fix: use cached state for version check notification

The previous non-blocking select pattern raced against the GitHub API
goroutine and the notification never appeared. Now reads cached state
from the previous run to display immediately, and refreshes the cache
in a fire-and-forget background goroutine for the next run.

Author: debidong

internal/cli/root.go

@@ -91,7 +91,7 @@ var (
 	flagBaseURL string
 )
 
-var updateResultCh chan *update.CheckResult
+var updateNotice *update.CheckResult
 
 var rootCmd = &cobra.Command{
 	Use:           "flashduty",
@@ -100,38 +100,26 @@ var rootCmd = &cobra.Command{
 	SilenceUsage:  true,
 	SilenceErrors: true,
 	PersistentPreRun: func(cmd *cobra.Command, _ []string) {
-		path := cmd.CommandPath()
-		if path == "flashduty update" || path == "flashduty version" {
-			return
-		}
-		if !update.ShouldCheck(versionStr) {
+		if cmd.CommandPath() == "flashduty update" {
 			return
 		}
 		if !term.IsTerminal(int(os.Stderr.Fd())) {
 			return
 		}
-		updateResultCh = make(chan *update.CheckResult, 1)
-		go func() {
-			result, err := update.CheckForUpdate(versionStr)
-			if err != nil {
-				return
-			}
-			updateResultCh <- result
-		}()
+		updateNotice = update.StateHasUpdate(versionStr)
+		if update.ShouldCheck(versionStr) {
+			go func() {
+				_, _ = update.CheckForUpdate(versionStr)
+			}()
+		}
 	},
 	PersistentPostRun: func(_ *cobra.Command, _ []string) {
-		if updateResultCh == nil {
+		if updateNotice == nil {
 			return
 		}
-		select {
-		case result := <-updateResultCh:
-			if result != nil && result.UpdateAvailable {
-				fmt.Fprintf(os.Stderr, "\nA new version of flashduty is available: v%s -> %s\n",
-					update.StripV(result.CurrentVersion), result.LatestVersion)
-				fmt.Fprintf(os.Stderr, "To update, run: flashduty update\n")
-			}
-		default:
-		}
+		_, _ = fmt.Fprintf(os.Stderr, "\nA new version of flashduty is available: v%s -> %s\n",
+			update.StripV(updateNotice.CurrentVersion), updateNotice.LatestVersion)
+		_, _ = fmt.Fprintf(os.Stderr, "To update, run: flashduty update\n")
 	},
 }
 

internal/update/check.go

@@ -197,3 +197,22 @@ func CheckForUpdate(currentVersion string) (*CheckResult, error) {
 		UpdateAvailable: IsNewer(tag, currentVersion),
 	}, nil
 }
+
+func StateHasUpdate(currentVersion string) *CheckResult {
+	if currentVersion == "dev" || currentVersion == "(devel)" {
+		return nil
+	}
+	state := loadState()
+	if state.LatestVersion == "" {
+		return nil
+	}
+	if !IsNewer(state.LatestVersion, currentVersion) {
+		return nil
+	}
+	return &CheckResult{
+		CurrentVersion:  currentVersion,
+		LatestVersion:   state.LatestVersion,
+		LatestURL:       state.LatestURL,
+		UpdateAvailable: true,
+	}
+}

internal/update/check_test.go

@@ -306,3 +306,61 @@ func TestCheckForUpdate(t *testing.T) {
 		t.Errorf("state.LatestVersion = %q, want %q", state.LatestVersion, "v0.7.0")
 	}
 }
+
+func TestStateHasUpdate(t *testing.T) {
+	tmp := t.TempDir()
+	setTestHome(t, tmp)
+
+	if got := StateHasUpdate("0.6.0"); got != nil {
+		t.Error("StateHasUpdate should return nil when no state file exists")
+	}
+
+	_ = saveState(&State{
+		CheckedAt:     time.Now(),
+		LatestVersion: "v0.7.0",
+		LatestURL:     "https://example.com/v0.7.0",
+	})
+
+	got := StateHasUpdate("0.6.0")
+	if got == nil {
+		t.Fatal("StateHasUpdate should return non-nil when update is available")
+	}
+	if !got.UpdateAvailable {
+		t.Error("UpdateAvailable = false, want true")
+	}
+	if got.LatestVersion != "v0.7.0" {
+		t.Errorf("LatestVersion = %q, want %q", got.LatestVersion, "v0.7.0")
+	}
+}
+
+func TestStateHasUpdate_AlreadyCurrent(t *testing.T) {
+	tmp := t.TempDir()
+	setTestHome(t, tmp)
+
+	_ = saveState(&State{
+		CheckedAt:     time.Now(),
+		LatestVersion: "v0.6.0",
+		LatestURL:     "https://example.com/v0.6.0",
+	})
+
+	if got := StateHasUpdate("0.6.0"); got != nil {
+		t.Error("StateHasUpdate should return nil when already up to date")
+	}
+}
+
+func TestStateHasUpdate_DevVersion(t *testing.T) {
+	tmp := t.TempDir()
+	setTestHome(t, tmp)
+
+	_ = saveState(&State{
+		CheckedAt:     time.Now(),
+		LatestVersion: "v1.0.0",
+	})
+
+	if got := StateHasUpdate("dev"); got != nil {
+		t.Error("StateHasUpdate should return nil for dev version")
+	}
+	if got := StateHasUpdate("(devel)"); got != nil {
+		t.Error("StateHasUpdate should return nil for (devel) version")
+	}
+}