STET

agent_patch

runs/2026-02-21__03-36-16__gpt-5-1-codex-mini/flux-pr-1309/flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/agent-logs/agent.patch

95294 bytes

Back to adjudication
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/graphql_datasource/configuration.go b/app/v2/pkg/engine/datasource/graphql_datasource/configuration.go
index c5a7f3f..ec398c0 100644
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/graphql_datasource/configuration.go
+++ b/app/v2/pkg/engine/datasource/graphql_datasource/configuration.go
@@ -9,6 +9,7 @@ import (
 	"github.com/wundergraph/graphql-go-tools/v2/pkg/astparser"
 	"github.com/wundergraph/graphql-go-tools/v2/pkg/asttransform"
 	grpcdatasource "github.com/wundergraph/graphql-go-tools/v2/pkg/engine/datasource/grpc_datasource"
+	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/resolve"
 	"github.com/wundergraph/graphql-go-tools/v2/pkg/federation"
 	"github.com/wundergraph/graphql-go-tools/v2/pkg/operationreport"
 )
@@ -103,6 +104,11 @@ type SingleTypeField struct {
 	FieldName string
 }
 
+// SubscriptionOnStartFn defines a hook function that is called when a subscription starts.
+// It receives the resolve context and the input of the subscription.
+// The function can return an error.
+type SubscriptionOnStartFn func(ctx resolve.StartupHookContext, input []byte) (err error)
+
 type SubscriptionConfiguration struct {
 	URL           string
 	Header        http.Header
@@ -119,6 +125,8 @@ type SubscriptionConfiguration struct {
 	// these headers by itself.
 	ForwardedClientHeaderRegularExpressions []RegularExpression
 	WsSubProtocol                           string
+	// StartupHooks contains the method called when a subscription is started
+	StartupHooks []SubscriptionOnStartFn
 }
 
 type FetchConfiguration struct {
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/graphql_datasource/graphql_datasource.go b/app/v2/pkg/engine/datasource/graphql_datasource/graphql_datasource.go
index 11c61d9..23dea1a 100644
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/graphql_datasource/graphql_datasource.go
+++ b/app/v2/pkg/engine/datasource/graphql_datasource/graphql_datasource.go
@@ -449,7 +449,8 @@ func (p *Planner[T]) ConfigureSubscription() plan.SubscriptionConfiguration {
 	return plan.SubscriptionConfiguration{
 		Input: string(input),
 		DataSource: &SubscriptionSource{
-			client: p.subscriptionClient,
+			client:                 p.subscriptionClient,
+			subscriptionOnStartFns: p.config.subscription.StartupHooks,
 		},
 		Variables:      p.variables,
 		PostProcessing: DefaultPostProcessingConfiguration,
@@ -1953,7 +1954,8 @@ type RegularExpression struct {
 }
 
 type SubscriptionSource struct {
-	client GraphQLSubscriptionClient
+	client                 GraphQLSubscriptionClient
+	subscriptionOnStartFns []SubscriptionOnStartFn
 }
 
 func (s *SubscriptionSource) AsyncStart(ctx *resolve.Context, id uint64, input []byte, updater resolve.SubscriptionUpdater) error {
@@ -2003,3 +2005,16 @@ func (s *SubscriptionSource) UniqueRequestID(ctx *resolve.Context, input []byte,
 	}
 	return s.client.UniqueRequestID(ctx, options, xxh)
 }
+
+// SubscriptionOnStart is called when a subscription is started.
+// Hooks are invoked sequentially, short-circuiting on the first error.
+func (s *SubscriptionSource) SubscriptionOnStart(ctx resolve.StartupHookContext, input []byte) error {
+	for _, fn := range s.subscriptionOnStartFns {
+		err := fn(ctx, input)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/graphql_datasource/graphql_datasource_test.go b/app/v2/pkg/engine/datasource/graphql_datasource/graphql_datasource_test.go
index 7f41943..4f911b8 100644
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/graphql_datasource/graphql_datasource_test.go
+++ b/app/v2/pkg/engine/datasource/graphql_datasource/graphql_datasource_test.go
@@ -4006,7 +4006,7 @@ func TestGraphQLDataSource(t *testing.T) {
 				Trigger: resolve.GraphQLSubscriptionTrigger{
 					Input: []byte(`{"url":"wss://swapi.com/graphql","body":{"query":"subscription{remainingJedis}"}}`),
 					Source: &SubscriptionSource{
-						NewGraphQLSubscriptionClient(http.DefaultClient, http.DefaultClient, ctx),
+						client: NewGraphQLSubscriptionClient(http.DefaultClient, http.DefaultClient, ctx),
 					},
 					PostProcessing: DefaultPostProcessingConfiguration,
 				},
@@ -8239,7 +8239,6 @@ func (f *FailingSubscriptionClient) SubscribeAsync(ctx *resolve.Context, id uint
 }
 
 func (f *FailingSubscriptionClient) Unsubscribe(id uint64) {
-
 }
 
 func (f *FailingSubscriptionClient) Subscribe(ctx *resolve.Context, options GraphQLSubscriptionOptions, updater resolve.SubscriptionUpdater) error {
@@ -8272,6 +8271,19 @@ func (t *testSubscriptionUpdaterChan) Update(data []byte) {
 	t.updates <- string(data)
 }
 
+// empty method to satisfy the interface, not used in this tests
+func (t *testSubscriptionUpdaterChan) UpdateSubscription(id resolve.SubscriptionIdentifier, data []byte) {
+}
+
+// empty method to satisfy the interface, not used in this tests
+func (t *testSubscriptionUpdaterChan) CloseSubscription(kind resolve.SubscriptionCloseKind, id resolve.SubscriptionIdentifier) {
+}
+
+// empty method to satisfy the interface, not used in this tests
+func (t *testSubscriptionUpdaterChan) Subscriptions() map[context.Context]resolve.SubscriptionIdentifier {
+	return make(map[context.Context]resolve.SubscriptionIdentifier)
+}
+
 func (t *testSubscriptionUpdaterChan) Complete() {
 	close(t.complete)
 }
@@ -8397,6 +8409,19 @@ func (t *testSubscriptionUpdater) Close(kind resolve.SubscriptionCloseKind) {
 	t.closed = true
 }
 
+// empty method to satisfy the interface, not used in this tests
+func (t *testSubscriptionUpdater) CloseSubscription(kind resolve.SubscriptionCloseKind, id resolve.SubscriptionIdentifier) {
+}
+
+// empty method to satisfy the interface, not used in this tests
+func (t *testSubscriptionUpdater) Subscriptions() map[context.Context]resolve.SubscriptionIdentifier {
+	return make(map[context.Context]resolve.SubscriptionIdentifier)
+}
+
+// empty method to satisfy the interface, not used in this tests
+func (t *testSubscriptionUpdater) UpdateSubscription(id resolve.SubscriptionIdentifier, data []byte) {
+}
+
 func TestSubscriptionSource_Start(t *testing.T) {
 	chatServer := httptest.NewServer(subscriptiontesting.ChatGraphQLEndpointHandler())
 	defer chatServer.Close()
@@ -8970,6 +8995,60 @@ func TestSanitizeKey(t *testing.T) {
 	}
 }
 
+func TestSubscriptionSource_SubscriptionOnStart(t *testing.T) {
+
+	t.Run("SubscriptionOnStart calls subscriptionOnStartFns", func(t *testing.T) {
+		ctx := resolve.StartupHookContext{
+			Context: context.Background(),
+			Updater: func(data []byte) {},
+		}
+
+		type fnData struct {
+			ctx   resolve.StartupHookContext
+			input []byte
+		}
+
+		startFnCalled := make(chan fnData, 1)
+		subscriptionSource := SubscriptionSource{
+			subscriptionOnStartFns: []SubscriptionOnStartFn{
+				func(ctx resolve.StartupHookContext, input []byte) error {
+					startFnCalled <- fnData{ctx, input}
+					return nil
+				},
+			},
+		}
+
+		err := subscriptionSource.SubscriptionOnStart(ctx, []byte(`{"variables": {}, "extensions": {}, "operationName": "LiveMessages", "query": "subscription LiveMessages { messageAdded(roomName: \"#test\") { text createdBy } }"}`))
+		require.NoError(t, err)
+		var called fnData
+		select {
+		case called = <-startFnCalled:
+		case <-time.After(1 * time.Second):
+			t.Fatal("SubscriptionOnStartFn was not called")
+		}
+		assert.Equal(t, []byte(`{"variables": {}, "extensions": {}, "operationName": "LiveMessages", "query": "subscription LiveMessages { messageAdded(roomName: \"#test\") { text createdBy } }"}`), called.input)
+	})
+
+	t.Run("SubscriptionOnStart calls subscriptionOnStartFns and returns error if one of the functions returns an error", func(t *testing.T) {
+		ctx := resolve.StartupHookContext{
+			Context: context.Background(),
+			Updater: func(data []byte) {},
+		}
+
+		subscriptionSource := SubscriptionSource{
+			subscriptionOnStartFns: []SubscriptionOnStartFn{
+				func(ctx resolve.StartupHookContext, input []byte) error {
+					return errors.New("test error")
+				},
+			},
+		}
+
+		err := subscriptionSource.SubscriptionOnStart(ctx, []byte(`{"variables": {}, "extensions": {}, "operationName": "LiveMessages", "query": "subscription LiveMessages { messageAdded(roomName: \"#test\") { text createdBy } }"}`))
+		require.Error(t, err)
+		assert.ErrorContains(t, err, "test error")
+	})
+}
+
 const interfaceSelectionSchema = `
 
 scalar String
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/kafka_event_manager.go b/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/kafka_event_manager.go
deleted file mode 100644
index 80b02e1..0000000
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/kafka_event_manager.go
+++ /dev/null
@@ -1,72 +0,0 @@
-package pubsub_datasource
-
-import (
-	"encoding/json"
-	"fmt"
-	"slices"
-
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/plan"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/resolve"
-)
-
-type KafkaSubscriptionEventConfiguration struct {
-	ProviderID string   `json:"providerId"`
-	Topics     []string `json:"topics"`
-}
-
-type KafkaPublishEventConfiguration struct {
-	ProviderID string          `json:"providerId"`
-	Topic      string          `json:"topic"`
-	Data       json.RawMessage `json:"data"`
-}
-
-func (s *KafkaPublishEventConfiguration) MarshalJSONTemplate() string {
-	return fmt.Sprintf(`{"topic":"%s", "data": %s, "providerId":"%s"}`, s.Topic, s.Data, s.ProviderID)
-}
-
-type KafkaEventManager struct {
-	visitor                        *plan.Visitor
-	variables                      *resolve.Variables
-	eventMetadata                  EventMetadata
-	eventConfiguration             *KafkaEventConfiguration
-	publishEventConfiguration      *KafkaPublishEventConfiguration
-	subscriptionEventConfiguration *KafkaSubscriptionEventConfiguration
-}
-
-func (p *KafkaEventManager) eventDataBytes(ref int) ([]byte, error) {
-	return buildEventDataBytes(ref, p.visitor, p.variables)
-}
-
-func (p *KafkaEventManager) handlePublishEvent(ref int) {
-	if len(p.eventConfiguration.Topics) != 1 {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("publish and request events should define one subject but received %d", len(p.eventConfiguration.Topics)))
-		return
-	}
-	topic := p.eventConfiguration.Topics[0]
-	dataBytes, err := p.eventDataBytes(ref)
-	if err != nil {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to write event data bytes: %w", err))
-		return
-	}
-
-	p.publishEventConfiguration = &KafkaPublishEventConfiguration{
-		ProviderID: p.eventMetadata.ProviderID,
-		Topic:      topic,
-		Data:       dataBytes,
-	}
-}
-
-func (p *KafkaEventManager) handleSubscriptionEvent(ref int) {
-
-	if len(p.eventConfiguration.Topics) == 0 {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("expected at least one subscription topic but received %d", len(p.eventConfiguration.Topics)))
-		return
-	}
-
-	slices.Sort(p.eventConfiguration.Topics)
-
-	p.subscriptionEventConfiguration = &KafkaSubscriptionEventConfiguration{
-		ProviderID: p.eventMetadata.ProviderID,
-		Topics:     p.eventConfiguration.Topics,
-	}
-}
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/nats_event_manager.go b/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/nats_event_manager.go
deleted file mode 100644
index 04fc7e7..0000000
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/nats_event_manager.go
+++ /dev/null
@@ -1,189 +0,0 @@
-package pubsub_datasource
-
-import (
-	"encoding/json"
-	"fmt"
-	"regexp"
-	"slices"
-	"strings"
-
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/argument_templates"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/plan"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/resolve"
-)
-
-const (
-	fwc  = '>'
-	tsep = "."
-)
-
-// A variable template has form $$number$$ where the number can range from one to multiple digits
-var (
-	variableTemplateRegex = regexp.MustCompile(`\$\$\d+\$\$`)
-)
-
-type NatsSubscriptionEventConfiguration struct {
-	ProviderID          string                   `json:"providerId"`
-	Subjects            []string                 `json:"subjects"`
-	StreamConfiguration *NatsStreamConfiguration `json:"streamConfiguration,omitempty"`
-}
-
-type NatsPublishAndRequestEventConfiguration struct {
-	ProviderID string          `json:"providerId"`
-	Subject    string          `json:"subject"`
-	Data       json.RawMessage `json:"data"`
-}
-
-func (s *NatsPublishAndRequestEventConfiguration) MarshalJSONTemplate() string {
-	return fmt.Sprintf(`{"subject":"%s", "data": %s, "providerId":"%s"}`, s.Subject, s.Data, s.ProviderID)
-}
-
-type NatsEventManager struct {
-	visitor                             *plan.Visitor
-	variables                           *resolve.Variables
-	eventMetadata                       EventMetadata
-	eventConfiguration                  *NatsEventConfiguration
-	publishAndRequestEventConfiguration *NatsPublishAndRequestEventConfiguration
-	subscriptionEventConfiguration      *NatsSubscriptionEventConfiguration
-}
-
-func isValidNatsSubject(subject string) bool {
-	if subject == "" {
-		return false
-	}
-	sfwc := false
-	tokens := strings.Split(subject, tsep)
-	for _, t := range tokens {
-		length := len(t)
-		if length == 0 || sfwc {
-			return false
-		}
-		if length > 1 {
-			if strings.ContainsAny(t, "\t\n\f\r ") {
-				return false
-			}
-			continue
-		}
-		switch t[0] {
-		case fwc:
-			sfwc = true
-		case ' ', '\t', '\n', '\r', '\f':
-			return false
-		}
-	}
-	return true
-}
-
-func (p *NatsEventManager) addContextVariableByArgumentRef(argumentRef int, argumentPath []string) (string, error) {
-	variablePath, err := p.visitor.Operation.VariablePathByArgumentRefAndArgumentPath(argumentRef, argumentPath, p.visitor.Walker.Ancestors[0].Ref)
-	if err != nil {
-		return "", err
-	}
-	/* The definition is passed as both definition and operation below because getJSONRootType resolves the type
-	 * from the first argument, but finalInputValueTypeRef comes from the definition
-	 */
-	contextVariable := &resolve.ContextVariable{
-		Path:     variablePath,
-		Renderer: resolve.NewPlainVariableRenderer(),
-	}
-	variablePlaceHolder, _ := p.variables.AddVariable(contextVariable)
-	return variablePlaceHolder, nil
-}
-
-func (p *NatsEventManager) extractEventSubject(fieldRef int, subject string) (string, error) {
-	matches := argument_templates.ArgumentTemplateRegex.FindAllStringSubmatch(subject, -1)
-	// If no argument templates are defined, there are only static values
-	if len(matches) < 1 {
-		if isValidNatsSubject(subject) {
-			return subject, nil
-		}
-		return "", fmt.Errorf(`subject "%s" is not a valid NATS subject`, subject)
-	}
-	fieldNameBytes := p.visitor.Operation.FieldNameBytes(fieldRef)
-	// TODO: handling for interfaces and unions
-	fieldDefinitionRef, ok := p.visitor.Definition.ObjectTypeDefinitionFieldWithName(p.visitor.Walker.EnclosingTypeDefinition.Ref, fieldNameBytes)
-	if !ok {
-		return "", fmt.Errorf(`expected field definition to exist for field "%s"`, fieldNameBytes)
-	}
-	subjectWithVariableTemplateReplacements := subject
-	for templateNumber, groups := range matches {
-		// The first group is the whole template; the second is the period delimited argument path
-		if len(groups) != 2 {
-			return "", fmt.Errorf(`argument template #%d defined on field "%s" is invalid: expected 2 matching groups but received %d`, templateNumber+1, fieldNameBytes, len(groups)-1)
-		}
-		validationResult, err := argument_templates.ValidateArgumentPath(p.visitor.Definition, groups[1], fieldDefinitionRef)
-		if err != nil {
-			return "", fmt.Errorf(`argument template #%d defined on field "%s" is invalid: %w`, templateNumber+1, fieldNameBytes, err)
-		}
-		argumentNameBytes := []byte(validationResult.ArgumentPath[0])
-		argumentRef, ok := p.visitor.Operation.FieldArgument(fieldRef, argumentNameBytes)
-		if !ok {
-			return "", fmt.Errorf(`operation field "%s" does not define argument "%s"`, fieldNameBytes, argumentNameBytes)
-		}
-		// variablePlaceholder has the form $$0$$, $$1$$, etc.
-		variablePlaceholder, err := p.addContextVariableByArgumentRef(argumentRef, validationResult.ArgumentPath)
-		if err != nil {
-			return "", fmt.Errorf(`failed to retrieve variable placeholder for argument ""%s" defined on operation field "%s": %w`, argumentNameBytes, fieldNameBytes, err)
-		}
-		// Replace the template literal with the variable placeholder (and reuse the variable if it already exists)
-		subjectWithVariableTemplateReplacements = strings.ReplaceAll(subjectWithVariableTemplateReplacements, groups[0], variablePlaceholder)
-	}
-	// Substitute the variable templates for dummy values to check naïvely that the string is a valid NATS subject
-	if isValidNatsSubject(variableTemplateRegex.ReplaceAllLiteralString(subjectWithVariableTemplateReplacements, "a")) {
-		return subjectWithVariableTemplateReplacements, nil
-	}
-	return "", fmt.Errorf(`subject "%s" is not a valid NATS subject`, subject)
-}
-
-func (p *NatsEventManager) eventDataBytes(ref int) ([]byte, error) {
-	return buildEventDataBytes(ref, p.visitor, p.variables)
-}
-
-func (p *NatsEventManager) handlePublishAndRequestEvent(ref int) {
-	if len(p.eventConfiguration.Subjects) != 1 {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("publish and request events should define one subject but received %d", len(p.eventConfiguration.Subjects)))
-		return
-	}
-	rawSubject := p.eventConfiguration.Subjects[0]
-	extractedSubject, err := p.extractEventSubject(ref, rawSubject)
-	if err != nil {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("could not extract event subject: %w", err))
-		return
-	}
-	dataBytes, err := p.eventDataBytes(ref)
-	if err != nil {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to write event data bytes: %w", err))
-		return
-	}
-
-	p.publishAndRequestEventConfiguration = &NatsPublishAndRequestEventConfiguration{
-		ProviderID: p.eventMetadata.ProviderID,
-		Subject:    extractedSubject,
-		Data:       dataBytes,
-	}
-}
-
-func (p *NatsEventManager) handleSubscriptionEvent(ref int) {
-
-	if len(p.eventConfiguration.Subjects) == 0 {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("expected at least one subscription subject but received %d", len(p.eventConfiguration.Subjects)))
-		return
-	}
-	extractedSubjects := make([]string, 0, len(p.eventConfiguration.Subjects))
-	for _, rawSubject := range p.eventConfiguration.Subjects {
-		extractedSubject, err := p.extractEventSubject(ref, rawSubject)
-		if err != nil {
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("could not extract subscription event subjects: %w", err))
-			return
-		}
-		extractedSubjects = append(extractedSubjects, extractedSubject)
-	}
-
-	slices.Sort(extractedSubjects)
-
-	p.subscriptionEventConfiguration = &NatsSubscriptionEventConfiguration{
-		ProviderID:          p.eventMetadata.ProviderID,
-		Subjects:            extractedSubjects,
-		StreamConfiguration: p.eventConfiguration.StreamConfiguration,
-	}
-}
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_datasource.go b/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_datasource.go
deleted file mode 100644
index bdf1230..0000000
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_datasource.go
+++ /dev/null
@@ -1,346 +0,0 @@
-package pubsub_datasource
-
-import (
-	"bytes"
-	"context"
-	"encoding/json"
-	"fmt"
-	"regexp"
-	"strings"
-
-	"github.com/jensneuse/abstractlogger"
-
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/ast"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/plan"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/resolve"
-)
-
-type EventType string
-
-const (
-	EventTypePublish   EventType = "publish"
-	EventTypeRequest   EventType = "request"
-	EventTypeSubscribe EventType = "subscribe"
-)
-
-var eventSubjectRegex = regexp.MustCompile(`{{ args.([a-zA-Z0-9_]+) }}`)
-
-func EventTypeFromString(s string) (EventType, error) {
-	et := EventType(strings.ToLower(s))
-	switch et {
-	case EventTypePublish, EventTypeRequest, EventTypeSubscribe:
-		return et, nil
-	default:
-		return "", fmt.Errorf("invalid event type: %q", s)
-	}
-}
-
-type EventMetadata struct {
-	ProviderID string    `json:"providerId"`
-	Type       EventType `json:"type"`
-	TypeName   string    `json:"typeName"`
-	FieldName  string    `json:"fieldName"`
-}
-
-type EventConfiguration struct {
-	Metadata      *EventMetadata `json:"metadata"`
-	Configuration any            `json:"configuration"`
-}
-
-type Configuration struct {
-	Events []EventConfiguration `json:"events"`
-}
-
-type Planner[T Configuration] struct {
-	id                      int
-	config                  Configuration
-	natsPubSubByProviderID  map[string]NatsPubSub
-	kafkaPubSubByProviderID map[string]KafkaPubSub
-	eventManager            any
-	rootFieldRef            int
-	variables               resolve.Variables
-	visitor                 *plan.Visitor
-}
-
-func (p *Planner[T]) SetID(id int) {
-	p.id = id
-}
-
-func (p *Planner[T]) ID() (id int) {
-	return p.id
-}
-
-func (p *Planner[T]) EnterField(ref int) {
-	if p.rootFieldRef != -1 {
-		// This is a nested field; nothing needs to be done
-		return
-	}
-	p.rootFieldRef = ref
-
-	fieldName := p.visitor.Operation.FieldNameString(ref)
-	typeName := p.visitor.Walker.EnclosingTypeDefinition.NameString(p.visitor.Definition)
-
-	var eventConfig *EventConfiguration
-	for _, cfg := range p.config.Events {
-		if cfg.Metadata.TypeName == typeName && cfg.Metadata.FieldName == fieldName {
-			eventConfig = &cfg
-			break
-		}
-	}
-	if eventConfig == nil {
-		return
-	}
-
-	switch v := eventConfig.Configuration.(type) {
-	case *NatsEventConfiguration:
-		em := &NatsEventManager{
-			visitor:            p.visitor,
-			variables:          &p.variables,
-			eventMetadata:      *eventConfig.Metadata,
-			eventConfiguration: v,
-		}
-		p.eventManager = em
-
-		switch eventConfig.Metadata.Type {
-		case EventTypePublish, EventTypeRequest:
-			em.handlePublishAndRequestEvent(ref)
-		case EventTypeSubscribe:
-			em.handleSubscriptionEvent(ref)
-		default:
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("invalid EventType \"%s\" for Nats", eventConfig.Metadata.Type))
-		}
-	case *KafkaEventConfiguration:
-		em := &KafkaEventManager{
-			visitor:            p.visitor,
-			variables:          &p.variables,
-			eventMetadata:      *eventConfig.Metadata,
-			eventConfiguration: v,
-		}
-		p.eventManager = em
-
-		switch eventConfig.Metadata.Type {
-		case EventTypePublish:
-			em.handlePublishEvent(ref)
-		case EventTypeSubscribe:
-			em.handleSubscriptionEvent(ref)
-		default:
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("invalid EventType \"%s\" for Kafka", eventConfig.Metadata.Type))
-		}
-	default:
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("invalid event configuration type: %T", v))
-	}
-}
-
-func (p *Planner[T]) EnterDocument(_, _ *ast.Document) {
-	p.rootFieldRef = -1
-	p.eventManager = nil
-}
-
-func (p *Planner[T]) Register(visitor *plan.Visitor, configuration plan.DataSourceConfiguration[T], dataSourcePlannerConfiguration plan.DataSourcePlannerConfiguration) error {
-	p.visitor = visitor
-	visitor.Walker.RegisterEnterFieldVisitor(p)
-	visitor.Walker.RegisterEnterDocumentVisitor(p)
-	p.config = Configuration(configuration.CustomConfiguration())
-	return nil
-}
-
-func (p *Planner[T]) ConfigureFetch() resolve.FetchConfiguration {
-	if p.eventManager == nil {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to configure fetch: event manager is nil"))
-		return resolve.FetchConfiguration{}
-	}
-
-	var dataSource resolve.DataSource
-
-	switch v := p.eventManager.(type) {
-	case *NatsEventManager:
-		pubsub, ok := p.natsPubSubByProviderID[v.eventMetadata.ProviderID]
-		if !ok {
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("no pubsub connection exists with provider id \"%s\"", v.eventMetadata.ProviderID))
-			return resolve.FetchConfiguration{}
-		}
-
-		switch v.eventMetadata.Type {
-		case EventTypePublish:
-			dataSource = &NatsPublishDataSource{
-				pubSub: pubsub,
-			}
-		case EventTypeRequest:
-			dataSource = &NatsRequestDataSource{
-				pubSub: pubsub,
-			}
-		default:
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to configure fetch: invalid event type \"%s\" for Nats", v.eventMetadata.Type))
-			return resolve.FetchConfiguration{}
-		}
-
-		return resolve.FetchConfiguration{
-			Input:      v.publishAndRequestEventConfiguration.MarshalJSONTemplate(),
-			Variables:  p.variables,
-			DataSource: dataSource,
-			PostProcessing: resolve.PostProcessingConfiguration{
-				MergePath: []string{v.eventMetadata.FieldName},
-			},
-		}
-
-	case *KafkaEventManager:
-		pubsub, ok := p.kafkaPubSubByProviderID[v.eventMetadata.ProviderID]
-		if !ok {
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("no pubsub connection exists with provider id \"%s\"", v.eventMetadata.ProviderID))
-			return resolve.FetchConfiguration{}
-		}
-
-		switch v.eventMetadata.Type {
-		case EventTypePublish:
-			dataSource = &KafkaPublishDataSource{
-				pubSub: pubsub,
-			}
-		case EventTypeRequest:
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("event type \"%s\" is not supported for Kafka", v.eventMetadata.Type))
-			return resolve.FetchConfiguration{}
-		default:
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to configure fetch: invalid event type \"%s\" for Kafka", v.eventMetadata.Type))
-			return resolve.FetchConfiguration{}
-		}
-
-		return resolve.FetchConfiguration{
-			Input:      v.publishEventConfiguration.MarshalJSONTemplate(),
-			Variables:  p.variables,
-			DataSource: dataSource,
-			PostProcessing: resolve.PostProcessingConfiguration{
-				MergePath: []string{v.eventMetadata.FieldName},
-			},
-		}
-
-	default:
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to configure fetch: invalid event manager type: %T", p.eventManager))
-	}
-
-	return resolve.FetchConfiguration{}
-}
-
-func (p *Planner[T]) ConfigureSubscription() plan.SubscriptionConfiguration {
-	if p.eventManager == nil {
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to configure subscription: event manager is nil"))
-		return plan.SubscriptionConfiguration{}
-	}
-
-	switch v := p.eventManager.(type) {
-	case *NatsEventManager:
-		pubsub, ok := p.natsPubSubByProviderID[v.eventMetadata.ProviderID]
-		if !ok {
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("no pubsub connection exists with provider id \"%s\"", v.eventMetadata.ProviderID))
-			return plan.SubscriptionConfiguration{}
-		}
-		object, err := json.Marshal(v.subscriptionEventConfiguration)
-		if err != nil {
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to marshal event subscription streamConfiguration"))
-			return plan.SubscriptionConfiguration{}
-		}
-		return plan.SubscriptionConfiguration{
-			Input:     string(object),
-			Variables: p.variables,
-			DataSource: &NatsSubscriptionSource{
-				pubSub: pubsub,
-			},
-			PostProcessing: resolve.PostProcessingConfiguration{
-				MergePath: []string{v.eventMetadata.FieldName},
-			},
-		}
-	case *KafkaEventManager:
-		pubsub, ok := p.kafkaPubSubByProviderID[v.eventMetadata.ProviderID]
-		if !ok {
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("no pubsub connection exists with provider id \"%s\"", v.eventMetadata.ProviderID))
-			return plan.SubscriptionConfiguration{}
-		}
-		object, err := json.Marshal(v.subscriptionEventConfiguration)
-		if err != nil {
-			p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to marshal event subscription streamConfiguration"))
-			return plan.SubscriptionConfiguration{}
-		}
-		return plan.SubscriptionConfiguration{
-			Input:     string(object),
-			Variables: p.variables,
-			DataSource: &KafkaSubscriptionSource{
-				pubSub: pubsub,
-			},
-			PostProcessing: resolve.PostProcessingConfiguration{
-				MergePath: []string{v.eventMetadata.FieldName},
-			},
-		}
-	default:
-		p.visitor.Walker.StopWithInternalErr(fmt.Errorf("failed to configure subscription: invalid event manager type: %T", p.eventManager))
-	}
-
-	return plan.SubscriptionConfiguration{}
-}
-
-func (p *Planner[T]) DownstreamResponseFieldAlias(_ int) (alias string, exists bool) {
-	return "", false
-}
-
-func NewFactory[T Configuration](executionContext context.Context, natsPubSubByProviderID map[string]NatsPubSub, kafkaPubSubByProviderID map[string]KafkaPubSub) *Factory[T] {
-	return &Factory[T]{
-		executionContext:        executionContext,
-		natsPubSubByProviderID:  natsPubSubByProviderID,
-		kafkaPubSubByProviderID: kafkaPubSubByProviderID,
-	}
-}
-
-type Factory[T Configuration] struct {
-	executionContext        context.Context
-	natsPubSubByProviderID  map[string]NatsPubSub
-	kafkaPubSubByProviderID map[string]KafkaPubSub
-}
-
-func (f *Factory[T]) Planner(_ abstractlogger.Logger) plan.DataSourcePlanner[T] {
-	return &Planner[T]{
-		natsPubSubByProviderID:  f.natsPubSubByProviderID,
-		kafkaPubSubByProviderID: f.kafkaPubSubByProviderID,
-	}
-}
-
-func (f *Factory[T]) Context() context.Context {
-	return f.executionContext
-}
-
-func (f *Factory[T]) UpstreamSchema(_ plan.DataSourceConfiguration[T]) (*ast.Document, bool) {
-	return nil, false
-}
-
-func (f *Factory[T]) PlanningBehavior() plan.DataSourcePlanningBehavior {
-	return plan.DataSourcePlanningBehavior{
-		MergeAliasedRootNodes:      false,
-		OverrideFieldPathFromAlias: false,
-		AllowPlanningTypeName:      true,
-	}
-}
-
-func buildEventDataBytes(ref int, visitor *plan.Visitor, variables *resolve.Variables) ([]byte, error) {
-	// Collect the field arguments for fetch based operations
-	fieldArgs := visitor.Operation.FieldArguments(ref)
-	var dataBuffer bytes.Buffer
-	dataBuffer.WriteByte('{')
-	for i, arg := range fieldArgs {
-		if i > 0 {
-			dataBuffer.WriteByte(',')
-		}
-		argValue := visitor.Operation.ArgumentValue(arg)
-		variableName := visitor.Operation.VariableValueNameBytes(argValue.Ref)
-		contextVariable := &resolve.ContextVariable{
-			Path:     []string{string(variableName)},
-			Renderer: resolve.NewJSONVariableRenderer(),
-		}
-		variablePlaceHolder, _ := variables.AddVariable(contextVariable)
-		argumentName := visitor.Operation.ArgumentNameString(arg)
-		escapedKey, err := json.Marshal(argumentName)
-		if err != nil {
-			return nil, err
-		}
-		dataBuffer.Write(escapedKey)
-		dataBuffer.WriteByte(':')
-		dataBuffer.WriteString(variablePlaceHolder)
-	}
-	dataBuffer.WriteByte('}')
-	return dataBuffer.Bytes(), nil
-}
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_datasource_test.go b/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_datasource_test.go
deleted file mode 100644
index 28a37df..0000000
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_datasource_test.go
+++ /dev/null
@@ -1,669 +0,0 @@
-package pubsub_datasource
-
-import (
-	"bytes"
-	"context"
-	"errors"
-	"io"
-	"testing"
-
-	"github.com/stretchr/testify/require"
-
-	"github.com/wundergraph/astjson"
-
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/datasourcetesting"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/plan"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/resolve"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/internal/unsafeparser"
-)
-
-type testPubsub struct {
-}
-
-func (t *testPubsub) Subscribe(_ context.Context, _ NatsSubscriptionEventConfiguration, _ resolve.SubscriptionUpdater) error {
-	return errors.New("not implemented")
-}
-func (t *testPubsub) Publish(_ context.Context, _ NatsPublishAndRequestEventConfiguration) error {
-	return errors.New("not implemented")
-}
-
-func (t *testPubsub) Request(_ context.Context, _ NatsPublishAndRequestEventConfiguration, _ io.Writer) error {
-	return errors.New("not implemented")
-}
-
-func TestPubSub(t *testing.T) {
-	factory := &Factory[Configuration]{
-		natsPubSubByProviderID: map[string]NatsPubSub{"default": &testPubsub{}},
-	}
-
-	const schema = `
-	type Query {
-		helloQuery(userKey: UserKey!): User! @edfs__natsRequest(subject: "tenants.{{ args.userKey.tenantId }}.users.{{ args.userKey.id }}")
-	}
-
-	type Mutation {
-		helloMutation(userKey: UserKey!): edfs__PublishResult! @edfs__natsPublish(subject: "tenants.{{ args.userKey.tenantId }}.users.{{ args.userKey.id }}")
-	}
-
-	type Subscription {
-		helloSubscription(userKey: UserKey!): User! @edfs__natsSubscribe(subjects: ["tenants.{{ args.userKey.tenantId }}.users.{{ args.userKey.id }}"])
-		subscriptionWithMultipleSubjects(userKeyOne: UserKey!, userKeyTwo: UserKey!): User! @edfs__natsSubscribe(subjects: ["tenantsOne.{{ args.userKeyOne.tenantId }}.users.{{ args.userKeyOne.id }}", "tenantsTwo.{{ args.userKeyTwo.tenantId }}.users.{{ args.userKeyTwo.id }}"])
-		subscriptionWithStaticValues: User! @edfs__natsSubscribe(subjects: ["tenants.1.users.1"])
-		subscriptionWithArgTemplateAndStaticValue(nestedUserKey: NestedUserKey!): User! @edfs__natsSubscribe(subjects: ["tenants.1.users.{{ args.nestedUserKey.user.id }}"])
-	}
-	
-	type User @key(fields: "id tenant { id }") {
-		id: Int! @external
-		tenant: Tenant! @external
-	}
-
-	type Tenant {
-		id: Int! @external
-	}
-
-	input UserKey {
-		id: Int!
-		tenantId: Int!
-	}
-
-	input NestedUserKey {
-		user: UserInput!
-		tenant: TenantInput!
-	}
-	
-	input UserInput {
-		id: Int!
-	}
-	
-	input TenantInput {
-		id: Int!
-	}
-
-	type edfs__PublishResult {
-		success: Boolean!	
-	}
-
-	input edfs__NatsStreamConfiguration {
-		consumerName: String!
-		streamName: String!
-	}
-	`
-
-	dataSourceCustomConfig := Configuration{
-		Events: []EventConfiguration{
-			{
-				Metadata: &EventMetadata{
-					FieldName:  "helloQuery",
-					ProviderID: "default",
-					Type:       EventTypeRequest,
-					TypeName:   "Query",
-				},
-				Configuration: &NatsEventConfiguration{
-					Subjects: []string{"tenants.{{ args.userKey.tenantId }}.users.{{ args.userKey.id }}"},
-				},
-			},
-			{
-				Metadata: &EventMetadata{
-					FieldName:  "helloMutation",
-					ProviderID: "default",
-					Type:       EventTypePublish,
-					TypeName:   "Mutation",
-				},
-				Configuration: &NatsEventConfiguration{
-					Subjects: []string{"tenants.{{ args.userKey.tenantId }}.users.{{ args.userKey.id }}"},
-				},
-			},
-			{
-				Metadata: &EventMetadata{
-					FieldName:  "helloSubscription",
-					ProviderID: "default",
-					Type:       EventTypeSubscribe,
-					TypeName:   "Subscription",
-				},
-				Configuration: &NatsEventConfiguration{
-					Subjects: []string{"tenants.{{ args.userKey.tenantId }}.users.{{ args.userKey.id }}"},
-				},
-			},
-			{
-				Metadata: &EventMetadata{
-					FieldName:  "subscriptionWithMultipleSubjects",
-					ProviderID: "default",
-					Type:       EventTypeSubscribe,
-					TypeName:   "Subscription",
-				},
-				Configuration: &NatsEventConfiguration{
-					Subjects: []string{"tenantsOne.{{ args.userKeyOne.tenantId }}.users.{{ args.userKeyOne.id }}", "tenantsTwo.{{ args.userKeyTwo.tenantId }}.users.{{ args.userKeyTwo.id }}"},
-				},
-			},
-			{
-				Metadata: &EventMetadata{
-					FieldName:  "subscriptionWithStaticValues",
-					ProviderID: "default",
-					Type:       EventTypeSubscribe,
-					TypeName:   "Subscription",
-				},
-				Configuration: &NatsEventConfiguration{
-					Subjects: []string{"tenants.1.users.1"},
-				},
-			},
-			{
-				Metadata: &EventMetadata{
-					FieldName:  "subscriptionWithArgTemplateAndStaticValue",
-					ProviderID: "default",
-					Type:       EventTypeSubscribe,
-					TypeName:   "Subscription",
-				},
-				Configuration: &NatsEventConfiguration{
-					Subjects: []string{"tenants.1.users.{{ args.nestedUserKey.user.id }}"},
-				},
-			},
-		},
-	}
-
-	dataSourceConfiguration, err := plan.NewDataSourceConfiguration[Configuration](
-		"test",
-		factory,
-		&plan.DataSourceMetadata{
-			RootNodes: []plan.TypeField{
-				{
-					TypeName:   "Query",
-					FieldNames: []string{"helloQuery"},
-				},
-				{
-					TypeName:   "Mutation",
-					FieldNames: []string{"helloMutation"},
-				},
-				{
-					TypeName:   "Subscription",
-					FieldNames: []string{"helloSubscription"},
-				},
-				{
-					TypeName:   "Subscription",
-					FieldNames: []string{"subscriptionWithMultipleSubjects"},
-				},
-				{
-					TypeName:   "Subscription",
-					FieldNames: []string{"subscriptionWithStaticValues"},
-				},
-				{
-					TypeName:   "Subscription",
-					FieldNames: []string{"subscriptionWithArgTemplateAndStaticValue"},
-				},
-			},
-			ChildNodes: []plan.TypeField{
-				// Entities are child nodes in pubsub datasources
-				{
-					TypeName:   "User",
-					FieldNames: []string{"id", "tenant"},
-				},
-				{
-					TypeName:   "Tenant",
-					FieldNames: []string{"id"},
-				},
-				{
-					TypeName:   "edfs__PublishResult",
-					FieldNames: []string{"success"},
-				},
-			},
-		},
-		dataSourceCustomConfig,
-	)
-	require.NoError(t, err)
-
-	planConfig := plan.Configuration{
-		DataSources: []plan.DataSource{
-			dataSourceConfiguration,
-		},
-		Fields: []plan.FieldConfiguration{
-			{
-				TypeName:  "Query",
-				FieldName: "helloQuery",
-				Arguments: []plan.ArgumentConfiguration{
-					{
-						Name:       "userKey",
-						SourceType: plan.FieldArgumentSource,
-					},
-				},
-			},
-			{
-				TypeName:  "Mutation",
-				FieldName: "helloMutation",
-				Arguments: []plan.ArgumentConfiguration{
-					{
-						Name:       "userKey",
-						SourceType: plan.FieldArgumentSource,
-					},
-				},
-			},
-			{
-				TypeName:  "Subscription",
-				FieldName: "helloSubscription",
-				Arguments: []plan.ArgumentConfiguration{
-					{
-						Name:       "userKey",
-						SourceType: plan.FieldArgumentSource,
-					},
-				},
-			},
-			{
-				TypeName:  "Subscription",
-				FieldName: "subscriptionWithMultipleSubjects",
-				Arguments: []plan.ArgumentConfiguration{
-					{
-						Name:       "userKeyOne",
-						SourceType: plan.FieldArgumentSource,
-					},
-					{
-						Name:       "userKeyTwo",
-						SourceType: plan.FieldArgumentSource,
-					},
-				},
-			},
-			{
-				TypeName:  "Subscription",
-				FieldName: "subscriptionWithArgTemplateAndStaticValue",
-				Arguments: []plan.ArgumentConfiguration{
-					{
-						Name:       "nestedUserKey",
-						SourceType: plan.FieldArgumentSource,
-					},
-				},
-			},
-		},
-		DisableResolveFieldPositions: true,
-	}
-
-	t.Run("query", func(t *testing.T) {
-		const operation = "query HelloQuery { helloQuery(userKey:{id:42,tenantId:3}) { id } }"
-		const operationName = `HelloQuery`
-		expect := &plan.SynchronousResponsePlan{
-			Response: &resolve.GraphQLResponse{
-				RawFetches: []*resolve.FetchItem{
-					{
-						Fetch: &resolve.SingleFetch{
-							FetchConfiguration: resolve.FetchConfiguration{
-								Input: `{"subject":"tenants.$$0$$.users.$$1$$", "data": {"userKey":$$2$$}, "providerId":"default"}`,
-								Variables: resolve.Variables{
-									&resolve.ContextVariable{
-										Path:     []string{"a", "tenantId"},
-										Renderer: resolve.NewPlainVariableRenderer(),
-									},
-									&resolve.ContextVariable{
-										Path:     []string{"a", "id"},
-										Renderer: resolve.NewPlainVariableRenderer(),
-									},
-									&resolve.ContextVariable{
-										Path:     []string{"a"},
-										Renderer: resolve.NewJSONVariableRenderer(),
-									},
-								},
-								DataSource: &NatsRequestDataSource{
-									pubSub: &testPubsub{},
-								},
-								PostProcessing: resolve.PostProcessingConfiguration{
-									MergePath: []string{"helloQuery"},
-								},
-							},
-							DataSourceIdentifier: []byte("pubsub_datasource.NatsRequestDataSource"),
-						},
-					},
-				},
-				Data: &resolve.Object{
-					Fields: []*resolve.Field{
-						{
-							Name: []byte("helloQuery"),
-							Value: &resolve.Object{
-								Path:     []string{"helloQuery"},
-								Nullable: false,
-								PossibleTypes: map[string]struct{}{
-									"User": {},
-								},
-								TypeName: "User",
-								Fields: []*resolve.Field{
-									{
-										Name: []byte("id"),
-										Value: &resolve.Integer{
-											Path:     []string{"id"},
-											Nullable: false,
-										},
-									},
-								},
-							},
-						},
-					},
-				},
-			},
-		}
-		datasourcetesting.RunTest(schema, operation, operationName, expect, planConfig)(t)
-	})
-
-	t.Run("mutation", func(t *testing.T) {
-		const operation = "mutation HelloMutation { helloMutation(userKey:{id:42,tenantId:3}) { success } }"
-		const operationName = `HelloMutation`
-		expect := &plan.SynchronousResponsePlan{
-			Response: &resolve.GraphQLResponse{
-				RawFetches: []*resolve.FetchItem{
-					{
-						Fetch: &resolve.SingleFetch{
-							FetchConfiguration: resolve.FetchConfiguration{
-								Input: `{"subject":"tenants.$$0$$.users.$$1$$", "data": {"userKey":$$2$$}, "providerId":"default"}`,
-								Variables: resolve.Variables{
-									&resolve.ContextVariable{
-										Path:     []string{"a", "tenantId"},
-										Renderer: resolve.NewPlainVariableRenderer(),
-									},
-									&resolve.ContextVariable{
-										Path:     []string{"a", "id"},
-										Renderer: resolve.NewPlainVariableRenderer(),
-									},
-									&resolve.ContextVariable{
-										Path:     []string{"a"},
-										Renderer: resolve.NewJSONVariableRenderer(),
-									},
-								},
-								DataSource: &NatsPublishDataSource{
-									pubSub: &testPubsub{},
-								},
-								PostProcessing: resolve.PostProcessingConfiguration{
-									MergePath: []string{"helloMutation"},
-								},
-							},
-							DataSourceIdentifier: []byte("pubsub_datasource.NatsPublishDataSource"),
-						},
-					},
-				},
-				Data: &resolve.Object{
-					Fields: []*resolve.Field{
-						{
-							Name: []byte("helloMutation"),
-							Value: &resolve.Object{
-								Path:     []string{"helloMutation"},
-								Nullable: false,
-								PossibleTypes: map[string]struct{}{
-									"edfs__PublishResult": {},
-								},
-								TypeName: "edfs__PublishResult",
-								Fields: []*resolve.Field{
-									{
-										Name: []byte("success"),
-										Value: &resolve.Boolean{
-											Path:     []string{"success"},
-											Nullable: false,
-										},
-									},
-								},
-							},
-						},
-					},
-				},
-			},
-		}
-		datasourcetesting.RunTest(schema, operation, operationName, expect, planConfig)(t)
-	})
-
-	t.Run("subscription", func(t *testing.T) {
-		const operation = "subscription HelloSubscription { helloSubscription(userKey:{id:42,tenantId:3}) { id } }"
-		const operationName = `HelloSubscription`
-		expect := &plan.SubscriptionResponsePlan{
-			Response: &resolve.GraphQLSubscription{
-				Trigger: resolve.GraphQLSubscriptionTrigger{
-					Input: []byte(`{"providerId":"default","subjects":["tenants.$$0$$.users.$$1$$"]}`),
-					Variables: resolve.Variables{
-						&resolve.ContextVariable{
-							Path:     []string{"a", "tenantId"},
-							Renderer: resolve.NewPlainVariableRenderer(),
-						},
-						&resolve.ContextVariable{
-							Path:     []string{"a", "id"},
-							Renderer: resolve.NewPlainVariableRenderer(),
-						},
-					},
-					Source: &NatsSubscriptionSource{
-						pubSub: &testPubsub{},
-					},
-					PostProcessing: resolve.PostProcessingConfiguration{
-						MergePath: []string{"helloSubscription"},
-					},
-				},
-				Response: &resolve.GraphQLResponse{
-					Data: &resolve.Object{
-						Fields: []*resolve.Field{
-							{
-								Name: []byte("helloSubscription"),
-								Value: &resolve.Object{
-									Path:     []string{"helloSubscription"},
-									Nullable: false,
-									PossibleTypes: map[string]struct{}{
-										"User": {},
-									},
-									TypeName: "User",
-									Fields: []*resolve.Field{
-										{
-											Name: []byte("id"),
-											Value: &resolve.Integer{
-												Path:     []string{"id"},
-												Nullable: false,
-											},
-										},
-									},
-								},
-							},
-						},
-					},
-				},
-			},
-		}
-		datasourcetesting.RunTest(schema, operation, operationName, expect, planConfig)(t)
-	})
-
-	t.Run("subscription with multiple subjects", func(t *testing.T) {
-		const operation = "subscription SubscriptionWithMultipleSubjects { subscriptionWithMultipleSubjects(userKeyOne:{id:42,tenantId:3},userKeyTwo:{id:24,tenantId:99}) { id } }"
-		const operationName = `SubscriptionWithMultipleSubjects`
-		expect := &plan.SubscriptionResponsePlan{
-			Response: &resolve.GraphQLSubscription{
-				Trigger: resolve.GraphQLSubscriptionTrigger{
-					Input: []byte(`{"providerId":"default","subjects":["tenantsOne.$$0$$.users.$$1$$","tenantsTwo.$$2$$.users.$$3$$"]}`),
-					Variables: resolve.Variables{
-						&resolve.ContextVariable{
-							Path:     []string{"a", "tenantId"},
-							Renderer: resolve.NewPlainVariableRenderer(),
-						},
-						&resolve.ContextVariable{
-							Path:     []string{"a", "id"},
-							Renderer: resolve.NewPlainVariableRenderer(),
-						},
-						&resolve.ContextVariable{
-							Path:     []string{"b", "tenantId"},
-							Renderer: resolve.NewPlainVariableRenderer(),
-						},
-						&resolve.ContextVariable{
-							Path:     []string{"b", "id"},
-							Renderer: resolve.NewPlainVariableRenderer(),
-						},
-					},
-					Source: &NatsSubscriptionSource{
-						pubSub: &testPubsub{},
-					},
-					PostProcessing: resolve.PostProcessingConfiguration{
-						MergePath: []string{"subscriptionWithMultipleSubjects"},
-					},
-				},
-				Response: &resolve.GraphQLResponse{
-					Data: &resolve.Object{
-						Fields: []*resolve.Field{
-							{
-								Name: []byte("subscriptionWithMultipleSubjects"),
-								Value: &resolve.Object{
-									Path:     []string{"subscriptionWithMultipleSubjects"},
-									Nullable: false,
-									PossibleTypes: map[string]struct{}{
-										"User": {},
-									},
-									TypeName: "User",
-									Fields: []*resolve.Field{
-										{
-											Name: []byte("id"),
-											Value: &resolve.Integer{
-												Path:     []string{"id"},
-												Nullable: false,
-											},
-										},
-									},
-								},
-							},
-						},
-					},
-				},
-			},
-		}
-		datasourcetesting.RunTest(schema, operation, operationName, expect, planConfig)(t)
-	})
-
-	t.Run("subscription with only static values", func(t *testing.T) {
-		const operation = "subscription SubscriptionWithStaticValues { subscriptionWithStaticValues { id } }"
-		const operationName = `SubscriptionWithStaticValues`
-		expect := &plan.SubscriptionResponsePlan{
-			Response: &resolve.GraphQLSubscription{
-				Trigger: resolve.GraphQLSubscriptionTrigger{
-					Input: []byte(`{"providerId":"default","subjects":["tenants.1.users.1"]}`),
-					Source: &NatsSubscriptionSource{
-						pubSub: &testPubsub{},
-					},
-					PostProcessing: resolve.PostProcessingConfiguration{
-						MergePath: []string{"subscriptionWithStaticValues"},
-					},
-				},
-				Response: &resolve.GraphQLResponse{
-					Data: &resolve.Object{
-						Fields: []*resolve.Field{
-							{
-								Name: []byte("subscriptionWithStaticValues"),
-								Value: &resolve.Object{
-									Path:     []string{"subscriptionWithStaticValues"},
-									Nullable: false,
-									PossibleTypes: map[string]struct{}{
-										"User": {},
-									},
-									TypeName: "User",
-									Fields: []*resolve.Field{
-										{
-											Name: []byte("id"),
-											Value: &resolve.Integer{
-												Path:     []string{"id"},
-												Nullable: false,
-											},
-										},
-									},
-								},
-							},
-						},
-					},
-				},
-			},
-		}
-		datasourcetesting.RunTest(schema, operation, operationName, expect, planConfig)(t)
-	})
-
-	t.Run("subscription with deeply nested argument and static value", func(t *testing.T) {
-		const operation = "subscription SubscriptionWithArgTemplateAndStaticValue { subscriptionWithArgTemplateAndStaticValue(nestedUserKey: { user: { id: 44, tenantId: 2 } }) { id } }"
-		const operationName = `SubscriptionWithArgTemplateAndStaticValue`
-		expect := &plan.SubscriptionResponsePlan{
-			Response: &resolve.GraphQLSubscription{
-				Trigger: resolve.GraphQLSubscriptionTrigger{
-					Input: []byte(`{"providerId":"default","subjects":["tenants.1.users.$$0$$"]}`),
-					Variables: resolve.Variables{
-						&resolve.ContextVariable{
-							Path:     []string{"a", "user", "id"},
-							Renderer: resolve.NewPlainVariableRenderer(),
-						},
-					},
-					Source: &NatsSubscriptionSource{
-						pubSub: &testPubsub{},
-					},
-					PostProcessing: resolve.PostProcessingConfiguration{
-						MergePath: []string{"subscriptionWithArgTemplateAndStaticValue"},
-					},
-				},
-				Response: &resolve.GraphQLResponse{
-					Data: &resolve.Object{
-						Fields: []*resolve.Field{
-							{
-								Name: []byte("subscriptionWithArgTemplateAndStaticValue"),
-								Value: &resolve.Object{
-									Path:     []string{"subscriptionWithArgTemplateAndStaticValue"},
-									Nullable: false,
-									PossibleTypes: map[string]struct{}{
-										"User": {},
-									},
-									TypeName: "User",
-									Fields: []*resolve.Field{
-										{
-											Name: []byte("id"),
-											Value: &resolve.Integer{
-												Path:     []string{"id"},
-												Nullable: false,
-											},
-										},
-									},
-								},
-							},
-						},
-					},
-				},
-			},
-		}
-		datasourcetesting.RunTest(schema, operation, operationName, expect, planConfig)(t)
-	})
-}
-
-func TestBuildEventDataBytes(t *testing.T) {
-	t.Run("check string serialization", func(t *testing.T) {
-		const operation = "mutation HelloMutation($id: ID!) { helloMutation(userKey:{id:$id,tenantId:3}) { success } }"
-		op := unsafeparser.ParseGraphqlDocumentString(operation)
-		var vars resolve.Variables
-		visitor := plan.Visitor{
-			Operation: &op,
-		}
-		_, err := buildEventDataBytes(1, &visitor, &vars)
-		require.NoError(t, err)
-		require.Len(t, vars, 1)
-
-		template := resolve.InputTemplate{
-			Segments: []resolve.TemplateSegment{
-				vars[0].TemplateSegment(),
-			},
-		}
-		ctx := &resolve.Context{
-			Variables: astjson.MustParseBytes([]byte(`{"id":"asdf"}`)),
-		}
-		buf := &bytes.Buffer{}
-		err = template.Render(ctx, nil, buf)
-		require.NoError(t, err)
-		require.Equal(t, `"asdf"`, buf.String())
-	})
-
-	t.Run("check int serialization", func(t *testing.T) {
-		const operation = "mutation HelloMutation($id: Int!) { helloMutation(userKey:{id:$id,tenantId:3}) { success } }"
-		op := unsafeparser.ParseGraphqlDocumentString(operation)
-		var vars resolve.Variables
-		visitor := plan.Visitor{
-			Operation: &op,
-		}
-		_, err := buildEventDataBytes(1, &visitor, &vars)
-		require.NoError(t, err)
-		require.Len(t, vars, 1)
-
-		template := resolve.InputTemplate{
-			Segments: []resolve.TemplateSegment{
-				vars[0].TemplateSegment(),
-			},
-		}
-		ctx := &resolve.Context{
-			Variables: astjson.MustParseBytes([]byte(`{"id":5}`)),
-		}
-		buf := &bytes.Buffer{}
-		err = template.Render(ctx, nil, buf)
-		require.NoError(t, err)
-		require.Equal(t, `5`, buf.String())
-	})
-}
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_kafka.go b/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_kafka.go
deleted file mode 100644
index cc562b8..0000000
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_kafka.go
+++ /dev/null
@@ -1,88 +0,0 @@
-package pubsub_datasource
-
-import (
-	"bytes"
-	"context"
-	"encoding/json"
-	"io"
-
-	"github.com/buger/jsonparser"
-	"github.com/cespare/xxhash/v2"
-
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/datasource/httpclient"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/resolve"
-)
-
-type KafkaEventConfiguration struct {
-	Topics []string `json:"topics"`
-}
-
-type KafkaConnector interface {
-	New(ctx context.Context) KafkaPubSub
-}
-
-// KafkaPubSub describe the interface that implements the primitive operations for pubsub
-type KafkaPubSub interface {
-	// Subscribe starts listening on the given subjects and sends the received messages to the given next channel
-	Subscribe(ctx context.Context, config KafkaSubscriptionEventConfiguration, updater resolve.SubscriptionUpdater) error
-	// Publish sends the given data to the given subject
-	Publish(ctx context.Context, config KafkaPublishEventConfiguration) error
-}
-
-type KafkaSubscriptionSource struct {
-	pubSub KafkaPubSub
-}
-
-func (s *KafkaSubscriptionSource) UniqueRequestID(ctx *resolve.Context, input []byte, xxh *xxhash.Digest) error {
-
-	val, _, _, err := jsonparser.Get(input, "topics")
-	if err != nil {
-		return err
-	}
-
-	_, err = xxh.Write(val)
-	if err != nil {
-		return err
-	}
-
-	val, _, _, err = jsonparser.Get(input, "providerId")
-	if err != nil {
-		return err
-	}
-
-	_, err = xxh.Write(val)
-	return err
-}
-
-func (s *KafkaSubscriptionSource) Start(ctx *resolve.Context, input []byte, updater resolve.SubscriptionUpdater) error {
-	var subscriptionConfiguration KafkaSubscriptionEventConfiguration
-	err := json.Unmarshal(input, &subscriptionConfiguration)
-	if err != nil {
-		return err
-	}
-
-	return s.pubSub.Subscribe(ctx.Context(), subscriptionConfiguration, updater)
-}
-
-type KafkaPublishDataSource struct {
-	pubSub KafkaPubSub
-}
-
-func (s *KafkaPublishDataSource) Load(ctx context.Context, input []byte, out *bytes.Buffer) error {
-	var publishConfiguration KafkaPublishEventConfiguration
-	err := json.Unmarshal(input, &publishConfiguration)
-	if err != nil {
-		return err
-	}
-
-	if err := s.pubSub.Publish(ctx, publishConfiguration); err != nil {
-		_, err = io.WriteString(out, `{"success": false}`)
-		return err
-	}
-	_, err = io.WriteString(out, `{"success": true}`)
-	return err
-}
-
-func (s *KafkaPublishDataSource) LoadWithFiles(ctx context.Context, input []byte, files []*httpclient.FileUpload, out *bytes.Buffer) (err error) {
-	panic("not implemented")
-}
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_nats.go b/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_nats.go
deleted file mode 100644
index 31cb6d4..0000000
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/datasource/pubsub_datasource/pubsub_nats.go
+++ /dev/null
@@ -1,116 +0,0 @@
-package pubsub_datasource
-
-import (
-	"bytes"
-	"context"
-	"encoding/json"
-	"io"
-
-	"github.com/buger/jsonparser"
-	"github.com/cespare/xxhash/v2"
-
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/datasource/httpclient"
-	"github.com/wundergraph/graphql-go-tools/v2/pkg/engine/resolve"
-)
-
-type NatsStreamConfiguration struct {
-	Consumer                  string `json:"consumer"`
-	ConsumerInactiveThreshold int32  `json:"consumerInactiveThreshold"`
-	StreamName                string `json:"streamName"`
-}
-
-type NatsEventConfiguration struct {
-	StreamConfiguration *NatsStreamConfiguration `json:"streamConfiguration,omitempty"`
-	Subjects            []string                 `json:"subjects"`
-}
-
-type NatsConnector interface {
-	New(ctx context.Context) NatsPubSub
-}
-
-// NatsPubSub describe the interface that implements the primitive operations for pubsub
-type NatsPubSub interface {
-	// Subscribe starts listening on the given subjects and sends the received messages to the given next channel
-	Subscribe(ctx context.Context, event NatsSubscriptionEventConfiguration, updater resolve.SubscriptionUpdater) error
-	// Publish sends the given data to the given subject
-	Publish(ctx context.Context, event NatsPublishAndRequestEventConfiguration) error
-	// Request sends a request on the given subject and writes the response to the given writer
-	Request(ctx context.Context, event NatsPublishAndRequestEventConfiguration, w io.Writer) error
-}
-
-type NatsSubscriptionSource struct {
-	pubSub NatsPubSub
-}
-
-func (s *NatsSubscriptionSource) UniqueRequestID(ctx *resolve.Context, input []byte, xxh *xxhash.Digest) error {
-
-	val, _, _, err := jsonparser.Get(input, "subjects")
-	if err != nil {
-		return err
-	}
-
-	_, err = xxh.Write(val)
-	if err != nil {
-		return err
-	}
-
-	val, _, _, err = jsonparser.Get(input, "providerId")
-	if err != nil {
-		return err
-	}
-
-	_, err = xxh.Write(val)
-	return err
-}
-
-func (s *NatsSubscriptionSource) Start(ctx *resolve.Context, input []byte, updater resolve.SubscriptionUpdater) error {
-	var subscriptionConfiguration NatsSubscriptionEventConfiguration
-	err := json.Unmarshal(input, &subscriptionConfiguration)
-	if err != nil {
-		return err
-	}
-
-	return s.pubSub.Subscribe(ctx.Context(), subscriptionConfiguration, updater)
-}
-
-type NatsPublishDataSource struct {
-	pubSub NatsPubSub
-}
-
-func (s *NatsPublishDataSource) Load(ctx context.Context, input []byte, out *bytes.Buffer) error {
-	var publishConfiguration NatsPublishAndRequestEventConfiguration
-	err := json.Unmarshal(input, &publishConfiguration)
-	if err != nil {
-		return err
-	}
-
-	if err := s.pubSub.Publish(ctx, publishConfiguration); err != nil {
-		_, err = io.WriteString(out, `{"success": false}`)
-		return err
-	}
-
-	_, err = io.WriteString(out, `{"success": true}`)
-	return err
-}
-
-func (s *NatsPublishDataSource) LoadWithFiles(ctx context.Context, input []byte, files []*httpclient.FileUpload, out *bytes.Buffer) error {
-	panic("not implemented")
-}
-
-type NatsRequestDataSource struct {
-	pubSub NatsPubSub
-}
-
-func (s *NatsRequestDataSource) Load(ctx context.Context, input []byte, out *bytes.Buffer) error {
-	var subscriptionConfiguration NatsPublishAndRequestEventConfiguration
-	err := json.Unmarshal(input, &subscriptionConfiguration)
-	if err != nil {
-		return err
-	}
-
-	return s.pubSub.Request(ctx, subscriptionConfiguration, out)
-}
-
-func (s *NatsRequestDataSource) LoadWithFiles(ctx context.Context, input []byte, files []*httpclient.FileUpload, out *bytes.Buffer) error {
-	panic("not implemented")
-}
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/resolve/datasource.go b/app/v2/pkg/engine/resolve/datasource.go
index c679d76..27b421b 100644
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/resolve/datasource.go
+++ b/app/v2/pkg/engine/resolve/datasource.go
@@ -26,3 +26,15 @@ type AsyncSubscriptionDataSource interface {
 	AsyncStop(id uint64)
 	UniqueRequestID(ctx *Context, input []byte, xxh *xxhash.Digest) (err error)
 }
+
+// HookableSubscriptionDataSource is a hookable interface for subscription data sources.
+// It is used to call a function when a subscription is started.
+// This is useful for data sources that need to do some work when a subscription is started,
+// e.g. to establish a connection to the data source or to emit updates to the client.
+// The function is called with the context and the input of the subscription.
+// The function is called before the subscription is started and can be used to emit updates to the client.
+type HookableSubscriptionDataSource interface {
+	// SubscriptionOnStart is called when a new subscription is created
+	// If an error is returned, the error is propagated to the client.
+	SubscriptionOnStart(ctx StartupHookContext, input []byte) (err error)
+}
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/resolve/resolve.go b/app/v2/pkg/engine/resolve/resolve.go
index 14d8ad4..093538e 100644
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/resolve/resolve.go
+++ b/app/v2/pkg/engine/resolve/resolve.go
@@ -297,6 +297,15 @@ type trigger struct {
 	subscriptions map[*Context]*sub
 	// initialized is set to true when the trigger is started and initialized
 	initialized bool
+	updater     *subscriptionUpdater
+}
+
+func (t *trigger) subscriptionIds() map[context.Context]SubscriptionIdentifier {
+	subs := make(map[context.Context]SubscriptionIdentifier, len(t.subscriptions))
+	for ctx, sub := range t.subscriptions {
+		subs[ctx.Context()] = sub.id
+	}
+	return subs
 }
 
 // workItem is used to encapsulate a function that needs to be
@@ -507,6 +516,8 @@ func (r *Resolver) handleEvent(event subscriptionEvent) {
 		r.handleCompleteSubscription(event.id)
 	case subscriptionEventKindRemoveClient:
 		r.handleRemoveClient(event.id.ConnectionID)
+	case subscriptionEventKindUpdateSubscription:
+		r.handleUpdateSubscription(event.triggerID, event.data, event.id)
 	case subscriptionEventKindTriggerUpdate:
 		r.handleTriggerUpdate(event.triggerID, event.data)
 	case subscriptionEventKindTriggerComplete:
@@ -581,6 +592,36 @@ func (r *Resolver) handleTriggerComplete(triggerID uint64) {
 	r.completeTrigger(triggerID)
 }
 
+type StartupHookContext struct {
+	Context context.Context
+	Updater func(data []byte)
+}
+
+func (r *Resolver) executeStartupHooks(add *addSubscription, updater *subscriptionUpdater) error {
+	hook, ok := add.resolve.Trigger.Source.(HookableSubscriptionDataSource)
+	if ok {
+		hookCtx := StartupHookContext{
+			Context: add.ctx.Context(),
+			Updater: func(data []byte) {
+				// Writing on the updater channel is safe but has to happen outside of the event loop
+				// to respect order and not block the event loop
+				updater.UpdateSubscription(add.id, data)
+			},
+		}
+
+		err := hook.SubscriptionOnStart(hookCtx, add.input)
+		if err != nil {
+			if r.options.Debug {
+				fmt.Printf("resolver:trigger:subscription:startup:failed:%d\n", add.id.SubscriptionID)
+			}
+			r.asyncErrorWriter.WriteError(add.ctx, err, add.resolve.Response, add.writer)
+			_ = r.AsyncUnsubscribeSubscription(add.id)
+			return err
+		}
+	}
+	return nil
+}
+
 func (r *Resolver) handleAddSubscription(triggerID uint64, add *addSubscription) {
 	var (
 		err error
@@ -608,13 +649,23 @@ func (r *Resolver) handleAddSubscription(triggerID uint64, add *addSubscription)
 
 	trig, ok := r.triggers[triggerID]
 	if ok {
-		trig.subscriptions[add.ctx] = s
 		if r.reporter != nil {
 			r.reporter.SubscriptionCountInc(1)
 		}
 		if r.options.Debug {
 			fmt.Printf("resolver:trigger:subscription:added:%d:%d\n", triggerID, add.id.SubscriptionID)
 		}
+		// Execute the startup hooks in a separate goroutine to avoid blocking the event loop
+		s.workChan <- workItem{
+			fn: func() {
+				_ = r.executeStartupHooks(add, trig.updater)
+				// if the startup hooks return an error, we don't have to do anything else
+			},
+			final: false,
+		}
+		// After the startup hooks are executed, we can add the subscription to the subscriptions registry
+		// so that it can start receive events
+		trig.subscriptions[add.ctx] = s
 		return
 	}
 
@@ -633,9 +684,11 @@ func (r *Resolver) handleAddSubscription(triggerID uint64, add *addSubscription)
 		id:            triggerID,
 		subscriptions: make(map[*Context]*sub),
 		cancel:        cancel,
+		updater:       updater,
 	}
 	r.triggers[triggerID] = trig
 	trig.subscriptions[add.ctx] = s
+	updater.subsFn = trig.subscriptionIds
 
 	if r.reporter != nil {
 		r.reporter.SubscriptionCountInc(1)
@@ -655,10 +708,17 @@ func (r *Resolver) handleAddSubscription(triggerID uint64, add *addSubscription)
 		if r.options.Debug {
 			fmt.Printf("resolver:trigger:start:%d\n", triggerID)
 		}
+
+		// This is blocking so the startup hook can decide if a subscription should be started or not by returning an error
+		err = r.executeStartupHooks(add, trig.updater)
+		if err != nil {
+			return
+		}
+
 		if asyncDataSource != nil {
-			err = asyncDataSource.AsyncStart(cloneCtx, triggerID, add.input, updater)
+			err = asyncDataSource.AsyncStart(cloneCtx, triggerID, add.input, trig.updater)
 		} else {
-			err = add.resolve.Trigger.Source.Start(cloneCtx, add.input, updater)
+			err = add.resolve.Trigger.Source.Start(cloneCtx, add.input, trig.updater)
 		}
 		if err != nil {
 			if r.options.Debug {
@@ -779,32 +839,54 @@ func (r *Resolver) handleTriggerUpdate(id uint64, data []byte) {
 	}
 
 	for c, s := range trig.subscriptions {
-		c, s := c, s
-		if err := c.ctx.Err(); err != nil {
-			continue // no need to schedule an event update when the client already disconnected
-		}
-		skip, err := s.resolve.Filter.SkipEvent(c, data, r.triggerUpdateBuf)
-		if err != nil {
-			r.asyncErrorWriter.WriteError(c, err, s.resolve.Response, s.writer)
-			continue
-		}
-		if skip {
+		r.sendUpdateToSubscription(data, c, s)
+	}
+}
+
+func (r *Resolver) handleUpdateSubscription(id uint64, data []byte, subIdentifier SubscriptionIdentifier) {
+	trig, ok := r.triggers[id]
+	if !ok {
+		return
+	}
+
+	if r.options.Debug {
+		fmt.Printf("resolver:trigger:subscription:update:%d:%d,%d\n", id, subIdentifier.ConnectionID, subIdentifier.SubscriptionID)
+	}
+
+	for c, s := range trig.subscriptions {
+		if s.id != subIdentifier {
 			continue
 		}
+		r.sendUpdateToSubscription(data, c, s)
+		break
+	}
+}
 
-		fn := func() {
-			r.executeSubscriptionUpdate(c, s, data)
-		}
+func (r *Resolver) sendUpdateToSubscription(data []byte, c *Context, s *sub) {
+	if err := c.ctx.Err(); err != nil {
+		return // no need to schedule an event update when the client already disconnected
+	}
+	skip, err := s.resolve.Filter.SkipEvent(c, data, r.triggerUpdateBuf)
+	if err != nil {
+		r.asyncErrorWriter.WriteError(c, err, s.resolve.Response, s.writer)
+		return
+	}
+	if skip {
+		return
+	}
 
-		select {
-		case <-r.ctx.Done():
-			// Skip sending all events if the resolver is shutting down
-			return
-		case <-c.ctx.Done():
-			// Skip sending the event if the client disconnected
-		case s.workChan <- workItem{fn, false}:
-			// Send the event to the subscription worker
-		}
+	fn := func() {
+		r.executeSubscriptionUpdate(c, s, data)
+	}
+
+	select {
+	case <-r.ctx.Done():
+		// Skip sending all events if the resolver is shutting down
+		return
+	case <-c.ctx.Done():
+		// Skip sending the event if the client disconnected
+	case s.workChan <- workItem{fn, false}:
+		// Send the event to the subscription worker
 	}
 }
 
@@ -1205,6 +1287,7 @@ type subscriptionUpdater struct {
 	triggerID uint64
 	ch        chan subscriptionEvent
 	ctx       context.Context
+	subsFn    func() map[context.Context]SubscriptionIdentifier
 }
 
 func (s *subscriptionUpdater) Update(data []byte) {
@@ -1224,6 +1307,28 @@ func (s *subscriptionUpdater) Update(data []byte) {
 	}
 }
 
+func (s *subscriptionUpdater) UpdateSubscription(id SubscriptionIdentifier, data []byte) {
+	if s.debug {
+		fmt.Printf("resolver:subscription_updater:update:%d\n", s.triggerID)
+	}
+
+	select {
+	case <-s.ctx.Done():
+		// Skip sending events if trigger is already done
+		return
+	case s.ch <- subscriptionEvent{
+		triggerID: s.triggerID,
+		kind:      subscriptionEventKindUpdateSubscription,
+		data:      data,
+		id:        id,
+	}:
+	}
+}
+
+func (s *subscriptionUpdater) Subscriptions() map[context.Context]SubscriptionIdentifier {
+	return s.subsFn()
+}
+
 func (s *subscriptionUpdater) Complete() {
 	if s.debug {
 		fmt.Printf("resolver:subscription_updater:complete:%d\n", s.triggerID)
@@ -1269,6 +1374,30 @@ func (s *subscriptionUpdater) Close(kind SubscriptionCloseKind) {
 	}
 }
 
+func (s *subscriptionUpdater) CloseSubscription(kind SubscriptionCloseKind, id SubscriptionIdentifier) {
+	if s.debug {
+		fmt.Printf("resolver:subscription_updater:close:%d\n", s.triggerID)
+	}
+
+	select {
+	case <-s.ctx.Done():
+		// Skip sending events if trigger is already done
+		if s.debug {
+			fmt.Printf("resolver:subscription_updater:close:skip:%d\n", s.triggerID)
+		}
+		return
+	case s.ch <- subscriptionEvent{
+		triggerID: s.triggerID,
+		kind:      subscriptionEventKindRemoveSubscription,
+		closeKind: kind,
+		id:        id,
+	}:
+		if s.debug {
+			fmt.Printf("resolver:subscription_updater:close:sent_event:%d\n", s.triggerID)
+		}
+	}
+}
+
 type subscriptionEvent struct {
 	triggerID       uint64
 	id              SubscriptionIdentifier
@@ -1299,13 +1428,20 @@ const (
 	subscriptionEventKindRemoveClient
 	subscriptionEventKindTriggerInitialized
 	subscriptionEventKindTriggerClose
+	subscriptionEventKindUpdateSubscription
 )
 
 type SubscriptionUpdater interface {
 	// Update sends an update to the client. It is not guaranteed that the update is sent immediately.
 	Update(data []byte)
+	// UpdateSubscription sends an update to a single subscription. It is not guaranteed that the update is sent immediately.
+	UpdateSubscription(id SubscriptionIdentifier, data []byte)
 	// Complete also takes care of cleaning up the trigger and all subscriptions. No more updates should be sent after calling Complete.
 	Complete()
 	// Close closes the subscription and cleans up the trigger and all subscriptions. No more updates should be sent after calling Close.
 	Close(kind SubscriptionCloseKind)
+	// CloseSubscription closes a single subscription. No more updates should be sent to that subscription after calling CloseSubscription.
+	CloseSubscription(kind SubscriptionCloseKind, id SubscriptionIdentifier)
+	// Subscriptions return all the subscriptions associated to this Updater
+	Subscriptions() map[context.Context]SubscriptionIdentifier
 }
diff --git a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/resolve/resolve_test.go b/app/v2/pkg/engine/resolve/resolve_test.go
index 8e15ff9..967dd0b 100644
--- a/tmp/agent-patch-flux-pr-1309.1-of-1.2026-02-21__03-36-16__gpt-5-1-codex-mini/app/v2/pkg/engine/resolve/resolve_test.go
+++ b/app/v2/pkg/engine/resolve/resolve_test.go
@@ -4794,11 +4794,12 @@ func (s *SubscriptionRecorder) Messages() []string {
 	return s.messages
 }
 
-func createFakeStream(messageFunc messageFunc, delay time.Duration, onStart func(input []byte)) *_fakeStream {
+func createFakeStream(messageFunc messageFunc, delay time.Duration, onStart func(input []byte), subscriptionOnStartFn func(ctx StartupHookContext, input []byte) (err error)) *_fakeStream {
 	return &_fakeStream{
-		messageFunc: messageFunc,
-		delay:       delay,
-		onStart:     onStart,
+		messageFunc:           messageFunc,
+		delay:                 delay,
+		onStart:               onStart,
+		subscriptionOnStartFn: subscriptionOnStartFn,
 	}
 }
 
@@ -4807,10 +4808,19 @@ type messageFunc func(counter int) (message string, done bool)
 var fakeStreamRequestId atomic.Int32
 
 type _fakeStream struct {
-	messageFunc messageFunc
-	onStart     func(input []byte)
-	delay       time.Duration
-	isDone      atomic.Bool
+	uniqueRequestFn       func(ctx *Context, input []byte, xxh *xxhash.Digest) (err error)
+	messageFunc           messageFunc
+	onStart               func(input []byte)
+	delay                 time.Duration
+	isDone                atomic.Bool
+	subscriptionOnStartFn func(ctx StartupHookContext, input []byte) (err error)
+}
+
+func (f *_fakeStream) SubscriptionOnStart(ctx StartupHookContext, input []byte) (err error) {
+	if f.subscriptionOnStartFn == nil {
+		return nil
+	}
+	return f.subscriptionOnStartFn(ctx, input)
 }
 
 func (f *_fakeStream) AwaitIsDone(t *testing.T, timeout time.Duration) {
@@ -4828,6 +4838,10 @@ func (f *_fakeStream) AwaitIsDone(t *testing.T, timeout time.Duration) {
 }
 
 func (f *_fakeStream) UniqueRequestID(ctx *Context, input []byte, xxh *xxhash.Digest) (err error) {
+	if f.uniqueRequestFn != nil {
+		return f.uniqueRequestFn(ctx, input, xxh)
+	}
+
 	_, err = fmt.Fprint(xxh, fakeStreamRequestId.Add(1))
 	if err != nil {
 		return
@@ -5071,7 +5085,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return `{"errors":[{"message":"Validation error occurred","locations":[{"line":1,"column":1}],"extensions":{"code":"GRAPHQL_VALIDATION_FAILED"}}],"data":null}`, true
 		}, 0, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setup(c, fakeStream)
 
@@ -5109,7 +5123,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 2
 		}, 1*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setup(c, fakeStream)
 
@@ -5142,7 +5156,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 1
 		}, 1*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setup(c, fakeStream)
 
@@ -5200,7 +5214,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 2
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }","extensions":{"foo":"bar"}}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setup(c, fakeStream)
 
@@ -5228,7 +5242,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 2
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"},"initial_payload":{"hello":"world"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setup(c, fakeStream)
 
@@ -5256,7 +5270,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), false
 		}, time.Millisecond*10, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setup(c, fakeStream)
 
@@ -5281,7 +5295,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), false
 		}, time.Millisecond*10, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setup(c, fakeStream)
 
@@ -5306,7 +5320,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 0
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setup(c, fakeStream)
 
@@ -5335,7 +5349,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 0
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { countryUpdated { name time { local } } }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, recorder, id := setupWithAdditionalDataLoad(c, fakeStream)
 
@@ -5364,7 +5378,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), false
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, _, _ := setup(c, fakeStream)
 
@@ -5418,7 +5432,7 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), true
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
-		})
+		}, nil)
 
 		resolver, plan, _, id := setup(c, fakeStream)
 		recorder := &SubscriptionRecorder{
@@ -5441,6 +5455,460 @@ func TestResolver_ResolveGraphQLSubscription(t *testing.T) {
 		recorder.AwaitClosed(t, defaultTimeout)
 		fakeStream.AwaitIsDone(t, defaultTimeout)
 	})
+
+	t.Run("should call SubscriptionOnStart hook", func(t *testing.T) {
+		c, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		called := make(chan bool, 1)
+
+		fakeStream := createFakeStream(func(counter int) (message string, done bool) {
+			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 0
+		}, 1*time.Millisecond, func(input []byte) {
+			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
+		}, func(ctx StartupHookContext, input []byte) (err error) {
+			called <- true
+			return nil
+		})
+
+		resolver, plan, recorder, id := setup(c, fakeStream)
+
+		ctx := &Context{
+			ctx: context.Background(),
+		}
+
+		err := resolver.AsyncResolveGraphQLSubscription(ctx, plan, recorder, id)
+		assert.NoError(t, err)
+
+		select {
+		case <-called:
+			t.Log("SubscriptionOnStart hook was called")
+		case <-time.After(defaultTimeout):
+			t.Fatal("SubscriptionOnStart hook was not called")
+		}
+
+		recorder.AwaitComplete(t, defaultTimeout)
+	})
+
+	t.Run("SubscriptionOnStart ctx has a working subscription updater", func(t *testing.T) {
+		c, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		fakeStream := createFakeStream(func(counter int) (message string, done bool) {
+			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 0
+		}, 1*time.Millisecond, func(input []byte) {
+			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
+		}, func(ctx StartupHookContext, input []byte) (err error) {
+			ctx.Updater([]byte(`{"data":{"counter":1000}}`))
+			return nil
+		})
+
+		resolver, plan, recorder, id := setup(c, fakeStream)
+
+		ctx := &Context{
+			ctx: context.Background(),
+			ExecutionOptions: ExecutionOptions{
+				SendHeartbeat: true,
+			},
+		}
+
+		err := resolver.AsyncResolveGraphQLSubscription(ctx, plan, recorder, id)
+		assert.NoError(t, err)
+
+		recorder.AwaitComplete(t, defaultTimeout)
+		assert.Equal(t, 2, len(recorder.Messages()))
+		assert.Equal(t, `{"data":{"counter":1000}}`, recorder.Messages()[0])
+		assert.Equal(t, `{"data":{"counter":0}}`, recorder.Messages()[1])
+	})
+
+	t.Run("SubscriptionOnStart ctx updater only updates the right subscription", func(t *testing.T) {
+		c, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		executed := atomic.Bool{}
+
+		id2 := SubscriptionIdentifier{
+			ConnectionID:   1,
+			SubscriptionID: 2,
+		}
+
+		streamCanStart := make(chan struct{})
+		startupHookWaitGroup := sync.WaitGroup{}
+		startupHookWaitGroup.Add(2)
+
+		// this message must come as last, on both recorders.
+		messageFn := func(counter int) (message string, done bool) {
+			<-streamCanStart
+			return `{"data":{"counter":0}}`, true
+		}
+
+		onStartFn := func(input []byte) {
+			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
+		}
+
+		// this message must come first on the first recorder to be added to the trigger.
+		subscriptionOnStartFn := func(ctx StartupHookContext, input []byte) (err error) {
+			defer startupHookWaitGroup.Done()
+			if !executed.CompareAndSwap(false, true) {
+				return
+			}
+			ctx.Updater([]byte(`{"data":{"counter":1000}}`))
+			return nil
+		}
+
+		fakeStream := createFakeStream(messageFn, time.Millisecond, onStartFn, subscriptionOnStartFn)
+		fakeStream.uniqueRequestFn = func(ctx *Context, input []byte, xxh *xxhash.Digest) (err error) {
+			return nil
+		}
+
+		resolver, plan, recorder, id := setup(c, fakeStream)
+
+		recorder2 := &SubscriptionRecorder{
+			buf:      &bytes.Buffer{},
+			messages: []string{},
+			complete: atomic.Bool{},
+		}
+		recorder2.complete.Store(false)
+
+		ctx := &Context{
+			ctx: context.Background(),
+			ExecutionOptions: ExecutionOptions{
+				SendHeartbeat: false,
+			},
+		}
+
+		ctx2 := &Context{
+			ctx: context.Background(),
+			ExecutionOptions: ExecutionOptions{
+				SendHeartbeat: false,
+			},
+		}
+
+		err := resolver.AsyncResolveGraphQLSubscription(ctx, plan, recorder, id)
+		assert.NoError(t, err)
+
+		err2 := resolver.AsyncResolveGraphQLSubscription(ctx2, plan, recorder2, id2)
+		assert.NoError(t, err2)
+
+		done := make(chan struct{})
+		go func() {
+			startupHookWaitGroup.Wait()
+			close(done)
+		}()
+		select {
+		case <-done:
+		case <-time.After(defaultTimeout):
+			t.Fatal("timed out waiting for subscription startup hooks")
+		}
+
+		// Wait for both subscriptions startup hooks to be executed
+		startupHookWaitGroup.Wait()
+
+		// Signal the stream to send its message now that both subscriptions are ready
+		close(streamCanStart)
+
+		recorder.AwaitComplete(t, defaultTimeout)
+		recorder2.AwaitComplete(t, defaultTimeout)
+
+		recorderWith1Message := false
+		recorderWith2Messages := false
+
+		recorders := []*SubscriptionRecorder{recorder, recorder2}
+
+		for _, r := range recorders {
+			if len(r.Messages()) == 2 {
+				recorderWith2Messages = true
+				assert.Equal(t, `{"data":{"counter":1000}}`, r.Messages()[0])
+				assert.Equal(t, `{"data":{"counter":0}}`, r.Messages()[1])
+			}
+			if len(r.Messages()) == 1 {
+				recorderWith1Message = true
+				assert.Equal(t, `{"data":{"counter":0}}`, r.Messages()[0])
+			}
+		}
+
+		assert.True(t, recorderWith1Message, "recorder 1: %v, recorder 2: %v", recorder.messages, recorder2.messages)
+		assert.True(t, recorderWith2Messages, "recorder 1: %v, recorder 2: %v", recorder.messages, recorder2.messages)
+	})
+
+	t.Run("SubscriptionOnStart ctx updater on multiple subscriptions with same trigger works", func(t *testing.T) {
+		c, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		id2 := SubscriptionIdentifier{
+			ConnectionID:   1,
+			SubscriptionID: 2,
+		}
+
+		streamCanStart := make(chan struct{})
+
+		// Message function that waits for signal before sending the final message
+		messageFn := func(counter int) (message string, done bool) {
+			<-streamCanStart
+			return `{"data":{"counter":0}}`, true
+		}
+
+		onStartFn := func(input []byte) {
+			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
+		}
+
+		// this handler pushes the first message to both subscribers via subscription-on-start hook.
+		subscriptionOnStartFn := func(ctx StartupHookContext, input []byte) (err error) {
+			ctx.Updater([]byte(`{"data":{"counter":1000}}`))
+			return nil
+		}
+
+		fakeStream := createFakeStream(messageFn, 1*time.Millisecond, onStartFn, subscriptionOnStartFn)
+		fakeStream.uniqueRequestFn = func(ctx *Context, input []byte, xxh *xxhash.Digest) (err error) {
+			_, err = xxh.WriteString("unique")
+			return
+		}
+
+		resolver, plan, recorder, id := setup(c, fakeStream)
+
+		recorder2 := &SubscriptionRecorder{
+			buf:      &bytes.Buffer{},
+			messages: []string{},
+			complete: atomic.Bool{},
+		}
+		recorder2.complete.Store(false)
+
+		ctx := &Context{
+			ctx: context.Background(),
+			ExecutionOptions: ExecutionOptions{
+				SendHeartbeat: false,
+			},
+		}
+
+		ctx2 := &Context{
+			ctx: context.Background(),
+			ExecutionOptions: ExecutionOptions{
+				SendHeartbeat: false,
+			},
+		}
+
+		err := resolver.AsyncResolveGraphQLSubscription(ctx, plan, recorder, id)
+		assert.NoError(t, err)
+
+		err2 := resolver.AsyncResolveGraphQLSubscription(ctx2, plan, recorder2, id2)
+		assert.NoError(t, err2)
+
+		// Wait for subscriptions to receive their initial message from the subscription-on-start hook.
+		// Then we know the subscriptions are fully registered on the trigger and then we can send
+		// the next message (by closing the streamCanStart channel).
+		recorder.AwaitAnyMessageCount(t, defaultTimeout)
+		recorder2.AwaitAnyMessageCount(t, defaultTimeout)
+		close(streamCanStart)
+
+		recorder.AwaitComplete(t, defaultTimeout)
+		recorder2.AwaitComplete(t, defaultTimeout)
+
+		// Both recorders should have received both messages in the correct order.
+		for _, r := range []*SubscriptionRecorder{recorder, recorder2} {
+			assert.Len(t, r.Messages(), 2, "recorder messages: %v", r.messages)
+			assert.Equal(t, `{"data":{"counter":1000}}`, r.Messages()[0])
+			assert.Equal(t, `{"data":{"counter":0}}`, r.Messages()[1])
+		}
+	})
+
+	t.Run("SubscriptionOnStart can send a lot of updates without blocking", func(t *testing.T) {
+		c, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		workChanBufferSize := 10000
+
+		fakeStream := createFakeStream(func(counter int) (message string, done bool) {
+			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 0
+		}, 1*time.Millisecond, func(input []byte) {
+			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
+		}, func(ctx StartupHookContext, input []byte) (err error) {
+			for i := 0; i < workChanBufferSize+1; i++ {
+				ctx.Updater([]byte(fmt.Sprintf(`{"data":{"counter":%d}}`, i+100)))
+			}
+			return nil
+		})
+
+		resolver, plan, recorder, id := setup(c, fakeStream)
+
+		ctx := &Context{
+			ctx: context.Background(),
+			ExecutionOptions: ExecutionOptions{
+				SendHeartbeat: true,
+			},
+		}
+
+		err := resolver.AsyncResolveGraphQLSubscription(ctx, plan, recorder, id)
+		assert.NoError(t, err)
+
+		recorder.AwaitComplete(t, defaultTimeout)
+		assert.Equal(t, workChanBufferSize+2, len(recorder.Messages()))
+		for i := 0; i < workChanBufferSize; i++ {
+			assert.Equal(t, fmt.Sprintf(`{"data":{"counter":%d}}`, i+100), recorder.Messages()[i])
+		}
+		assert.Equal(t, `{"data":{"counter":0}}`, recorder.Messages()[workChanBufferSize+1])
+	})
+
+	t.Run("SubscriptionOnStart can send a lot of updates in a go routine while updates are coming from other sources", func(t *testing.T) {
+		c, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		messagesToSendFromHook := int32(100)
+		messagesToSendFromOtherSources := int32(100)
+
+		firstMessageArrived := make(chan bool, 1)
+		completionWg := sync.WaitGroup{}
+		completionWg.Add(2) // Wait for both the fakeStream and the hook goroutine to complete
+
+		fakeStream := createFakeStream(func(counter int) (message string, done bool) {
+			if counter == 0 {
+				select {
+				case firstMessageArrived <- true:
+				default:
+				}
+			}
+			if counter == int(messagesToSendFromOtherSources)-1 {
+				completionWg.Done()
+			}
+			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == int(messagesToSendFromOtherSources)-1
+		}, 1*time.Millisecond, func(input []byte) {
+			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
+		}, func(ctx StartupHookContext, input []byte) (err error) {
+			// send the first update immediately
+			ctx.Updater([]byte(fmt.Sprintf(`{"data":{"counter":%d}}`, 0+20000)))
+
+			// start a go routine to send the updates after the source started emitting messages
+			go func() {
+				defer completionWg.Done()
+				// Wait for the first message to arrive before sending updates
+				select {
+				case <-firstMessageArrived:
+					for i := 1; i < int(messagesToSendFromHook); i++ {
+						ctx.Updater([]byte(fmt.Sprintf(`{"data":{"counter":%d}}`, i+20000)))
+					}
+				case <-time.After(defaultTimeout):
+					// if the first message did not arrive, do not send any updates
+					return
+				}
+			}()
+
+			return nil
+		})
+
+		resolver, plan, recorder, id := setup(c, fakeStream)
+
+		ctx := &Context{
+			ctx: context.Background(),
+			ExecutionOptions: ExecutionOptions{
+				SendHeartbeat: false,
+			},
+		}
+
+		err := resolver.AsyncResolveGraphQLSubscription(ctx, plan, recorder, id)
+		assert.NoError(t, err)
+
+		// Wait for both the hook goroutine and the fakeStream to complete
+		done := make(chan struct{})
+		go func() {
+			completionWg.Wait()
+			close(done)
+		}()
+		select {
+		case <-done:
+		case <-time.After(defaultTimeout * 2):
+			t.Fatal("timed out waiting for completion")
+		}
+
+		recorder.AwaitComplete(t, defaultTimeout*2)
+
+		var messagesHeartbeat int32
+		for _, m := range recorder.Messages() {
+			if m == "heartbeat" {
+				messagesHeartbeat++
+			}
+		}
+		assert.Equal(t, int32(messagesToSendFromHook+messagesToSendFromOtherSources+messagesHeartbeat), int32(len(recorder.Messages())))
+		assert.Equal(t, `{"data":{"counter":20000}}`, recorder.Messages()[0])
+	})
+
+	t.Run("it is possible to have two subscriptions to the same trigger", func(t *testing.T) {
+		c, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		fakeStream := createFakeStream(func(counter int) (message string, done bool) {
+			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 100
+		}, 1*time.Millisecond, func(input []byte) {
+			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
+		}, func(ctx StartupHookContext, input []byte) (err error) {
+			return nil
+		})
+		fakeStream.uniqueRequestFn = func(ctx *Context, input []byte, xxh *xxhash.Digest) (err error) {
+			_, err = xxh.WriteString("unique")
+			if err != nil {
+				return
+			}
+			_, err = xxh.Write(input)
+			return err
+		}
+
+		resolver1, plan1, recorder1, id1 := setup(c, fakeStream)
+		_, _, recorder2, id2 := setup(c, fakeStream)
+		id2.ConnectionID = id1.ConnectionID + 1
+		id2.SubscriptionID = id1.SubscriptionID + 1
+
+		ctx1 := &Context{
+			ctx: context.Background(),
+		}
+		ctx2 := &Context{
+			ctx: context.Background(),
+		}
+
+		err1 := resolver1.AsyncResolveGraphQLSubscription(ctx1, plan1, recorder1, id1)
+		assert.NoError(t, err1)
+
+		err2 := resolver1.AsyncResolveGraphQLSubscription(ctx2, plan1, recorder2, id2)
+		assert.NoError(t, err2)
+
+		// complete is called only on the last recorder
+		recorder1.AwaitComplete(t, defaultTimeout)
+		require.Equal(t, 101, len(recorder1.Messages()))
+		assert.Equal(t, `{"data":{"counter":0}}`, recorder1.Messages()[0])
+		assert.Equal(t, `{"data":{"counter":100}}`, recorder1.Messages()[100])
+
+		recorder2.AwaitComplete(t, defaultTimeout)
+		require.Equal(t, 101, len(recorder2.Messages()))
+		assert.Equal(t, `{"data":{"counter":0}}`, recorder2.Messages()[0])
+		assert.Equal(t, `{"data":{"counter":100}}`, recorder2.Messages()[100])
+	})
+
+	t.Run("should propagate errors from SubscriptionOnStart hook", func(t *testing.T) {
+		c, cancel := context.WithCancel(context.Background())
+		defer cancel()
+
+		expectedErr := errors.New("startup hook failed")
+		fakeStream := createFakeStream(func(counter int) (message string, done bool) {
+			return fmt.Sprintf(`{"data":{"counter":%d}}`, counter), counter == 0
+		}, 1*time.Millisecond, func(input []byte) {
+			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000","body":{"query":"subscription { counter }"}}`, string(input))
+		}, func(ctx StartupHookContext, input []byte) (err error) {
+			return expectedErr
+		})
+
+		resolver, plan, recorder, id := setup(c, fakeStream)
+
+		ctx := &Context{
+			ctx: context.Background(),
+		}
+
+		err := resolver.AsyncResolveGraphQLSubscription(ctx, plan, recorder, id)
+		assert.NoError(t, err)
+
+		recorder.AwaitAnyMessageCount(t, defaultTimeout)
+		messages := recorder.Messages()
+		require.Greater(t, len(messages), 0, "Expected error message to be written to recorder")
+
+		errorMessage := messages[0]
+		assert.Contains(t, errorMessage, "errors", "Expected error message in GraphQL format")
+		assert.Contains(t, errorMessage, expectedErr.Error(), "Expected actual error message to be included")
+	})
 }
 
 func Test_ResolveGraphQLSubscriptionWithFilter(t *testing.T) {
@@ -5513,7 +5981,7 @@ func Test_ResolveGraphQLSubscriptionWithFilter(t *testing.T) {
 			return `{"id":2}`, true
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000"}`, string(input))
-		})
+		}, nil)
 
 		plan := &GraphQLSubscription{
 			Trigger: GraphQLSubscriptionTrigger{
@@ -5609,7 +6077,7 @@ func Test_ResolveGraphQLSubscriptionWithFilter(t *testing.T) {
 			return `{"id":2}`, true
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000"}`, string(input))
-		})
+		}, nil)
 
 		plan := &GraphQLSubscription{
 			Trigger: GraphQLSubscriptionTrigger{
@@ -5703,7 +6171,7 @@ func Test_ResolveGraphQLSubscriptionWithFilter(t *testing.T) {
 			return `{"id":4}`, true
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000"}`, string(input))
-		})
+		}, nil)
 
 		plan := &GraphQLSubscription{
 			Trigger: GraphQLSubscriptionTrigger{
@@ -5798,7 +6266,7 @@ func Test_ResolveGraphQLSubscriptionWithFilter(t *testing.T) {
 			return `{"id":"x.4"}`, true
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000"}`, string(input))
-		})
+		}, nil)
 
 		plan := &GraphQLSubscription{
 			Trigger: GraphQLSubscriptionTrigger{
@@ -5897,7 +6365,7 @@ func Test_ResolveGraphQLSubscriptionWithFilter(t *testing.T) {
 			return `{"id":"x.2"}`, true
 		}, 100*time.Millisecond, func(input []byte) {
 			assert.Equal(t, `{"method":"POST","url":"http://localhost:4000"}`, string(input))
-		})
+		}, nil)
 
 		plan := &GraphQLSubscription{
 			Trigger: GraphQLSubscriptionTrigger{