[PoC] publish resolved stack to the engine compose stack extension point

go.mod

@@ -219,3 +219,5 @@ exclude (
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2
 )
+
+replace github.com/docker/cli => github.com/ndeloof/cli v0.0.0-20260812152003-b90d88ea3ad1

go.sum

@@ -177,8 +177,6 @@ github.com/dlclark/regexp2 v1.11.0 h1:G/nrcoOa7ZXlpoa/91N3X7mM3r8eIlMBBJZvsz/mxK
 github.com/dlclark/regexp2 v1.11.0/go.mod h1:DHkYz0B9wPfa6wondMfaivmHpzrQ3v9q8cnmRbL6yW8=
 github.com/docker/buildx v0.36.1 h1:U7JTUSSeooFXbG+0HcI+CMjEIkvuZgJegXRZ1q7K63Q=
 github.com/docker/buildx v0.36.1/go.mod h1:pkpx66TqJD4HOS65fORu9MYBEDbeiRxnGdN3VpH8SPM=
-github.com/docker/cli v29.6.2+incompatible h1:/bjePvcbbFTnRrMfWJBY7AjfICdsiLVgHn6LwTVOcqw=
-github.com/docker/cli v29.6.2+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
 github.com/docker/cli-docs-tool v0.11.0 h1:7d8QARFb7QEobizqxmEM7fOteZEHwH/zWgHQtHZEcfE=
 github.com/docker/cli-docs-tool v0.11.0/go.mod h1:ma8BKiisUo8D6W05XEYIh3oa1UbgrZhi1nowyKFJa8Q=
 github.com/docker/distribution v2.8.3+incompatible h1:AtKxIZ36LoNK51+Z6RpzLpddBirtxJnzDrHLEKxTAYk=
@@ -443,6 +441,8 @@ github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq
 github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
 github.com/natefinch/atomic v1.0.1 h1:ZPYKxkqQOx3KZ+RsbnP/YsgvxWQPGxjC0oBt2AhwV0A=
 github.com/natefinch/atomic v1.0.1/go.mod h1:N/D/ELrljoqDyT3rZrsUmtsuzvHkeB/wWjHV22AZRbM=
+github.com/ndeloof/cli v0.0.0-20260812152003-b90d88ea3ad1 h1:+piSMfZKPEtnnhalfeK4h7tNhcq5HdCBdDufN0TD6fs=
+github.com/ndeloof/cli v0.0.0-20260812152003-b90d88ea3ad1/go.mod h1:wxmb4t3v3ZwISBr3B/B631+3VJe+erAxkl3vXQwXj2c=
 github.com/oklog/ulid/v2 v2.1.1 h1:suPZ4ARWLOJLegGFiZZ1dFAkqzhMjL3J1TzI+5wHz8s=
 github.com/oklog/ulid/v2 v2.1.1/go.mod h1:rcEKHmBBKfef9DhnvX7y1HZBYxjXb0cP5ExxNsTT1QQ=
 github.com/open-policy-agent/opa v1.14.1 h1:MhurLB9mSbXmojYFCmGbiC1Uagu1+aFAV4XVotDA86M=

internal/stackext/stackext.go

@@ -0,0 +1,93 @@
+/*
+   Copyright 2026 Docker Compose CLI authors
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+// Package stackext is a proof of concept for publishing the resolved Compose
+// project to the engine through the com.docker.compose.stack.v0 extension
+// point of the moby extensions framework (moby/moby#53021): a gRPC service
+// exposed by the daemon on the API socket itself (h2c). Best effort by
+// design: an engine without the extension answers codes.Unimplemented, an
+// engine without h2c support fails at transport level, and both are treated
+// as "feature absent".
+package stackext
+
+import (
+	"context"
+	"time"
+
+	"github.com/compose-spec/compose-go/v2/types"
+	cligrpc "github.com/docker/cli/cli/grpc"
+	"github.com/sirupsen/logrus"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/encoding/protowire"
+)
+
+const publishMethod = "/com.docker.compose.stack.v0.Stack/Publish"
+
+// rawCodec sends pre-encoded protobuf wire bytes as-is, mirroring the
+// passthrough codec the extensions gRPC proxy uses daemon-side. It reports
+// "proto" so the request carries the default content-subtype.
+type rawCodec struct{}
+
+func (rawCodec) Marshal(v any) ([]byte, error)    { return v.([]byte), nil }
+func (rawCodec) Unmarshal(data []byte, v any) error { *(v.(*[]byte)) = data; return nil }
+func (rawCodec) Name() string                     { return "proto" }
+
+// Publish pushes the resolved project definition to the engine's compose
+// stack extension point, when the engine exposes one. Never fails the caller.
+// The connection goes through cli/grpc.Connect (docker/cli#7183), which hides
+// the transport of the current context (unix/npipe socket, tcp with or
+// without TLS, connection helpers) and the h2c/legacy-upgrade negotiation.
+func Publish(ctx context.Context, dockerCli cligrpc.DockerCLI, project *types.Project, complete bool) {
+	model, err := project.MarshalYAML()
+	if err != nil {
+		logrus.Debugf("stackext: cannot marshal project: %v", err)
+		return
+	}
+
+	// hand-encoded com.docker.compose.stack.v0.PublishRequest
+	var payload []byte
+	payload = protowire.AppendTag(payload, 1, protowire.BytesType)
+	payload = protowire.AppendString(payload, project.Name)
+	payload = protowire.AppendTag(payload, 2, protowire.BytesType)
+	payload = protowire.AppendBytes(payload, model)
+	if complete {
+		payload = protowire.AppendTag(payload, 3, protowire.VarintType)
+		payload = protowire.AppendVarint(payload, 1)
+	}
+
+	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+
+	conn, err := cligrpc.Connect(ctx, dockerCli)
+	if err != nil {
+		logrus.Debugf("stackext: cannot connect to the engine gRPC endpoint: %v", err)
+		return
+	}
+	defer func() { _ = conn.Close() }()
+
+	var reply []byte
+	err = conn.Invoke(ctx, publishMethod, payload, &reply, grpc.ForceCodec(rawCodec{}))
+	switch status.Code(err) {
+	case codes.OK:
+		logrus.Infof("stackext: compose stack definition published to engine extension")
+	case codes.Unimplemented:
+		logrus.Debugf("stackext: engine does not expose the compose stack extension point")
+	default:
+		logrus.Debugf("stackext: publish failed: %v", err)
+	}
+}

pkg/compose/up.go

@@ -37,11 +37,17 @@ import (
 
 	"github.com/docker/compose/v5/cmd/formatter"
 	"github.com/docker/compose/v5/internal/desktop"
+	"github.com/docker/compose/v5/internal/stackext"
 	"github.com/docker/compose/v5/internal/tracing"
 	"github.com/docker/compose/v5/pkg/api"
 )
 
 func (s *composeService) Up(ctx context.Context, project *types.Project, options api.UpOptions) error { //nolint:gocyclo
+	// PoC: publish the resolved stack definition to the engine's compose
+	// stack extension point (moby extensions framework) before anything else,
+	// best effort
+	stackext.Publish(ctx, s.dockerCli, project, len(options.Create.Services) == 0)
+
 	err := Run(ctx, tracing.SpanWrapFunc("project/up", tracing.ProjectOptions(ctx, project), func(ctx context.Context) error {
 		err := s.create(ctx, project, options.Create)
 		if err != nil {