feat(tracing): integrate langsmith-go for LLM request tracing

cmd/gateway.go

@@ -129,6 +129,8 @@ func runGateway() {
 		defer traceCollector.Stop()
 		// OTel OTLP export: compiled via build tags. Build with 'go build -tags otel' to enable.
 		initOTelExporter(context.Background(), cfg, traceCollector)
+		// LangSmith export: compiled via build tags. Build with 'go build -tags langsmith' to enable.
+		initLangSmithExporter(context.Background(), cfg, traceCollector)
 	}
 	if snapshotWorker != nil {
 		defer snapshotWorker.Stop()

cmd/gateway_langsmith.go

@@ -0,0 +1,42 @@
+//go:build langsmith
+
+package cmd
+
+import (
+	"context"
+	"log/slog"
+
+	"github.com/nextlevelbuilder/goclaw/internal/config"
+	"github.com/nextlevelbuilder/goclaw/internal/tracing"
+	"github.com/nextlevelbuilder/goclaw/internal/tracing/langsmithexport"
+)
+
+// initLangSmithExporter creates and wires the LangSmith exporter when
+// the API key is configured. Only compiled with -tags langsmith.
+func initLangSmithExporter(_ context.Context, cfg *config.Config, collector *tracing.Collector) {
+	if collector == nil {
+		return
+	}
+	if cfg.LangSmith.APIKey == "" {
+		slog.Debug("LangSmith export available but not enabled (set LANGSMITH_API_KEY)")
+		return
+	}
+
+	exp, err := langsmithexport.New(langsmithexport.Config{
+		APIKey:  cfg.LangSmith.APIKey,
+		Project: cfg.LangSmith.Project,
+		APIUrl:  cfg.LangSmith.APIUrl,
+	})
+	if err != nil {
+		slog.Warn("failed to create LangSmith exporter", "error", err)
+		return
+	}
+
+	collector.AddExporter(exp)
+
+	project := cfg.LangSmith.Project
+	if project == "" {
+		project = "default"
+	}
+	slog.Info("LangSmith export enabled", "project", project)
+}

cmd/gateway_langsmith_noop.go

@@ -0,0 +1,15 @@
+//go:build !langsmith
+
+package cmd
+
+import (
+	"context"
+
+	"github.com/nextlevelbuilder/goclaw/internal/config"
+	"github.com/nextlevelbuilder/goclaw/internal/tracing"
+)
+
+// initLangSmithExporter is a no-op when built without the "langsmith" tag.
+// Build with `go build -tags langsmith` to enable LangSmith export.
+func initLangSmithExporter(_ context.Context, _ *config.Config, _ *tracing.Collector) {
+}

go.mod

@@ -22,11 +22,11 @@ require (
 	github.com/titanous/json5 v1.0.0
 	github.com/wailsapp/wails/v2 v2.11.0
 	github.com/zalando/go-keyring v0.2.8
-	go.opentelemetry.io/otel v1.40.0
+	go.opentelemetry.io/otel v1.42.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.40.0
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.40.0
-	go.opentelemetry.io/otel/sdk v1.40.0
-	go.opentelemetry.io/otel/trace v1.40.0
+	go.opentelemetry.io/otel/sdk v1.42.0
+	go.opentelemetry.io/otel/trace v1.42.0
 	golang.org/x/time v0.14.0
 	modernc.org/sqlite v1.47.0
 	tailscale.com v1.94.2
@@ -84,6 +84,7 @@ require (
 	github.com/jsimonetti/rtnetlink v1.4.0 // indirect
 	github.com/labstack/echo/v4 v4.13.3 // indirect
 	github.com/labstack/gommon v0.4.2 // indirect
+	github.com/langchain-ai/langsmith-go v0.2.2 // indirect
 	github.com/leaanthony/go-ansi-parser v1.6.1 // indirect
 	github.com/leaanthony/gosod v1.0.4 // indirect
 	github.com/leaanthony/slicer v1.6.0 // indirect
@@ -114,6 +115,10 @@ require (
 	github.com/tailscale/peercred v0.0.0-20250107143737-35a0c7bd7edc // indirect
 	github.com/tailscale/web-client-prebuilt v0.0.0-20250124233751-d4cd19a26976 // indirect
 	github.com/tailscale/wireguard-go v0.0.0-20250716170648-1d0488a3d7da // indirect
+	github.com/tidwall/gjson v1.18.0 // indirect
+	github.com/tidwall/match v1.1.1 // indirect
+	github.com/tidwall/pretty v1.2.1 // indirect
+	github.com/tidwall/sjson v1.2.5 // indirect
 	github.com/tkrajina/go-reflector v0.5.8 // indirect
 	github.com/valyala/fasttemplate v1.2.2 // indirect
 	github.com/wailsapp/go-webview2 v1.0.22 // indirect
@@ -154,7 +159,7 @@ require (
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
-	github.com/klauspost/compress v1.18.2 // indirect
+	github.com/klauspost/compress v1.18.4 // indirect
 	github.com/klauspost/cpuid/v2 v2.2.9 // indirect
 	github.com/lib/pq v1.10.9
 	github.com/mark3labs/mcp-go v0.44.0
@@ -172,7 +177,7 @@ require (
 	github.com/ysmood/leakless v0.9.0 // indirect
 	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
 	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.40.0 // indirect
-	go.opentelemetry.io/otel/metric v1.40.0 // indirect
+	go.opentelemetry.io/otel/metric v1.42.0 // indirect
 	go.opentelemetry.io/proto/otlp v1.9.0 // indirect
 	golang.org/x/arch v0.0.0-20210923205945-b76863e36670 // indirect
 	golang.org/x/crypto v0.47.0 // indirect
@@ -183,6 +188,6 @@ require (
 	golang.org/x/text v0.33.0 // indirect
 	google.golang.org/genproto/googleapis/api v0.0.0-20260128011058-8636f8732409 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20260128011058-8636f8732409 // indirect
-	google.golang.org/grpc v1.78.0 // indirect
+	google.golang.org/grpc v1.79.3 // indirect
 	google.golang.org/protobuf v1.36.11 // indirect
 )

go.sum

@@ -251,6 +251,8 @@ github.com/jsimonetti/rtnetlink v1.4.0 h1:Z1BF0fRgcETPEa0Kt0MRk3yV5+kF1FWTni6KUF
 github.com/jsimonetti/rtnetlink v1.4.0/go.mod h1:5W1jDvWdnthFJ7fxYX1GMK07BUpI4oskfOqvPteYS6E=
 github.com/klauspost/compress v1.18.2 h1:iiPHWW0YrcFgpBYhsA6D1+fqHssJscY/Tm/y2Uqnapk=
 github.com/klauspost/compress v1.18.2/go.mod h1:R0h/fSBs8DE4ENlcrlib3PsXS61voFxhIs2DeRhCvJ4=
+github.com/klauspost/compress v1.18.4 h1:RPhnKRAQ4Fh8zU2FY/6ZFDwTVTxgJ/EMydqSTzE9a2c=
+github.com/klauspost/compress v1.18.4/go.mod h1:R0h/fSBs8DE4ENlcrlib3PsXS61voFxhIs2DeRhCvJ4=
 github.com/klauspost/cpuid/v2 v2.2.9 h1:66ze0taIn2H33fBvCkXuv9BmCwDfafmiIVpKV9kKGuY=
 github.com/klauspost/cpuid/v2 v2.2.9/go.mod h1:rqkxqrZ1EhYM9G+hXH7YdowN5R5RGN6NK4QwQ3WMXF8=
 github.com/kortschak/wol v0.0.0-20200729010619-da482cc4850a h1:+RR6SqnTkDLWyICxS1xpjCi/3dhyV+TgZwA6Ww3KncQ=
@@ -267,6 +269,8 @@ github.com/labstack/echo/v4 v4.13.3 h1:pwhpCPrTl5qry5HRdM5FwdXnhXSLSY+WE+YQSeCaa
 github.com/labstack/echo/v4 v4.13.3/go.mod h1:o90YNEeQWjDozo584l7AwhJMHN0bOC4tAfg+Xox9q5g=
 github.com/labstack/gommon v0.4.2 h1:F8qTUNXgG1+6WQmqoUWnz8WiEU60mXVVw0P4ht1WRA0=
 github.com/labstack/gommon v0.4.2/go.mod h1:QlUFxVM+SNXhDL/Z7YhocGIBYOiwB0mXm1+1bAPHPyU=
+github.com/langchain-ai/langsmith-go v0.2.2 h1:WVNUR9dhnuieIaXrKxmZWva6TX1DV/RHCVgc67wbAbs=
+github.com/langchain-ai/langsmith-go v0.2.2/go.mod h1:xdfOA0EBT7KF9ylz+gGq8EM6srRkv2PtpazQ+4oraWk=
 github.com/leaanthony/debme v1.2.1 h1:9Tgwf+kjcrbMQ4WnPcEIUcQuIZYqdWftzZkBr+i/oOc=
 github.com/leaanthony/debme v1.2.1/go.mod h1:3V+sCm5tYAgQymvSOfYQ5Xx2JCr+OXiD9Jkw3otUjiA=
 github.com/leaanthony/go-ansi-parser v1.6.1 h1:xd8bzARK3dErqkPFtoF9F3/HgN8UQk0ed1YDKpEz01A=
@@ -415,6 +419,16 @@ github.com/tailscale/xnet v0.0.0-20240729143630-8497ac4dab2e h1:zOGKqN5D5hHhiYUp
 github.com/tailscale/xnet v0.0.0-20240729143630-8497ac4dab2e/go.mod h1:orPd6JZXXRyuDusYilywte7k094d7dycXXU5YnWsrwg=
 github.com/tc-hib/winres v0.3.1 h1:CwRjEGrKdbi5CvZ4ID+iyVhgyfatxFoizjPhzez9Io4=
 github.com/tc-hib/winres v0.3.1/go.mod h1:C/JaNhH3KBvhNKVbvdlDWkbMDO9H4fKKDaN7/07SSuk=
+github.com/tidwall/gjson v1.14.2/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
+github.com/tidwall/gjson v1.18.0 h1:FIDeeyB800efLX89e5a8Y0BNH+LOngJyGrIWxG2FKQY=
+github.com/tidwall/gjson v1.18.0/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
+github.com/tidwall/match v1.1.1 h1:+Ho715JplO36QYgwN9PGYNhgZvoUSc9X2c80KVTi+GA=
+github.com/tidwall/match v1.1.1/go.mod h1:eRSPERbgtNPcGhD8UCthc6PmLEQXEWd3PRB5JTxsfmM=
+github.com/tidwall/pretty v1.2.0/go.mod h1:ITEVvHYasfjBbM0u2Pg8T2nJnzm8xPwvNhhsoaGGjNU=
+github.com/tidwall/pretty v1.2.1 h1:qjsOFOWWQl+N3RsoF5/ssm1pHmJJwhjlSbZ51I6wMl4=
+github.com/tidwall/pretty v1.2.1/go.mod h1:ITEVvHYasfjBbM0u2Pg8T2nJnzm8xPwvNhhsoaGGjNU=
+github.com/tidwall/sjson v1.2.5 h1:kLy8mja+1c9jlljvWTlSazM7cKDRfJuR/bOJhcY5NcY=
+github.com/tidwall/sjson v1.2.5/go.mod h1:Fvgq9kS/6ociJEDnK0Fk1cpYF4FIW6ZF7LAe+6jwd28=
 github.com/titanous/json5 v1.0.0 h1:hJf8Su1d9NuI/ffpxgxQfxh/UiBFZX7bMPid0rIL/7s=
 github.com/titanous/json5 v1.0.0/go.mod h1:7JH1M8/LHKc6cyP5o5g3CSaRj+mBrIimTxzpvmckH8c=
 github.com/tkrajina/go-reflector v0.5.8 h1:yPADHrwmUbMq4RGEyaOUpz2H90sRsETNVpjzo3DLVQQ=
@@ -475,6 +489,8 @@ go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.64.0 h1:ssfIgGN
 go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.64.0/go.mod h1:GQ/474YrbE4Jx8gZ4q5I4hrhUzM6UPzyrqJYV2AqPoQ=
 go.opentelemetry.io/otel v1.40.0 h1:oA5YeOcpRTXq6NN7frwmwFR0Cn3RhTVZvXsP4duvCms=
 go.opentelemetry.io/otel v1.40.0/go.mod h1:IMb+uXZUKkMXdPddhwAHm6UfOwJyh4ct1ybIlV14J0g=
+go.opentelemetry.io/otel v1.42.0 h1:lSQGzTgVR3+sgJDAU/7/ZMjN9Z+vUip7leaqBKy4sho=
+go.opentelemetry.io/otel v1.42.0/go.mod h1:lJNsdRMxCUIWuMlVJWzecSMuNjE7dOYyWlqOXWkdqCc=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.40.0 h1:QKdN8ly8zEMrByybbQgv8cWBcdAarwmIPZ6FThrWXJs=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.40.0/go.mod h1:bTdK1nhqF76qiPoCCdyFIV+N/sRHYXYCTQc+3VCi3MI=
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.40.0 h1:DvJDOPmSWQHWywQS6lKL+pb8s3gBLOZUtw4N+mavW1I=
@@ -483,12 +499,19 @@ go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.40.0 h1:wVZXI
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.40.0/go.mod h1:khvBS2IggMFNwZK/6lEeHg/W57h/IX6J4URh57fuI40=
 go.opentelemetry.io/otel/metric v1.40.0 h1:rcZe317KPftE2rstWIBitCdVp89A2HqjkxR3c11+p9g=
 go.opentelemetry.io/otel/metric v1.40.0/go.mod h1:ib/crwQH7N3r5kfiBZQbwrTge743UDc7DTFVZrrXnqc=
+go.opentelemetry.io/otel/metric v1.42.0 h1:2jXG+3oZLNXEPfNmnpxKDeZsFI5o4J+nz6xUlaFdF/4=
+go.opentelemetry.io/otel/metric v1.42.0/go.mod h1:RlUN/7vTU7Ao/diDkEpQpnz3/92J9ko05BIwxYa2SSI=
 go.opentelemetry.io/otel/sdk v1.40.0 h1:KHW/jUzgo6wsPh9At46+h4upjtccTmuZCFAc9OJ71f8=
 go.opentelemetry.io/otel/sdk v1.40.0/go.mod h1:Ph7EFdYvxq72Y8Li9q8KebuYUr2KoeyHx0DRMKrYBUE=
+go.opentelemetry.io/otel/sdk v1.42.0 h1:LyC8+jqk6UJwdrI/8VydAq/hvkFKNHZVIWuslJXYsDo=
+go.opentelemetry.io/otel/sdk v1.42.0/go.mod h1:rGHCAxd9DAph0joO4W6OPwxjNTYWghRWmkHuGbayMts=
 go.opentelemetry.io/otel/sdk/metric v1.40.0 h1:mtmdVqgQkeRxHgRv4qhyJduP3fYJRMX4AtAlbuWdCYw=
 go.opentelemetry.io/otel/sdk/metric v1.40.0/go.mod h1:4Z2bGMf0KSK3uRjlczMOeMhKU2rhUqdWNoKcYrtcBPg=
+go.opentelemetry.io/otel/sdk/metric v1.42.0 h1:D/1QR46Clz6ajyZ3G8SgNlTJKBdGp84q9RKCAZ3YGuA=
 go.opentelemetry.io/otel/trace v1.40.0 h1:WA4etStDttCSYuhwvEa8OP8I5EWu24lkOzp+ZYblVjw=
 go.opentelemetry.io/otel/trace v1.40.0/go.mod h1:zeAhriXecNGP/s2SEG3+Y8X9ujcJOTqQ5RgdEJcawiA=
+go.opentelemetry.io/otel/trace v1.42.0 h1:OUCgIPt+mzOnaUTpOQcBiM/PLQ/Op7oq6g4LenLmOYY=
+go.opentelemetry.io/otel/trace v1.42.0/go.mod h1:f3K9S+IFqnumBkKhRJMeaZeNk9epyhnCmQh/EysQCdc=
 go.opentelemetry.io/proto/otlp v1.9.0 h1:l706jCMITVouPOqEnii2fIAuO3IVGBRPV5ICjceRb/A=
 go.opentelemetry.io/proto/otlp v1.9.0/go.mod h1:xE+Cx5E/eEHw+ISFkwPLwCZefwVjY+pqKg1qcK03+/4=
 go.uber.org/atomic v1.11.0 h1:ZvwS0R+56ePWxUNi+Atn9dWONBPp/AUETXlHW0DxSjE=
@@ -559,6 +582,8 @@ google.golang.org/genproto/googleapis/rpc v0.0.0-20260128011058-8636f8732409 h1:
 google.golang.org/genproto/googleapis/rpc v0.0.0-20260128011058-8636f8732409/go.mod h1:j9x/tPzZkyxcgEFkiKEEGxfvyumM01BEtsW8xzOahRQ=
 google.golang.org/grpc v1.78.0 h1:K1XZG/yGDJnzMdd/uZHAkVqJE+xIDOcmdSFZkBUicNc=
 google.golang.org/grpc v1.78.0/go.mod h1:I47qjTo4OKbMkjA/aOOwxDIiPSBofUtQUI5EfpWvW7U=
+google.golang.org/grpc v1.79.3 h1:sybAEdRIEtvcD68Gx7dmnwjZKlyfuc61Dyo9pGXXkKE=
+google.golang.org/grpc v1.79.3/go.mod h1:KmT0Kjez+0dde/v2j9vzwoAScgEPx/Bw1CYChhHLrHQ=
 google.golang.org/protobuf v1.36.11 h1:fV6ZwhNocDyBLK0dj+fg8ektcVegBBuEolpbTQyBNVE=
 google.golang.org/protobuf v1.36.11/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

internal/config/config.go

@@ -51,6 +51,7 @@ type Config struct {
 	Tts       TtsConfig       `json:"tts"`
 	Cron      CronConfig      `json:"cron"`
 	Telemetry TelemetryConfig `json:"telemetry"`
+	LangSmith LangSmithConfig `json:"langsmith"`
 	Tailscale TailscaleConfig `json:"tailscale"`
 	Bindings  []AgentBinding  `json:"bindings,omitempty"`
 	mu        sync.RWMutex
@@ -316,6 +317,15 @@ type TelemetryConfig struct {
 	ModelPricing map[string]*ModelPricing    `json:"model_pricing,omitempty"` // cost per model, key = "provider/model" or just "model"
 }
 
+// LangSmithConfig configures the LangSmith tracing exporter.
+// When APIKey is set (or LANGSMITH_API_KEY env var), spans are exported to
+// LangSmith as runs for AI-specific observability.
+type LangSmithConfig struct {
+	APIKey  string `json:"api_key,omitempty"`  // LangSmith API key (required to enable)
+	Project string `json:"project,omitempty"`  // project name (default: "default")
+	APIUrl  string `json:"api_url,omitempty"`  // API URL override (default: LangSmith cloud)
+}
+
 // CronConfig configures the cron job system.
 type CronConfig struct {
 	MaxRetries      int    `json:"max_retries,omitempty"`      // max retry attempts on failure (default 3, 0 = no retry)
@@ -389,6 +399,7 @@ func (c *Config) ReplaceFrom(src *Config) {
 	c.Tts = src.Tts
 	c.Cron = src.Cron
 	c.Telemetry = src.Telemetry
+	c.LangSmith = src.LangSmith
 	c.Tailscale = src.Tailscale
 	c.Bindings = src.Bindings
 }

internal/config/config_load.go

@@ -203,6 +203,11 @@ func (c *Config) applyEnvOverrides() {
 		c.Telemetry.Insecure = v == "true" || v == "1"
 	}
 
+	// LangSmith (uses standard LangSmith env var names)
+	envStr("LANGSMITH_API_KEY", &c.LangSmith.APIKey)
+	envStr("LANGSMITH_PROJECT", &c.LangSmith.Project)
+	envStr("LANGSMITH_ENDPOINT", &c.LangSmith.APIUrl)
+
 	// Owner IDs from env (comma-separated, whitespace-trimmed)
 	if v := os.Getenv("GOCLAW_OWNER_IDS"); v != "" {
 		var ids []string

internal/config/config_secrets.go

@@ -64,6 +64,9 @@ func (c *Config) MaskedCopy() *Config {
 	// Mask Tailscale auth key
 	maskNonEmpty(&cp.Tailscale.AuthKey)
 
+	// Mask LangSmith API key
+	maskNonEmpty(&cp.LangSmith.APIKey)
+
 	return cp
 }
 
@@ -113,6 +116,9 @@ func (c *Config) StripSecrets() {
 
 	// Tailscale auth key
 	c.Tailscale.AuthKey = ""
+
+	// LangSmith API key
+	c.LangSmith.APIKey = ""
 }
 
 // StripMaskedSecrets strips only fields that still contain the mask value "***".
@@ -168,6 +174,9 @@ func (c *Config) StripMaskedSecrets() {
 
 	// Tailscale auth key
 	stripIfMasked(&c.Tailscale.AuthKey)
+
+	// LangSmith API key
+	stripIfMasked(&c.LangSmith.APIKey)
 }
 
 // ApplyDBSecrets overlays secrets from the config_secrets table onto the config.

internal/tracing/collector.go

@@ -21,16 +21,31 @@ const (
 )
 
 // SpanExporter is implemented by backends that receive span data alongside
-// the PostgreSQL store (e.g. OpenTelemetry OTLP).  Keeping this as an
-// interface lets the OTel dependency live in a separate sub-package that can
-// be swapped out by commenting one import line.
+// the PostgreSQL store (e.g. OpenTelemetry OTLP, LangSmith).  Keeping this
+// as an interface lets each dependency live in a separate sub-package gated
+// by build tags.
 type SpanExporter interface {
 	ExportSpans(ctx context.Context, spans []store.SpanData)
 	Shutdown(ctx context.Context) error
 }
 
-// spanUpdate represents a deferred span field update, buffered alongside new
-// spans and applied during the same flush cycle (after batch INSERT).
+// SpanUpdateExporter is an optional extension of SpanExporter for exporters
+// that need to receive two-phase span updates (e.g. LangSmith RunUpdate).
+// Exporters that implement this interface will receive deferred span updates
+// during the flush cycle, after the initial spans have been exported.
+type SpanUpdateExporter interface {
+	ExportSpanUpdates(ctx context.Context, updates []SpanUpdate)
+}
+
+// SpanUpdate is the exported form of a deferred span field update, passed to
+// SpanUpdateExporter implementations during the flush cycle.
+type SpanUpdate struct {
+	SpanID  uuid.UUID
+	TraceID uuid.UUID
+	Updates map[string]any
+}
+
+// spanUpdate is the internal buffered form used by the collector channel.
 type spanUpdate struct {
 	SpanID  uuid.UUID
 	TraceID uuid.UUID
@@ -55,8 +70,8 @@ type Collector struct {
 	dirtyTraces   map[uuid.UUID]struct{}
 	dirtyTracesMu sync.Mutex
 
-	verbose  bool         // when true, LLM spans include full input messages
-	exporter SpanExporter // optional external exporter (nil = disabled)
+	verbose   bool           // when true, LLM spans include full input messages
+	exporters []SpanExporter // optional external exporters (OTel, LangSmith, etc.)
 
 	// OnFlush is called after each flush cycle with the trace IDs that had
 	// their aggregates updated. Used to broadcast realtime trace events.
@@ -91,10 +106,16 @@ func (c *Collector) PreviewMaxLen() int {
 	return previewMaxLen
 }
 
-// SetExporter attaches an external span exporter (e.g. OpenTelemetry OTLP).
-// When set, spans are exported to the external backend during each flush cycle.
+// SetExporter replaces all exporters with a single one (backward compat).
+// Prefer AddExporter for multi-exporter setups.
 func (c *Collector) SetExporter(exp SpanExporter) {
-	c.exporter = exp
+	c.exporters = []SpanExporter{exp}
+}
+
+// AddExporter appends an exporter to the list. Multiple exporters receive
+// the same batch of spans during each flush cycle (fan-out).
+func (c *Collector) AddExporter(exp SpanExporter) {
+	c.exporters = append(c.exporters, exp)
 }
 
 // Start begins the background flush loop.
@@ -109,12 +130,14 @@ func (c *Collector) Stop() {
 	close(c.stopCh)
 	c.wg.Wait()
 
-	// Shutdown external exporter (flushes remaining spans)
-	if c.exporter != nil {
+	// Shutdown all external exporters (flushes remaining spans).
+	if len(c.exporters) > 0 {
 		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		defer cancel()
-		if err := c.exporter.Shutdown(ctx); err != nil {
-			slog.Warn("tracing: span exporter shutdown failed", "error", err)
+		for _, exp := range c.exporters {
+			if err := exp.Shutdown(ctx); err != nil {
+				slog.Warn("tracing: span exporter shutdown failed", "error", err)
+			}
 		}
 	}
 
@@ -263,9 +286,9 @@ done:
 			slog.Debug("tracing: flushed spans", "count", len(spans))
 		}
 
-		// Export to external backend (non-blocking — errors logged, not propagated)
-		if c.exporter != nil {
-			c.exporter.ExportSpans(ctx, spans)
+		// Export to external backends (non-blocking — errors logged, not propagated).
+		for _, exp := range c.exporters {
+			exp.ExportSpans(ctx, spans)
 		}
 	}
 
@@ -290,6 +313,17 @@ doneUpdates:
 			}
 		}
 		slog.Debug("tracing: applied span updates", "count", len(updates))
+
+		// Fan out span updates to exporters that support two-phase tracing.
+		exported := make([]SpanUpdate, len(updates))
+		for i, u := range updates {
+			exported[i] = SpanUpdate{SpanID: u.SpanID, TraceID: u.TraceID, Updates: u.Updates}
+		}
+		for _, exp := range c.exporters {
+			if sue, ok := exp.(SpanUpdateExporter); ok {
+				sue.ExportSpanUpdates(ctx, exported)
+			}
+		}
 	}
 
 	// Update aggregates for dirty traces