SMOODEV-2026: Go observability transport via SmooAI/fetch

go/fiber/go.mod

@@ -8,6 +8,7 @@ require (
 )
 
 require (
+	github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a // indirect
 	github.com/andybalholm/brotli v1.0.5 // indirect
 	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
@@ -20,6 +21,7 @@ require (
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/mattn/go-runewidth v0.0.15 // indirect
 	github.com/rivo/uniseg v0.2.0 // indirect
+	github.com/sony/gobreaker/v2 v2.0.0 // indirect
 	github.com/valyala/bytebufferpool v1.0.0 // indirect
 	github.com/valyala/fasthttp v1.51.0 // indirect
 	github.com/valyala/tcplisten v1.0.0 // indirect

go/fiber/go.sum

@@ -1,3 +1,5 @@
+github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a h1:PC/sAX6DhpTSqqqNg0hBczWktpxgjRYSUMbX0jPqmyw=
+github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a/go.mod h1:U+FFF0sdcQEdn98GltLEqRfviH6uHebuxOxfZIVR14A=
 github.com/andybalholm/brotli v1.0.5 h1:8uQZIdzKmjc/iuPu7O2ioW48L81FgatrcpfFmiq/cCs=
 github.com/andybalholm/brotli v1.0.5/go.mod h1:fO7iG3H7G2nSZ7m0zPUDn85XEX2GTukHGRSepvi9Eig=
 github.com/cenkalti/backoff/v5 v5.0.3 h1:ZN+IMa753KfX5hd8vVaMixjnqRZ3y8CuJKRKj1xcsSM=
@@ -34,6 +36,8 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rivo/uniseg v0.2.0 h1:S1pD9weZBuJdFmowNwbpi7BJ8TNftyUImj/0WQi72jY=
 github.com/rivo/uniseg v0.2.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
+github.com/sony/gobreaker/v2 v2.0.0 h1:23AaR4JQ65y4rz8JWMzgXw2gKOykZ/qfqYunll4OwJ4=
+github.com/sony/gobreaker/v2 v2.0.0/go.mod h1:8JnRUz80DJ1/ne8M8v7nmTs2713i58nIt4s7XcGe/DI=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/valyala/bytebufferpool v1.0.0 h1:GqA5TC/0021Y/b9FG4Oi9Mr3q7XYx6KllzawFIhcdPw=

go/gin/go.mod

@@ -8,6 +8,7 @@ require (
 )
 
 require (
+	github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a // indirect
 	github.com/bytedance/sonic v1.11.6 // indirect
 	github.com/bytedance/sonic/loader v0.1.1 // indirect
 	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
@@ -31,6 +32,7 @@ require (
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.2 // indirect
+	github.com/sony/gobreaker/v2 v2.0.0 // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.2.12 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect

go/gin/go.sum

@@ -1,3 +1,5 @@
+github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a h1:PC/sAX6DhpTSqqqNg0hBczWktpxgjRYSUMbX0jPqmyw=
+github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a/go.mod h1:U+FFF0sdcQEdn98GltLEqRfviH6uHebuxOxfZIVR14A=
 github.com/bytedance/sonic v1.11.6 h1:oUp34TzMlL+OY1OUWxHqsdkgC/Zfc85zGqw9siXjrc0=
 github.com/bytedance/sonic v1.11.6/go.mod h1:LysEHSvpvDySVdC2f87zGWf6CIKJcAvqab1ZaiQtds4=
 github.com/bytedance/sonic/loader v0.1.1 h1:c+e5Pt1k/cy5wMveRDyk2X4B9hF4g7an8N3zCYjJFNM=
@@ -68,6 +70,8 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rogpeppe/go-internal v1.14.1 h1:UQB4HGPB6osV0SQTLymcB4TgvyWu6ZyliaW0tI/otEQ=
 github.com/rogpeppe/go-internal v1.14.1/go.mod h1:MaRKkUm5W0goXpeCfT7UZI6fk/L7L7so1lCWt35ZSgc=
+github.com/sony/gobreaker/v2 v2.0.0 h1:23AaR4JQ65y4rz8JWMzgXw2gKOykZ/qfqYunll4OwJ4=
+github.com/sony/gobreaker/v2 v2.0.0/go.mod h1:8JnRUz80DJ1/ne8M8v7nmTs2713i58nIt4s7XcGe/DI=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
 github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=

go/go.mod

@@ -3,6 +3,7 @@ module github.com/SmooAI/observability/go
 go 1.25.0
 
 require (
+	github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a
 	github.com/google/uuid v1.6.0
 	go.opentelemetry.io/otel v1.44.0
 	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp v1.44.0
@@ -19,6 +20,7 @@ require (
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.29.0 // indirect
+	github.com/sony/gobreaker/v2 v2.0.0 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.44.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.10.0 // indirect

go/go.sum

@@ -1,3 +1,5 @@
+github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a h1:PC/sAX6DhpTSqqqNg0hBczWktpxgjRYSUMbX0jPqmyw=
+github.com/SmooAI/fetch/go/fetch v0.0.0-20260518194757-88f518b7813a/go.mod h1:U+FFF0sdcQEdn98GltLEqRfviH6uHebuxOxfZIVR14A=
 github.com/cenkalti/backoff/v5 v5.0.3 h1:ZN+IMa753KfX5hd8vVaMixjnqRZ3y8CuJKRKj1xcsSM=
 github.com/cenkalti/backoff/v5 v5.0.3/go.mod h1:rkhZdG3JZukswDf7f0cwqPNk4K0sa+F97BxZthm/crw=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
@@ -19,6 +21,8 @@ github.com/grpc-ecosystem/grpc-gateway/v2 v2.29.0 h1:5VipnvEpbqr2gA2VbM+nYVbkIF2
 github.com/grpc-ecosystem/grpc-gateway/v2 v2.29.0/go.mod h1:Hyl3n6Twe1hvtd9XUXDec4pTvgMSEixRuQKPTMH2bNs=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sony/gobreaker/v2 v2.0.0 h1:23AaR4JQ65y4rz8JWMzgXw2gKOykZ/qfqYunll4OwJ4=
+github.com/sony/gobreaker/v2 v2.0.0/go.mod h1:8JnRUz80DJ1/ne8M8v7nmTs2713i58nIt4s7XcGe/DI=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=

go/otel.go

@@ -203,6 +203,17 @@ func buildResource(opts SetupOtelOptions) *resource.Resource {
 
 // buildHTTPClient returns the custom-auth HTTP client when a TokenProvider is
 // set, the caller's override, or nil to let the exporter use its default.
+//
+// SMOODEV-2026 note: the OTLP/HTTP exporters are deliberately left on plain
+// net/http rather than routed through github.com/SmooAI/fetch/go/fetch. The
+// otlptracehttp/otlpmetrichttp exporters only accept a *http.Client (via
+// WithHTTPClient) and speak protobuf, while fetch is a generics-over-JSON client
+// that exposes no http.RoundTripper adapter — there is no clean seam to drive
+// the protobuf export through fetch's resilient pipeline without re-implementing
+// the exporter transport. The exporters already carry their own sane retry
+// (otlptracehttp.WithRetry, on by default with backoff), so wrapping them in
+// fetch would also double the retry layer. Only the webhook batch transport
+// (transport.go) was migrated to fetch. Revisit if fetch grows a RoundTripper.
 func buildHTTPClient(opts SetupOtelOptions) *http.Client {
 	if opts.TokenProvider == nil && opts.HTTPClient == nil {
 		return nil

go/transport.go

@@ -1,18 +1,29 @@
 package observability
 
 import (
-	"bytes"
 	"context"
-	"encoding/json"
+	"errors"
 	"net/http"
 	"sync"
 	"time"
+
+	"github.com/SmooAI/fetch/go/fetch"
 )
 
 // Batched HTTP transport. Holds a bounded queue, flushes on a timer or when
 // MaxBatchSize events are buffered, and retries a failed batch by pushing it
 // back to the front of the queue. Errors are swallowed — observability must
 // never throw into host code. Mirrors the TS Transport.
+//
+// Outbound delivery goes through github.com/SmooAI/fetch/go/fetch (SMOODEV-2026)
+// so each batch POST gets the resilient stack — jittered exponential-backoff
+// retries on 429/5xx + network errors, a per-request timeout, and an optional
+// circuit breaker — instead of a bare net/http call. fetch handles transient
+// blips within a single Flush; the transport's re-queue-on-failure handles
+// longer outages across Flush cycles, so the two retry layers are complementary
+// (fast in-call recovery vs. durable cross-cycle persistence), not duplicative:
+// fetch aborts immediately on 4xx (RetryAbort), matching the old permanent-error
+// behavior, so a persistent client error is not retried twice in a row.
 
 const (
 	defaultFlushMillis = 1000
@@ -26,7 +37,7 @@ type Transport struct {
 	flushInterval time.Duration
 	maxBatch      int
 	maxQueue      int
-	client        *http.Client
+	client        *fetch.Client
 
 	mu       sync.Mutex
 	queue    []ObservabilityEvent
@@ -41,7 +52,8 @@ type TransportOptions struct {
 	FlushInterval time.Duration
 	MaxBatchSize  int
 	MaxQueueSize  int
-	// HTTPClient overrides the default client (test seam).
+	// HTTPClient overrides the underlying *http.Client that the resilient fetch
+	// client drives (test seam). When nil, fetch's default transport is used.
 	HTTPClient *http.Client
 }
 
@@ -59,19 +71,31 @@ func NewTransport(opts TransportOptions) *Transport {
 	if queue <= 0 {
 		queue = defaultQueueMax
 	}
-	client := opts.HTTPClient
-	if client == nil {
-		client = &http.Client{Timeout: 10 * time.Second}
-	}
 	return &Transport{
 		dsn:           opts.DSN,
 		flushInterval: flush,
 		maxBatch:      batch,
 		maxQueue:      queue,
-		client:        client,
+		client:        buildFetchClient(opts.HTTPClient),
 	}
 }
 
+// buildFetchClient assembles the resilient fetch client used for batch delivery.
+// It keeps the prior 10s timeout and JSON content type, adds default retries
+// (429/5xx + network, jittered backoff, aborts on 4xx), and lets a test seam
+// swap the underlying *http.Client.
+func buildFetchClient(httpClient *http.Client) *fetch.Client {
+	retry := fetch.DefaultRetryOptions
+	b := fetch.NewClientBuilder().
+		WithTimeout(10 * time.Second).
+		WithRetry(&retry).
+		WithBaseHeaders(http.Header{"Content-Type": []string{"application/json"}})
+	if httpClient != nil {
+		b = b.WithHTTPClient(httpClient)
+	}
+	return b.Build()
+}
+
 // newTransportFromClientOptions wires a Transport from ClientOptions, used by
 // the bootstrap / default init when a DSN is configured.
 func newTransportFromClientOptions(opts ClientOptions) *Transport {
@@ -149,21 +173,19 @@ func (t *Transport) Flush(ctx context.Context) error {
 
 func (t *Transport) send(ctx context.Context, batch []ObservabilityEvent) error {
 	payload := IngestPayload{Type: "error", Events: batch}
-	body, err := json.Marshal(payload)
-	if err != nil {
-		return err
-	}
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost, t.dsn, bytes.NewReader(body))
-	if err != nil {
-		return err
-	}
-	req.Header.Set("content-type", "application/json")
-	resp, err := t.client.Do(req)
+	// fetch marshals the body to JSON and applies retries/timeout/backoff. It
+	// returns a typed *fetch.HTTPResponseError for non-2xx responses after
+	// retries are exhausted; normalize that to httpStatusError so callers and
+	// tests see the same surface as before.
+	resp, err := fetch.SimplePost(ctx, t.client, t.dsn, payload, nil)
 	if err != nil {
+		var httpErr *fetch.HTTPResponseError
+		if errors.As(err, &httpErr) {
+			return &httpStatusError{status: httpErr.StatusCode}
+		}
 		return err
 	}
-	defer resp.Body.Close()
-	if resp.StatusCode >= 400 {
+	if !resp.OK {
 		return &httpStatusError{status: resp.StatusCode}
 	}
 	return nil

go/transport_test.go

@@ -3,6 +3,7 @@ package observability
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -108,6 +109,55 @@ func TestFlushEmptyNoop(t *testing.T) {
 	}
 }
 
+// TestTransportFetchInCallRetry verifies the resilient fetch stack retries a
+// transient 5xx within a single send/Flush (SMOODEV-2026) — the first attempt
+// 500s, fetch backs off and retries, and the batch lands without ever needing
+// the transport's slower re-queue path. queueSize stays 0 after the flush.
+func TestTransportFetchInCallRetry(t *testing.T) {
+	var hits int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if atomic.AddInt32(&hits, 1) == 1 {
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	tr := NewTransport(TransportOptions{DSN: srv.URL, MaxBatchSize: 1})
+	tr.Enqueue(ObservabilityEvent{EventID: "1"}) // full batch -> synchronous Flush
+
+	// fetch retried the 500 in-call and succeeded, so the server saw >= 2 hits
+	// and the queue drained without a re-queue.
+	waitFor(t, func() bool { return atomic.LoadInt32(&hits) >= 2 })
+	waitFor(t, func() bool { return tr.queueSize() == 0 })
+}
+
+// TestTransportSendErrorOnPersistent4xx confirms a persistent client error
+// surfaces as httpStatusError (fetch aborts retries on 4xx) so Flush re-queues
+// the batch rather than dropping it.
+func TestTransportSendErrorOnPersistent4xx(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+	}))
+	defer srv.Close()
+
+	tr := NewTransport(TransportOptions{DSN: srv.URL, MaxBatchSize: 10})
+	tr.Enqueue(ObservabilityEvent{EventID: "1"})
+	err := tr.Flush(context.Background())
+	var statusErr *httpStatusError
+	if !errors.As(err, &statusErr) {
+		t.Fatalf("expected *httpStatusError, got %v", err)
+	}
+	if statusErr.status != http.StatusBadRequest {
+		t.Errorf("status = %d, want 400", statusErr.status)
+	}
+	// Batch was re-queued for a later attempt, not dropped.
+	if tr.queueSize() != 1 {
+		t.Errorf("queue size = %d, want 1 (re-queued)", tr.queueSize())
+	}
+}
+
 func waitFor(t *testing.T, cond func() bool) {
 	t.Helper()
 	deadline := time.Now().Add(2 * time.Second)