diff --git a/composed_project_test.go b/composed_project_test.go
new file mode 100644
index 0000000..1185516
--- /dev/null
+++ b/composed_project_test.go
@@ -0,0 +1,89 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	basev0 "github.com/codefly-dev/core/generated/go/codefly/base/v0"
+	"github.com/codefly-dev/core/resources"
+	"github.com/codefly-dev/core/shared"
+	"github.com/codefly-dev/core/standards"
+	"github.com/stretchr/testify/require"
+)
+
+// TestContainerEnvironmentCarriesAProjectOutsideTheWorkspace pins the mount a
+// composed service depends on.
+//
+// A service the user authored lives in the workspace tree; a service a
+// workspace *composes* does not — it is resolved into the module cache, or to
+// wherever an overlay points. Both are outside the workspace path, and every
+// process this environment runs is given the project directory as its working
+// directory. Mounting only the workspace therefore produced a container whose
+// working directory did not exist inside it: "chdir to cwd ... no such file or
+// directory", surfacing as `uv sync` exiting 127 before the service ever
+// started.
+func TestContainerEnvironmentCarriesAProjectOutsideTheWorkspace(t *testing.T) {
+	ownTestContainers(t)
+	ctx := context.Background()
+
+	// Docker on macOS only bind-mounts shared paths, and the per-user temp dir
+	// is not one — keep both trees inside the repo, as the other container
+	// tests do.
+	workspace, err := os.MkdirTemp("testdata", "composed-workspace-")
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = os.RemoveAll(workspace) })
+	workspace = shared.MustSolvePath(workspace)
+
+	source, err := os.MkdirTemp("testdata", "composed-project-")
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = os.RemoveAll(source) })
+	source = shared.MustSolvePath(source)
+	require.NoError(t, os.MkdirAll(filepath.Join(source, "src"), 0o700))
+	require.NoError(t, os.WriteFile(filepath.Join(source, "pyproject.toml"), []byte(probeProject), 0o600))
+	require.NoError(t, os.WriteFile(filepath.Join(source, "src", "main.py"), []byte("app = None\n"), 0o600))
+
+	runtime := NewRuntime(NewService())
+	runtime.Location = workspace
+	runtime.Logger = runtime.Wool
+	runtime.Base.Runtime.RuntimeContext = resources.NewRuntimeContextContainer()
+	runtime.Identity = &resources.ServiceIdentity{
+		Name:          fmt.Sprintf("composed-%d", time.Now().UnixMilli()),
+		Module:        "mod",
+		Workspace:     "test",
+		WorkspacePath: workspace,
+	}
+	runtime.Environment = shared.Must(resources.LocalEnvironment().Proto())
+	runtime.Service.SourceLocation = source
+
+	endpoint := &basev0.Endpoint{Module: "mod", Service: runtime.Identity.Name, Name: "rest", Api: standards.REST}
+	runtime.FastAPI.RestEndpoint = endpoint
+	runtime.NetworkMappings = []*basev0.NetworkMapping{{
+		Endpoint: endpoint,
+		Instances: []*basev0.NetworkInstance{{
+			Access:   resources.NewNativeNetworkAccess(),
+			Hostname: "localhost",
+			Port:     9998,
+			Address:  "http://localhost:9998",
+		}},
+	}}
+
+	require.False(t, within(workspace, source),
+		"the fixture must place the project outside the workspace, as a composed module is")
+
+	env, _, err := runtime.CreateRunnerEnvironment(ctx)
+	if err != nil {
+		t.Skipf("docker is not available: %v", err)
+	}
+	t.Cleanup(func() { _ = env.Shutdown(context.Background()) })
+	require.NoError(t, env.Init(ctx))
+
+	proc, err := env.NewProcess("sh", "-c", "test -f pyproject.toml")
+	require.NoError(t, err)
+	proc.WithDir(source)
+	require.NoError(t, proc.Run(ctx),
+		"the composed project must exist at its own path inside the container")
+}
diff --git a/runtime.go b/runtime.go
index f7e86d6..44d53ad 100644
--- a/runtime.go
+++ b/runtime.go
@@ -255,6 +255,18 @@ func (s *Runtime) CreateRunnerEnvironment(ctx context.Context) (runners.RunnerEn
 		if err != nil {
 			return nil, "", s.Wool.Wrapf(err, "cannot create docker runner")
 		}
+		// Every process this environment runs is given the project directory as
+		// its working directory, so the project has to be inside a mount. The
+		// workspace mount above carries it only for a service that lives in the
+		// workspace tree. A composed service does not: it is resolved into the
+		// module cache, or to wherever an overlay points, both outside the
+		// workspace — and the container then starts with a working directory
+		// that does not exist inside it ("chdir to cwd ... no such file or
+		// directory", reported as `uv sync` exiting 127). Mount the project at
+		// its own path when the workspace mount does not already cover it.
+		if !within(s.Identity.WorkspacePath, s.Service.SourceLocation) {
+			dockerEnv.WithMount(s.Service.SourceLocation, s.Service.SourceLocation)
+		}
 		dockerEnv.WithPause()
 		// Run as the invoking host user. uv sync writes uv.lock into the
 		// bind-mounted source and populates the venv; as root those files