Preserve streamed tool delta identity

Why: Backend emitted tool deltas from a separate goroutine, racing with serialized run events and occasionally losing a UI delta.

Evidence: Backend race detector reproduced concurrent event writes; Agent-Native identity test RED→GREEN; full vet and tests pass.

Impact: runtime tool delta events now carry provider slot and call ID for single-owner downstream projection.

Refs: runtime/loop.go; runtime/event_vocabulary_test.go

runtime/event_vocabulary_test.go

@@ -39,7 +39,7 @@ func vocabScript() llm.StreamFunc {
 				step++
 				ch <- llm.Event{Kind: llm.KindReasoningDelta, ReasoningDelta: "思考"}
 				ch <- llm.Event{Kind: llm.KindTextDelta, Text: "正文"}
-				ch <- llm.Event{Kind: llm.KindToolCallDelta, ToolName: "list_dir", ArgumentsDelta: `{"path":"."}`}
+				ch <- llm.Event{Kind: llm.KindToolCallDelta, ToolIndex: 2, ToolID: "c1", ToolName: "list_dir", ArgumentsDelta: `{"path":"."}`}
 				ch <- llm.Event{Kind: llm.KindMessageEnd, Message: llm.Message{
 					Role: llm.RoleAssistant, StopReason: llm.StopToolCalls,
 					ToolCalls: []llm.ToolCall{{ID: "c1", Name: "list_dir", Arguments: `{"path":"."}`}},
@@ -54,6 +54,25 @@ func vocabScript() llm.StreamFunc {
 	}
 }
 
+func TestLoopPreservesToolCallDeltaIdentity(t *testing.T) {
+	reg := tools.WorkspaceTools(t.TempDir())
+	var got Event
+	_, err := Run(context.Background(), Config{
+		Model: "fake", Tools: reg, Stream: vocabScript(), MaxTurns: 4,
+		OnEvent: func(ev Event) {
+			if ev.Type == "tool_call_delta" {
+				got = ev
+			}
+		},
+	}, llm.Message{Role: llm.RoleUser, Content: "run"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.ToolIndex != 2 || got.CallID != "c1" || got.Tool != "list_dir" || got.Detail != `{"path":"."}` {
+		t.Fatalf("tool delta lost its provider identity: %#v", got)
+	}
+}
+
 func TestLoopEmitsProcessVocabulary(t *testing.T) {
 	reg := tools.WorkspaceTools(t.TempDir())
 	var observed []string

runtime/loop.go

@@ -38,8 +38,10 @@ type Event struct {
 	Message llm.Message
 	Tool    string
 	Text    string
+	// ToolIndex preserves the provider's call slot for tool_call_delta.
+	ToolIndex int
 	// CallID 在 tool_execution_start / tool_execution_end 时携带工具调用的
-	// ID：并行执行下同回合多个调用并发进出，消费方按 ID 配对而非按顺序。
+	// ID；tool_call_delta 也携带同一 ID。消费方按 ID 配对而非按顺序。
 	CallID string
 	// Detail carries tool arguments/results or reasoning deltas for
 	// process-visualization consumers; log writers may ignore it.
@@ -535,7 +537,8 @@ func consume(ctx context.Context, cfg Config, messages []llm.Message) (llm.Event
 		case llm.KindReasoningDelta:
 			emit(cfg, Event{Type: "reasoning_delta", Text: ev.ReasoningDelta})
 		case llm.KindToolCallDelta:
-			emit(cfg, Event{Type: "tool_call_delta", Tool: ev.ToolName, Detail: ev.ArgumentsDelta})
+			emit(cfg, Event{Type: "tool_call_delta", ToolIndex: ev.ToolIndex,
+				CallID: ev.ToolID, Tool: ev.ToolName, Detail: ev.ArgumentsDelta})
 		case llm.KindError:
 			return ev, ev.Err
 		case llm.KindMessageEnd: