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/llm/sse.go

@@ -58,6 +58,19 @@ func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
 	var usage Usage
 	finished := ""
 	sawDone := false
+	sawUsage := false
+	sendTerminalFailure := func(why string) {
+		message := Message{Role: RoleAssistant, Content: content.String(), StopReason: StopError}
+		if reasoning.Len() > 0 {
+			message.Thinking = []ThinkingBlock{{Thinking: reasoning.String()}}
+		}
+		failed := terminalStreamFailure(message, usage, finished, sawDone, why)
+		select {
+		case <-ctx.Done():
+			emitAbort(out, content.String(), ctx.Err())
+		case out <- failed:
+		}
+	}
 	sc := bufio.NewScanner(r)
 	sc.Buffer(make([]byte, 0, 64*1024), 4*1024*1024)
 	reader := &sseEventReader{sc: sc}
@@ -76,17 +89,26 @@ func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
 		}
 		var chunk sseChunk
 		if err := json.Unmarshal([]byte(data), &chunk); err != nil {
+			if sawUsage {
+				sendTerminalFailure("malformed stream chunk after reported usage")
+				return
+			}
 			emitError(out, content.String(), false, "malformed stream chunk: "+err.Error())
 			return
 		}
 		if chunk.Error != nil && chunk.Error.Message != "" {
 			msg := chunk.Error.Message
+			if sawUsage {
+				sendTerminalFailure("provider error after reported usage: " + msg)
+				return
+			}
 			retryable := CapacityLimited(msg) && !ContextOverflow(msg)
 			emitError(out, content.String(), retryable, msg)
 			return
 		}
 		if chunk.Usage != nil {
 			usage = chunk.Usage.Usage
+			sawUsage = true
 			if chunk.Usage.Details.Cached > 0 {
 				usage.CacheReadTokens = chunk.Usage.Details.Cached
 			}
@@ -157,6 +179,10 @@ func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
 			emitAbort(out, content.String(), ctx.Err())
 			return
 		}
+		if sawUsage {
+			sendTerminalFailure("stream read failed after reported usage")
+			return
+		}
 		emitError(out, content.String(), true, err.Error())
 		return
 	}
@@ -166,9 +192,34 @@ func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
 		emitAbort(out, content.String(), ctx.Err())
 		return
 	}
-	// length、空结束原因，或没有 [DONE] 的中断，都不把半截工具调用交给执行层。
-	if !toolFinishExecutable(finished, sawDone) {
-		order = nil
+	// A finish reason alone does not prove the tool arguments arrived intact.
+	// Preserve returned usage when rejecting a partial terminal, so the host
+	// can charge this call and stop rather than treating it as a free retry.
+	if len(order) > 0 {
+		problem := ""
+		switch {
+		case !sawDone:
+			problem = "tool call stream ended before [DONE]"
+		case !toolFinishExecutable(finished, sawDone):
+			problem = "tool call ended without a supported finish reason"
+		default:
+			for _, idx := range order {
+				call := calls[idx]
+				var args map[string]json.RawMessage
+				if call.ID == "" || call.Name == "" {
+					problem = "tool call identity is incomplete"
+					break
+				}
+				if err := json.Unmarshal([]byte(call.Arguments), &args); err != nil || args == nil {
+					problem = "tool call arguments are not a JSON object"
+					break
+				}
+			}
+		}
+		if problem != "" {
+			sendTerminalFailure(problem)
+			return
+		}
 	}
 	msg := Message{Role: RoleAssistant, Content: content.String(), StopReason: mapFinish(finished, len(order) > 0)}
 	if reasoning.Len() > 0 {
@@ -183,10 +234,17 @@ func emitParsed(ctx context.Context, r io.Reader, out chan<- Event) {
 	select {
 	case <-ctx.Done():
 		emitAbort(out, content.String(), ctx.Err())
-	case out <- Event{Kind: KindMessageEnd, Message: msg, Usage: usage, FinishReason: finished}:
+	case out <- Event{Kind: KindMessageEnd, Message: msg, Usage: usage, FinishReason: finished, StreamComplete: sawDone}:
 	}
 }
 
+func terminalStreamFailure(message Message, usage Usage, reason string, complete bool, why string) Event {
+	err := &StreamError{Message: why, Retryable: false}
+	return Event{Kind: KindMessageEnd, Message: message, Usage: usage,
+		FinishReason: reason, StreamComplete: complete, Err: err,
+		ErrorMessage: why, Retryable: false}
+}
+
 // sseEventReader 按空行切事件，并把同一事件里的多行 data: 用换行拼回。
 // 已经是完整 JSON 的 data 行单独成事件，这样单行流不用空行也能解析。
 type sseEventReader struct {
@@ -241,17 +299,16 @@ func (r *sseEventReader) next() (string, bool) {
 // toolFinishExecutable 只在供应商明确以工具调用或正常 stop 结束时执行。
 // length、缺失的结束原因，以及没有 [DONE] 的断开，都视为未完成。
 func toolFinishExecutable(reason string, sawDone bool) bool {
+	if !sawDone {
+		return false
+	}
 	switch reason {
 	case "tool_calls", "function_call":
 		return true
 	case "stop":
 		return true
-	case "length":
-		return false
-	case "":
-		return false
 	default:
-		return sawDone && reason != "error" && reason != "content_filter"
+		return false
 	}
 }
 

runtime/llm/sse_test.go

@@ -93,7 +93,7 @@ func TestParseSSEToolCallIncrements(t *testing.T) {
 	}
 }
 
-func TestParseSSELengthDropsUnfinishedToolCall(t *testing.T) {
+func TestParseSSELengthFailsUnfinishedToolCall(t *testing.T) {
 	body := strings.Join([]string{
 		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"name":"read_file","arguments":"{\"path\":"}}]}}]}`,
 		`data: {"choices":[{"delta":{},"finish_reason":"length"}]}`,
@@ -106,15 +106,15 @@ func TestParseSSELengthDropsUnfinishedToolCall(t *testing.T) {
 			end = ev
 		}
 	}
-	if end.Message.StopReason != StopEnd || len(end.Message.ToolCalls) != 0 {
-		t.Fatalf("truncated tool call must not be executable: %#v", end.Message)
+	if end.Message.StopReason != StopError || len(end.Message.ToolCalls) != 0 || end.Err == nil {
+		t.Fatalf("truncated tool call must fail without execution: %#v", end)
 	}
 	if end.FinishReason != "length" {
 		t.Fatalf("finish %q", end.FinishReason)
 	}
 }
 
-func TestParseSSEUncleanEndDropsToolCall(t *testing.T) {
+func TestParseSSEUncleanEndFailsToolCall(t *testing.T) {
 	body := `data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"name":"read_file","arguments":"{\"path\":"}}]}}]}`
 	var end Event
 	for ev := range ParseSSE(context.Background(), strings.NewReader(body)) {
@@ -122,8 +122,97 @@ func TestParseSSEUncleanEndDropsToolCall(t *testing.T) {
 			end = ev
 		}
 	}
-	if end.Kind != KindMessageEnd || end.Message.StopReason != StopEnd || len(end.Message.ToolCalls) != 0 {
-		t.Fatalf("unclean stream must not execute tools: %#v", end)
+	if end.Kind != KindMessageEnd || end.Message.StopReason != StopError || len(end.Message.ToolCalls) != 0 || end.Err == nil {
+		t.Fatalf("unclean stream must fail without executing tools: %#v", end)
+	}
+}
+
+func TestParseSSEToolFinishWithoutDone(t *testing.T) {
+	body := strings.Join([]string{
+		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"name":"echo","arguments":"{}"}}]}}]}`,
+		`data: {"choices":[{"delta":{},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":12,"completion_tokens":5,"total_tokens":17}}`,
+		"",
+	}, "\n\n")
+	var end Event
+	for ev := range ParseSSE(context.Background(), strings.NewReader(body)) {
+		if ev.Kind == KindMessageEnd {
+			end = ev
+		}
+	}
+	if end.Kind != KindMessageEnd || end.Message.StopReason != StopError ||
+		len(end.Message.ToolCalls) != 0 || end.Err == nil || end.Retryable ||
+		end.Usage.TotalTokens != 17 {
+		t.Fatalf("unsafe tool call from unfinished stream: %#v", end)
+	}
+}
+
+func TestParseSSEInvalidToolArguments(t *testing.T) {
+	body := strings.Join([]string{
+		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"name":"publish_work_checkpoint","arguments":"{\"findings\":"}}]}}]}`,
+		`data: {"choices":[{"delta":{},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":12,"completion_tokens":5,"total_tokens":17}}`,
+		`data: [DONE]`,
+		"",
+	}, "\n\n")
+	var end Event
+	for ev := range ParseSSE(context.Background(), strings.NewReader(body)) {
+		if ev.Kind == KindMessageEnd {
+			end = ev
+		}
+	}
+	if end.Kind != KindMessageEnd || end.Message.StopReason != StopError ||
+		len(end.Message.ToolCalls) != 0 || end.Err == nil || end.Retryable ||
+		end.Usage.TotalTokens != 17 {
+		t.Fatalf("unsafe tool call with invalid JSON arguments: %#v", end)
+	}
+}
+
+func TestParseSSERejectsMissingToolIdentity(t *testing.T) {
+	for _, tc := range []struct{ name, firstChunk string }{
+		{"missing-id", `data: {"choices":[{"delta":{"tool_calls":[{"index":0,"function":{"name":"echo","arguments":"{}"}}]}}]}`},
+		{"missing-name", `data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"arguments":"{}"}}]}}]}`},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			body := strings.Join([]string{
+				tc.firstChunk,
+				`data: {"choices":[{"delta":{},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":12,"completion_tokens":5,"total_tokens":17}}`,
+				`data: [DONE]`,
+				"",
+			}, "\n\n")
+			var end Event
+			for ev := range ParseSSE(context.Background(), strings.NewReader(body)) {
+				if ev.Kind == KindMessageEnd {
+					end = ev
+				}
+			}
+			if end.Message.StopReason != StopError || len(end.Message.ToolCalls) != 0 || end.Err == nil {
+				t.Fatalf("missing tool identity reached execution: %#v", end)
+			}
+		})
+	}
+}
+
+func TestParseSSERejectsNonObjectToolArguments(t *testing.T) {
+	for _, tc := range []struct{ name, arguments string }{
+		{"array", "[]"},
+		{"null", "null"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			body := strings.Join([]string{
+				`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"name":"echo","arguments":"` + tc.arguments + `"}}]}}]}`,
+				`data: {"choices":[{"delta":{},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":12,"completion_tokens":5,"total_tokens":17}}`,
+				`data: [DONE]`,
+				"",
+			}, "\n\n")
+			var end Event
+			for ev := range ParseSSE(context.Background(), strings.NewReader(body)) {
+				if ev.Kind == KindMessageEnd {
+					end = ev
+				}
+			}
+			if end.Message.StopReason != StopError || len(end.Message.ToolCalls) != 0 || end.Err == nil {
+				t.Fatalf("non-object tool arguments reached execution: %#v", end)
+			}
+		})
 	}
 }
 
@@ -149,6 +238,66 @@ func TestParseSSEMalformedIsError(t *testing.T) {
 	}
 }
 
+func TestParseSSEMalformedChunkAfterUsageKeepsUsage(t *testing.T) {
+	body := strings.Join([]string{
+		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"name":"echo","arguments":"{}"}}]},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":12,"completion_tokens":5,"total_tokens":17}}`,
+		`data: {not-json}`,
+		"",
+	}, "\n\n")
+	var end Event
+	for ev := range ParseSSE(context.Background(), strings.NewReader(body)) {
+		end = ev
+	}
+	if end.Kind != KindMessageEnd || end.Message.StopReason != StopError ||
+		len(end.Message.ToolCalls) != 0 || end.Err == nil || end.Retryable ||
+		end.Usage.TotalTokens != 17 {
+		t.Fatalf("malformed chunk dropped already returned usage: %#v", end)
+	}
+}
+
+func TestParseSSEProviderErrorAfterUsageKeepsUsage(t *testing.T) {
+	body := strings.Join([]string{
+		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"name":"echo","arguments":"{}"}}]}}],"usage":{"prompt_tokens":12,"completion_tokens":5,"total_tokens":17}}`,
+		`data: {"error":{"message":"server is at capacity"}}`,
+		"",
+	}, "\n\n")
+	var end Event
+	for ev := range ParseSSE(context.Background(), strings.NewReader(body)) {
+		end = ev
+	}
+	if end.Kind != KindMessageEnd || end.Message.StopReason != StopError ||
+		len(end.Message.ToolCalls) != 0 || end.Err == nil || end.Retryable ||
+		end.Usage.TotalTokens != 17 {
+		t.Fatalf("provider error after usage retried or lost its charge: %#v", end)
+	}
+}
+
+type errorAfterDataReader struct{ data *strings.Reader }
+
+func (r *errorAfterDataReader) Read(p []byte) (int, error) {
+	n, err := r.data.Read(p)
+	if err == io.EOF {
+		return 0, io.ErrUnexpectedEOF
+	}
+	return n, err
+}
+
+func TestParseSSEReaderErrorAfterUsageKeepsUsage(t *testing.T) {
+	body := strings.Join([]string{
+		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_1","function":{"name":"echo","arguments":"{}"}}]}}],"usage":{"prompt_tokens":12,"completion_tokens":5,"total_tokens":17}}`,
+		"",
+	}, "\n\n")
+	var end Event
+	for ev := range ParseSSE(context.Background(), &errorAfterDataReader{data: strings.NewReader(body)}) {
+		end = ev
+	}
+	if end.Kind != KindMessageEnd || end.Message.StopReason != StopError ||
+		len(end.Message.ToolCalls) != 0 || end.Err == nil || end.Retryable ||
+		end.Usage.TotalTokens != 17 {
+		t.Fatalf("reader error after usage retried or lost its charge: %#v", end)
+	}
+}
+
 func TestParseSSECancel(t *testing.T) {
 	pr, pw := io.Pipe()
 	ctx, cancel := context.WithCancel(context.Background())

runtime/llm/types.go

@@ -113,9 +113,12 @@ type Event struct {
 	// FinishReason 是供应商原始结束原因（stop、length、tool_calls 等）。
 	// 空表示这条事件不携带结束原因。StopReason 的映射不受此字段影响。
 	FinishReason string
-	Err          error
-	Retryable    bool
-	ErrorMessage string
+	// StreamComplete records whether the OpenAI-compatible SSE stream supplied
+	// its explicit [DONE] marker. Tool calls require this before execution.
+	StreamComplete bool
+	Err            error
+	Retryable      bool
+	ErrorMessage   string
 	// HTTPStatus 是提供方的 HTTP 状态。0 表示这条错误不是 HTTP 响应。
 	HTTPStatus int
 	// RetryAfter is the provider's requested wait. HasRetryAfter distinguishes

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.
@@ -72,8 +74,8 @@ type Config struct {
 	// SerialTools 是并行执行下的顺序敏感工具名集合：这些调用按模型给出的
 	// 原顺序在调用方 goroutine 逐个执行（互斥且保序），其余调用并发执行。
 	SerialTools map[string]bool
-	GetSteering   func() []llm.Message
-	GetFollowUp   func() []llm.Message
+	GetSteering func() []llm.Message
+	GetFollowUp func() []llm.Message
 	// OnEvent 观察循环事件。同一次 Run 内不会并发调用
 	// （与 BeforeTool、AfterTool 共用一把锁串行）。
 	OnEvent func(Event)
@@ -227,9 +229,9 @@ func Run(ctx context.Context, cfg Config, user llm.Message) (Result, error) {
 	}
 	cfg.traceCtx = newTraceContext()
 	endRun := startSpan(cfg, "invoke_agent "+agentName(cfg), map[string]string{
-		"gen_ai.system":          providerName(cfg),
-		"gen_ai.agent.name":      agentName(cfg),
-		"gen_ai.request.model":   cfg.Model,
+		"gen_ai.system":        providerName(cfg),
+		"gen_ai.agent.name":    agentName(cfg),
+		"gen_ai.request.model": cfg.Model,
 	}, true)
 	defer endRun()
 	var messages []llm.Message
@@ -354,6 +356,12 @@ func Run(ctx context.Context, cfg Config, user llm.Message) (Result, error) {
 		usage.LastPromptTokens = end.Usage.PromptTokens
 		usage.LastCompletionTokens = end.Usage.CompletionTokens
 		usage.LastTotalTokens = end.Usage.TotalTokens
+		if end.Err != nil {
+			cfg.logger().Error("runtime terminal stream failed", end.Err)
+			emitUsage(cfg, usage)
+			return Result{Text: last.Content, Messages: messages, StopReason: llm.StopError,
+				Usage: usage, Err: end.Err, Retryable: false}, nil
+		}
 		if err := persist(cfg, last); err != nil {
 			return Result{}, err
 		}
@@ -529,7 +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:
@@ -1156,7 +1165,7 @@ func drain(fn func() []llm.Message) []llm.Message {
 
 func emitUsage(cfg Config, usage llm.Usage) {
 	emit(cfg, Event{
-		Type: "usage",
+		Type:         "usage",
 		PromptTokens: usage.PromptTokens, CompletionTokens: usage.CompletionTokens, TotalTokens: usage.TotalTokens,
 		LastPromptTokens: usage.LastPromptTokens, LastCompletionTokens: usage.LastCompletionTokens, LastTotalTokens: usage.LastTotalTokens,
 		CacheReadTokens: usage.CacheReadTokens, CacheWriteTokens: usage.CacheWriteTokens,

runtime/loop_test.go

@@ -2,6 +2,7 @@ package runtime
 
 import (
 	"context"
+	"errors"
 	"path/filepath"
 	"strings"
 	"sync"
@@ -12,6 +13,54 @@ import (
 	"agent-native/runtime/tools"
 )
 
+func TestRunTerminalToolFailureKeepsUsage(t *testing.T) {
+	hits, calls := 0, 0
+	reg := tools.NewRegistry(t.TempDir())
+	reg.Register(hitTool{hits: &hits})
+	stream := func(context.Context, string, []llm.Message, []llm.ToolDecl, llm.StreamOptions) <-chan llm.Event {
+		calls++
+		out := make(chan llm.Event, 1)
+		out <- llm.Event{
+			Kind:    llm.KindMessageEnd,
+			Message: llm.Message{Role: llm.RoleAssistant, StopReason: llm.StopError},
+			Usage:   llm.Usage{PromptTokens: 12, CompletionTokens: 5, TotalTokens: 17},
+			Err:     errors.New("incomplete tool call"),
+		}
+		close(out)
+		return out
+	}
+	res, err := Run(context.Background(), Config{Model: "fixture", Tools: reg, Stream: stream},
+		llm.Message{Role: llm.RoleUser, Content: "organize materials"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Err == nil || res.StopReason != llm.StopError || res.Usage.TotalTokens != 17 ||
+		hits != 0 || calls != 1 {
+		t.Fatalf("terminal failure retried, executed a tool, or lost usage: result=%#v hits=%d calls=%d", res, hits, calls)
+	}
+}
+
+func TestRunTerminalErrorCannotMasqueradeAsSuccess(t *testing.T) {
+	stream := func(context.Context, string, []llm.Message, []llm.ToolDecl, llm.StreamOptions) <-chan llm.Event {
+		out := make(chan llm.Event, 1)
+		out <- llm.Event{Kind: llm.KindMessageEnd,
+			Message: llm.Message{Role: llm.RoleAssistant, Content: "incomplete", StopReason: llm.StopEnd},
+			Usage:   llm.Usage{PromptTokens: 12, CompletionTokens: 5, TotalTokens: 17},
+			Err:     errors.New("terminal failed"),
+		}
+		close(out)
+		return out
+	}
+	res, err := Run(context.Background(), Config{Model: "fixture", Stream: stream},
+		llm.Message{Role: llm.RoleUser, Content: "go"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Err == nil || res.StopReason != llm.StopError || res.Usage.TotalTokens != 17 {
+		t.Fatalf("error-bearing terminal was accepted as success: %#v", res)
+	}
+}
+
 func script(turns ...llm.Message) llm.StreamFunc {
 	var mu sync.Mutex
 	i := 0