diff --git a/internal/conversation/conversation.go b/internal/conversation/conversation.go
index a9e0b55..3ce4171 100644
--- a/internal/conversation/conversation.go
+++ b/internal/conversation/conversation.go
@@ -190,9 +190,9 @@ type AssistantUpdate struct {
 func (AssistantUpdate) Type() EventType { return EventAssistantUpdate }
 
 // Done reports that the Inference the subscriber joined has returned.
-// Err is nil on success.
+// Error is empty on success.
 type Done struct {
-	Err error `json:"err"`
+	Error string `json:"error,omitempty"`
 }
 
 func (Done) Type() EventType { return EventDone }
@@ -297,7 +297,11 @@ func (inf *Inference) follow(
 			}
 		}
 		if done {
-			return send(ctx, ch, Done{Err: err})
+			var errStr string
+			if err != nil {
+				errStr = err.Error()
+			}
+			return send(ctx, ch, Done{Error: errStr})
 		}
 		// Wait for the call to close wait (when it appends new
 		// events or finishes), or for the subscriber to cancel ctx.
diff --git a/internal/conversation/conversation_test.go b/internal/conversation/conversation_test.go
index 3527ced..d166fe9 100644
--- a/internal/conversation/conversation_test.go
+++ b/internal/conversation/conversation_test.go
@@ -1500,8 +1500,8 @@ func TestSubscribeInference(t *testing.T) {
 			}
 			asst = &e
 		case Done:
-			if e.Err != nil {
-				t.Errorf("Done.Err = %v, want nil", e.Err)
+			if e.Error != "" {
+				t.Errorf("Done.Error = %q, want empty", e.Error)
 			}
 		default:
 			t.Fatalf("unexpected event %v", e)
@@ -1593,8 +1593,8 @@ func TestSubscribeInferenceError(t *testing.T) {
 	if !ok {
 		t.Fatalf("last event = %v, want Done", got[len(got)-1])
 	}
-	if done.Err == nil {
-		t.Fatal("Done.Err = nil, want the stream error")
+	if done.Error == "" {
+		t.Fatal("Done.Error = empty, want the stream error")
 	}
 	rows, err := db.New(c.db.Reader).
 		SelectMessagesConversationId(ctx, c.id)
@@ -1710,8 +1710,8 @@ func TestSubscribeToolResult(t *testing.T) {
 				}
 			}
 		case Done:
-			if e.Err != nil {
-				t.Errorf("Done.Err = %v, want nil", e.Err)
+			if e.Error != "" {
+				t.Errorf("Done.Error = %q, want empty", e.Error)
 			}
 		default:
 			t.Errorf("event %d = %v, want MessageSaved or Done", i, e)
@@ -1902,8 +1902,8 @@ func TestSubscribeStartupError(t *testing.T) {
 			}
 			sawTool = true
 		case Done:
-			if e.Err == nil {
-				t.Error("Done.Err = nil, want the startup failure")
+			if e.Error == "" {
+				t.Error("Done.Error = empty, want the startup failure")
 			}
 		}
 	}
@@ -2582,8 +2582,8 @@ func TestInferenceEventsFastFailure(t *testing.T) {
 	if !ok {
 		t.Fatalf("event = %v, want Done", got[0])
 	}
-	if done.Err == nil || done.Err.Error() != runErr.Error() {
-		t.Fatalf("Done.Err = %v, want %v", done.Err, runErr)
+	if done.Error != runErr.Error() {
+		t.Fatalf("Done.Error = %q, want %q", done.Error, runErr.Error())
 	}
 }