fix(version): report the tagged module version for go install builds

`go install github.com/GrayCodeAI/rho/cmd/rho@vX.Y.Z` builds without
ldflags, so main.Version stays "dev". DisplayVersion then fell back to
any VERSION file in the working directory or its parents (so running rho
inside another project could print that project's version) and
otherwise "dev"; `rho update` compared the raw "dev" string, which never
parses, and always reported an update.

DisplayVersion now prefers, after the ldflags version, the main module
version from debug.ReadBuildInfo when it is a clean release (e.g.
v0.3.0 -> "0.3.0"); "(devel)", pseudo-versions (@main, untagged commits)
and +dirty builds still fall back to the VERSION file, then "dev".
`rho update` uses DisplayVersion, so go-install and source builds compare
their real version.

Tests stub the build info for a tagged module, each development form,
and the ldflags precedence.

Refs: F018, F025

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

Author: Patel230

cmd/root.go

@@ -585,10 +585,9 @@ var updateCmd = &cobra.Command{
 	Long:  "Check GitHub for a newer rho release and print upgrade instructions.",
 	Args:  cobra.NoArgs,
 	RunE: func(cmd *cobra.Command, args []string) error {
-		ver := version
-		if ver == "" {
-			ver = "dev"
-		}
+		// Same resolution as `rho --version`, so `go install ...@vX.Y.Z` and
+		// source builds compare their real version instead of "dev".
+		ver := DisplayVersion()
 		prog := NewCLIProgress("Update check", []string{"Checking GitHub for updates"})
 		defer prog.Abort()
 		prog.StartStep(0)

cmd/version_display.go

@@ -3,7 +3,11 @@ package cmd
 import (
 	"os"
 	"path/filepath"
+	"runtime/debug"
 	"strings"
+
+	"golang.org/x/mod/module"
+	"golang.org/x/mod/semver"
 )
 
 // versionLine is the single user-facing version format shared by
@@ -21,12 +25,20 @@ func versionLine() string {
 }
 
 // DisplayVersion returns the user-facing version string for banners and /version.
-// Release builds inject version via ldflags; local builds fall back to VERSION file.
+//
+// In order of preference:
+//  1. the version injected via ldflags (release archives, `make build`);
+//  2. the module version recorded by `go install .../cmd/rho@vX.Y.Z`;
+//  3. the repository VERSION file (local `go build` / `go run` checkouts);
+//  4. "dev".
 func DisplayVersion() string {
 	v := strings.TrimSpace(version)
 	if v != "" && v != "dev" {
 		return v
 	}
+	if mv := releaseModuleVersion(); mv != "" {
+		return mv
+	}
 	if fromFile := readRepoVERSIONFile(); fromFile != "" {
 		return fromFile
 	}
@@ -36,6 +48,26 @@ func DisplayVersion() string {
 	return "dev"
 }
 
+// readBuildInfo is debug.ReadBuildInfo, replaceable in tests.
+var readBuildInfo = debug.ReadBuildInfo
+
+// releaseModuleVersion returns the main module's version without the leading
+// "v" when the binary was built from a tagged module (`go install
+// github.com/GrayCodeAI/rho/cmd/rho@v0.3.0`), and "" for development builds:
+// "(devel)", pseudo-versions (untagged commits such as @main) and versions
+// with build metadata (e.g. "+dirty" from a modified checkout).
+func releaseModuleVersion() string {
+	info, ok := readBuildInfo()
+	if !ok || info == nil {
+		return ""
+	}
+	mv := info.Main.Version
+	if !semver.IsValid(mv) || module.IsPseudoVersion(mv) || semver.Build(mv) != "" {
+		return ""
+	}
+	return strings.TrimPrefix(mv, "v")
+}
+
 func readRepoVERSIONFile() string {
 	candidates := versionFileCandidates()
 	for _, path := range candidates {

cmd/version_display_test.go

@@ -3,6 +3,7 @@ package cmd
 import (
 	"os"
 	"path/filepath"
+	"runtime/debug"
 	"testing"
 
 	rhoconfig "github.com/GrayCodeAI/rho/internal/config"
@@ -21,6 +22,56 @@ func TestDisplayVersion_FromVERSIONFile(t *testing.T) {
 	}
 }
 
+func stubBuildInfo(t *testing.T, mainVersion string) {
+	t.Helper()
+	prev := readBuildInfo
+	readBuildInfo = func() (*debug.BuildInfo, bool) {
+		return &debug.BuildInfo{Main: debug.Module{Path: "github.com/GrayCodeAI/rho", Version: mainVersion}}, true
+	}
+	t.Cleanup(func() { readBuildInfo = prev })
+}
+
+func TestDisplayVersion_GoInstallTaggedModule(t *testing.T) {
+	t.Chdir(t.TempDir()) // no VERSION file nearby
+	SetVersion("dev")
+	stubBuildInfo(t, "v0.3.0")
+	if got := DisplayVersion(); got != "0.3.0" {
+		t.Fatalf("DisplayVersion() = %q, want 0.3.0 for go install ...@v0.3.0", got)
+	}
+}
+
+func TestDisplayVersion_DevelopmentModuleVersionsFallBack(t *testing.T) {
+	for _, mv := range []string{
+		"(devel)",
+		"v0.0.0-20260921005105-13e05ceb15e5",   // go install ...@main
+		"v0.3.1-0.20260930120000-abcdefabcdef", // untagged commit after v0.3.0
+		"v0.3.0+dirty",                         // modified checkout at the tag
+		"",
+	} {
+		t.Run(mv, func(t *testing.T) {
+			dir := t.TempDir()
+			if err := os.WriteFile(filepath.Join(dir, "VERSION"), []byte("0.3.0\n"), 0o644); err != nil {
+				t.Fatal(err)
+			}
+			t.Chdir(dir)
+			SetVersion("dev")
+			stubBuildInfo(t, mv)
+			if got := DisplayVersion(); got != "0.3.0" {
+				t.Fatalf("DisplayVersion() = %q, want the VERSION file value for module version %q", got, mv)
+			}
+		})
+	}
+}
+
+func TestDisplayVersion_LdflagsWinOverModuleVersion(t *testing.T) {
+	SetVersion("1.4.2")
+	t.Cleanup(func() { SetVersion("dev") })
+	stubBuildInfo(t, "v0.3.0")
+	if got := DisplayVersion(); got != "1.4.2" {
+		t.Fatalf("DisplayVersion() = %q, want the ldflags version 1.4.2", got)
+	}
+}
+
 func TestDisplayVersion_ReleaseBuild(t *testing.T) {
 	SetVersion("1.4.2")
 	if got := DisplayVersion(); got != "1.4.2" {