Sub2API v1.0 - AI API 网关（二开初始版本，基于上游 Wei-Shaw/sub2api）

backend/internal/service/openai_ws_v2/caddy_adapter.go

@@ -0,0 +1,24 @@
+package openai_ws_v2
+
+import (
+	"context"
+)
+
+// runCaddyStyleRelay 采用 Caddy reverseproxy 的双向隧道思想：
+// 连接建立后并发复制两个方向，任一方向退出触发收敛关闭。
+//
+// Reference:
+// - Project: caddyserver/caddy (Apache-2.0)
+// - Commit: f283062d37c50627d53ca682ebae2ce219b35515
+// - Files:
+//   - modules/caddyhttp/reverseproxy/streaming.go
+//   - modules/caddyhttp/reverseproxy/reverseproxy.go
+func runCaddyStyleRelay(
+	ctx context.Context,
+	clientConn FrameConn,
+	upstreamConn FrameConn,
+	firstClientMessage []byte,
+	options RelayOptions,
+) (RelayResult, *RelayExit) {
+	return Relay(ctx, clientConn, upstreamConn, firstClientMessage, options)
+}

backend/internal/service/openai_ws_v2/entry.go

@@ -0,0 +1,23 @@
+package openai_ws_v2
+
+import "context"
+
+// EntryInput 是 passthrough v2 数据面的入口参数。
+type EntryInput struct {
+	Ctx                context.Context
+	ClientConn         FrameConn
+	UpstreamConn       FrameConn
+	FirstClientMessage []byte
+	Options            RelayOptions
+}
+
+// RunEntry 是 openai_ws_v2 包对外的统一入口。
+func RunEntry(input EntryInput) (RelayResult, *RelayExit) {
+	return runCaddyStyleRelay(
+		input.Ctx,
+		input.ClientConn,
+		input.UpstreamConn,
+		input.FirstClientMessage,
+		input.Options,
+	)
+}

backend/internal/service/openai_ws_v2/metrics.go

@@ -0,0 +1,29 @@
+package openai_ws_v2
+
+import (
+	"sync/atomic"
+)
+
+// MetricsSnapshot 是 OpenAI WS v2 passthrough 路径的轻量运行时指标快照。
+type MetricsSnapshot struct {
+	SemanticMutationTotal  int64 `json:"semantic_mutation_total"`
+	UsageParseFailureTotal int64 `json:"usage_parse_failure_total"`
+}
+
+var (
+	// passthrough 路径默认不会做语义改写，该计数通常应保持为 0（保留用于未来防御性校验）。
+	passthroughSemanticMutationTotal  atomic.Int64
+	passthroughUsageParseFailureTotal atomic.Int64
+)
+
+func recordUsageParseFailure() {
+	passthroughUsageParseFailureTotal.Add(1)
+}
+
+// SnapshotMetrics 返回当前 passthrough 指标快照。
+func SnapshotMetrics() MetricsSnapshot {
+	return MetricsSnapshot{
+		SemanticMutationTotal:  passthroughSemanticMutationTotal.Load(),
+		UsageParseFailureTotal: passthroughUsageParseFailureTotal.Load(),
+	}
+}

backend/internal/service/openai_ws_v2/passthrough_relay_internal_test.go

@@ -0,0 +1,570 @@
+package openai_ws_v2
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	coderws "github.com/coder/websocket"
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/gjson"
+)
+
+func TestRunEntry_DelegatesRelay(t *testing.T) {
+	t.Parallel()
+
+	clientConn := newPassthroughTestFrameConn(nil, false)
+	upstreamConn := newPassthroughTestFrameConn([]passthroughTestFrame{
+		{
+			msgType: coderws.MessageText,
+			payload: []byte(`{"type":"response.completed","response":{"id":"resp_entry","usage":{"input_tokens":1,"output_tokens":1}}}`),
+		},
+	}, true)
+
+	result, relayExit := RunEntry(EntryInput{
+		Ctx:                context.Background(),
+		ClientConn:         clientConn,
+		UpstreamConn:       upstreamConn,
+		FirstClientMessage: []byte(`{"type":"response.create","model":"gpt-4o","input":[]}`),
+	})
+	require.Nil(t, relayExit)
+	require.Equal(t, "resp_entry", result.RequestID)
+}
+
+func TestRunClientToUpstream_ErrorPaths(t *testing.T) {
+	t.Parallel()
+
+	t.Run("read client eof", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		runClientToUpstream(
+			context.Background(),
+			newPassthroughTestFrameConn(nil, true),
+			nil,
+			func(_ coderws.MessageType, _ []byte) error { return nil },
+			func() {},
+			nil,
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "read_client", sig.stage)
+		require.True(t, sig.graceful)
+	})
+
+	t.Run("write upstream failed", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		runClientToUpstream(
+			context.Background(),
+			newPassthroughTestFrameConn([]passthroughTestFrame{
+				{msgType: coderws.MessageText, payload: []byte(`{"x":1}`)},
+			}, true),
+			nil,
+			func(_ coderws.MessageType, _ []byte) error { return errors.New("boom") },
+			func() {},
+			nil,
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "write_upstream", sig.stage)
+		require.False(t, sig.graceful)
+	})
+
+	t.Run("forwarded counter and trace callback", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		forwarded := &atomic.Int64{}
+		traces := make([]RelayTraceEvent, 0, 2)
+		runClientToUpstream(
+			context.Background(),
+			newPassthroughTestFrameConn([]passthroughTestFrame{
+				{msgType: coderws.MessageText, payload: []byte(`{"x":1}`)},
+			}, true),
+			nil,
+			func(_ coderws.MessageType, _ []byte) error { return nil },
+			func() {},
+			forwarded,
+			func(event RelayTraceEvent) {
+				traces = append(traces, event)
+			},
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "read_client", sig.stage)
+		require.Equal(t, int64(1), forwarded.Load())
+		require.NotEmpty(t, traces)
+	})
+}
+
+func TestRunUpstreamToClient_ErrorAndDropPaths(t *testing.T) {
+	t.Parallel()
+
+	t.Run("read upstream eof", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		drop := &atomic.Bool{}
+		drop.Store(false)
+		runUpstreamToClient(
+			context.Background(),
+			newPassthroughTestFrameConn(nil, true),
+			func(_ coderws.MessageType, _ []byte) error { return nil },
+			time.Now(),
+			time.Now,
+			&relayState{},
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			drop,
+			nil,
+			nil,
+			func() {},
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "read_upstream", sig.stage)
+		require.True(t, sig.graceful)
+	})
+
+	t.Run("write client failed", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		drop := &atomic.Bool{}
+		drop.Store(false)
+		runUpstreamToClient(
+			context.Background(),
+			newPassthroughTestFrameConn([]passthroughTestFrame{
+				{msgType: coderws.MessageText, payload: []byte(`{"type":"response.output_text.delta","delta":"x"}`)},
+			}, true),
+			func(_ coderws.MessageType, _ []byte) error { return errors.New("write failed") },
+			time.Now(),
+			time.Now,
+			&relayState{},
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			drop,
+			nil,
+			nil,
+			func() {},
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "write_client", sig.stage)
+	})
+
+	t.Run("drop downstream and stop on terminal", func(t *testing.T) {
+		t.Parallel()
+
+		exitCh := make(chan relayExitSignal, 1)
+		drop := &atomic.Bool{}
+		drop.Store(true)
+		dropped := &atomic.Int64{}
+		runUpstreamToClient(
+			context.Background(),
+			newPassthroughTestFrameConn([]passthroughTestFrame{
+				{
+					msgType: coderws.MessageText,
+					payload: []byte(`{"type":"response.completed","response":{"id":"resp_drop","usage":{"input_tokens":1,"output_tokens":1}}}`),
+				},
+			}, true),
+			func(_ coderws.MessageType, _ []byte) error { return nil },
+			time.Now(),
+			time.Now,
+			&relayState{},
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			nil,
+			drop,
+			nil,
+			dropped,
+			func() {},
+			nil,
+			exitCh,
+		)
+		sig := <-exitCh
+		require.Equal(t, "drain_terminal", sig.stage)
+		require.True(t, sig.graceful)
+		require.Equal(t, int64(1), dropped.Load())
+	})
+}
+
+func TestRunIdleWatchdog_NoTimeoutWhenDisabled(t *testing.T) {
+	t.Parallel()
+
+	exitCh := make(chan relayExitSignal, 1)
+	lastActivity := &atomic.Int64{}
+	lastActivity.Store(time.Now().UnixNano())
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	go runIdleWatchdog(ctx, time.Now, 0, lastActivity, nil, exitCh)
+	select {
+	case <-exitCh:
+		t.Fatal("unexpected idle timeout signal")
+	case <-time.After(200 * time.Millisecond):
+	}
+}
+
+func TestHelperFunctionsCoverage(t *testing.T) {
+	t.Parallel()
+
+	require.Equal(t, "text", relayMessageTypeString(coderws.MessageText))
+	require.Equal(t, "binary", relayMessageTypeString(coderws.MessageBinary))
+	require.Contains(t, relayMessageTypeString(coderws.MessageType(99)), "unknown(")
+
+	require.Equal(t, "", relayErrorString(nil))
+	require.Equal(t, "x", relayErrorString(errors.New("x")))
+
+	require.True(t, isDisconnectError(io.EOF))
+	require.True(t, isDisconnectError(net.ErrClosed))
+	require.True(t, isDisconnectError(context.Canceled))
+	require.True(t, isDisconnectError(coderws.CloseError{Code: coderws.StatusGoingAway}))
+	require.True(t, isDisconnectError(errors.New("broken pipe")))
+	require.False(t, isDisconnectError(errors.New("unrelated")))
+
+	require.True(t, isTokenEvent("response.output_text.delta"))
+	require.True(t, isTokenEvent("response.output_audio.delta"))
+	require.False(t, isTokenEvent("response.completed"))
+	require.False(t, isTokenEvent(""))
+	require.False(t, isTokenEvent("response.created"))
+
+	require.Equal(t, 2*time.Second, minDuration(2*time.Second, 5*time.Second))
+	require.Equal(t, 2*time.Second, minDuration(5*time.Second, 2*time.Second))
+	require.Equal(t, 5*time.Second, minDuration(0, 5*time.Second))
+	require.Equal(t, 2*time.Second, minDuration(2*time.Second, 0))
+
+	ch := make(chan relayExitSignal, 1)
+	ch <- relayExitSignal{stage: "ok"}
+	sig, ok := waitRelayExit(ch, 10*time.Millisecond)
+	require.True(t, ok)
+	require.Equal(t, "ok", sig.stage)
+	ch <- relayExitSignal{stage: "ok2"}
+	sig, ok = waitRelayExit(ch, 0)
+	require.True(t, ok)
+	require.Equal(t, "ok2", sig.stage)
+	_, ok = waitRelayExit(ch, 10*time.Millisecond)
+	require.False(t, ok)
+
+	n, ok := parseUsageIntField(gjson.Get(`{"n":3}`, "n"), true)
+	require.True(t, ok)
+	require.Equal(t, 3, n)
+	_, ok = parseUsageIntField(gjson.Get(`{"n":"x"}`, "n"), true)
+	require.False(t, ok)
+	n, ok = parseUsageIntField(gjson.Result{}, false)
+	require.True(t, ok)
+	require.Equal(t, 0, n)
+	_, ok = parseUsageIntField(gjson.Result{}, true)
+	require.False(t, ok)
+}
+
+func TestParseUsageAndEnrichCoverage(t *testing.T) {
+	t.Parallel()
+
+	state := &relayState{}
+	parseUsageAndAccumulate(state, []byte(`{"type":"response.completed","response":{"usage":{"input_tokens":"bad"}}}`), "response.completed", nil)
+	require.Equal(t, 0, state.usage.InputTokens)
+
+	parseUsageAndAccumulate(
+		state,
+		[]byte(`{"type":"response.completed","response":{"usage":{"input_tokens":9,"output_tokens":"bad","input_tokens_details":{"cached_tokens":2}}}}`),
+		"response.completed",
+		nil,
+	)
+	require.Equal(t, 0, state.usage.InputTokens, "部分字段解析失败时不应累加 usage")
+	require.Equal(t, 0, state.usage.OutputTokens)
+	require.Equal(t, 0, state.usage.CacheReadInputTokens)
+
+	parseUsageAndAccumulate(
+		state,
+		[]byte(`{"type":"response.completed","response":{"usage":{"input_tokens_details":{"cached_tokens":2}}}}`),
+		"response.completed",
+		nil,
+	)
+	require.Equal(t, 0, state.usage.InputTokens, "必填 usage 字段缺失时不应累加 usage")
+	require.Equal(t, 0, state.usage.OutputTokens)
+	require.Equal(t, 0, state.usage.CacheReadInputTokens)
+
+	parseUsageAndAccumulate(state, []byte(`{"type":"response.completed","response":{"usage":{"input_tokens":2,"output_tokens":1,"input_tokens_details":{"cached_tokens":1,"cache_write_tokens":4},"output_tokens_details":{"image_tokens":3}}}}`), "response.completed", nil)
+	require.Equal(t, 2, state.usage.InputTokens)
+	require.Equal(t, 1, state.usage.OutputTokens)
+	require.Equal(t, 1, state.usage.CacheReadInputTokens)
+	require.Equal(t, 4, state.usage.CacheCreationInputTokens)
+	require.Equal(t, 3, state.usage.ImageOutputTokens)
+
+	result := &RelayResult{}
+	enrichResult(result, state, 5*time.Millisecond)
+	require.Equal(t, state.usage.InputTokens, result.Usage.InputTokens)
+	require.Equal(t, state.usage.CacheCreationInputTokens, result.Usage.CacheCreationInputTokens)
+	require.Equal(t, state.usage.ImageOutputTokens, result.Usage.ImageOutputTokens)
+	require.Equal(t, 5*time.Millisecond, result.Duration)
+	parseUsageAndAccumulate(state, []byte(`{"type":"response.in_progress","response":{"usage":{"input_tokens":9}}}`), "response.in_progress", nil)
+	require.Equal(t, 2, state.usage.InputTokens)
+	enrichResult(nil, state, 0)
+}
+
+func TestParseUsageAndAccumulateAcceptsChatUsageAliases(t *testing.T) {
+	t.Parallel()
+
+	state := &relayState{}
+	got := parseUsageAndAccumulate(
+		state,
+		[]byte(`{"type":"response.done","response":{"usage":{"prompt_tokens":12,"completion_tokens":6,"prompt_tokens_details":{"cached_tokens":4},"completion_tokens_details":{"image_tokens":2}}}}`),
+		"response.done",
+		nil,
+	)
+	require.Equal(t, 12, got.InputTokens)
+	require.Equal(t, 6, got.OutputTokens)
+	require.Equal(t, 4, got.CacheReadInputTokens)
+	require.Equal(t, 2, got.ImageOutputTokens)
+	require.Equal(t, got, state.usage)
+}
+
+func TestOpenAICacheCreationTokensFromUsageNestedZeroWins(t *testing.T) {
+	t.Parallel()
+
+	usage := gjson.Parse(`{"input_tokens_details":{"cache_write_tokens":0},"cache_creation_input_tokens":19}`)
+	require.Zero(t, openAICacheCreationTokensFromUsage(usage))
+}
+
+func TestEmitTurnCompleteCoverage(t *testing.T) {
+	t.Parallel()
+
+	// 非 terminal 事件不应触发。
+	called := 0
+	emitTurnComplete(func(turn RelayTurnResult) {
+		called++
+	}, &relayState{requestModel: "gpt-5"}, observedUpstreamEvent{
+		terminal:   false,
+		eventType:  "response.output_text.delta",
+		responseID: "resp_ignored",
+		usage:      Usage{InputTokens: 1},
+	})
+	require.Equal(t, 0, called)
+
+	// 缺少 response_id 时不应触发。
+	emitTurnComplete(func(turn RelayTurnResult) {
+		called++
+	}, &relayState{requestModel: "gpt-5"}, observedUpstreamEvent{
+		terminal:  true,
+		eventType: "response.completed",
+	})
+	require.Equal(t, 0, called)
+
+	// terminal 且 response_id 存在，应该触发；state=nil 时 model 为空串。
+	var got RelayTurnResult
+	emitTurnComplete(func(turn RelayTurnResult) {
+		called++
+		got = turn
+	}, nil, observedUpstreamEvent{
+		terminal:   true,
+		eventType:  "response.completed",
+		responseID: "resp_emit",
+		usage:      Usage{InputTokens: 2, OutputTokens: 3},
+	})
+	require.Equal(t, 1, called)
+	require.Equal(t, "resp_emit", got.RequestID)
+	require.Equal(t, "response.completed", got.TerminalEventType)
+	require.Equal(t, 2, got.Usage.InputTokens)
+	require.Equal(t, 3, got.Usage.OutputTokens)
+	require.Equal(t, "", got.RequestModel)
+}
+
+func TestIsDisconnectErrorCoverage_CloseStatusesAndMessageBranches(t *testing.T) {
+	t.Parallel()
+
+	require.True(t, isDisconnectError(coderws.CloseError{Code: coderws.StatusNormalClosure}))
+	require.True(t, isDisconnectError(coderws.CloseError{Code: coderws.StatusNoStatusRcvd}))
+	require.True(t, isDisconnectError(coderws.CloseError{Code: coderws.StatusAbnormalClosure}))
+	require.True(t, isDisconnectError(errors.New("connection reset by peer")))
+	require.False(t, isDisconnectError(errors.New("   ")))
+}
+
+func TestIsTokenEventCoverageBranches(t *testing.T) {
+	t.Parallel()
+
+	require.False(t, isTokenEvent("response.in_progress"))
+	require.False(t, isTokenEvent("response.output_item.added"))
+	require.True(t, isTokenEvent("response.output_audio.delta"))
+	require.True(t, isTokenEvent("response.function_call_arguments.delta"))
+	require.True(t, isTokenEvent("response.reasoning_summary_text.delta"))
+	require.True(t, isTokenEvent("response.output_text.done"))
+	require.True(t, isTokenEvent("response.function_call_arguments.done"))
+	require.False(t, isTokenEvent("response.output"))
+	require.False(t, isTokenEvent("response.output_audio.done"))
+	require.False(t, isTokenEvent("response.content_part.done"))
+	require.False(t, isTokenEvent("response.output_item.done"))
+	require.False(t, isTokenEvent("response.output_text.annotation.added"))
+	require.False(t, isTokenEvent("response.done"))
+}
+
+func TestTerminalAndTokenEventSetsAreDisjoint(t *testing.T) {
+	t.Parallel()
+
+	for _, eventType := range []string{
+		"response.completed",
+		"response.done",
+		"response.failed",
+		"response.incomplete",
+		"response.cancelled",
+		"response.canceled",
+	} {
+		require.True(t, isTerminalEvent(eventType), eventType)
+		require.False(t, isTokenEvent(eventType), eventType)
+	}
+}
+
+func TestShouldParseUsageTerminalEvents(t *testing.T) {
+	t.Parallel()
+
+	for _, eventType := range []string{
+		"response.completed",
+		"response.done",
+		"response.failed",
+		"response.incomplete",
+		"response.cancelled",
+		"response.canceled",
+	} {
+		require.True(t, shouldParseUsage(eventType), eventType)
+	}
+	require.False(t, shouldParseUsage("response.output_text.delta"))
+	require.False(t, shouldParseUsage(""))
+}
+
+func TestRelayTurnTimingHelpersCoverage(t *testing.T) {
+	t.Parallel()
+
+	now := time.Unix(100, 0)
+	// nil state
+	require.Nil(t, openAIWSRelayGetOrInitTurnTiming(nil, "resp_nil", now))
+	_, ok := openAIWSRelayDeleteTurnTiming(nil, "resp_nil")
+	require.False(t, ok)
+
+	state := &relayState{}
+	timing := openAIWSRelayGetOrInitTurnTiming(state, "resp_a", now)
+	require.NotNil(t, timing)
+	require.Equal(t, now, timing.startAt)
+
+	// 再次获取返回同一条 timing
+	timing2 := openAIWSRelayGetOrInitTurnTiming(state, "resp_a", now.Add(5*time.Second))
+	require.NotNil(t, timing2)
+	require.Equal(t, now, timing2.startAt)
+
+	// 删除存在键
+	deleted, ok := openAIWSRelayDeleteTurnTiming(state, "resp_a")
+	require.True(t, ok)
+	require.Equal(t, now, deleted.startAt)
+
+	// 删除不存在键
+	_, ok = openAIWSRelayDeleteTurnTiming(state, "resp_a")
+	require.False(t, ok)
+}
+
+func TestObserveUpstreamMessage_ResponseModelIsTurnLocalAndTerminalWins(t *testing.T) {
+	t.Parallel()
+
+	state := &relayState{requestModel: "gpt-5.6-sol"}
+	startAt := time.Unix(0, 0)
+	now := startAt
+	nowFn := func() time.Time {
+		now = now.Add(5 * time.Millisecond)
+		return now
+	}
+
+	created := observeUpstreamMessage(
+		state,
+		[]byte(`{"type":"response.created","response":{"id":"resp_1","model":"gpt-5.5"}}`),
+		startAt,
+		nowFn,
+		nil,
+	)
+	require.False(t, created.terminal)
+
+	completed := observeUpstreamMessage(
+		state,
+		[]byte(`{"type":"response.completed","response":{"id":"resp_1","model":"gpt-5.4","usage":{"input_tokens":1,"output_tokens":2}}}`),
+		startAt,
+		nowFn,
+		nil,
+	)
+	require.True(t, completed.terminal)
+	require.Equal(t, "gpt-5.4", completed.responseModel)
+	require.True(t, completed.responseConflict)
+
+	var firstTurn RelayTurnResult
+	emitTurnComplete(func(turn RelayTurnResult) { firstTurn = turn }, state, completed)
+	require.Equal(t, "gpt-5.4", firstTurn.ResponseModel)
+	require.True(t, firstTurn.ResponseModelConflict)
+
+	observeUpstreamMessage(
+		state,
+		[]byte(`{"type":"response.created","response":{"id":"resp_2","model":"gpt-5.3"}}`),
+		startAt,
+		nowFn,
+		nil,
+	)
+	second := observeUpstreamMessage(
+		state,
+		[]byte(`{"type":"response.completed","response":{"id":"resp_2","model":"GPT-5.3","usage":{"input_tokens":3,"output_tokens":4}}}`),
+		startAt,
+		nowFn,
+		nil,
+	)
+	require.Equal(t, "GPT-5.3", second.responseModel)
+	require.False(t, second.responseConflict, "the previous turn must not contaminate this turn")
+}
+
+func TestObserveUpstreamMessage_ResponseIDFallbackPolicy(t *testing.T) {
+	t.Parallel()
+
+	state := &relayState{requestModel: "gpt-5"}
+	startAt := time.Unix(0, 0)
+	now := startAt
+	nowFn := func() time.Time {
+		now = now.Add(5 * time.Millisecond)
+		return now
+	}
+
+	// 非 terminal：仅有顶层 id，不应把 event id 当成 response_id。
+	observed := observeUpstreamMessage(
+		state,
+		[]byte(`{"type":"response.output_text.delta","id":"evt_123","delta":"hi"}`),
+		startAt,
+		nowFn,
+		nil,
+	)
+	require.False(t, observed.terminal)
+	require.Equal(t, "", observed.responseID)
+
+	// terminal：允许兜底用顶层 id（用于兼容少数字段变体）。
+	observed = observeUpstreamMessage(
+		state,
+		[]byte(`{"type":"response.completed","id":"resp_fallback","response":{"usage":{"input_tokens":1,"output_tokens":1}}}`),
+		startAt,
+		nowFn,
+		nil,
+	)
+	require.True(t, observed.terminal)
+	require.Equal(t, "resp_fallback", observed.responseID)
+}