/EEAK+ls5wF+NeqDpk5+iNdMDXrh3z3nPnH1Wvgk=
 github.com/bahlo/generic-list-go v0.2.0/go.mod h1:2KvAjgMlE5NNynlg/5iLrrCCZ2+5xWbdbCW3pNTGyYg=
 github.com/buger/jsonparser v1.1.1 h1:2PnMjfWD7wBILjqQbt530v576A/cAbQvEW9gGIpYMUs=
@@ -219,8 +221,6 @@ github.com/json-iterator/go v1.1.12 h1:PV8peI4a0ysnczrg+LtxykD8LfKY9ML6u2jnxaEnr
 github.com/json-iterator/go v1.1.12/go.mod h1:e30LSqwooZae/UwlEbR2852Gd8hjQvJoHmT4TnhNGBo=
 github.com/jstemmer/go-junit-report v0.0.0-20190106144839-af01ea7f8024/go.mod h1:6v2b51hI/fHJwM22ozAgKL4VKDeJcHhJFhtBdhmNjmU=
 github.com/jstemmer/go-junit-report v0.9.1/go.mod h1:Brl9GWCQeLvo8nXZwPNNblvFj/XSXhF0NWZEnDohbsk=
-github.com/kdlbs/acp-go-sdk v0.6.3-fix.1 h1:zLSz0WHHtFvNTVa43LDvX8G3QTM6TnvCFU31HZMthKY=
-github.com/kdlbs/acp-go-sdk v0.6.3-fix.1/go.mod h1:yKzM/3R9uELp4+nBAwwtkS0aN1FOFjo11CNPy37yFko=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
 github.com/klauspost/compress v1.17.0 h1:Rnbp4K9EjcDuVuHtd0dgA4qNuv9yKDYKK1ulpJwgrqM=
 github.com/klauspost/compress v1.17.0/go.mod h1:ntbaceVETuRiXiv4DpjP66DpAtAGkEQskQzEyD//IeE=

apps/backend/internal/agentctl/server/adapter/transport/acp/adapter.go

@@ -102,7 +102,7 @@ type Adapter struct {
 
 	// Available models from the most recent session creation/load.
 	// Used by SetModel to validate the requested model exists.
-	availableModels []acp.ModelInfo
+	availableModels []acp.UnstableModelInfo
 
 	// Synchronization
 	mu     sync.RWMutex
@@ -266,7 +266,7 @@ func (a *Adapter) NewSession(ctx context.Context, mcpServers []types.McpServer)
 
 	// Emit session models if the agent returned model state
 	if resp.Models != nil {
-		a.emitSessionModels(sessionID, resp.Models, resp.Meta)
+		a.emitSessionModels(sessionID, resp.Models, resp.Meta, resp.ConfigOptions)
 	}
 
 	// Emit session status event to normalize with other adapters.
@@ -315,7 +315,7 @@ func toACPMcpServers(servers []types.McpServer) []acp.McpServer {
 		switch server.Type {
 		case "sse":
 			out = append(out, acp.McpServer{
-				Sse: &acp.McpServerSse{
+				Sse: &acp.McpServerSseInline{
 					Name:    server.Name,
 					Url:     server.URL,
 					Type:    "sse",
@@ -394,7 +394,7 @@ func (a *Adapter) LoadSession(ctx context.Context, sessionID string) error {
 
 	// Emit session models if the agent returned model state
 	if resp.Models != nil {
-		a.emitSessionModels(sessionID, resp.Models, resp.Meta)
+		a.emitSessionModels(sessionID, resp.Models, resp.Meta, resp.ConfigOptions)
 	}
 
 	// Emit session status event to normalize with other adapters.
@@ -838,8 +838,8 @@ func (a *Adapter) convertAvailableCommands(sessionID string, update *acp.Session
 			Name:        cmd.Name,
 			Description: cmd.Description,
 		}
-		if cmd.Input != nil && cmd.Input.UnstructuredCommandInput != nil {
-			ac.InputHint = cmd.Input.UnstructuredCommandInput.Hint
+		if cmd.Input != nil && cmd.Input.Unstructured != nil {
+			ac.InputHint = cmd.Input.Unstructured.Hint
 		}
 		commands[i] = ac
 	}
@@ -870,16 +870,50 @@ func (a *Adapter) emitInitialModeState(modes *acp.SessionModeState) {
 }
 
 // emitSessionModels emits a session_models event from the session response.
-func (a *Adapter) emitSessionModels(sessionID string, models *acp.SessionModelState, meta any) {
+func (a *Adapter) emitSessionModels(sessionID string, models *acp.UnstableSessionModelState, meta map[string]any, acpConfigOptions []acp.SessionConfigOption) {
+	currentModelID := string(models.CurrentModelId)
+	// Prefer typed config options from the response; fall back to _meta extraction for older agents
+	configOptions := convertACPConfigOptions(acpConfigOptions)
+	if len(configOptions) == 0 {
+		configOptions = extractConfigOptions(meta)
+	}
+
+	// Fallback: if the SDK didn't parse currentModelId (some agents omit it),
+	// try to resolve it from configOptions or the first available model.
+	if currentModelID == "" {
+		currentModelID = resolveCurrentModelFromConfig(configOptions)
+	}
+	if currentModelID == "" && len(models.AvailableModels) > 0 {
+		currentModelID = string(models.AvailableModels[0].ModelId)
+		a.logger.Info("currentModelId empty, using first available model as fallback",
+			zap.String("fallback_model", currentModelID),
+		)
+	}
+
+	a.logger.Info("emitting session_models event",
+		zap.String("session_id", sessionID),
+		zap.String("current_model_id", currentModelID),
+		zap.Int("available_models", len(models.AvailableModels)),
+	)
 	a.sendUpdate(AgentEvent{
 		Type:           streams.EventTypeSessionModels,
 		SessionID:      sessionID,
-		CurrentModelID: string(models.CurrentModelId),
+		CurrentModelID: currentModelID,
 		SessionModels:  convertSessionModels(models.AvailableModels),
-		ConfigOptions:  extractConfigOptions(meta),
+		ConfigOptions:  configOptions,
 	})
 }
 
+// resolveCurrentModelFromConfig extracts current model ID from configOptions.
+func resolveCurrentModelFromConfig(options []streams.ConfigOption) string {
+	for _, opt := range options {
+		if opt.ID == "model" || opt.Category == "model" {
+			return opt.CurrentValue
+		}
+	}
+	return ""
+}
+
 // SetMode changes the agent's session mode via ACP session/set_mode.
 func (a *Adapter) SetMode(ctx context.Context, modeID string) error {
 	a.mu.RLock()
@@ -937,9 +971,9 @@ func (a *Adapter) SetModel(ctx context.Context, modelID string) error {
 		}
 	}
 
-	_, err := conn.SetSessionModel(ctx, acp.SetSessionModelRequest{
+	_, err := conn.UnstableSetSessionModel(ctx, acp.UnstableSetSessionModelRequest{
 		SessionId: acp.SessionId(sessionID),
-		ModelId:   acp.ModelId(modelID),
+		ModelId:   acp.UnstableModelId(modelID),
 	})
 	if err != nil {
 		return fmt.Errorf("set session model failed: %w", err)
@@ -958,7 +992,7 @@ func (a *Adapter) Authenticate(ctx context.Context, methodID string) error {
 	}
 
 	_, err := conn.Authenticate(ctx, acp.AuthenticateRequest{
-		MethodId: acp.AuthMethodId(methodID),
+		MethodId: methodID,
 	})
 	if err != nil {
 		return fmt.Errorf("authenticate failed: %w", err)

apps/backend/internal/agentctl/server/adapter/transport/acp/conversion_test.go

@@ -646,7 +646,7 @@ func TestConvertAvailableCommands_WithInputHint(t *testing.T) {
 				Name:        "search",
 				Description: "Search codebase",
 				Input: &acp.AvailableCommandInput{
-					UnstructuredCommandInput: &acp.AvailableCommandUnstructuredCommandInput{
+					Unstructured: &acp.UnstructuredCommandInput{
 						Hint: "Enter search query",
 					},
 				},

apps/backend/internal/agentctl/server/adapter/transport/acp/meta_convert.go

@@ -64,7 +64,7 @@ func extractTerminalAuth(meta map[string]any) *streams.TerminalAuth {
 
 // convertSessionModels converts ACP model info to stream types,
 // normalizing known _meta patterns (copilotUsage) while preserving raw _meta.
-func convertSessionModels(models []acp.ModelInfo) []streams.SessionModelInfo {
+func convertSessionModels(models []acp.UnstableModelInfo) []streams.SessionModelInfo {
 	if len(models) == 0 {
 		return nil
 	}
@@ -106,6 +106,41 @@ func extractUsageMultiplier(meta map[string]any) string {
 	}
 }
 
+// convertACPConfigOptions converts typed ACP SessionConfigOption to stream ConfigOption.
+// This is the preferred path when the SDK properly parses configOptions from the response.
+func convertACPConfigOptions(opts []acp.SessionConfigOption) []streams.ConfigOption {
+	if len(opts) == 0 {
+		return nil
+	}
+	result := make([]streams.ConfigOption, 0, len(opts))
+	for _, opt := range opts {
+		if opt.Select == nil {
+			continue
+		}
+		s := opt.Select
+		co := streams.ConfigOption{
+			Type:         s.Type,
+			ID:           string(s.Id),
+			Name:         s.Name,
+			CurrentValue: string(s.CurrentValue),
+		}
+		if s.Category != nil {
+			co.Category = string(*s.Category)
+		}
+		// Extract options from ungrouped list (most common case)
+		if s.Options.Ungrouped != nil {
+			for _, o := range *s.Options.Ungrouped {
+				co.Options = append(co.Options, streams.ConfigOptionValue{
+					Value: string(o.Value),
+					Name:  o.Name,
+				})
+			}
+		}
+		result = append(result, co)
+	}
+	return result
+}
+
 // extractConfigOptions extracts config options from ACP session _meta.
 // Example _meta: {"configOptions": [{"type": "select", "id": "mode", "name": "Mode", ...}]}
 func extractConfigOptions(meta any) []streams.ConfigOption {

apps/backend/internal/orchestrator/event_handlers_streaming.go

@@ -608,6 +608,11 @@ func (s *Service) handleSessionModelsEvent(ctx context.Context, payload *lifecyc
 		ConfigOptions:  payload.Data.ConfigOptions,
 		Timestamp:      time.Now().UTC().Format(time.RFC3339),
 	}
+	s.logger.Info("publishing session_models event to WS",
+		zap.String("session_id", sessionID),
+		zap.String("current_model_id", payload.Data.CurrentModelID),
+		zap.Int("models_count", len(payload.Data.SessionModels)),
+	)
 	subject := events.BuildSessionModelsSubject(sessionID)
 	_ = s.eventBus.Publish(ctx, subject, bus.NewEvent(events.SessionModelsUpdated, "orchestrator", eventPayload))
 }

apps/web/components/task/model-selector.tsx

@@ -78,6 +78,24 @@ function buildModelOptions(
   return options;
 }
 
+function resolveProfileModel(profileId: string | null | undefined, agents: Agent[]): string | null {
+  if (!profileId) return null;
+  for (const agent of agents) {
+    const profile = agent.profiles.find((p: AgentProfile) => p.id === profileId);
+    if (profile?.model) return profile.model;
+  }
+  return null;
+}
+
+function resolveCurrentModel(
+  activeModel: string | null,
+  acpCurrentModel: string | null,
+  snapshotModel: string | null,
+  profileModel: string | null,
+): string | null {
+  return activeModel || acpCurrentModel || snapshotModel || profileModel;
+}
+
 /** Resolves available models and current model from store state. */
 function useModelSelectorState(sessionId: string | null) {
   useSettingsData(true);
@@ -93,15 +111,23 @@ function useModelSelectorState(sessionId: string | null) {
 
   const session = sessionId ? (taskSessions[sessionId] ?? null) : null;
   const snapshotModel = resolveSnapshotModel(session?.agent_profile_snapshot);
+  const profileModel = useMemo(
+    () => resolveProfileModel(session?.agent_profile_id, settingsAgents as Agent[]),
+    [session?.agent_profile_id, settingsAgents],
+  );
 
-  // Prefer dynamic ACP session models when available, fall back to static registry models
   const availableModels = sessionModelsData?.models?.length
     ? sessionModelsToOptions(sessionModelsData.models)
     : resolveStaticModels(settingsAgents as Agent[], session?.agent_profile_id, availableAgents);
 
   const activeModel = sessionId ? activeModels[sessionId] || null : null;
   const acpCurrentModel = sessionModelsData?.currentModelId || null;
-  const currentModel = activeModel || acpCurrentModel || snapshotModel;
+  const currentModel = resolveCurrentModel(
+    activeModel,
+    acpCurrentModel,
+    snapshotModel,
+    profileModel,
+  );
   const modelOptions = buildModelOptions(availableModels, currentModel);
 
   const handleModelChange = useCallback(

apps/web/hooks/domains/session/use-session-model.ts

@@ -17,12 +17,23 @@ export function useSessionModel(
     return null;
   }, [agentProfileId, settingsAgents]);
 
-  const sessionModel = sessionProfile?.model ?? null;
+  const profileModel = sessionProfile?.model ?? null;
+
+  // ACP agents report their actual current model via session_models events.
+  // Use that as the authoritative "session model" so comparisons in useMessageHandler
+  // use the same ID space (ACP IDs) as the model selector dropdown.
+  const acpCurrentModel = useAppStore((state) =>
+    resolvedSessionId
+      ? state.sessionModels.bySessionId[resolvedSessionId]?.currentModelId || null
+      : null,
+  );
 
   // Get active model state for this session (user's selected model)
   const activeModels = useAppStore((state) => state.activeModel.bySessionId);
   const activeModel = resolvedSessionId ? (activeModels[resolvedSessionId] ?? null) : null;
 
+  const sessionModel = acpCurrentModel || profileModel;
+
   return {
     sessionModel,
     activeModel,

apps/web/lib/ws/handlers/session-models.ts

@@ -10,9 +10,27 @@ export function registerSessionModelsHandlers(store: StoreApi<AppState>): WsHand
       if (!payload?.session_id) {
         return;
       }
+      const acpModels = payload.models ?? [];
+      // Resolve currentModelId: prefer the explicit field, fall back to the "model"
+      // config option's currentValue (some ACP agents send currentModelId as empty).
+      let currentModelId = payload.current_model_id || "";
+      if (!currentModelId) {
+        const modelOpt = (payload.config_options ?? []).find(
+          (o) => o.id === "model" || o.category === "model",
+        );
+        if (modelOpt?.current_value) {
+          currentModelId = modelOpt.current_value;
+        }
+      }
+      console.debug("[session-models] received session.models_updated", {
+        sessionId: payload.session_id,
+        rawCurrentModelId: payload.current_model_id,
+        resolvedCurrentModelId: currentModelId,
+        models: acpModels.map((m) => m.model_id),
+      });
       store.getState().setSessionModels(payload.session_id, {
-        currentModelId: payload.current_model_id,
-        models: (payload.models ?? []).map((m) => ({
+        currentModelId,
+        models: acpModels.map((m) => ({
           modelId: m.model_id,
           name: m.name,
           description: m.description,
@@ -28,6 +46,20 @@ export function registerSessionModelsHandlers(store: StoreApi<AppState>): WsHand
           options: o.options,
         })),
       });
+
+      // Clear stale activeModel if it uses a profile ID that doesn't exist in ACP models.
+      // This happens when a user selected a static model before ACP models arrived.
+      if (acpModels.length > 0) {
+        const state = store.getState();
+        const currentActive = state.activeModel.bySessionId[payload.session_id];
+        if (currentActive && !acpModels.some((m) => m.model_id === currentActive)) {
+          console.debug("[session-models] clearing stale activeModel", {
+            sessionId: payload.session_id,
+            staleModel: currentActive,
+          });
+          state.setActiveModel(payload.session_id, "");
+        }
+      }
     },
   };
 }