fix(composer): expand template expressions in elicitation messages

pkg/vmcp/composer/elicitation_integration_test.go

@@ -527,3 +527,79 @@ func TestDefaultElicitationHandler_SDKErrorHandling(t *testing.T) {
 		})
 	}
 }
+
+func TestWorkflowEngine_ElicitationMessageTemplateExpansion(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name            string
+		message         string
+		params          map[string]any
+		expectedMessage string
+	}{
+		{
+			name:            "expands template message",
+			message:         "Deploy {{.params.repo}} to {{.params.env}}?",
+			params:          map[string]any{"repo": "acme/widget", "env": "production"},
+			expectedMessage: "Deploy acme/widget to production?",
+		},
+		{
+			name:            "passes through plain message",
+			message:         "Deploy now?",
+			params:          map[string]any{},
+			expectedMessage: "Deploy now?",
+		},
+	}
+
+	for _, tt := range testCases {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			te := newTestEngine(t)
+			mockSDK := mocks.NewMockSDKElicitationRequester(te.Ctrl)
+
+			var capturedReq mcp.ElicitationRequest
+			mockSDK.EXPECT().RequestElicitation(gomock.Any(), gomock.Any()).DoAndReturn(
+				func(_ context.Context, req mcp.ElicitationRequest) (*mcp.ElicitationResult, error) {
+					capturedReq = req
+					return &mcp.ElicitationResult{
+						ElicitationResponse: mcp.ElicitationResponse{
+							Action:  mcp.ElicitationResponseActionAccept,
+							Content: map[string]any{"confirmed": true},
+						},
+					}, nil
+				},
+			)
+
+			handler := NewDefaultElicitationHandler(mockSDK)
+			stateStore := NewInMemoryStateStore(1*time.Minute, 1*time.Hour)
+			engine := NewWorkflowEngine(te.Router, te.Backend, handler, stateStore, nil, nil)
+
+			workflow := &WorkflowDefinition{
+				Name: "template-elicit",
+				Steps: []WorkflowStep{
+					{
+						ID:   "ask",
+						Type: StepTypeElicitation,
+						Elicitation: &ElicitationConfig{
+							Message: tt.message,
+							Schema: map[string]any{
+								"type": "object",
+								"properties": map[string]any{
+									"confirmed": map[string]any{"type": "boolean"},
+								},
+							},
+							Timeout: 1 * time.Minute,
+						},
+					},
+				},
+			}
+
+			result, err := engine.ExecuteWorkflow(context.Background(), workflow, tt.params)
+			require.NoError(t, err)
+			assert.Equal(t, WorkflowStatusCompleted, result.Status)
+			assert.Equal(t, tt.expectedMessage, capturedReq.Params.Message)
+			assert.Equal(t, tt.message, workflow.Steps[0].Elicitation.Message)
+		})
+	}
+}

pkg/vmcp/composer/workflow_engine.go

@@ -634,9 +634,26 @@ func (e *workflowEngine) executeElicitationStep(
 		return err
 	}
 
+	// Expand template expressions in elicitation message (e.g. {{.params.owner}})
+	// without mutating the workflow step definition.
+	elicitationCfg := *step.Elicitation
+	if elicitationCfg.Message != "" {
+		wrapper := map[string]any{"message": elicitationCfg.Message}
+		expanded, expandErr := e.templateExpander.Expand(ctx, wrapper, workflowCtx)
+		if expandErr != nil {
+			err := fmt.Errorf("%w: failed to expand elicitation message for step %s: %v",
+				ErrTemplateExpansion, step.ID, expandErr)
+			workflowCtx.RecordStepFailure(step.ID, err)
+			return err
+		}
+		if msg, ok := expanded["message"].(string); ok {
+			elicitationCfg.Message = msg
+		}
+	}
+
 	// Request elicitation (synchronous - blocks until response or timeout)
 	// Per MCP 2025-06-18: SDK handles JSON-RPC ID correlation internally
-	response, err := e.elicitationHandler.RequestElicitation(ctx, workflowCtx.WorkflowID, step.ID, step.Elicitation)
+	response, err := e.elicitationHandler.RequestElicitation(ctx, workflowCtx.WorkflowID, step.ID, &elicitationCfg)
 	if err != nil {
 		// Handle timeout
 		if errors.Is(err, ErrElicitationTimeout) {