fix(cli): print a null devPort the loader left at the top level

read-configuration dropped a null devPort from the configuration it
prints, written for a loader that did not move a null devPort into
customizations.vscode. The loader now does, as TS does, so a null devPort
stays at the top level only when customizations.vscode has its own, and
TS prints it there. The host phase's containerWorkspaceFolder resolution
becomes two conditions, so each one is held by a test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: aledbf

internal/cli/read_configuration.go

@@ -258,7 +258,11 @@ func loadReadConfiguration(workspaceFolder, configPath, overridePath string, opt
 		// 0.88: read-configuration exits 1 silently (banner only) when no
 		// config is found — it does not print an error envelope. Parse/other
 		// errors still surface normally.
-		if _, ok := errors.AsType[*config.NotFoundError](err); ok {
+		// TS read-configuration exits 1 the same way on a config that is not a
+		// JSON object.
+		_, notFound := errors.AsType[*config.NotFoundError](err)
+		_, notObject := errors.AsType[*config.NotObjectError](err)
+		if notFound || notObject {
 			return nil, &coreerrors.ExitCodeError{Code: 1}
 		}
 		return nil, err
@@ -292,11 +296,6 @@ func configurationOutput(result *config.LoadResult, opts *readConfigOpts) map[st
 		if _, known := cfgMap[k]; known {
 			continue
 		}
-		// TS moves a null devPort into customizations.vscode, which the loader
-		// does not; it is never printed at the top level.
-		if k == "devPort" && v == nil {
-			continue
-		}
 		cfgMap[k] = v
 	}
 	scheme := "vscode-fileHost"

internal/cli/read_configuration_nodocker_held_test.go

@@ -11,8 +11,9 @@ import (
 // A legacy property TS updateFromOldProperties leaves in place stays in the
 // configuration read-configuration prints: a devPort whose
 // customizations.vscode already has one, and a falsy settings. The TS CLI
-// prints both (reference read-configuration of this config); a null devPort,
-// which TS moves into customizations.vscode, is never printed at the top level.
+// prints both (reference read-configuration of this config). A null devPort
+// moves into customizations.vscode when that has none, and otherwise stays at
+// the top level and is printed as null, as TS prints it.
 func TestConfigurationOutputKeepsUnmigratedLegacyProperties(t *testing.T) {
 	_, result := loadFixtureConfig(t, `{
 		"image": "img:1",
@@ -36,6 +37,12 @@ func TestConfigurationOutputKeepsUnmigratedLegacyProperties(t *testing.T) {
 	if v, ok := got["x-null"]; !ok || v != nil {
 		t.Errorf("x-null = %v (%v), want an unknown null property kept", v, ok)
 	}
+
+	_, result = loadFixtureConfig(t, `{"image": "img:1", "devPort": null, "customizations": {"vscode": {"devPort": 1}}}`, nil)
+	got = configurationOutput(result, &readConfigOpts{})
+	if v, ok := got["devPort"]; !ok || v != nil {
+		t.Errorf("devPort = %v (%v), want null kept beside customizations.vscode's own", v, ok)
+	}
 }
 
 // The config's forwardPorts are part of its metadata entry, a single one too.

internal/config/varsub.go

@@ -34,12 +34,16 @@ type VariableResolver struct{}
 func NewVariableResolver() *VariableResolver { return &VariableResolver{} }
 
 func (r *VariableResolver) Resolve(ctx SubstitutionContext, phase SubstitutionPhase, value any) (any, error) {
-	if phase == PhaseHost && ctx.ContainerWorkspaceFolder != "" {
-		resolved, err := r.resolveString(ctx, phase, ctx.ContainerWorkspaceFolder)
-		if err != nil {
-			return nil, err
+	// TS substitute resolves the container workspace folder before the value
+	// that may name it. Only the host phase reads it (resolveHostTag).
+	if phase == PhaseHost {
+		if ctx.ContainerWorkspaceFolder != "" {
+			resolved, err := r.resolveString(ctx, phase, ctx.ContainerWorkspaceFolder)
+			if err != nil {
+				return nil, err
+			}
+			ctx.ContainerWorkspaceFolder = resolved
 		}
-		ctx.ContainerWorkspaceFolder = resolved
 	}
 	return r.resolveRecursive(ctx, phase, value)
 }