Add plugin management commands

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

cmd/flux/main.go

@@ -186,6 +186,8 @@ func main() {
 	// logger, we configure it's logger to do nothing.
 	ctrllog.SetLogger(logr.New(ctrllog.NullLogSink{}))
 
+	registerPlugins()
+
 	if err := rootCmd.Execute(); err != nil {
 
 		if err, ok := err.(*RequestError); ok {

cmd/flux/plugin.go

@@ -0,0 +1,340 @@
+/*
+Copyright 2026 The Flux 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 main
+
+import (
+	"fmt"
+	"runtime"
+	"strings"
+	"time"
+
+	"github.com/briandowns/spinner"
+	"github.com/spf13/cobra"
+
+	"github.com/fluxcd/flux2/v2/internal/plugin"
+	"github.com/fluxcd/flux2/v2/pkg/printers"
+)
+
+var pluginHandler = plugin.NewHandler()
+
+var pluginCmd = &cobra.Command{
+	Use:   "plugin",
+	Short: "Manage Flux CLI plugins",
+	Long:  `The plugin sub-commands manage Flux CLI plugins.`,
+	PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
+		// No-op: skip root's namespace DNS validation for plugin commands.
+		return nil
+	},
+}
+
+var pluginListCmd = &cobra.Command{
+	Use:     "list",
+	Aliases: []string{"ls"},
+	Short:   "List installed plugins",
+	Long:    `The plugin list command shows all installed plugins with their versions and paths.`,
+	RunE:    pluginListCmdRun,
+}
+
+var pluginInstallCmd = &cobra.Command{
+	Use:   "install <name>[@<version>]",
+	Short: "Install a plugin from the catalog",
+	Long: `The plugin install command downloads and installs a plugin from the Flux plugin catalog.
+
+Examples:
+  # Install the latest version
+  flux plugin install operator
+
+  # Install a specific version
+  flux plugin install operator@0.45.0`,
+	Args: cobra.ExactArgs(1),
+	RunE: pluginInstallCmdRun,
+}
+
+var pluginUninstallCmd = &cobra.Command{
+	Use:   "uninstall <name>",
+	Short: "Uninstall a plugin",
+	Long:  `The plugin uninstall command removes a plugin binary and its receipt from the plugin directory.`,
+	Args:  cobra.ExactArgs(1),
+	RunE:  pluginUninstallCmdRun,
+}
+
+var pluginUpdateCmd = &cobra.Command{
+	Use:   "update [name]",
+	Short: "Update installed plugins",
+	Long: `The plugin update command updates installed plugins to their latest versions.
+
+Examples:
+  # Update a single plugin
+  flux plugin update operator
+
+  # Update all installed plugins
+  flux plugin update`,
+	Args: cobra.MaximumNArgs(1),
+	RunE: pluginUpdateCmdRun,
+}
+
+var pluginSearchCmd = &cobra.Command{
+	Use:   "search [query]",
+	Short: "Search the plugin catalog",
+	Long:  `The plugin search command lists available plugins from the Flux plugin catalog.`,
+	Args:  cobra.MaximumNArgs(1),
+	RunE:  pluginSearchCmdRun,
+}
+
+func init() {
+	pluginCmd.AddCommand(pluginListCmd)
+	pluginCmd.AddCommand(pluginInstallCmd)
+	pluginCmd.AddCommand(pluginUninstallCmd)
+	pluginCmd.AddCommand(pluginUpdateCmd)
+	pluginCmd.AddCommand(pluginSearchCmd)
+	rootCmd.AddCommand(pluginCmd)
+}
+
+// builtinCommandNames returns the names of all non-plugin commands on rootCmd.
+func builtinCommandNames() []string {
+	var names []string
+	for _, c := range rootCmd.Commands() {
+		if c.GroupID != "plugin" {
+			names = append(names, c.Name())
+		}
+	}
+	return names
+}
+
+// registerPlugins scans the plugin directory and registers discovered
+// plugins as Cobra subcommands on rootCmd.
+func registerPlugins() {
+	plugins := pluginHandler.Discover(builtinCommandNames())
+	if len(plugins) == 0 {
+		return
+	}
+
+	if !rootCmd.ContainsGroup("plugin") {
+		rootCmd.AddGroup(&cobra.Group{
+			ID:    "plugin",
+			Title: "Plugin Commands:",
+		})
+	}
+
+	for _, p := range plugins {
+		cmd := &cobra.Command{
+			Use:                p.Name,
+			Short:              fmt.Sprintf("Runs the %s plugin", p.Name),
+			Long:               fmt.Sprintf("This command runs the %s plugin.\nUse 'flux %s --help' for full plugin help.", p.Name, p.Name),
+			DisableFlagParsing: true,
+			GroupID:            "plugin",
+			ValidArgsFunction:  plugin.CompleteFunc(p.Path),
+			PersistentPreRunE: func(cmd *cobra.Command, args []string) error {
+				return nil
+			},
+			RunE: func(cmd *cobra.Command, args []string) error {
+				return plugin.Exec(p.Path, args)
+			},
+		}
+		rootCmd.AddCommand(cmd)
+	}
+}
+
+func pluginListCmdRun(cmd *cobra.Command, args []string) error {
+	pluginDir := pluginHandler.PluginDir()
+	plugins := pluginHandler.Discover(builtinCommandNames())
+	if len(plugins) == 0 {
+		cmd.Println("No plugins found")
+		return nil
+	}
+
+	header := []string{"NAME", "VERSION", "PATH"}
+	var rows [][]string
+	for _, p := range plugins {
+		version := "manual"
+		if receipt := plugin.ReadReceipt(pluginDir, p.Name); receipt != nil {
+			version = receipt.Version
+		}
+		rows = append(rows, []string{p.Name, version, p.Path})
+	}
+
+	return printers.TablePrinter(header).Print(cmd.OutOrStdout(), rows)
+}
+
+func pluginInstallCmdRun(cmd *cobra.Command, args []string) error {
+	nameVersion := args[0]
+	name, version := parseNameVersion(nameVersion)
+
+	catalogClient := newCatalogClient()
+	manifest, err := catalogClient.FetchManifest(name)
+	if err != nil {
+		return err
+	}
+
+	pv, err := plugin.ResolveVersion(manifest, version)
+	if err != nil {
+		return err
+	}
+
+	plat, err := plugin.ResolvePlatform(pv, runtime.GOOS, runtime.GOARCH)
+	if err != nil {
+		return fmt.Errorf("plugin %q v%s has no binary for %s/%s", name, pv.Version, runtime.GOOS, runtime.GOARCH)
+	}
+
+	pluginDir := pluginHandler.EnsurePluginDir()
+
+	installer := plugin.NewInstaller()
+	sp := newPluginSpinner(fmt.Sprintf("installing %s v%s", name, pv.Version))
+	sp.Start()
+	if err := installer.Install(pluginDir, manifest, pv, plat); err != nil {
+		sp.Stop()
+		return err
+	}
+	sp.Stop()
+
+	logger.Successf("installed %s v%s", name, pv.Version)
+	return nil
+}
+
+func pluginUninstallCmdRun(cmd *cobra.Command, args []string) error {
+	name := args[0]
+	pluginDir := pluginHandler.PluginDir()
+
+	if err := plugin.Uninstall(pluginDir, name); err != nil {
+		return err
+	}
+
+	logger.Successf("uninstalled %s", name)
+	return nil
+}
+
+func pluginUpdateCmdRun(cmd *cobra.Command, args []string) error {
+	catalogClient := newCatalogClient()
+
+	plugins := pluginHandler.Discover(builtinCommandNames())
+	if len(plugins) == 0 {
+		cmd.Println("No plugins found")
+		return nil
+	}
+
+	// If a specific plugin is requested, filter to just that one.
+	if len(args) == 1 {
+		name := args[0]
+		var found bool
+		for _, p := range plugins {
+			if p.Name == name {
+				plugins = []plugin.Plugin{p}
+				found = true
+				break
+			}
+		}
+		if !found {
+			return fmt.Errorf("plugin %q is not installed", name)
+		}
+	}
+
+	pluginDir := pluginHandler.EnsurePluginDir()
+	installer := plugin.NewInstaller()
+	for _, p := range plugins {
+		result := plugin.CheckUpdate(pluginDir, p.Name, catalogClient, runtime.GOOS, runtime.GOARCH)
+		if result.Err != nil {
+			logger.Failuref("error checking %s: %v", p.Name, result.Err)
+			continue
+		}
+		if result.Skipped {
+			if result.SkipReason == plugin.SkipReasonManual {
+				logger.Warningf("skipping %s (%s)", p.Name, result.SkipReason)
+			} else {
+				logger.Successf("%s already up to date (v%s)", p.Name, result.FromVersion)
+			}
+			continue
+		}
+
+		sp := newPluginSpinner(fmt.Sprintf("updating %s v%s → v%s", p.Name, result.FromVersion, result.ToVersion))
+		sp.Start()
+		if err := installer.Install(pluginDir, result.Manifest, result.Version, result.Platform); err != nil {
+			sp.Stop()
+			logger.Failuref("error updating %s: %v", p.Name, err)
+			continue
+		}
+		sp.Stop()
+		logger.Successf("updated %s v%s → v%s", p.Name, result.FromVersion, result.ToVersion)
+	}
+
+	return nil
+}
+
+func pluginSearchCmdRun(cmd *cobra.Command, args []string) error {
+	catalogClient := newCatalogClient()
+	catalog, err := catalogClient.FetchCatalog()
+	if err != nil {
+		return err
+	}
+
+	var query string
+	if len(args) == 1 {
+		query = strings.ToLower(args[0])
+	}
+
+	pluginDir := pluginHandler.PluginDir()
+	header := []string{"NAME", "DESCRIPTION", "INSTALLED"}
+	var rows [][]string
+	for _, entry := range catalog.Plugins {
+		if query != "" {
+			if !strings.Contains(strings.ToLower(entry.Name), query) &&
+				!strings.Contains(strings.ToLower(entry.Description), query) {
+				continue
+			}
+		}
+
+		installed := ""
+		if receipt := plugin.ReadReceipt(pluginDir, entry.Name); receipt != nil {
+			installed = receipt.Version
+		}
+
+		rows = append(rows, []string{entry.Name, entry.Description, installed})
+	}
+
+	if len(rows) == 0 {
+		if query != "" {
+			cmd.Printf("No plugins matching %q found in catalog\n", query)
+		} else {
+			cmd.Println("No plugins found in catalog")
+		}
+		return nil
+	}
+
+	return printers.TablePrinter(header).Print(cmd.OutOrStdout(), rows)
+}
+
+// parseNameVersion splits "operator@0.45.0" into ("operator", "0.45.0").
+// If no @ is present, version is empty (latest).
+func parseNameVersion(s string) (string, string) {
+	name, version, found := strings.Cut(s, "@")
+	if found {
+		return name, version
+	}
+	return s, ""
+}
+
+// newCatalogClient creates a CatalogClient that respects FLUXCD_PLUGIN_CATALOG.
+func newCatalogClient() *plugin.CatalogClient {
+	client := plugin.NewCatalogClient()
+	client.GetEnv = pluginHandler.GetEnv
+	return client
+}
+
+func newPluginSpinner(message string) *spinner.Spinner {
+	s := spinner.New(spinner.CharSets[14], 100*time.Millisecond)
+	s.Suffix = " " + message
+	return s
+}

cmd/flux/plugin_test.go

@@ -0,0 +1,265 @@
+/*
+Copyright 2026 The Flux 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 main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/fluxcd/flux2/v2/internal/plugin"
+)
+
+func TestPluginAppearsInHelp(t *testing.T) {
+	origHandler := pluginHandler
+	defer func() { pluginHandler = origHandler }()
+
+	pluginDir := t.TempDir()
+
+	fakeBin := pluginDir + "/flux-testplugin"
+	os.WriteFile(fakeBin, []byte("#!/bin/sh\necho test"), 0o755)
+
+	pluginHandler = &plugin.Handler{
+		ReadDir: os.ReadDir,
+		Stat:    os.Stat,
+		GetEnv: func(key string) string {
+			if key == "FLUXCD_PLUGINS" {
+				return pluginDir
+			}
+			return ""
+		},
+		HomeDir: func() (string, error) { return t.TempDir(), nil },
+	}
+
+	registerPlugins()
+	defer func() {
+		cmds := rootCmd.Commands()
+		for _, cmd := range cmds {
+			if cmd.Name() == "testplugin" {
+				rootCmd.RemoveCommand(cmd)
+				break
+			}
+		}
+		rootCmd.SetHelpTemplate("")
+	}()
+
+	output, err := executeCommand("--help")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !strings.Contains(output, "Plugin Commands:") {
+		t.Error("expected 'Plugin Commands:' in help output")
+	}
+	if !strings.Contains(output, "testplugin") {
+		t.Error("expected 'testplugin' in help output")
+	}
+}
+
+func TestPluginListOutput(t *testing.T) {
+	origHandler := pluginHandler
+	defer func() { pluginHandler = origHandler }()
+
+	pluginDir := t.TempDir()
+
+	fakeBin := pluginDir + "/flux-myplugin"
+	os.WriteFile(fakeBin, []byte("#!/bin/sh\necho test"), 0o755)
+
+	pluginHandler = &plugin.Handler{
+		ReadDir: os.ReadDir,
+		Stat:    os.Stat,
+		GetEnv: func(key string) string {
+			if key == "FLUXCD_PLUGINS" {
+				return pluginDir
+			}
+			return ""
+		},
+		HomeDir: func() (string, error) { return t.TempDir(), nil },
+	}
+
+	output, err := executeCommand("plugin list")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !strings.Contains(output, "myplugin") {
+		t.Errorf("expected 'myplugin' in output, got: %s", output)
+	}
+	if !strings.Contains(output, "manual") {
+		t.Errorf("expected 'manual' in output (no receipt), got: %s", output)
+	}
+}
+
+func TestPluginListWithReceipt(t *testing.T) {
+	origHandler := pluginHandler
+	defer func() { pluginHandler = origHandler }()
+
+	pluginDir := t.TempDir()
+
+	fakeBin := pluginDir + "/flux-myplugin"
+	os.WriteFile(fakeBin, []byte("#!/bin/sh\necho test"), 0o755)
+	receipt := pluginDir + "/flux-myplugin.yaml"
+	os.WriteFile(receipt, []byte("name: myplugin\nversion: \"1.2.3\"\n"), 0o644)
+
+	pluginHandler = &plugin.Handler{
+		ReadDir: os.ReadDir,
+		Stat:    os.Stat,
+		GetEnv: func(key string) string {
+			if key == "FLUXCD_PLUGINS" {
+				return pluginDir
+			}
+			return ""
+		},
+		HomeDir: func() (string, error) { return t.TempDir(), nil },
+	}
+
+	output, err := executeCommand("plugin list")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !strings.Contains(output, "1.2.3") {
+		t.Errorf("expected version '1.2.3' in output, got: %s", output)
+	}
+}
+
+func TestPluginListEmpty(t *testing.T) {
+	origHandler := pluginHandler
+	defer func() { pluginHandler = origHandler }()
+
+	pluginDir := t.TempDir()
+
+	pluginHandler = &plugin.Handler{
+		ReadDir: os.ReadDir,
+		Stat:    os.Stat,
+		GetEnv: func(key string) string {
+			if key == "FLUXCD_PLUGINS" {
+				return pluginDir
+			}
+			return ""
+		},
+		HomeDir: func() (string, error) { return t.TempDir(), nil },
+	}
+
+	output, err := executeCommand("plugin list")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !strings.Contains(output, "No plugins found") {
+		t.Errorf("expected 'No plugins found', got: %s", output)
+	}
+}
+
+func TestNoPluginsNoRegistration(t *testing.T) {
+	origHandler := pluginHandler
+	defer func() { pluginHandler = origHandler }()
+
+	pluginHandler = &plugin.Handler{
+		ReadDir: func(name string) ([]os.DirEntry, error) {
+			return nil, fmt.Errorf("no dir")
+		},
+		Stat: os.Stat,
+		GetEnv: func(key string) string {
+			if key == "FLUXCD_PLUGINS" {
+				return "/nonexistent"
+			}
+			return ""
+		},
+		HomeDir: func() (string, error) { return t.TempDir(), nil },
+	}
+
+	// Verify that registerPlugins with no plugins doesn't add any commands.
+	before := len(rootCmd.Commands())
+	registerPlugins()
+	after := len(rootCmd.Commands())
+	if after != before {
+		t.Errorf("expected no new commands, got %d new", after-before)
+	}
+}
+
+func TestPluginSkipsPersistentPreRun(t *testing.T) {
+	// Plugin commands override root's PersistentPreRunE with a no-op,
+	// so an invalid namespace should not trigger a validation error.
+	_, err := executeCommand("plugin list")
+	if err != nil {
+		t.Fatalf("plugin list should not trigger root's namespace validation: %v", err)
+	}
+}
+
+func TestParseNameVersion(t *testing.T) {
+	tests := []struct {
+		input       string
+		wantName    string
+		wantVersion string
+	}{
+		{"operator", "operator", ""},
+		{"operator@0.45.0", "operator", "0.45.0"},
+		{"my-tool@1.0.0", "my-tool", "1.0.0"},
+		{"plugin@", "plugin", ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			name, version := parseNameVersion(tt.input)
+			if name != tt.wantName {
+				t.Errorf("name: got %q, want %q", name, tt.wantName)
+			}
+			if version != tt.wantVersion {
+				t.Errorf("version: got %q, want %q", version, tt.wantVersion)
+			}
+		})
+	}
+}
+
+func TestPluginDiscoverSkipsBuiltins(t *testing.T) {
+	origHandler := pluginHandler
+	defer func() { pluginHandler = origHandler }()
+
+	pluginDir := t.TempDir()
+
+	for _, name := range []string{"flux-get", "flux-create", "flux-version"} {
+		os.WriteFile(pluginDir+"/"+name, []byte("#!/bin/sh"), 0o755)
+	}
+	os.WriteFile(pluginDir+"/flux-myplugin", []byte("#!/bin/sh"), 0o755)
+
+	pluginHandler = &plugin.Handler{
+		ReadDir: os.ReadDir,
+		Stat:    os.Stat,
+		GetEnv: func(key string) string {
+			if key == "FLUXCD_PLUGINS" {
+				return pluginDir
+			}
+			return ""
+		},
+		HomeDir: func() (string, error) { return t.TempDir(), nil },
+	}
+
+	plugins := pluginHandler.Discover(builtinCommandNames())
+
+	if len(plugins) != 1 {
+		names := make([]string, len(plugins))
+		for i, p := range plugins {
+			names[i] = p.Name
+		}
+		t.Fatalf("expected 1 plugin, got %d: %v", len(plugins), names)
+	}
+	if plugins[0].Name != "myplugin" {
+		t.Errorf("expected 'myplugin', got %q", plugins[0].Name)
+	}
+}

go.mod

@@ -8,6 +8,7 @@ replace gopkg.in/yaml.v3 => gopkg.in/yaml.v3 v3.0.1
 require (
 	github.com/Masterminds/semver/v3 v3.4.0
 	github.com/ProtonMail/go-crypto v1.3.0
+	github.com/briandowns/spinner v1.23.2
 	github.com/cyphar/filepath-securejoin v0.6.1
 	github.com/distribution/distribution/v3 v3.0.0
 	github.com/fluxcd/cli-utils v0.37.2-flux.1
@@ -40,6 +41,7 @@ require (
 	github.com/google/go-cmp v0.7.0
 	github.com/google/go-containerregistry v0.20.7
 	github.com/hashicorp/go-cleanhttp v0.5.2
+	github.com/hashicorp/go-retryablehttp v0.7.8
 	github.com/homeport/dyff v1.10.2
 	github.com/lucasb-eyer/go-colorful v1.2.0
 	github.com/manifoldco/promptui v0.9.0
@@ -49,7 +51,6 @@ require (
 	github.com/onsi/gomega v1.39.1
 	github.com/phayes/freeport v0.0.0-20220201140144-74d24b5ae9f5
 	github.com/spf13/cobra v1.10.2
-	github.com/theckman/yacspin v0.13.12
 	golang.org/x/crypto v0.48.0
 	golang.org/x/term v0.40.0
 	golang.org/x/text v0.34.0
@@ -162,7 +163,6 @@ require (
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.27.7 // indirect
 	github.com/hashicorp/errwrap v1.1.0 // indirect
 	github.com/hashicorp/go-multierror v1.1.1 // indirect
-	github.com/hashicorp/go-retryablehttp v0.7.8 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/hashicorp/golang-lru/arc/v2 v2.0.5 // indirect
 	github.com/hashicorp/golang-lru/v2 v2.0.5 // indirect

go.sum

@@ -91,6 +91,8 @@ github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
 github.com/blang/semver/v4 v4.0.0 h1:1PFHFE6yCCTv8C1TeyNNarDzntLi7wMI5i/pzqYIsAM=
 github.com/blang/semver/v4 v4.0.0/go.mod h1:IbckMUScFkM3pff0VJDNKRiT6TG/YpiHIM2yvyW5YoQ=
+github.com/briandowns/spinner v1.23.2 h1:Zc6ecUnI+YzLmJniCfDNaMbW0Wid1d5+qcTq4L2FW8w=
+github.com/briandowns/spinner v1.23.2/go.mod h1:LaZeM4wm2Ywy6vO571mvhQNRcWfRUnXOs0RcKV0wYKM=
 github.com/bshuster-repo/logrus-logstash-hook v1.0.0 h1:e+C0SB5R1pu//O4MQ3f9cFuPGoOVeF2fE4Og9otCc70=
 github.com/bshuster-repo/logrus-logstash-hook v1.0.0/go.mod h1:zsTqEiSzDgAa/8GZR7E1qaXrhYNDKBYy5/dWPTIflbk=
 github.com/bsm/ginkgo/v2 v2.7.0/go.mod h1:AiKlXPm7ItEHNc/2+OkrNG4E0ITzojb9/xWzvQ9XZ9w=
@@ -535,8 +537,6 @@ github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/texttheater/golang-levenshtein v1.0.1 h1:+cRNoVrfiwufQPhoMzB6N0Yf/Mqajr6t1lOv8GyGE2U=
 github.com/texttheater/golang-levenshtein v1.0.1/go.mod h1:PYAKrbF5sAiq9wd+H82hs7gNaen0CplQ9uvm6+enD/8=
-github.com/theckman/yacspin v0.13.12 h1:CdZ57+n0U6JMuh2xqjnjRq5Haj6v1ner2djtLQRzJr4=
-github.com/theckman/yacspin v0.13.12/go.mod h1:Rd2+oG2LmQi5f3zC3yeZAOl245z8QOvrH4OPOJNZxLg=
 github.com/vbatts/tar-split v0.12.2 h1:w/Y6tjxpeiFMR47yzZPlPj/FcPLpXbTUi/9H7d3CPa4=
 github.com/vbatts/tar-split v0.12.2/go.mod h1:eF6B6i6ftWQcDqEn3/iGFRFRo8cBIMSJVOpnNdfTMFA=
 github.com/virtuald/go-ordered-json v0.0.0-20170621173500-b18e6e673d74 h1:JwtAtbp7r/7QSyGz8mKUbYJBg2+6Cd7OjM8o/GNOcVo=

internal/build/build.go

@@ -30,7 +30,7 @@ import (
 	"sync"
 	"time"
 
-	"github.com/theckman/yacspin"
+	"github.com/briandowns/spinner"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/api/meta"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
@@ -81,7 +81,7 @@ type Builder struct {
 	action        kustomize.Action
 	kustomization *kustomizev1.Kustomization
 	timeout       time.Duration
-	spinner       *yacspin.Spinner
+	spinner       *spinner.Spinner
 	dryRun        bool
 	strictSubst   bool
 	recursive     bool
@@ -111,22 +111,9 @@ func WithTimeout(timeout time.Duration) BuilderOptionFunc {
 
 func WithProgressBar() BuilderOptionFunc {
 	return func(b *Builder) error {
-		// Add a spinner
+		s := spinner.New(spinner.CharSets[14], 100*time.Millisecond)
-		cfg := yacspin.Config{
+		s.Suffix = " Kustomization diffing... " + spinnerDryRunMessage
-			Frequency:       100 * time.Millisecond,
+		b.spinner = s
-			CharSet:         yacspin.CharSets[59],
-			Suffix:          "Kustomization diffing...",
-			SuffixAutoColon: true,
-			Message:         spinnerDryRunMessage,
-			StopCharacter:   "✓",
-			StopColors:      []string{"fgGreen"},
-		}
-		spinner, err := yacspin.New(cfg)
-		if err != nil {
-			return fmt.Errorf("failed to create spinner: %w", err)
-		}
-		b.spinner = spinner
-
 		return nil
 	}
 }
@@ -215,7 +202,7 @@ func withClientConfigFrom(in *Builder) BuilderOptionFunc {
 	}
 }
 
-// withClientConfigFrom copies spinner field
+// withSpinnerFrom copies the spinner field from another Builder.
 func withSpinnerFrom(in *Builder) BuilderOptionFunc {
 	return func(b *Builder) error {
 		b.spinner = in.spinner
@@ -746,12 +733,7 @@ func (b *Builder) StartSpinner() error {
 	if b.spinner == nil {
 		return nil
 	}
-
+	b.spinner.Start()
-	err := b.spinner.Start()
-	if err != nil {
-		return fmt.Errorf("failed to start spinner: %w", err)
-	}
-
 	return nil
 }
 
@@ -759,14 +741,6 @@ func (b *Builder) StopSpinner() error {
 	if b.spinner == nil {
 		return nil
 	}
-
+	b.spinner.Stop()
-	status := b.spinner.Status()
-	if status == yacspin.SpinnerRunning || status == yacspin.SpinnerPaused {
-		err := b.spinner.Stop()
-		if err != nil {
-			return fmt.Errorf("failed to stop spinner: %w", err)
-		}
-	}
-
 	return nil
 }

internal/build/diff.go

@@ -173,14 +173,14 @@ func (b *Builder) diff() (string, bool, error) {
 
 				// finished with Kustomization diff
 				if b.spinner != nil {
-					b.spinner.Message(spinnerDryRunMessage)
+					b.spinner.Suffix = " " + spinnerDryRunMessage
 				}
 			}
 		}
 	}
 
 	if b.spinner != nil {
-		b.spinner.Message("processing inventory")
+		b.spinner.Suffix = " processing inventory"
 	}
 
 	if b.kustomization.Spec.Prune && len(diffErrs) == 0 {
@@ -204,7 +204,7 @@ func (b *Builder) diff() (string, bool, error) {
 
 func (b *Builder) kustomizationDiff(kustomization *kustomizev1.Kustomization) (string, bool, error) {
 	if b.spinner != nil {
-		b.spinner.Message(fmt.Sprintf("%s in %s", spinnerDryRunMessage, kustomization.Name))
+		b.spinner.Suffix = " " + fmt.Sprintf("%s in %s", spinnerDryRunMessage, kustomization.Name)
 	}
 
 	sourceRef := kustomization.Spec.SourceRef.DeepCopy()

internal/plugin/catalog.go

@@ -0,0 +1,213 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+
+	"github.com/hashicorp/go-retryablehttp"
+	"sigs.k8s.io/yaml"
+)
+
+const (
+	defaultCatalogBase = "https://raw.githubusercontent.com/fluxcd/plugins/main/"
+	envCatalogBase     = "FLUXCD_PLUGIN_CATALOG"
+
+	pluginAPIVersion = "cli.fluxcd.io/v1beta1"
+	pluginKind       = "Plugin"
+	catalogKind      = "PluginCatalog"
+)
+
+// PluginManifest represents a single plugin's manifest from the catalog.
+type PluginManifest struct {
+	APIVersion  string          `json:"apiVersion"`
+	Kind        string          `json:"kind"`
+	Name        string          `json:"name"`
+	Description string          `json:"description"`
+	Homepage    string          `json:"homepage,omitempty"`
+	Source      string          `json:"source,omitempty"`
+	Bin         string          `json:"bin"`
+	Versions    []PluginVersion `json:"versions"`
+}
+
+// PluginVersion represents a version entry in a plugin manifest.
+type PluginVersion struct {
+	Version   string           `json:"version"`
+	Platforms []PluginPlatform `json:"platforms"`
+}
+
+// PluginPlatform represents a platform-specific binary entry.
+type PluginPlatform struct {
+	OS       string `json:"os"`
+	Arch     string `json:"arch"`
+	URL      string `json:"url"`
+	Checksum string `json:"checksum"`
+}
+
+// PluginCatalog represents the generated catalog.yaml file.
+type PluginCatalog struct {
+	APIVersion string         `json:"apiVersion"`
+	Kind       string         `json:"kind"`
+	Plugins    []CatalogEntry `json:"plugins"`
+}
+
+// CatalogEntry is a single entry in the plugin catalog.
+type CatalogEntry struct {
+	Name        string `json:"name"`
+	Description string `json:"description"`
+	Homepage    string `json:"homepage,omitempty"`
+	Source      string `json:"source,omitempty"`
+	License     string `json:"license,omitempty"`
+}
+
+// Receipt records what was installed for a plugin.
+type Receipt struct {
+	Name        string         `json:"name"`
+	Version     string         `json:"version"`
+	InstalledAt string         `json:"installedAt"`
+	Platform    PluginPlatform `json:"platform"`
+}
+
+// CatalogClient fetches plugin manifests and catalogs from a remote URL.
+type CatalogClient struct {
+	BaseURL    string
+	HTTPClient *http.Client
+	GetEnv     func(key string) string
+}
+
+// NewCatalogClient returns a CatalogClient with production defaults.
+func NewCatalogClient() *CatalogClient {
+	return &CatalogClient{
+		BaseURL:    defaultCatalogBase,
+		HTTPClient: newHTTPClient(30 * time.Second),
+		GetEnv:     func(key string) string { return "" },
+	}
+}
+
+// baseURL returns the effective catalog base URL.
+func (c *CatalogClient) baseURL() string {
+	if env := c.GetEnv(envCatalogBase); env != "" {
+		return env
+	}
+	return c.BaseURL
+}
+
+// FetchManifest fetches a single plugin manifest from the catalog.
+func (c *CatalogClient) FetchManifest(name string) (*PluginManifest, error) {
+	url := c.baseURL() + "plugins/" + name + ".yaml"
+	body, err := c.fetch(url)
+	if err != nil {
+		return nil, fmt.Errorf("plugin %q not found in catalog", name)
+	}
+
+	var manifest PluginManifest
+	if err := yaml.Unmarshal(body, &manifest); err != nil {
+		return nil, fmt.Errorf("failed to parse plugin manifest for %q: %w", name, err)
+	}
+
+	if manifest.APIVersion != pluginAPIVersion {
+		return nil, fmt.Errorf("plugin %q has unsupported apiVersion %q (expected %q)", name, manifest.APIVersion, pluginAPIVersion)
+	}
+	if manifest.Kind != pluginKind {
+		return nil, fmt.Errorf("plugin %q has unexpected kind %q (expected %q)", name, manifest.Kind, pluginKind)
+	}
+
+	return &manifest, nil
+}
+
+// FetchCatalog fetches the generated catalog.yaml.
+func (c *CatalogClient) FetchCatalog() (*PluginCatalog, error) {
+	url := c.baseURL() + "catalog.yaml"
+	body, err := c.fetch(url)
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch plugin catalog: %w", err)
+	}
+
+	var catalog PluginCatalog
+	if err := yaml.Unmarshal(body, &catalog); err != nil {
+		return nil, fmt.Errorf("failed to parse plugin catalog: %w", err)
+	}
+
+	if catalog.APIVersion != pluginAPIVersion {
+		return nil, fmt.Errorf("plugin catalog has unsupported apiVersion %q (expected %q)", catalog.APIVersion, pluginAPIVersion)
+	}
+	if catalog.Kind != catalogKind {
+		return nil, fmt.Errorf("plugin catalog has unexpected kind %q (expected %q)", catalog.Kind, catalogKind)
+	}
+
+	return &catalog, nil
+}
+
+const maxResponseBytes = 10 << 20 // 10 MiB
+
+func (c *CatalogClient) fetch(url string) ([]byte, error) {
+	resp, err := c.HTTPClient.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("HTTP %d from %s", resp.StatusCode, url)
+	}
+
+	return io.ReadAll(io.LimitReader(resp.Body, maxResponseBytes))
+}
+
+// newHTTPClient returns a retrying HTTP client with the given timeout.
+func newHTTPClient(timeout time.Duration) *http.Client {
+	rc := retryablehttp.NewClient()
+	rc.RetryMax = 3
+	rc.Logger = nil
+	c := rc.StandardClient()
+	c.Timeout = timeout
+	return c
+}
+
+// ResolveVersion finds the requested version in the manifest.
+// If version is empty, returns the first (latest) version.
+func ResolveVersion(manifest *PluginManifest, version string) (*PluginVersion, error) {
+	if len(manifest.Versions) == 0 {
+		return nil, fmt.Errorf("plugin %q has no versions", manifest.Name)
+	}
+
+	if version == "" {
+		return &manifest.Versions[0], nil
+	}
+
+	for i := range manifest.Versions {
+		if manifest.Versions[i].Version == version {
+			return &manifest.Versions[i], nil
+		}
+	}
+
+	return nil, fmt.Errorf("version %q not found for plugin %q", version, manifest.Name)
+}
+
+// ResolvePlatform finds the platform entry matching the given OS and arch.
+func ResolvePlatform(pv *PluginVersion, goos, goarch string) (*PluginPlatform, error) {
+	for i := range pv.Platforms {
+		if pv.Platforms[i].OS == goos && pv.Platforms[i].Arch == goarch {
+			return &pv.Platforms[i], nil
+		}
+	}
+
+	return nil, fmt.Errorf("no binary for %s/%s", goos, goarch)
+}

internal/plugin/catalog_test.go

@@ -0,0 +1,239 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestFetchManifest(t *testing.T) {
+	manifest := `
+apiVersion: cli.fluxcd.io/v1beta1
+kind: Plugin
+name: operator
+description: Flux Operator CLI
+bin: flux-operator
+versions:
+  - version: 0.45.0
+    platforms:
+      - os: linux
+        arch: amd64
+        url: https://example.com/flux-operator_0.45.0_linux_amd64.tar.gz
+        checksum: sha256:abc123
+`
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/plugins/operator.yaml" {
+			w.Write([]byte(manifest))
+			return
+		}
+		http.NotFound(w, r)
+	}))
+	defer server.Close()
+
+	client := &CatalogClient{
+		BaseURL:    server.URL + "/",
+		HTTPClient: server.Client(),
+		GetEnv:     func(key string) string { return "" },
+	}
+
+	m, err := client.FetchManifest("operator")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if m.Name != "operator" {
+		t.Errorf("expected name 'operator', got %q", m.Name)
+	}
+	if m.Bin != "flux-operator" {
+		t.Errorf("expected bin 'flux-operator', got %q", m.Bin)
+	}
+	if len(m.Versions) != 1 {
+		t.Fatalf("expected 1 version, got %d", len(m.Versions))
+	}
+	if m.Versions[0].Version != "0.45.0" {
+		t.Errorf("expected version '0.45.0', got %q", m.Versions[0].Version)
+	}
+}
+
+func TestFetchManifestNotFound(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.NotFound(w, r)
+	}))
+	defer server.Close()
+
+	client := &CatalogClient{
+		BaseURL:    server.URL + "/",
+		HTTPClient: server.Client(),
+		GetEnv:     func(key string) string { return "" },
+	}
+
+	_, err := client.FetchManifest("nonexistent")
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+}
+
+func TestFetchCatalog(t *testing.T) {
+	catalog := `
+apiVersion: cli.fluxcd.io/v1beta1
+kind: PluginCatalog
+plugins:
+  - name: operator
+    description: Flux Operator CLI
+    homepage: https://fluxoperator.dev/
+    source: https://github.com/controlplaneio-fluxcd/flux-operator
+    license: AGPL-3.0
+  - name: schema
+    description: CRD schemas
+    homepage: https://example.com/
+    source: https://github.com/example/flux-schema
+    license: Apache-2.0
+`
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/catalog.yaml" {
+			w.Write([]byte(catalog))
+			return
+		}
+		http.NotFound(w, r)
+	}))
+	defer server.Close()
+
+	client := &CatalogClient{
+		BaseURL:    server.URL + "/",
+		HTTPClient: server.Client(),
+		GetEnv:     func(key string) string { return "" },
+	}
+
+	c, err := client.FetchCatalog()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(c.Plugins) != 2 {
+		t.Fatalf("expected 2 plugins, got %d", len(c.Plugins))
+	}
+	if c.Plugins[0].Name != "operator" {
+		t.Errorf("expected name 'operator', got %q", c.Plugins[0].Name)
+	}
+	if c.Plugins[1].Name != "schema" {
+		t.Errorf("expected name 'schema', got %q", c.Plugins[1].Name)
+	}
+}
+
+func TestCatalogEnvOverride(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/custom/catalog.yaml" {
+			w.Write([]byte(`apiVersion: cli.fluxcd.io/v1beta1
+kind: PluginCatalog
+plugins: []
+`))
+			return
+		}
+		http.NotFound(w, r)
+	}))
+	defer server.Close()
+
+	client := &CatalogClient{
+		BaseURL:    "https://should-not-be-used/",
+		HTTPClient: server.Client(),
+		GetEnv: func(key string) string {
+			if key == envCatalogBase {
+				return server.URL + "/custom/"
+			}
+			return ""
+		},
+	}
+
+	c, err := client.FetchCatalog()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(c.Plugins) != 0 {
+		t.Fatalf("expected 0 plugins, got %d", len(c.Plugins))
+	}
+}
+
+func TestResolveVersion(t *testing.T) {
+	manifest := &PluginManifest{
+		Name: "operator",
+		Versions: []PluginVersion{
+			{Version: "0.45.0"},
+			{Version: "0.44.0"},
+		},
+	}
+
+	t.Run("latest", func(t *testing.T) {
+		v, err := ResolveVersion(manifest, "")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if v.Version != "0.45.0" {
+			t.Errorf("expected '0.45.0', got %q", v.Version)
+		}
+	})
+
+	t.Run("specific", func(t *testing.T) {
+		v, err := ResolveVersion(manifest, "0.44.0")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if v.Version != "0.44.0" {
+			t.Errorf("expected '0.44.0', got %q", v.Version)
+		}
+	})
+
+	t.Run("not found", func(t *testing.T) {
+		_, err := ResolveVersion(manifest, "0.99.0")
+		if err == nil {
+			t.Fatal("expected error, got nil")
+		}
+	})
+
+	t.Run("no versions", func(t *testing.T) {
+		_, err := ResolveVersion(&PluginManifest{Name: "empty"}, "")
+		if err == nil {
+			t.Fatal("expected error, got nil")
+		}
+	})
+}
+
+func TestResolvePlatform(t *testing.T) {
+	pv := &PluginVersion{
+		Version: "0.45.0",
+		Platforms: []PluginPlatform{
+			{OS: "darwin", Arch: "arm64", URL: "https://example.com/darwin_arm64.tar.gz"},
+			{OS: "linux", Arch: "amd64", URL: "https://example.com/linux_amd64.tar.gz"},
+		},
+	}
+
+	t.Run("found", func(t *testing.T) {
+		p, err := ResolvePlatform(pv, "darwin", "arm64")
+		if err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+		if p.OS != "darwin" || p.Arch != "arm64" {
+			t.Errorf("unexpected platform: %s/%s", p.OS, p.Arch)
+		}
+	})
+
+	t.Run("not found", func(t *testing.T) {
+		_, err := ResolvePlatform(pv, "windows", "amd64")
+		if err == nil {
+			t.Fatal("expected error, got nil")
+		}
+	})
+}

internal/plugin/completion.go

@@ -0,0 +1,75 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"os/exec"
+	"strconv"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+// commandFunc is an alias to allow DI in tests.
+var commandFunc = exec.Command
+
+// CompleteFunc returns a ValidArgsFunction that delegates completion
+// to the plugin binary via Cobra's __complete protocol.
+func CompleteFunc(pluginPath string) func(*cobra.Command, []string, string) ([]string, cobra.ShellCompDirective) {
+	return func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		completeArgs := append([]string{"__complete"}, args...)
+		completeArgs = append(completeArgs, toComplete)
+
+		out, err := commandFunc(pluginPath, completeArgs...).Output()
+		if err != nil {
+			return nil, cobra.ShellCompDirectiveError
+		}
+
+		return parseCompletionOutput(string(out))
+	}
+}
+
+// parseCompletionOutput parses Cobra's __complete output format.
+// Each line is a completion, last line is :<directive_int>.
+func parseCompletionOutput(out string) ([]string, cobra.ShellCompDirective) {
+	out = strings.TrimRight(out, "\n")
+	if out == "" {
+		return nil, cobra.ShellCompDirectiveError
+	}
+	lines := strings.Split(out, "\n")
+
+	// Last line is the directive in format ":N"
+	lastLine := lines[len(lines)-1]
+	completions := lines[:len(lines)-1]
+
+	directive := cobra.ShellCompDirectiveDefault
+	if strings.HasPrefix(lastLine, ":") {
+		if val, err := strconv.Atoi(lastLine[1:]); err == nil {
+			directive = cobra.ShellCompDirective(val)
+		}
+	}
+
+	var results []string
+	for _, c := range completions {
+		if c == "" {
+			continue
+		}
+		results = append(results, c)
+	}
+
+	return results, directive
+}

internal/plugin/completion_test.go

@@ -0,0 +1,80 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"testing"
+
+	"github.com/spf13/cobra"
+)
+
+func TestParseCompletionOutput(t *testing.T) {
+	tests := []struct {
+		name                string
+		input               string
+		expectedCompletions []string
+		expectedDirective   cobra.ShellCompDirective
+	}{
+		{
+			name:                "standard output",
+			input:               "instance\nrset\nrsip\nall\n:4\n",
+			expectedCompletions: []string{"instance", "rset", "rsip", "all"},
+			expectedDirective:   cobra.ShellCompDirective(4),
+		},
+		{
+			name:                "default directive",
+			input:               "foo\nbar\n:0\n",
+			expectedCompletions: []string{"foo", "bar"},
+			expectedDirective:   cobra.ShellCompDirectiveDefault,
+		},
+		{
+			name:                "with descriptions",
+			input:               "get\tGet resources\nbuild\tBuild resources\n:4\n",
+			expectedCompletions: []string{"get\tGet resources", "build\tBuild resources"},
+			expectedDirective:   cobra.ShellCompDirective(4),
+		},
+		{
+			name:                "empty completions",
+			input:               ":4\n",
+			expectedCompletions: nil,
+			expectedDirective:   cobra.ShellCompDirective(4),
+		},
+		{
+			name:                "empty input",
+			input:               "",
+			expectedCompletions: nil,
+			expectedDirective:   cobra.ShellCompDirectiveError,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			completions, directive := parseCompletionOutput(tt.input)
+			if directive != tt.expectedDirective {
+				t.Errorf("directive: got %d, want %d", directive, tt.expectedDirective)
+			}
+			if len(completions) != len(tt.expectedCompletions) {
+				t.Fatalf("completions count: got %d, want %d", len(completions), len(tt.expectedCompletions))
+			}
+			for i, c := range completions {
+				if c != tt.expectedCompletions[i] {
+					t.Errorf("completion[%d]: got %q, want %q", i, c, tt.expectedCompletions[i])
+				}
+			}
+		})
+	}
+}

internal/plugin/discovery.go

@@ -0,0 +1,195 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+const (
+	pluginPrefix   = "flux-"
+	defaultDirName = "plugins"
+	defaultBaseDir = ".fluxcd"
+	envPluginDir   = "FLUXCD_PLUGINS"
+)
+
+// reservedNames are command names that cannot be used as plugin names.
+var reservedNames = map[string]bool{
+	"plugin": true,
+	"help":   true,
+}
+
+// Plugin represents a discovered plugin binary.
+type Plugin struct {
+	Name string // e.g., "operator" (derived from "flux-operator")
+	Path string // absolute path to binary
+}
+
+// Handler discovers and executes plugins. Uses dependency injection
+// for testability.
+type Handler struct {
+	ReadDir func(name string) ([]os.DirEntry, error)
+	Stat    func(name string) (os.FileInfo, error)
+	GetEnv  func(key string) string
+	HomeDir func() (string, error)
+}
+
+// NewHandler returns a Handler with production defaults.
+func NewHandler() *Handler {
+	return &Handler{
+		ReadDir: os.ReadDir,
+		Stat:    os.Stat,
+		GetEnv:  os.Getenv,
+		HomeDir: os.UserHomeDir,
+	}
+}
+
+// Discover scans the plugin directory for executables matching flux-*.
+// It skips builtins, reserved names, directories, non-executable files,
+// and broken symlinks.
+func (h *Handler) Discover(builtinNames []string) []Plugin {
+	dir := h.PluginDir()
+	if dir == "" {
+		return nil
+	}
+
+	entries, err := h.ReadDir(dir)
+	if err != nil {
+		return nil
+	}
+
+	builtins := make(map[string]bool, len(builtinNames))
+	for _, name := range builtinNames {
+		builtins[name] = true
+	}
+
+	var plugins []Plugin
+	for _, entry := range entries {
+		name := entry.Name()
+		if !strings.HasPrefix(name, pluginPrefix) {
+			continue
+		}
+		if entry.IsDir() {
+			continue
+		}
+
+		pluginName := pluginNameFromBinary(name)
+		if pluginName == "" {
+			continue
+		}
+		if reservedNames[pluginName] || builtins[pluginName] {
+			continue
+		}
+
+		fullPath := filepath.Join(dir, name)
+
+		// Use Stat to follow symlinks and check the target.
+		info, err := h.Stat(fullPath)
+		if err != nil {
+			// Broken symlink, permission denied, etc.
+			continue
+		}
+		if !info.Mode().IsRegular() {
+			continue
+		}
+		if !isExecutable(info) {
+			continue
+		}
+
+		plugins = append(plugins, Plugin{
+			Name: pluginName,
+			Path: fullPath,
+		})
+	}
+
+	return plugins
+}
+
+// PluginDir returns the plugin directory path. If FLUXCD_PLUGINS is set,
+// returns that path. Otherwise returns ~/.fluxcd/plugins/.
+// Does not create the directory — callers that write (install, update)
+// should call EnsurePluginDir first.
+func (h *Handler) PluginDir() string {
+	if dir := h.GetEnv(envPluginDir); dir != "" {
+		return dir
+	}
+
+	home, err := h.HomeDir()
+	if err != nil {
+		return ""
+	}
+
+	return filepath.Join(home, defaultBaseDir, defaultDirName)
+}
+
+// EnsurePluginDir creates the plugin directory if it doesn't exist
+// and returns the path. Best-effort — ignores mkdir errors for
+// read-only filesystems. User-managed directories (via $FLUXCD_PLUGINS)
+// are not auto-created.
+func (h *Handler) EnsurePluginDir() string {
+	if envDir := h.GetEnv(envPluginDir); envDir != "" {
+		return envDir
+	}
+
+	home, err := h.HomeDir()
+	if err != nil {
+		return ""
+	}
+
+	dir := filepath.Join(home, defaultBaseDir, defaultDirName)
+	_ = os.MkdirAll(dir, 0o755)
+	return dir
+}
+
+// pluginNameFromBinary extracts the plugin name from a binary filename.
+// "flux-operator" → "operator", "flux-my-tool" → "my-tool".
+// Returns empty string for invalid names.
+func pluginNameFromBinary(filename string) string {
+	if !strings.HasPrefix(filename, pluginPrefix) {
+		return ""
+	}
+
+	name := strings.TrimPrefix(filename, pluginPrefix)
+
+	// On Windows, strip known extensions.
+	if runtime.GOOS == "windows" {
+		for _, ext := range []string{".exe", ".cmd", ".bat"} {
+			if strings.HasSuffix(strings.ToLower(name), ext) {
+				name = name[:len(name)-len(ext)]
+				break
+			}
+		}
+	}
+
+	if name == "" {
+		return ""
+	}
+
+	return name
+}
+
+// isExecutable checks if a file has the executable bit set.
+// On Windows, this always returns true (executability is determined by extension).
+func isExecutable(info os.FileInfo) bool {
+	if runtime.GOOS == "windows" {
+		return true
+	}
+	return info.Mode().Perm()&0o111 != 0
+}

internal/plugin/discovery_test.go

@@ -0,0 +1,302 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"testing"
+	"time"
+)
+
+// mockDirEntry implements os.DirEntry for testing.
+type mockDirEntry struct {
+	name  string
+	isDir bool
+	mode  fs.FileMode
+}
+
+func (m *mockDirEntry) Name() string               { return m.name }
+func (m *mockDirEntry) IsDir() bool                { return m.isDir }
+func (m *mockDirEntry) Type() fs.FileMode          { return m.mode }
+func (m *mockDirEntry) Info() (fs.FileInfo, error) { return nil, nil }
+
+// mockFileInfo implements os.FileInfo for testing.
+type mockFileInfo struct {
+	name    string
+	mode    fs.FileMode
+	isDir   bool
+	regular bool
+}
+
+func (m *mockFileInfo) Name() string       { return m.name }
+func (m *mockFileInfo) Size() int64        { return 0 }
+func (m *mockFileInfo) Mode() fs.FileMode  { return m.mode }
+func (m *mockFileInfo) ModTime() time.Time { return time.Time{} }
+func (m *mockFileInfo) IsDir() bool        { return m.isDir }
+func (m *mockFileInfo) Sys() any           { return nil }
+
+func newTestHandler(entries []os.DirEntry, statResults map[string]*mockFileInfo, envVars map[string]string) *Handler {
+	return &Handler{
+		ReadDir: func(name string) ([]os.DirEntry, error) {
+			if entries == nil {
+				return nil, fmt.Errorf("directory not found")
+			}
+			return entries, nil
+		},
+		Stat: func(name string) (os.FileInfo, error) {
+			if info, ok := statResults[name]; ok {
+				return info, nil
+			}
+			return nil, fmt.Errorf("file not found: %s", name)
+		},
+		GetEnv: func(key string) string {
+			return envVars[key]
+		},
+		HomeDir: func() (string, error) {
+			return "/home/testuser", nil
+		},
+	}
+}
+
+func TestDiscover(t *testing.T) {
+	entries := []os.DirEntry{
+		&mockDirEntry{name: "flux-operator", mode: 0},
+		&mockDirEntry{name: "flux-local", mode: 0},
+	}
+	stats := map[string]*mockFileInfo{
+		"/test/plugins/flux-operator": {name: "flux-operator", mode: 0o755},
+		"/test/plugins/flux-local":    {name: "flux-local", mode: 0o755},
+	}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/test/plugins"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 2 {
+		t.Fatalf("expected 2 plugins, got %d", len(plugins))
+	}
+	if plugins[0].Name != "operator" {
+		t.Errorf("expected name 'operator', got %q", plugins[0].Name)
+	}
+	if plugins[1].Name != "local" {
+		t.Errorf("expected name 'local', got %q", plugins[1].Name)
+	}
+}
+
+func TestDiscoverSkipsBuiltins(t *testing.T) {
+	entries := []os.DirEntry{
+		&mockDirEntry{name: "flux-version", mode: 0},
+		&mockDirEntry{name: "flux-get", mode: 0},
+		&mockDirEntry{name: "flux-operator", mode: 0},
+	}
+	stats := map[string]*mockFileInfo{
+		"/test/plugins/flux-version":  {name: "flux-version", mode: 0o755},
+		"/test/plugins/flux-get":      {name: "flux-get", mode: 0o755},
+		"/test/plugins/flux-operator": {name: "flux-operator", mode: 0o755},
+	}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/test/plugins"})
+
+	plugins := h.Discover([]string{"version", "get"})
+	if len(plugins) != 1 {
+		t.Fatalf("expected 1 plugin, got %d", len(plugins))
+	}
+	if plugins[0].Name != "operator" {
+		t.Errorf("expected name 'operator', got %q", plugins[0].Name)
+	}
+}
+
+func TestDiscoverSkipsReserved(t *testing.T) {
+	entries := []os.DirEntry{
+		&mockDirEntry{name: "flux-plugin", mode: 0},
+		&mockDirEntry{name: "flux-help", mode: 0},
+		&mockDirEntry{name: "flux-operator", mode: 0},
+	}
+	stats := map[string]*mockFileInfo{
+		"/test/plugins/flux-plugin":   {name: "flux-plugin", mode: 0o755},
+		"/test/plugins/flux-help":     {name: "flux-help", mode: 0o755},
+		"/test/plugins/flux-operator": {name: "flux-operator", mode: 0o755},
+	}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/test/plugins"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 1 {
+		t.Fatalf("expected 1 plugin, got %d", len(plugins))
+	}
+	if plugins[0].Name != "operator" {
+		t.Errorf("expected name 'operator', got %q", plugins[0].Name)
+	}
+}
+
+func TestDiscoverSkipsNonExecutable(t *testing.T) {
+	entries := []os.DirEntry{
+		&mockDirEntry{name: "flux-noperm", mode: 0},
+	}
+	stats := map[string]*mockFileInfo{
+		"/test/plugins/flux-noperm": {name: "flux-noperm", mode: 0o644},
+	}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/test/plugins"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 0 {
+		t.Fatalf("expected 0 plugins, got %d", len(plugins))
+	}
+}
+
+func TestDiscoverSkipsDirectories(t *testing.T) {
+	entries := []os.DirEntry{
+		&mockDirEntry{name: "flux-somedir", isDir: true, mode: fs.ModeDir},
+	}
+	stats := map[string]*mockFileInfo{}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/test/plugins"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 0 {
+		t.Fatalf("expected 0 plugins, got %d", len(plugins))
+	}
+}
+
+func TestDiscoverFollowsSymlinks(t *testing.T) {
+	entries := []os.DirEntry{
+		// Symlink entry — Type() returns symlink, but Stat resolves to regular executable.
+		&mockDirEntry{name: "flux-linked", mode: fs.ModeSymlink},
+	}
+	stats := map[string]*mockFileInfo{
+		"/test/plugins/flux-linked": {name: "flux-linked", mode: 0o755},
+	}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/test/plugins"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 1 {
+		t.Fatalf("expected 1 plugin, got %d", len(plugins))
+	}
+	if plugins[0].Name != "linked" {
+		t.Errorf("expected name 'linked', got %q", plugins[0].Name)
+	}
+}
+
+func TestDiscoverDirNotExist(t *testing.T) {
+	h := newTestHandler(nil, nil, map[string]string{envPluginDir: "/nonexistent"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 0 {
+		t.Fatalf("expected 0 plugins, got %d", len(plugins))
+	}
+}
+
+func TestDiscoverCustomDir(t *testing.T) {
+	entries := []os.DirEntry{
+		&mockDirEntry{name: "flux-custom", mode: 0},
+	}
+	stats := map[string]*mockFileInfo{
+		"/custom/path/flux-custom": {name: "flux-custom", mode: 0o755},
+	}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/custom/path"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 1 {
+		t.Fatalf("expected 1 plugin, got %d", len(plugins))
+	}
+	if plugins[0].Path != "/custom/path/flux-custom" {
+		t.Errorf("expected path '/custom/path/flux-custom', got %q", plugins[0].Path)
+	}
+}
+
+func TestDiscoverSkipsNonFluxPrefix(t *testing.T) {
+	entries := []os.DirEntry{
+		&mockDirEntry{name: "kubectl-foo", mode: 0},
+		&mockDirEntry{name: "random-binary", mode: 0},
+		&mockDirEntry{name: "flux-operator", mode: 0},
+	}
+	stats := map[string]*mockFileInfo{
+		"/test/plugins/flux-operator": {name: "flux-operator", mode: 0o755},
+	}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/test/plugins"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 1 {
+		t.Fatalf("expected 1 plugin, got %d", len(plugins))
+	}
+}
+
+func TestDiscoverBrokenSymlink(t *testing.T) {
+	entries := []os.DirEntry{
+		&mockDirEntry{name: "flux-broken", mode: fs.ModeSymlink},
+	}
+	// No stat entry for flux-broken — simulates a broken symlink.
+	stats := map[string]*mockFileInfo{}
+	h := newTestHandler(entries, stats, map[string]string{envPluginDir: "/test/plugins"})
+
+	plugins := h.Discover(nil)
+	if len(plugins) != 0 {
+		t.Fatalf("expected 0 plugins, got %d", len(plugins))
+	}
+}
+
+func TestPluginNameFromBinary(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"flux-operator", "operator"},
+		{"flux-my-tool", "my-tool"},
+		{"flux-", ""},
+		{"notflux-thing", ""},
+		{"flux-a", "a"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			got := pluginNameFromBinary(tt.input)
+			if got != tt.expected {
+				t.Errorf("pluginNameFromBinary(%q) = %q, want %q", tt.input, got, tt.expected)
+			}
+		})
+	}
+}
+
+func TestPluginDir(t *testing.T) {
+	t.Run("uses env var", func(t *testing.T) {
+		h := &Handler{
+			GetEnv: func(key string) string {
+				if key == envPluginDir {
+					return "/custom/plugins"
+				}
+				return ""
+			},
+			HomeDir: func() (string, error) {
+				return "/home/user", nil
+			},
+		}
+		dir := h.PluginDir()
+		if dir != "/custom/plugins" {
+			t.Errorf("expected '/custom/plugins', got %q", dir)
+		}
+	})
+
+	t.Run("uses default", func(t *testing.T) {
+		h := &Handler{
+			GetEnv: func(key string) string { return "" },
+			HomeDir: func() (string, error) {
+				return "/home/user", nil
+			},
+		}
+		dir := h.PluginDir()
+		if dir != "/home/user/.fluxcd/plugins" {
+			t.Errorf("expected '/home/user/.fluxcd/plugins', got %q", dir)
+		}
+	})
+}

internal/plugin/exec_unix.go

@@ -0,0 +1,30 @@
+//go:build !windows
+
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"os"
+	"syscall"
+)
+
+// Exec replaces the current process with the plugin binary.
+// This is what kubectl does — no signal forwarding or exit code propagation needed.
+func Exec(path string, args []string) error {
+	return syscall.Exec(path, append([]string{path}, args...), os.Environ())
+}

internal/plugin/exec_windows.go

@@ -0,0 +1,42 @@
+//go:build windows
+
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"os"
+	"os/exec"
+)
+
+// Exec runs the plugin as a child process with full I/O passthrough.
+// Matches kubectl's Windows fallback pattern.
+func Exec(path string, args []string) error {
+	cmd := exec.Command(path, args...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	cmd.Env = os.Environ()
+	err := cmd.Run()
+	if err == nil {
+		os.Exit(0)
+	}
+	if exitErr, ok := err.(*exec.ExitError); ok {
+		os.Exit(exitErr.ExitCode())
+	}
+	return err
+}

internal/plugin/install.go

@@ -0,0 +1,235 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"archive/tar"
+	"archive/zip"
+	"compress/gzip"
+	"crypto/sha256"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"time"
+
+	"sigs.k8s.io/yaml"
+)
+
+// Installer handles downloading, verifying, and installing plugins.
+type Installer struct {
+	HTTPClient *http.Client
+}
+
+// NewInstaller returns an Installer with production defaults.
+func NewInstaller() *Installer {
+	return &Installer{
+		HTTPClient: newHTTPClient(5 * time.Minute),
+	}
+}
+
+// Install downloads, verifies, extracts, and installs a plugin binary
+// to the given plugin directory.
+func (inst *Installer) Install(pluginDir string, manifest *PluginManifest, pv *PluginVersion, plat *PluginPlatform) error {
+	tmpFile, err := os.CreateTemp("", "flux-plugin-*")
+	if err != nil {
+		return fmt.Errorf("failed to create temp file: %w", err)
+	}
+	defer os.Remove(tmpFile.Name())
+	defer tmpFile.Close()
+
+	resp, err := inst.HTTPClient.Get(plat.URL)
+	if err != nil {
+		return fmt.Errorf("failed to download plugin: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("failed to download plugin: HTTP %d", resp.StatusCode)
+	}
+
+	hasher := sha256.New()
+	writer := io.MultiWriter(tmpFile, hasher)
+	if _, err := io.Copy(writer, resp.Body); err != nil {
+		return fmt.Errorf("failed to download plugin: %w", err)
+	}
+	tmpFile.Close()
+
+	actualChecksum := fmt.Sprintf("sha256:%x", hasher.Sum(nil))
+	if actualChecksum != plat.Checksum {
+		return fmt.Errorf("checksum verification failed (expected: %s, got: %s)", plat.Checksum, actualChecksum)
+	}
+
+	binName := manifest.Bin
+	if runtime.GOOS == "windows" {
+		binName += ".exe"
+	}
+
+	destName := pluginPrefix + manifest.Name
+	if runtime.GOOS == "windows" {
+		destName += ".exe"
+	}
+	destPath := filepath.Join(pluginDir, destName)
+
+	if strings.HasSuffix(plat.URL, ".zip") {
+		err = extractFromZip(tmpFile.Name(), binName, destPath)
+	} else {
+		err = extractFromTarGz(tmpFile.Name(), binName, destPath)
+	}
+	if err != nil {
+		return err
+	}
+
+	receipt := Receipt{
+		Name:        manifest.Name,
+		Version:     pv.Version,
+		InstalledAt: time.Now().UTC().Format(time.RFC3339),
+		Platform:    *plat,
+	}
+	return writeReceipt(pluginDir, manifest.Name, &receipt)
+}
+
+// Uninstall removes a plugin binary (or symlink) and its receipt from the
+// plugin directory. Returns an error if the plugin is not installed.
+func Uninstall(pluginDir, name string) error {
+	binName := pluginPrefix + name
+	if runtime.GOOS == "windows" {
+		binName += ".exe"
+	}
+
+	binPath := filepath.Join(pluginDir, binName)
+
+	// Use Lstat so we detect symlinks without following them.
+	if _, err := os.Lstat(binPath); os.IsNotExist(err) {
+		return fmt.Errorf("plugin %q is not installed", name)
+	}
+
+	if err := os.Remove(binPath); err != nil {
+		return fmt.Errorf("failed to remove plugin binary: %w", err)
+	}
+
+	// Receipt is optional (manually installed plugins don't have one).
+	if err := os.Remove(receiptPath(pluginDir, name)); err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("failed to remove plugin receipt: %w", err)
+	}
+
+	return nil
+}
+
+// ReadReceipt reads the install receipt for a plugin.
+// Returns nil if no receipt exists.
+func ReadReceipt(pluginDir, name string) *Receipt {
+	data, err := os.ReadFile(receiptPath(pluginDir, name))
+	if err != nil {
+		return nil
+	}
+
+	var receipt Receipt
+	if err := yaml.Unmarshal(data, &receipt); err != nil {
+		return nil
+	}
+
+	return &receipt
+}
+
+func receiptPath(pluginDir, name string) string {
+	return filepath.Join(pluginDir, pluginPrefix+name+".yaml")
+}
+
+func writeReceipt(pluginDir, name string, receipt *Receipt) error {
+	data, err := yaml.Marshal(receipt)
+	if err != nil {
+		return fmt.Errorf("failed to marshal receipt: %w", err)
+	}
+
+	return os.WriteFile(receiptPath(pluginDir, name), data, 0o644)
+}
+
+// extractFromTarGz extracts a named file from a tar.gz archive
+// and streams it directly to destPath.
+func extractFromTarGz(archivePath, targetName, destPath string) error {
+	f, err := os.Open(archivePath)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	gr, err := gzip.NewReader(f)
+	if err != nil {
+		return fmt.Errorf("failed to read gzip: %w", err)
+	}
+	defer gr.Close()
+
+	tr := tar.NewReader(gr)
+	for {
+		header, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return fmt.Errorf("failed to read tar: %w", err)
+		}
+
+		if filepath.IsAbs(header.Name) || strings.Contains(header.Name, "..") {
+			continue
+		}
+		if filepath.Base(header.Name) == targetName && header.Typeflag == tar.TypeReg {
+			return writeStreamToFile(tr, destPath)
+		}
+	}
+
+	return fmt.Errorf("binary %q not found in archive", targetName)
+}
+
+// extractFromZip extracts a named file from a zip archive
+// and streams it directly to destPath.
+func extractFromZip(archivePath, targetName, destPath string) error {
+	r, err := zip.OpenReader(archivePath)
+	if err != nil {
+		return fmt.Errorf("failed to open zip: %w", err)
+	}
+	defer r.Close()
+
+	for _, f := range r.File {
+		if filepath.Base(f.Name) == targetName && !f.FileInfo().IsDir() {
+			rc, err := f.Open()
+			if err != nil {
+				return fmt.Errorf("failed to open %q in zip: %w", targetName, err)
+			}
+			defer rc.Close()
+			return writeStreamToFile(rc, destPath)
+		}
+	}
+
+	return fmt.Errorf("binary %q not found in archive", targetName)
+}
+
+func writeStreamToFile(r io.Reader, destPath string) error {
+	out, err := os.OpenFile(destPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o755)
+	if err != nil {
+		return fmt.Errorf("failed to create %s: %w", destPath, err)
+	}
+
+	if _, err := io.Copy(out, r); err != nil {
+		out.Close()
+		return fmt.Errorf("failed to write plugin binary: %w", err)
+	}
+	return out.Close()
+}

internal/plugin/install_test.go

@@ -0,0 +1,331 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"archive/tar"
+	"bytes"
+	"compress/gzip"
+	"crypto/sha256"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+// createTestTarGz creates a tar.gz archive containing a single file.
+func createTestTarGz(name string, content []byte) ([]byte, error) {
+	var buf bytes.Buffer
+
+	gw := gzip.NewWriter(&buf)
+	tw := tar.NewWriter(gw)
+
+	hdr := &tar.Header{
+		Name: name,
+		Mode: 0o755,
+		Size: int64(len(content)),
+	}
+	if err := tw.WriteHeader(hdr); err != nil {
+		return nil, err
+	}
+	if _, err := tw.Write(content); err != nil {
+		return nil, err
+	}
+
+	tw.Close()
+	gw.Close()
+	return buf.Bytes(), nil
+}
+
+func TestInstall(t *testing.T) {
+	binaryContent := []byte("#!/bin/sh\necho hello")
+	archive, err := createTestTarGz("flux-operator", binaryContent)
+	if err != nil {
+		t.Fatalf("failed to create test archive: %v", err)
+	}
+
+	checksum := fmt.Sprintf("sha256:%x", sha256.Sum256(archive))
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write(archive)
+	}))
+	defer server.Close()
+
+	pluginDir := t.TempDir()
+
+	manifest := &PluginManifest{
+		Name: "operator",
+		Bin:  "flux-operator",
+	}
+	pv := &PluginVersion{Version: "0.45.0"}
+	plat := &PluginPlatform{
+		OS:       "linux",
+		Arch:     "amd64",
+		URL:      server.URL + "/flux-operator_0.45.0_linux_amd64.tar.gz",
+		Checksum: checksum,
+	}
+
+	installer := &Installer{HTTPClient: server.Client()}
+	if err := installer.Install(pluginDir, manifest, pv, plat); err != nil {
+		t.Fatalf("install failed: %v", err)
+	}
+
+	// Verify binary was written.
+	binPath := filepath.Join(pluginDir, "flux-operator")
+	data, err := os.ReadFile(binPath)
+	if err != nil {
+		t.Fatalf("binary not found: %v", err)
+	}
+	if string(data) != string(binaryContent) {
+		t.Errorf("binary content mismatch")
+	}
+
+	// Verify receipt was written.
+	receipt := ReadReceipt(pluginDir, "operator")
+	if receipt == nil {
+		t.Fatal("receipt not found")
+	}
+	if receipt.Version != "0.45.0" {
+		t.Errorf("expected version '0.45.0', got %q", receipt.Version)
+	}
+	if receipt.Name != "operator" {
+		t.Errorf("expected name 'operator', got %q", receipt.Name)
+	}
+}
+
+func TestInstallChecksumMismatch(t *testing.T) {
+	binaryContent := []byte("#!/bin/sh\necho hello")
+	archive, err := createTestTarGz("flux-operator", binaryContent)
+	if err != nil {
+		t.Fatalf("failed to create test archive: %v", err)
+	}
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write(archive)
+	}))
+	defer server.Close()
+
+	pluginDir := t.TempDir()
+
+	manifest := &PluginManifest{Name: "operator", Bin: "flux-operator"}
+	pv := &PluginVersion{Version: "0.45.0"}
+	plat := &PluginPlatform{
+		OS:       "linux",
+		Arch:     "amd64",
+		URL:      server.URL + "/archive.tar.gz",
+		Checksum: "sha256:0000000000000000000000000000000000000000000000000000000000000000",
+	}
+
+	installer := &Installer{HTTPClient: server.Client()}
+	err = installer.Install(pluginDir, manifest, pv, plat)
+	if err == nil {
+		t.Fatal("expected checksum error, got nil")
+	}
+	if !bytes.Contains([]byte(err.Error()), []byte("checksum verification failed")) {
+		t.Errorf("expected checksum error, got: %v", err)
+	}
+}
+
+func TestInstallBinaryNotInArchive(t *testing.T) {
+	// Archive contains "wrong-name" instead of "flux-operator".
+	archive, err := createTestTarGz("wrong-name", []byte("content"))
+	if err != nil {
+		t.Fatalf("failed to create test archive: %v", err)
+	}
+
+	checksum := fmt.Sprintf("sha256:%x", sha256.Sum256(archive))
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write(archive)
+	}))
+	defer server.Close()
+
+	pluginDir := t.TempDir()
+
+	manifest := &PluginManifest{Name: "operator", Bin: "flux-operator"}
+	pv := &PluginVersion{Version: "0.45.0"}
+	plat := &PluginPlatform{
+		OS:       "linux",
+		Arch:     "amd64",
+		URL:      server.URL + "/archive.tar.gz",
+		Checksum: checksum,
+	}
+
+	installer := &Installer{HTTPClient: server.Client()}
+	err = installer.Install(pluginDir, manifest, pv, plat)
+	if err == nil {
+		t.Fatal("expected error for missing binary, got nil")
+	}
+	if !bytes.Contains([]byte(err.Error()), []byte("not found in archive")) {
+		t.Errorf("expected 'not found in archive' error, got: %v", err)
+	}
+}
+
+func TestUninstall(t *testing.T) {
+	pluginDir := t.TempDir()
+
+	// Create fake binary and receipt.
+	binPath := filepath.Join(pluginDir, "flux-testplugin")
+	os.WriteFile(binPath, []byte("binary"), 0o755)
+	receiptPath := filepath.Join(pluginDir, "flux-testplugin.yaml")
+	os.WriteFile(receiptPath, []byte("name: testplugin"), 0o644)
+
+	if err := Uninstall(pluginDir, "testplugin"); err != nil {
+		t.Fatalf("uninstall failed: %v", err)
+	}
+
+	if _, err := os.Stat(binPath); !os.IsNotExist(err) {
+		t.Error("binary was not removed")
+	}
+	if _, err := os.Stat(receiptPath); !os.IsNotExist(err) {
+		t.Error("receipt was not removed")
+	}
+}
+
+func TestUninstallNonExistent(t *testing.T) {
+	pluginDir := t.TempDir()
+
+	err := Uninstall(pluginDir, "nonexistent")
+	if err == nil {
+		t.Fatal("expected error for non-existent plugin, got nil")
+	}
+	if !strings.Contains(err.Error(), "is not installed") {
+		t.Errorf("expected 'is not installed' error, got: %v", err)
+	}
+}
+
+func TestUninstallSymlink(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("symlinks require elevated privileges on Windows")
+	}
+
+	pluginDir := t.TempDir()
+
+	// Create a real binary and symlink it into the plugin dir.
+	realBin := filepath.Join(t.TempDir(), "flux-operator")
+	os.WriteFile(realBin, []byte("real binary"), 0o755)
+
+	linkPath := filepath.Join(pluginDir, "flux-linked")
+	os.Symlink(realBin, linkPath)
+
+	if err := Uninstall(pluginDir, "linked"); err != nil {
+		t.Fatalf("uninstall symlink failed: %v", err)
+	}
+
+	// Symlink should be removed.
+	if _, err := os.Lstat(linkPath); !os.IsNotExist(err) {
+		t.Error("symlink was not removed")
+	}
+	// Original binary should still exist.
+	if _, err := os.Stat(realBin); err != nil {
+		t.Error("original binary was removed — symlink removal should not affect target")
+	}
+}
+
+func TestUninstallManualBinary(t *testing.T) {
+	pluginDir := t.TempDir()
+
+	// Manually copied binary with no receipt.
+	binPath := filepath.Join(pluginDir, "flux-manual")
+	os.WriteFile(binPath, []byte("binary"), 0o755)
+
+	if err := Uninstall(pluginDir, "manual"); err != nil {
+		t.Fatalf("uninstall manual binary failed: %v", err)
+	}
+
+	if _, err := os.Stat(binPath); !os.IsNotExist(err) {
+		t.Error("binary was not removed")
+	}
+}
+
+func TestReadReceipt(t *testing.T) {
+	pluginDir := t.TempDir()
+
+	t.Run("exists", func(t *testing.T) {
+		receiptData := `name: operator
+version: "0.45.0"
+installedAt: "2026-03-28T20:05:00Z"
+platform:
+  os: darwin
+  arch: arm64
+  url: https://example.com/archive.tar.gz
+  checksum: sha256:abc123
+`
+		os.WriteFile(filepath.Join(pluginDir, "flux-operator.yaml"), []byte(receiptData), 0o644)
+
+		receipt := ReadReceipt(pluginDir, "operator")
+		if receipt == nil {
+			t.Fatal("expected receipt, got nil")
+		}
+		if receipt.Version != "0.45.0" {
+			t.Errorf("expected version '0.45.0', got %q", receipt.Version)
+		}
+		if receipt.Platform.OS != "darwin" {
+			t.Errorf("expected OS 'darwin', got %q", receipt.Platform.OS)
+		}
+	})
+
+	t.Run("not exists", func(t *testing.T) {
+		receipt := ReadReceipt(pluginDir, "nonexistent")
+		if receipt != nil {
+			t.Error("expected nil receipt")
+		}
+	})
+}
+
+func TestExtractFromTarGz(t *testing.T) {
+	content := []byte("test binary content")
+	archive, err := createTestTarGz("flux-operator", content)
+	if err != nil {
+		t.Fatalf("failed to create archive: %v", err)
+	}
+
+	tmpFile := filepath.Join(t.TempDir(), "test.tar.gz")
+	os.WriteFile(tmpFile, archive, 0o644)
+
+	destPath := filepath.Join(t.TempDir(), "flux-operator")
+	if err := extractFromTarGz(tmpFile, "flux-operator", destPath); err != nil {
+		t.Fatalf("extract failed: %v", err)
+	}
+	data, err := os.ReadFile(destPath)
+	if err != nil {
+		t.Fatalf("failed to read extracted file: %v", err)
+	}
+	if string(data) != string(content) {
+		t.Errorf("content mismatch: got %q, want %q", string(data), string(content))
+	}
+}
+
+func TestExtractFromTarGzNotFound(t *testing.T) {
+	archive, err := createTestTarGz("other-binary", []byte("content"))
+	if err != nil {
+		t.Fatalf("failed to create archive: %v", err)
+	}
+
+	tmpFile := filepath.Join(t.TempDir(), "test.tar.gz")
+	os.WriteFile(tmpFile, archive, 0o644)
+
+	destPath := filepath.Join(t.TempDir(), "flux-operator")
+	err = extractFromTarGz(tmpFile, "flux-operator", destPath)
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+}

internal/plugin/update.go

@@ -0,0 +1,85 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+const (
+	SkipReasonManual   = "manually installed"
+	SkipReasonUpToDate = "already up to date"
+)
+
+// UpdateResult represents the outcome of updating a single plugin.
+// When an update is available, Manifest, Version and Platform are
+// populated so the caller can install without re-fetching or re-resolving.
+type UpdateResult struct {
+	Name        string
+	FromVersion string
+	ToVersion   string
+	Skipped     bool
+	SkipReason  string
+	Manifest    *PluginManifest
+	Version     *PluginVersion
+	Platform    *PluginPlatform
+	Err         error
+}
+
+// CheckUpdate compares the installed version against the latest in the catalog.
+// Returns an UpdateResult describing what should happen. When an update is
+// available, Manifest is populated so the caller can install without re-fetching.
+func CheckUpdate(pluginDir string, name string, catalog *CatalogClient, goos, goarch string) UpdateResult {
+	receipt := ReadReceipt(pluginDir, name)
+	if receipt == nil {
+		return UpdateResult{
+			Name:       name,
+			Skipped:    true,
+			SkipReason: SkipReasonManual,
+		}
+	}
+
+	manifest, err := catalog.FetchManifest(name)
+	if err != nil {
+		return UpdateResult{Name: name, Err: err}
+	}
+
+	latest, err := ResolveVersion(manifest, "")
+	if err != nil {
+		return UpdateResult{Name: name, Err: err}
+	}
+
+	if receipt.Version == latest.Version {
+		return UpdateResult{
+			Name:        name,
+			FromVersion: receipt.Version,
+			ToVersion:   latest.Version,
+			Skipped:     true,
+			SkipReason:  SkipReasonUpToDate,
+		}
+	}
+
+	plat, err := ResolvePlatform(latest, goos, goarch)
+	if err != nil {
+		return UpdateResult{Name: name, Err: err}
+	}
+
+	return UpdateResult{
+		Name:        name,
+		FromVersion: receipt.Version,
+		ToVersion:   latest.Version,
+		Manifest:    manifest,
+		Version:     latest,
+		Platform:    plat,
+	}
+}

internal/plugin/update_test.go

@@ -0,0 +1,153 @@
+/*
+Copyright 2026 The Flux 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 plugin
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestCheckUpdateUpToDate(t *testing.T) {
+	manifest := `
+apiVersion: cli.fluxcd.io/v1beta1
+kind: Plugin
+name: operator
+bin: flux-operator
+versions:
+  - version: 0.45.0
+    platforms:
+      - os: linux
+        arch: amd64
+        url: https://example.com/archive.tar.gz
+        checksum: sha256:abc123
+`
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte(manifest))
+	}))
+	defer server.Close()
+
+	pluginDir := t.TempDir()
+
+	// Write receipt with same version.
+	receiptData := `name: operator
+version: "0.45.0"
+installedAt: "2026-03-28T20:05:00Z"
+platform:
+  os: linux
+  arch: amd64
+`
+	os.WriteFile(filepath.Join(pluginDir, "flux-operator.yaml"), []byte(receiptData), 0o644)
+
+	catalog := &CatalogClient{
+		BaseURL:    server.URL + "/",
+		HTTPClient: server.Client(),
+		GetEnv:     func(key string) string { return "" },
+	}
+
+	result := CheckUpdate(pluginDir, "operator", catalog, "linux", "amd64")
+	if result.Err != nil {
+		t.Fatalf("unexpected error: %v", result.Err)
+	}
+	if !result.Skipped {
+		t.Error("expected skipped=true")
+	}
+	if result.SkipReason != SkipReasonUpToDate {
+		t.Errorf("expected %q, got %q", SkipReasonUpToDate, result.SkipReason)
+	}
+}
+
+func TestCheckUpdateAvailable(t *testing.T) {
+	manifest := `
+apiVersion: cli.fluxcd.io/v1beta1
+kind: Plugin
+name: operator
+bin: flux-operator
+versions:
+  - version: 0.46.0
+    platforms:
+      - os: linux
+        arch: amd64
+        url: https://example.com/archive.tar.gz
+        checksum: sha256:abc123
+  - version: 0.45.0
+    platforms:
+      - os: linux
+        arch: amd64
+        url: https://example.com/archive.tar.gz
+        checksum: sha256:def456
+`
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte(manifest))
+	}))
+	defer server.Close()
+
+	pluginDir := t.TempDir()
+
+	receiptData := `name: operator
+version: "0.45.0"
+installedAt: "2026-03-28T20:05:00Z"
+platform:
+  os: linux
+  arch: amd64
+`
+	os.WriteFile(filepath.Join(pluginDir, "flux-operator.yaml"), []byte(receiptData), 0o644)
+
+	catalog := &CatalogClient{
+		BaseURL:    server.URL + "/",
+		HTTPClient: server.Client(),
+		GetEnv:     func(key string) string { return "" },
+	}
+
+	result := CheckUpdate(pluginDir, "operator", catalog, "linux", "amd64")
+	if result.Err != nil {
+		t.Fatalf("unexpected error: %v", result.Err)
+	}
+	if result.Skipped {
+		t.Error("expected skipped=false")
+	}
+	if result.FromVersion != "0.45.0" {
+		t.Errorf("expected from '0.45.0', got %q", result.FromVersion)
+	}
+	if result.ToVersion != "0.46.0" {
+		t.Errorf("expected to '0.46.0', got %q", result.ToVersion)
+	}
+}
+
+func TestCheckUpdateManualInstall(t *testing.T) {
+	pluginDir := t.TempDir()
+
+	// No receipt — manually installed.
+	catalog := &CatalogClient{
+		BaseURL:    "https://example.com/",
+		HTTPClient: http.DefaultClient,
+		GetEnv:     func(key string) string { return "" },
+	}
+
+	result := CheckUpdate(pluginDir, "operator", catalog, "linux", "amd64")
+	if result.Err != nil {
+		t.Fatalf("unexpected error: %v", result.Err)
+	}
+	if !result.Skipped {
+		t.Error("expected skipped=true")
+	}
+	if result.SkipReason != SkipReasonManual {
+		t.Errorf("expected 'manually installed', got %q", result.SkipReason)
+	}
+}