diff --git a/apps/backend/internal/agent/lifecycle/manager.go b/apps/backend/internal/agent/lifecycle/manager.go
index 00c125cd96..6487e7d034 100644
--- a/apps/backend/internal/agent/lifecycle/manager.go
+++ b/apps/backend/internal/agent/lifecycle/manager.go
@@ -1698,7 +1698,7 @@ func (m *Manager) updateExecutionError(executionID, errorMsg string) {
 func (m *Manager) PromptAgent(ctx context.Context, executionID string, prompt string, attachments []v1.MessageAttachment) (*PromptResult, error) {
 	execution, exists := m.executionStore.Get(executionID)
 	if !exists {
-		return nil, fmt.Errorf("execution %q not found", executionID)
+		return nil, fmt.Errorf("execution %q not found: %w", executionID, ErrExecutionNotFound)
 	}
 	return m.sessionManager.SendPrompt(ctx, execution, prompt, true, attachments, m.MarkReady)
 }
diff --git a/apps/backend/internal/orchestrator/executor/executor.go b/apps/backend/internal/orchestrator/executor/executor.go
index bed16b7380..f7e085a57d 100644
--- a/apps/backend/internal/orchestrator/executor/executor.go
+++ b/apps/backend/internal/orchestrator/executor/executor.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/google/uuid"
+	"github.com/kandev/kandev/internal/agent/lifecycle"
 	"github.com/kandev/kandev/internal/common/logger"
 	"github.com/kandev/kandev/internal/task/models"
 	"github.com/kandev/kandev/internal/task/repository"
@@ -898,7 +899,14 @@ func (e *Executor) Prompt(ctx context.Context, taskID, sessionID string, prompt
 		zap.Int("prompt_length", len(prompt)),
 		zap.Int("attachments_count", len(attachments)))
 
-	return e.agentManager.PromptAgent(ctx, session.AgentExecutionID, prompt, attachments)
+	result, err := e.agentManager.PromptAgent(ctx, session.AgentExecutionID, prompt, attachments)
+	if err != nil {
+		if errors.Is(err, lifecycle.ErrExecutionNotFound) {
+			return nil, ErrExecutionNotFound
+		}
+		return nil, err
+	}
+	return result, nil
 }
 
 // SwitchModel stops the current agent, restarts it with a new model, and sends the prompt.