Merge pull request #2926 from slicenferqin/fix-tool-use-name-loss-and-duplicates

fix(openai→claude): suppress empty/duplicate tool_use content_block_start

internal/translator/openai/claude/openai_claude_response.go

@@ -8,6 +8,7 @@ package claude
 import (
 	"bytes"
 	"context"
+	"sort"
 	"strings"
 
 	translatorcommon "github.com/router-for-me/CLIProxyAPI/v7/internal/translator/common"
@@ -26,6 +27,9 @@ type ConvertOpenAIResponseToAnthropicParams struct {
 	Model       string
 	CreatedAt   int64
 	ToolNameMap map[string]string
+	// SawToolCall is true once at least one tool_use content_block_start has
+	// been emitted on the wire. Using raw upstream tool_calls presence here
+	// can produce stop_reason=tool_use with zero announced tool blocks.
 	SawToolCall bool
 	// Content accumulator for streaming
 	ContentAccumulator strings.Builder
@@ -60,6 +64,9 @@ type ToolCallAccumulator struct {
 	ID        string
 	Name      string
 	Arguments strings.Builder
+	// StartEmitted tracks whether content_block_start has already been sent
+	// for this tool index.
+	StartEmitted bool
 }
 
 // ConvertOpenAIResponseToClaude converts OpenAI streaming response format to Anthropic API format.
@@ -218,9 +225,7 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
 			}
 
 			toolCalls.ForEach(func(_, toolCall gjson.Result) bool {
-				param.SawToolCall = true
 				index := int(toolCall.Get("index").Int())
-				blockIndex := param.toolContentBlockIndex(index)
 
 				// Initialize accumulator if needed
 				if _, exists := param.ToolCallsAccumulator[index]; !exists {
@@ -229,27 +234,25 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
 
 				accumulator := param.ToolCallsAccumulator[index]
 
-				// Handle tool call ID
+				// Handle tool call ID. Only accept JSON-string, non-empty
-				if id := toolCall.Get("id"); id.Exists() {
+				// values so malformed upstream fields do not overwrite a
-					accumulator.ID = id.String()
+				// valid ID or coerce into a content_block.id.
+				if id := toolCall.Get("id"); id.Exists() && id.Type == gjson.String {
+					if idStr := id.String(); idStr != "" {
+						accumulator.ID = idStr
+					}
 				}
 
-				// Handle function name
+				// Handle function name and arguments
 				if function := toolCall.Get("function"); function.Exists() {
-					if name := function.Get("name"); name.Exists() && name.String() != "" {
+					// Only record the name until content_block_start has been
-						accumulator.Name = util.MapToolName(param.ToolNameMap, name.String())
+					// emitted. Some upstreams send "name": "" or repeat the
-
+					// field across chunks; reassigning after start could drift
-						stopThinkingContentBlock(param, &results)
+					// from what was already announced.
-
+					if !accumulator.StartEmitted {
-						stopTextContentBlock(param, &results)
+						if name := function.Get("name"); name.Exists() && name.Type == gjson.String && name.String() != "" {
-
+							accumulator.Name = util.MapToolName(param.ToolNameMap, name.String())
-						// Send content_block_start for tool_use
+						}
-						contentBlockStartJSON := `{"type":"content_block_start","index":0,"content_block":{"type":"tool_use","id":"","name":"","input":{}}}`
-						contentBlockStartJSONBytes := []byte(contentBlockStartJSON)
-						contentBlockStartJSONBytes, _ = sjson.SetBytes(contentBlockStartJSONBytes, "index", blockIndex)
-						contentBlockStartJSONBytes, _ = sjson.SetBytes(contentBlockStartJSONBytes, "content_block.id", util.SanitizeClaudeToolID(accumulator.ID))
-						contentBlockStartJSONBytes, _ = sjson.SetBytes(contentBlockStartJSONBytes, "content_block.name", accumulator.Name)
-						results = append(results, translatorcommon.AppendSSEEventBytes(nil, "content_block_start", contentBlockStartJSONBytes, 2))
 					}
 
 					// Handle function arguments
@@ -261,6 +264,13 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
 					}
 				}
 
+				// Re-check on every chunk, not only chunks with a function
+				// object. Some upstreams split function.name and id across
+				// separate deltas.
+				if !accumulator.StartEmitted && accumulator.Name != "" && accumulator.ID != "" && !param.ContentBlocksStopped {
+					emitToolUseStart(param, index, accumulator, &results)
+				}
+
 				return true
 			})
 		}
@@ -269,9 +279,12 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
 	// Handle finish_reason (but don't send message_delta/message_stop yet)
 	if finishReason := root.Get("choices.0.finish_reason"); finishReason.Exists() && finishReason.String() != "" {
 		reason := finishReason.String()
-		if param.SawToolCall {
+		switch {
+		case param.SawToolCall:
 			param.FinishReason = "tool_calls"
-		} else {
+		case reason == "tool_calls":
+			param.FinishReason = "stop"
+		default:
 			param.FinishReason = reason
 		}
 
@@ -289,8 +302,17 @@ func convertOpenAIStreamingChunkToAnthropic(rawJSON []byte, param *ConvertOpenAI
 
 		// Send content_block_stop for any tool calls
 		if !param.ContentBlocksStopped {
-			for index := range param.ToolCallsAccumulator {
+			for _, index := range toolCallAccumulatorIndexes(param.ToolCallsAccumulator) {
 				accumulator := param.ToolCallsAccumulator[index]
+				if !accumulator.StartEmitted {
+					// Belated emit for streams that supplied a valid name but
+					// never sent an id. SanitizeClaudeToolID("") produces the
+					// expected stable synthetic toolu_<nanos>_<n> ID shape.
+					if accumulator.Name == "" {
+						continue
+					}
+					emitToolUseStart(param, index, accumulator, &results)
+				}
 				blockIndex := param.toolContentBlockIndex(index)
 
 				// Send complete input_json_delta with all accumulated arguments
@@ -353,8 +375,16 @@ func convertOpenAIDoneToAnthropic(param *ConvertOpenAIResponseToAnthropicParams)
 	stopTextContentBlock(param, &results)
 
 	if !param.ContentBlocksStopped {
-		for index := range param.ToolCallsAccumulator {
+		for _, index := range toolCallAccumulatorIndexes(param.ToolCallsAccumulator) {
 			accumulator := param.ToolCallsAccumulator[index]
+			if !accumulator.StartEmitted {
+				// Belated emit at [DONE]; same behavior as the finish_reason
+				// path for name-but-no-id streams.
+				if accumulator.Name == "" {
+					continue
+				}
+				emitToolUseStart(param, index, accumulator, &results)
+			}
 			blockIndex := param.toolContentBlockIndex(index)
 
 			if accumulator.Arguments.Len() > 0 {
@@ -547,6 +577,29 @@ func stopTextContentBlock(param *ConvertOpenAIResponseToAnthropicParams, results
 	param.TextContentBlockIndex = -1
 }
 
+func emitToolUseStart(param *ConvertOpenAIResponseToAnthropicParams, openAIToolIndex int, accumulator *ToolCallAccumulator, results *[][]byte) {
+	stopThinkingContentBlock(param, results)
+	stopTextContentBlock(param, results)
+
+	blockIndex := param.toolContentBlockIndex(openAIToolIndex)
+	contentBlockStartJSON := []byte(`{"type":"content_block_start","index":0,"content_block":{"type":"tool_use","id":"","name":"","input":{}}}`)
+	contentBlockStartJSON, _ = sjson.SetBytes(contentBlockStartJSON, "index", blockIndex)
+	contentBlockStartJSON, _ = sjson.SetBytes(contentBlockStartJSON, "content_block.id", util.SanitizeClaudeToolID(accumulator.ID))
+	contentBlockStartJSON, _ = sjson.SetBytes(contentBlockStartJSON, "content_block.name", accumulator.Name)
+	*results = append(*results, translatorcommon.AppendSSEEventBytes(nil, "content_block_start", contentBlockStartJSON, 2))
+	accumulator.StartEmitted = true
+	param.SawToolCall = true
+}
+
+func toolCallAccumulatorIndexes(accumulators map[int]*ToolCallAccumulator) []int {
+	indexes := make([]int, 0, len(accumulators))
+	for index := range accumulators {
+		indexes = append(indexes, index)
+	}
+	sort.Ints(indexes)
+	return indexes
+}
+
 // ConvertOpenAIResponseToClaudeNonStream converts a non-streaming OpenAI response to a non-streaming Anthropic response.
 //
 // Parameters:

internal/translator/openai/claude/openai_claude_response_test.go

@@ -3,11 +3,108 @@ package claude
 import (
 	"bytes"
 	"context"
+	"strings"
 	"testing"
+
+	"github.com/tidwall/gjson"
 )
 
+type sseEvent struct {
+	Type    string
+	Payload string
+}
+
+func runStream(t *testing.T, originalReq string, chunks ...string) []sseEvent {
+	t.Helper()
+
+	var paramAny any
+	var emitted [][]byte
+	for _, chunk := range chunks {
+		emitted = append(emitted, ConvertOpenAIResponseToClaude(
+			context.Background(),
+			"",
+			[]byte(originalReq),
+			nil,
+			[]byte("data: "+chunk),
+			&paramAny,
+		)...)
+	}
+	emitted = append(emitted, ConvertOpenAIResponseToClaude(
+		context.Background(),
+		"",
+		[]byte(originalReq),
+		nil,
+		[]byte("data: [DONE]"),
+		&paramAny,
+	)...)
+
+	var events []sseEvent
+	for _, raw := range emitted {
+		s := string(raw)
+		if !strings.HasPrefix(s, "event: ") {
+			continue
+		}
+		nl := strings.Index(s, "\n")
+		if nl < 0 {
+			continue
+		}
+		typ := strings.TrimPrefix(s[:nl], "event: ")
+		rest := s[nl+1:]
+		if !strings.HasPrefix(rest, "data: ") {
+			continue
+		}
+		payload := strings.TrimRight(strings.TrimPrefix(rest, "data: "), "\n")
+		events = append(events, sseEvent{Type: typ, Payload: payload})
+	}
+	return events
+}
+
+func countByType(events []sseEvent, typ string) int {
+	n := 0
+	for _, e := range events {
+		if e.Type == typ {
+			n++
+		}
+	}
+	return n
+}
+
+func toolUseStarts(events []sseEvent) []sseEvent {
+	var out []sseEvent
+	for _, e := range events {
+		if e.Type != "content_block_start" {
+			continue
+		}
+		if gjson.Get(e.Payload, "content_block.type").String() == "tool_use" {
+			out = append(out, e)
+		}
+	}
+	return out
+}
+
+func blockIndices(events []sseEvent) []int64 {
+	var idx []int64
+	for _, e := range events {
+		if e.Type == "content_block_start" {
+			idx = append(idx, gjson.Get(e.Payload, "index").Int())
+		}
+	}
+	return idx
+}
+
+func lastStopReason(events []sseEvent) string {
+	for i := len(events) - 1; i >= 0; i-- {
+		if events[i].Type == "message_delta" {
+			return gjson.Get(events[i].Payload, "delta.stop_reason").String()
+		}
+	}
+	return ""
+}
+
+const streamReq = `{"stream":true}`
+
 func TestConvertOpenAIResponseToClaude_StreamIgnoresNullToolNameDelta(t *testing.T) {
-	originalRequest := []byte(`{"stream":true}`)
+	originalRequest := []byte(streamReq)
 	var param any
 
 	firstChunks := ConvertOpenAIResponseToClaude(
@@ -39,3 +136,231 @@ func TestConvertOpenAIResponseToClaude_StreamIgnoresNullToolNameDelta(t *testing
 		t.Fatalf("did not expect null tool name delta to emit an empty tool name, got %s", string(secondOutput))
 	}
 }
+
+func TestStreamingTool_EmptyNameThroughout(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"id":"call_a","function":{"name":"","arguments":""}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"function":{"name":"","arguments":"{\"x\":1}"}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+
+	if got := len(toolUseStarts(events)); got != 0 {
+		t.Fatalf("expected zero tool_use content_block_start, got %d (events=%+v)", got, events)
+	}
+	if got := countByType(events, "content_block_delta"); got != 0 {
+		t.Fatalf("expected zero content_block_delta when start was suppressed, got %d", got)
+	}
+	if got := countByType(events, "content_block_stop"); got != 0 {
+		t.Fatalf("expected zero content_block_stop when start was suppressed, got %d", got)
+	}
+	if got := lastStopReason(events); got == "tool_use" {
+		t.Fatalf("stop_reason must not be tool_use when zero tool_use blocks were emitted; got %q", got)
+	}
+}
+
+func TestStreamingTool_NullName(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"id":"call_a","function":{"name":null,"arguments":""}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+	if got := len(toolUseStarts(events)); got != 0 {
+		t.Fatalf("null name must not produce a tool_use start; got %d", got)
+	}
+	if got := countByType(events, "content_block_stop"); got != 0 {
+		t.Fatalf("null name must not produce content_block_stop; got %d", got)
+	}
+}
+
+func TestStreamingTool_NonStringName(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"id":"call_a","function":{"name":123,"arguments":""}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+	if got := len(toolUseStarts(events)); got != 0 {
+		t.Fatalf("non-string name must not produce a tool_use start; got %d", got)
+	}
+}
+
+func TestStreamingTool_RepeatedName(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"id":"call_a","function":{"name":"do_it","arguments":""}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"function":{"name":"do_it","arguments":"{\"x\""}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"function":{"name":"do_it","arguments":":1}"}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+
+	starts := toolUseStarts(events)
+	if len(starts) != 1 {
+		t.Fatalf("expected exactly one tool_use start, got %d", len(starts))
+	}
+	if name := gjson.Get(starts[0].Payload, "content_block.name").String(); name != "do_it" {
+		t.Fatalf("announced tool name = %q, want %q", name, "do_it")
+	}
+	if got := countByType(events, "content_block_stop"); got != 1 {
+		t.Fatalf("expected exactly one content_block_stop, got %d", got)
+	}
+}
+
+func TestStreamingTool_MixedSuppressedAndValid(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[
+			{"index":0,"id":"call_skip","function":{"name":"","arguments":""}},
+			{"index":1,"id":"call_real","function":{"name":"do_it","arguments":""}}
+		]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[
+			{"index":1,"function":{"arguments":"{}"}}
+		]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+
+	starts := toolUseStarts(events)
+	if len(starts) != 1 {
+		t.Fatalf("expected exactly one tool_use start, got %d", len(starts))
+	}
+	if got := countByType(events, "content_block_stop"); got != 1 {
+		t.Fatalf("expected exactly one content_block_stop, got %d", got)
+	}
+
+	indices := blockIndices(events)
+	if len(indices) == 0 || indices[0] != 0 {
+		t.Fatalf("first content_block_start index must be 0, got %v", indices)
+	}
+}
+
+func TestStreamingTool_EmptyIDDeferStart(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"id":"","function":{"name":"do_it","arguments":""}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"id":"call_real","function":{"arguments":"{}"}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+
+	starts := toolUseStarts(events)
+	if len(starts) != 1 {
+		t.Fatalf("expected exactly one tool_use start once id arrived, got %d", len(starts))
+	}
+	if id := gjson.Get(starts[0].Payload, "content_block.id").String(); id != "call_real" {
+		t.Fatalf("announced tool id = %q, want %q", id, "call_real")
+	}
+}
+
+func TestStreamingTool_IDInDeltaWithoutFunction(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"function":{"name":"do_it"}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"id":"call_real"}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"function":{"arguments":"{}"}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+
+	starts := toolUseStarts(events)
+	if len(starts) != 1 {
+		t.Fatalf("expected exactly one tool_use start when id arrives in a function-less delta, got %d", len(starts))
+	}
+	if id := gjson.Get(starts[0].Payload, "content_block.id").String(); id != "call_real" {
+		t.Fatalf("announced tool id = %q, want %q", id, "call_real")
+	}
+	if name := gjson.Get(starts[0].Payload, "content_block.name").String(); name != "do_it" {
+		t.Fatalf("announced tool name = %q, want %q", name, "do_it")
+	}
+	if got := countByType(events, "content_block_stop"); got != 1 {
+		t.Fatalf("expected exactly one content_block_stop, got %d", got)
+	}
+}
+
+func TestStreamingTool_StopReasonWithEmittedTool(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"id":"call_a","function":{"name":"do_it","arguments":"{}"}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":1,"completion_tokens":1}}`,
+	)
+	if got := lastStopReason(events); got != "tool_use" {
+		t.Fatalf("stop_reason = %q, want %q", got, "tool_use")
+	}
+}
+
+func TestStreamingTool_StopReasonWhenIDNeverArrives(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"function":{"name":"do_it","arguments":""}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"function":{"arguments":"{}"}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+
+	starts := toolUseStarts(events)
+	if len(starts) != 1 {
+		t.Fatalf("expected one belated tool_use start with synthetic id, got %d", len(starts))
+	}
+	id := gjson.Get(starts[0].Payload, "content_block.id").String()
+	if !strings.HasPrefix(id, "toolu_") {
+		t.Fatalf("synthetic id should match toolu_<nanos>_<n>, got %q", id)
+	}
+	if name := gjson.Get(starts[0].Payload, "content_block.name").String(); name != "do_it" {
+		t.Fatalf("announced tool name = %q, want %q", name, "do_it")
+	}
+	if got := lastStopReason(events); got != "tool_use" {
+		t.Fatalf("stop_reason = %q, want %q", got, "tool_use")
+	}
+}
+
+func TestStreamingTool_BelatedStartsUseOpenAIToolIndexOrder(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[
+			{"index":2,"function":{"name":"third_tool","arguments":"{}"}},
+			{"index":0,"function":{"name":"first_tool","arguments":"{}"}},
+			{"index":1,"function":{"name":"second_tool","arguments":"{}"}}
+		]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+
+	starts := toolUseStarts(events)
+	if len(starts) != 3 {
+		t.Fatalf("expected three belated tool_use starts, got %d", len(starts))
+	}
+
+	wantNames := []string{"first_tool", "second_tool", "third_tool"}
+	for i, wantName := range wantNames {
+		if name := gjson.Get(starts[i].Payload, "content_block.name").String(); name != wantName {
+			t.Fatalf("tool_use start %d name = %q, want %q (starts=%+v)", i, name, wantName, starts)
+		}
+		if blockIndex := gjson.Get(starts[i].Payload, "index").Int(); blockIndex != int64(i) {
+			t.Fatalf("tool_use start %d block index = %d, want %d", i, blockIndex, i)
+		}
+	}
+}
+
+func TestStreamingTool_LateIDAfterFinalization(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[{"index":0,"function":{"name":"do_it"}}]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}],"usage":{"prompt_tokens":1,"completion_tokens":1}}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"tool_calls":[{"index":0,"id":"call_late"}]}}]}`,
+	)
+
+	starts := toolUseStarts(events)
+	if len(starts) != 1 {
+		t.Fatalf("expected one belated tool_use start, got %d", len(starts))
+	}
+
+	var sawMessageStop bool
+	for _, e := range events {
+		if e.Type == "message_stop" {
+			sawMessageStop = true
+			continue
+		}
+		if sawMessageStop {
+			switch e.Type {
+			case "content_block_start", "content_block_delta", "content_block_stop":
+				t.Fatalf("event %q emitted after message_stop (events=%+v)", e.Type, events)
+			}
+		}
+	}
+}
+
+func TestStreamingTool_StopReasonMixedSuppressedAndValid(t *testing.T) {
+	events := runStream(t, streamReq,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{"role":"assistant","tool_calls":[
+			{"index":0,"id":"call_skip","function":{"name":"","arguments":""}},
+			{"index":1,"id":"call_real","function":{"name":"do_it","arguments":"{}"}}
+		]}}]}`,
+		`{"id":"c1","model":"m","choices":[{"index":0,"delta":{},"finish_reason":"tool_calls"}]}`,
+	)
+	if got := lastStopReason(events); got != "tool_use" {
+		t.Fatalf("stop_reason = %q, want %q", got, "tool_use")
+	}
+}