magpie/internal/plugin/store.go

// Package plugin runs OpenCode's provider plugins for magpie.
//
// A subscription a vendor may object to being used outside its own app is
// not built into magpie: a plugin signs in to it and makes its requests,
// the way OpenCode's plugins do (opencode-gemini-auth and the like), and
// magpie runs those same plugins. They are npm packages (or local files)
// written against OpenCode's plugin API (@opencode-ai/plugin, v1): their
// auth hook gives the sign-in methods and a loader whose fetch carries the
// requests, their config and provider hooks the models. magpie runs them
// under Bun, downloaded the first time a plugin is added, in one process
// (host.js) it talks to over stdin and stdout.
//
// What magpie keeps: plugins.json, the plugins and the config handed to
// them (OpenCode's, its provider section: a plugin's options); the npm
// packages under plugins/; plugin-auth.json, the sign-ins, in OpenCode's
// auth.json shape (so one can be moved between the two).
package plugin

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"maps"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"slices"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/yetone/magpie/internal/netproxy"
	"github.com/yetone/magpie/internal/proc"
	"github.com/yetone/magpie/internal/settings"
	"github.com/yetone/magpie/internal/steady"
	"github.com/yetone/magpie/internal/update"
)

// Entry is one plugin the user added.
type Entry struct {
	// Spec is how it was added: an npm package (name, name@version), a git
	// repository (github:owner/repo, git+https://…) or a path to a file
	// or folder.
	Spec string `json:"spec"`
	// Off is set on a plugin the user turned off.
	Off bool `json:"off,omitempty"`
	// Options are handed to the plugin as its second argument, as
	// OpenCode's ["name", {options}] does.
	Options map[string]any `json:"options,omitempty"`
}

// List is plugins.json.
type List struct {
	Plugins []Entry `json:"plugins"`
	// Config is OpenCode's config the plugins are handed: its provider
	// section says what a plugin reads of it
	// (provider.google.options.projectId).
	Config map[string]any `json:"config,omitempty"`
	// Prefer is the plugin the user picked for a provider id more than
	// one plugin signs in to (a plugin of their own beside a third
	// party's): provider id → that plugin's spec. Without it the last of
	// them in Plugins serves the id, as in OpenCode.
	Prefer map[string]string `json:"prefer,omitempty"`
}

var listMu sync.Mutex

// Dir is the folder magpie installs npm plugins into.
func Dir() string { return filepath.Join(settings.Dir(), "plugins") }

// AuthPath is the plugins' sign-ins, OpenCode's auth.json in shape.
func AuthPath() string { return filepath.Join(settings.Dir(), "plugin-auth.json") }

// authLockStale is how long plugin-auth.json.lock is held at most: one
// older was left by a host or a magpie that died holding it.
const authLockStale = 10 * time.Second

// lockAuth takes plugin-auth.json.lock, which host.js takes too, for a
// change to plugin-auth.json read afresh under it: two hosts (one being
// restarted) and magpie never write each other's accounts away. It gives
// the unlock.
func lockAuth() func() {
	lock := AuthPath() + ".lock"
	start := time.Now()
	for {
		f, err := os.OpenFile(lock, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
		if err == nil {
			f.Close()
			return func() { os.Remove(lock) }
		}
		if !os.IsExist(err) && !os.IsPermission(err) {
			return func() {} // no folder to lock in: no file to change either
		}
		if fi, err := os.Stat(lock); err == nil && time.Since(fi.ModTime()) > authLockStale || time.Since(start) > 2*authLockStale {
			os.Remove(lock)
		}
		time.Sleep(5 * time.Millisecond)
	}
}

func listPath() string { return filepath.Join(settings.Dir(), "plugins.json") }

// pluginsList is plugins.json as last read, with the bytes it was parsed
// from. The file is read every time: an edit that keeps the file's size and
// time (a swap of two accounts of one length, a replaced file whose time is
// put back) would be missed by a stamp, and only the parse is reused.
var pluginsList struct {
	sync.Mutex
	path string
	raw  []byte
	list List
}

// list is plugins.json, read now. What it gives is shared and must not be
// changed; Load gives the mutable copy.
func list() List {
	path := listPath()
	b, err := steady.ReadFile(path)
	if err != nil {
		// Do not cache read failures; a later call will read the file again.
		return List{}
	}
	pluginsList.Lock()
	defer pluginsList.Unlock()
	if pluginsList.path == path && bytes.Equal(pluginsList.raw, b) {
		return pluginsList.list
	}
	var l List
	// Preserve partially decoded values on type errors, as Load has always done.
	_ = json.Unmarshal(b, &l)
	pluginsList.path, pluginsList.raw, pluginsList.list = path, b, l
	return l
}

// Load reads plugins.json. What it gives is the caller's to change at every
// level: the mutators (Add, Remove, SetOff, SetConfig) each get their own
// copy, so nothing they change reaches what list keeps.
func Load() List {
	l := list()
	return List{Plugins: clonePlugins(l.Plugins), Config: cloneMap(l.Config), Prefer: maps.Clone(l.Prefer)}
}

// clonePlugins copies the entries, their options with them.
func clonePlugins(es []Entry) []Entry {
	if es == nil {
		return nil
	}
	out := make([]Entry, len(es))
	for i, e := range es {
		out[i] = e
		out[i].Options = cloneMap(e.Options)
	}
	return out
}

// cloneMap copies a JSON object and everything under it.
func cloneMap(m map[string]any) map[string]any {
	if m == nil {
		return nil
	}
	out := make(map[string]any, len(m))
	for k, v := range m {
		out[k] = cloneJSON(v)
	}
	return out
}

// cloneJSON copies a JSON value: Unmarshal into any gives only objects,
// arrays, strings, numbers, bools and nil, so this reaches every part of one.
func cloneJSON(v any) any {
	switch x := v.(type) {
	case map[string]any:
		return cloneMap(x)
	case []any:
		out := make([]any, len(x))
		for i, e := range x {
			out[i] = cloneJSON(e)
		}
		return out
	default:
		return v
	}
}

// writeWhole writes b to p by a rename, so a magpie or the host reading
// p meanwhile reads the old file or the new one, never one half-written;
// read back with steady.ReadFile, which waits out the rename on Windows.
func writeWhole(p string, b []byte) error {
	f, err := os.CreateTemp(filepath.Dir(p), filepath.Base(p)+".*")
	if err != nil {
		return err
	}
	_, err = f.Write(b)
	if cerr := f.Close(); err == nil {
		err = cerr
	}
	if err == nil {
		err = steady.Rename(f.Name(), p)
	}
	if err != nil {
		os.Remove(f.Name())
	}
	return err
}

func save(l List) error {
	b, err := json.MarshalIndent(l, "", "  ")
	if err != nil {
		return err
	}
	if err := os.MkdirAll(settings.Dir(), 0o700); err != nil {
		return err
	}
	if err := writeWhole(listPath(), append(b, '\n')); err != nil {
		return err
	}
	listSeen.Lock()
	listSeen.stamp, listSeen.set = listStamp(), true
	listSeen.Unlock()
	return nil
}

// listSeen is plugins.json as this magpie last wrote or read it.
var listSeen struct {
	sync.Mutex
	stamp string
	set   bool
}

// listStamp is plugins.json as it is now, and what is installed: bun's
// package.json and lockfile in Dir(), which `magpie plugin update` changes
// without touching plugins.json (#952: a terminal's update to 0.1.18 left
// the app's host answering with 0.1.17 until it was killed).
func listStamp() string {
	var b strings.Builder
	for _, p := range []string{listPath(), filepath.Join(Dir(), "package.json"), filepath.Join(Dir(), "bun.lock"), filepath.Join(Dir(), "bun.lockb")} {
		if fi, err := os.Stat(p); err == nil {
			fmt.Fprint(&b, fi.ModTime().UnixNano(), " ", fi.Size())
		}
		b.WriteString(";")
	}
	return b.String()
}

// hostStale is set when another magpie changed the plugins (magpie plugin
// add, remove, update or move in a terminal while the app runs): the host
// running has the old ones loaded.
var hostStale atomic.Bool

// checkList notices plugins.json changed by another magpie: the host is
// started again with the plugins as they are, and the providers the other
// magpie last saw asked for are the ones known meanwhile.
func checkList() {
	st := listStamp()
	listSeen.Lock()
	moved := listSeen.set && listSeen.stamp != st
	listSeen.stamp, listSeen.set = st, true
	listSeen.Unlock()
	if !moved {
		return
	}
	provMu.Lock()
	provCache = nil
	provMu.Unlock()
	hostStale.Store(true)
	changed()
}

// IsPath is whether spec names a file or folder rather than a package,
// as OpenCode tells them apart.
func IsPath(spec string) bool {
	return strings.HasPrefix(spec, "file://") || strings.HasPrefix(spec, ".") || filepath.IsAbs(spec) || regexp.MustCompile(`^[A-Za-z]:[\\/]`).MatchString(spec)
}

var pkgName = regexp.MustCompile(`^(@[a-z0-9][a-z0-9._~-]*/)?[a-z0-9][a-z0-9._~-]*$`)

// gitSpec is a package bun fetches from a git repository, not npm:
// github:owner/repo[#ref] (gitlab: and bitbucket: alike), a git+https://,
// git+ssh://, git+file:// or git:// URL, a GitHub, GitLab or Bitbucket
// page's URL, or owner/repo, GitHub's shorthand.
var gitSpec = regexp.MustCompile(`^(?:(?:github|gitlab|bitbucket):|git\+[a-z]+://|git://)\S+$|^https?://(?:www\.)?(?:github\.com|gitlab\.com|bitbucket\.org)/\S+$|^[A-Za-z0-9][A-Za-z0-9_.-]*/[A-Za-z0-9_.-]+(?:#\S+)?$`)

// IsGit is whether spec names a git repository rather than an npm package
// or a path. The package bun installs from it is named by its own
// package.json, not by spec.
func IsGit(spec string) bool { return !IsPath(spec) && gitSpec.MatchString(spec) }

// gitName is the package bun installed from the git spec: the dependency
// of plugins/package.json bun added it as (it keeps spec as given), ""
// when there is none.
func gitName(spec string) string {
	var pj struct {
		Dependencies map[string]string `json:"dependencies"`
	}
	b, err := os.ReadFile(filepath.Join(Dir(), "package.json"))
	if err != nil || json.Unmarshal(b, &pj) != nil {
		return ""
	}
	for name, s := range pj.Dependencies {
		if s == spec {
			return name
		}
	}
	return ""
}

// Name is the package spec names, without its version: "@scope/x" of
// "@scope/x@1.2", the package installed from a git repository (the spec
// itself until it is), or the path.
func Name(spec string) string {
	if IsPath(spec) {
		return spec
	}
	if IsGit(spec) {
		if n := gitName(spec); n != "" {
			return n
		}
		return spec
	}
	at := strings.LastIndex(spec, "@")
	if at > 0 {
		return spec[:at]
	}
	return spec
}

// Target is where the plugin is to load from: the installed package's
// folder, or the path.
func Target(spec string) string {
	if IsPath(spec) {
		p := strings.TrimPrefix(spec, "file://")
		if abs, err := filepath.Abs(p); err == nil {
			return abs
		}
		return p
	}
	return filepath.Join(Dir(), "node_modules", filepath.FromSlash(Name(spec)))
}

// Add installs a plugin and adds it to the list, in place of one of the
// same package. A package is installed with its scripts left unrun.
func Add(ctx context.Context, spec string) (Entry, error) { return add(ctx, spec, "") }

// add is Add, an npm package installed at the version given when there is
// one (installAt), its spec kept as given.
func add(ctx context.Context, spec, version string) (Entry, error) {
	spec = strings.TrimSpace(spec)
	if spec == "" {
		return Entry{}, errors.New("no plugin given")
	}
	// the package each plugin is before the install, which may take a git
	// one's name over (one repository in place of another, or of npm's)
	was := map[string]string{}
	for _, x := range Load().Plugins {
		was[x.Spec] = Name(x.Spec)
	}
	if IsPath(spec) {
		t := Target(spec)
		if _, err := os.Stat(t); err != nil {
			return Entry{}, err
		}
		spec = t
	} else if IsGit(spec) {
		if err := install(ctx, spec); err != nil {
			return Entry{}, err
		}
		if Name(spec) == spec {
			return Entry{}, fmt.Errorf("bun installed %s but plugins/package.json doesn't list it", spec)
		}
	} else {
		if !pkgName.MatchString(Name(spec)) {
			return Entry{}, fmt.Errorf("%q isn't an npm package name", spec)
		}
		if Name(spec) == spec {
			spec += "@latest"
		}
		if version != "" {
			if err := installAt(ctx, Name(spec), version); err != nil {
				return Entry{}, err
			}
		} else if err := install(ctx, spec); err != nil {
			return Entry{}, err
		}
	}
	if err := notPlugin(Target(spec)); err != nil {
		// installed just now for this, and nothing loads it: taken out again
		if !IsPath(spec) && !slices.Contains(slices.Collect(maps.Values(was)), Name(spec)) {
			if bun, berr := Bun(ctx); berr == nil {
				_ = bunCommand(ctx, bun, Dir(), "remove", "--ignore-scripts", Name(spec)).Run()
			}
		}
		return Entry{}, err
	}
	if err := ensurePi(ctx, Target(spec)); err != nil {
		return Entry{}, err
	}
	listMu.Lock()
	defer listMu.Unlock()
	l := Load()
	e := Entry{Spec: spec}
	name := Name(spec)
	if i := slices.IndexFunc(l.Plugins, func(x Entry) bool {
		n, ok := was[x.Spec]
		if !ok {
			n = Name(x.Spec)
		}
		return x.Spec == spec || n == name
	}); i >= 0 {
		e.Options = l.Plugins[i].Options
		// a provider id the user picked it for stays its (another version,
		// or its package from a git repository in place of npm's)
		for id, s := range l.Prefer {
			if s == l.Plugins[i].Spec {
				l.Prefer[id] = spec
			}
		}
		l.Plugins[i] = e
	} else {
		l.Plugins = append(l.Plugins, e)
	}
	if err := save(l); err != nil {
		return Entry{}, err
	}
	Restart()
	return e, nil
}

// indexFiles are the files a package that names none loads, as the host
// looks for them (host.js's INDEX_FILES).
var indexFiles = []string{"index.ts", "index.tsx", "index.js", "index.mjs", "index.cjs"}

// notPlugin says why the plugin at target is nothing the host can load,
// or nil: a package that names no file to import (main, exports), has no
// index file, and is neither pi's nor a middleware — a command alone
// (bin), an MCP server like magpie-x-search, is installed fine and then
// never loads (#1327).
func notPlugin(target string) error {
	st, err := os.Stat(target)
	if err != nil || !st.IsDir() || IsPi(target) {
		return nil
	}
	if f, _ := Middleware(target); f != "" {
		return nil
	}
	var pkg struct {
		Name    string          `json:"name"`
		Main    string          `json:"main"`
		Exports json.RawMessage `json:"exports"`
		Bin     json.RawMessage `json:"bin"`
	}
	b, err := os.ReadFile(filepath.Join(target, "package.json"))
	if err != nil || json.Unmarshal(b, &pkg) != nil {
		return nil
	}
	if strings.TrimSpace(pkg.Main) != "" || len(pkg.Exports) > 0 && string(pkg.Exports) != "null" {
		return nil
	}
	for _, f := range indexFiles {
		if _, err := os.Stat(filepath.Join(target, f)); err == nil {
			return nil
		}
	}
	name := pkg.Name
	if name == "" {
		name = filepath.Base(target)
	}
	why := fmt.Sprintf("%s isn't an OpenCode or magpie plugin: its package names no file to load (no main or exports in package.json, no index file)", name)
	if len(pkg.Bin) > 0 && string(pkg.Bin) != "null" {
		why += ", only a command (bin). If it is an MCP server, add it under Library → MCP servers instead"
	}
	return errors.New(why)
}

// Update installs the version of each npm plugin its spec says now
// (latest, for the most part: npm's newest, asked now, installAt), and
// fetches each git one again.
func Update(ctx context.Context) error {
	var errs []error
	for _, e := range Load().Plugins {
		if !IsPath(e.Spec) {
			v := ""
			if !IsGit(e.Spec) && !Pinned(e.Spec) {
				v = newestOf(ctx, Name(e.Spec))
			}
			var err error
			if v != "" {
				err = installAt(ctx, Name(e.Spec), v)
			} else {
				// pinned, a git one, or npm not answering: as its spec says
				err = reinstall(ctx, e.Spec)
			}
			if err != nil {
				errs = append(errs, fmt.Errorf("%s: %w", e.Spec, err))
				continue
			}
		}
		if err := ensurePi(ctx, Target(e.Spec)); err != nil {
			errs = append(errs, fmt.Errorf("%s: %w", e.Spec, err))
		}
	}
	Restart()
	return errors.Join(errs...)
}

// indexOf is the plugin name means in l: the one added as name exactly,
// else the one of that package. A plugin of the user's own (a folder)
// beside a third party's is each told apart by its own spec, so taking
// one away or switching it off never reaches the other.
func indexOf(l List, name string) int {
	if i := slices.IndexFunc(l.Plugins, func(x Entry) bool { return x.Spec == name }); i >= 0 {
		return i
	}
	return slices.IndexFunc(l.Plugins, func(x Entry) bool { return Name(x.Spec) == name })
}

// Remove takes a plugin off the list (and out of plugins/).
func Remove(ctx context.Context, name string) error {
	listMu.Lock()
	l := Load()
	i := indexOf(l, name)
	if i < 0 {
		listMu.Unlock()
		return fmt.Errorf("no plugin %q", name)
	}
	e := l.Plugins[i]
	l.Plugins = slices.Delete(l.Plugins, i, i+1)
	maps.DeleteFunc(l.Prefer, func(_, s string) bool { return s == e.Spec })
	err := save(l)
	listMu.Unlock()
	if err != nil {
		return err
	}
	if !IsPath(e.Spec) {
		if bun, err := Bun(ctx); err == nil {
			_ = bunCommand(ctx, bun, Dir(), "remove", "--ignore-scripts", Name(e.Spec)).Run()
		}
	}
	Restart()
	return nil
}

// SetOff turns a plugin off or back on.
func SetOff(name string, off bool) error {
	listMu.Lock()
	defer listMu.Unlock()
	l := Load()
	i := indexOf(l, name)
	if i < 0 {
		return fmt.Errorf("no plugin %q", name)
	}
	l.Plugins[i].Off = off
	if err := save(l); err != nil {
		return err
	}
	Restart()
	return nil
}

// Prefer has the plugin named serve provider id, which another plugin
// signs in to as well (Clash): the host runs it for id from now on, the
// other one keeping its other providers. A plugin removed takes its picks
// with it; one switched off leaves the id to the others until it is on
// again.
func Prefer(name, id string) error {
	listMu.Lock()
	defer listMu.Unlock()
	l := Load()
	i := indexOf(l, name)
	if i < 0 {
		return fmt.Errorf("no plugin %q", name)
	}
	if id == "" {
		return errors.New("no provider given")
	}
	if l.Prefer == nil {
		l.Prefer = map[string]string{}
	}
	l.Prefer[id] = l.Plugins[i].Spec
	if err := save(l); err != nil {
		return err
	}
	Restart()
	return nil
}

// SetOptions sets the options a plugin is handed (a middleware's
// ctx.options); nil takes them away.
func SetOptions(name string, opts map[string]any) error {
	listMu.Lock()
	defer listMu.Unlock()
	l := Load()
	i := indexOf(l, name)
	if i < 0 {
		// a short name, as the community's READMEs write it: param-override
		// for @magpie-community/middleware-param-override
		i = slices.IndexFunc(l.Plugins, func(x Entry) bool { return ShortName(Name(x.Spec)) == name })
	}
	if i < 0 {
		return fmt.Errorf("no plugin %q", name)
	}
	if len(opts) == 0 {
		opts = nil
	}
	l.Plugins[i].Options = opts
	if err := save(l); err != nil {
		return err
	}
	Restart()
	return nil
}

// ShortName is a package's name without its scope and the words every
// package of its kind has: model-map for @magpie-community/middleware-model-map,
// zed for @magpie-community/opencode-zed-auth.
func ShortName(pkg string) string {
	if i := strings.LastIndex(pkg, "/"); i >= 0 {
		pkg = pkg[i+1:]
	}
	pkg = strings.TrimPrefix(strings.TrimPrefix(pkg, "middleware-"), "opencode-")
	return strings.TrimSuffix(pkg, "-auth")
}

// install puts an npm package into plugins/ with bun add, its scripts
// left unrun as OpenCode leaves them.
func install(ctx context.Context, spec string) error {
	bun, err := Bun(ctx)
	if err != nil {
		return err
	}
	if err := os.MkdirAll(Dir(), 0o755); err != nil {
		return err
	}
	pj := filepath.Join(Dir(), "package.json")
	if _, err := os.Stat(pj); err != nil {
		if err := os.WriteFile(pj, []byte("{\n  \"name\": \"magpie-plugins\",\n  \"private\": true\n}\n"), 0o644); err != nil {
			return err
		}
	}
	out, err := bunCommand(ctx, bun, Dir(), "add", "--ignore-scripts", spec).CombinedOutput()
	if err != nil {
		return fmt.Errorf("bun add %s: %v: %s", spec, err, lastLines(string(out), 6))
	}
	return nil
}

// installAt installs the version of the npm package given, not a tag, and
// checks it is the one installed. Asked for pkg@latest, bun resolves
// "latest" by its own config: a minimumReleaseAge in the user's bunfig
// holds back every version younger than it, and a registry of the user's
// own (an .npmrc) may not have the newest yet. Either way bun installs an
// older version and exits 0, so an update said it was done and nothing
// changed (sweanng424 on Discord: Factory stayed at 0.1.18 with 0.1.21 out,
// through restarts and the hourly updates). Asked for the version, bun
// says why it can't install it.
func installAt(ctx context.Context, pkg, version string) error {
	if err := install(ctx, pkg+"@"+version); err != nil {
		// what bun said comes first: the page's status line shows the
		// start of a long message
		if m := minAge.FindStringSubmatch(err.Error()); m != nil {
			return fmt.Errorf("%s %s isn't installed yet: Bun's minimumReleaseAge (in a .bunfig.toml) holds back versions published less than %s ago, and magpie installs it once it is older (%w)", pkg, version, ageText(m[1]), err)
		}
		var said []string
		for _, l := range strings.Split(err.Error(), "\n") {
			if l = strings.TrimSpace(l); strings.HasPrefix(l, "error:") {
				said = append(said, strings.TrimSpace(strings.TrimPrefix(l, "error:")))
			}
		}
		if len(said) > 0 {
			return fmt.Errorf("%s %s isn't installed: %s (%w)", pkg, version, strings.Join(said, "; "), err)
		}
		return err
	}
	if got := Installed(pkg); got == "" || update.Newer(version, got) {
		if got == "" {
			got = "nothing"
		}
		return fmt.Errorf("bun add %s@%s installed %s", pkg, version, got)
	}
	return nil
}

// minAge is bun's word for a version its minimumReleaseAge holds back.
var minAge = regexp.MustCompile(`minimum-release-age: (\d+) seconds`)

// ageText is a number of seconds as a reader says it: 2 days, 12 hours.
func ageText(secs string) string {
	n, err := strconv.Atoi(secs)
	switch {
	case err != nil:
		return secs + " seconds"
	case n >= 86400 && n%86400 == 0:
		return plural(n/86400, "day")
	case n >= 3600 && n%3600 == 0:
		return plural(n/3600, "hour")
	case n >= 60 && n%60 == 0:
		return plural(n/60, "minute")
	}
	return plural(n, "second")
}

func plural(n int, unit string) string {
	if n == 1 {
		return "1 " + unit
	}
	return strconv.Itoa(n) + " " + unit + "s"
}

// newestOf is npm's newest version of the package, asked now, "" when npm
// didn't say; what it says is kept, as Info keeps it (tests stub it).
var newestOf = func(ctx context.Context, name string) string {
	c, cancel := context.WithTimeout(ctx, checkEach)
	info, err := npmAsk(c, name)
	cancel()
	if err == nil || errors.Is(err, errNotFound) {
		npmMu.Lock()
		npmCached()[name] = npmEntry{info, time.Now()}
		saveNPM()
		npmMu.Unlock()
	}
	if err != nil {
		return ""
	}
	return info.Version
}

// piAgent is the package pi's extensions import pi from; the host loads
// them with it (pi.js), whichever of its names they import.
const piAgent = "@earendil-works/pi-coding-agent"

// IsPi is whether the plugin at target is pi's (a pi package or
// extension) rather than OpenCode's, as host.js's pi.js tells them.
func IsPi(target string) bool {
	st, err := os.Stat(target)
	if err != nil {
		return false
	}
	if !st.IsDir() {
		b, err := os.ReadFile(target)
		if err != nil {
			return false
		}
		s := string(b)
		for _, n := range []string{piAgent, "@mariozechner/pi-coding-agent"} {
			if strings.Contains(s, `"`+n+`"`) || strings.Contains(s, `'`+n+`'`) {
				return true
			}
		}
		return false
	}
	b, err := os.ReadFile(filepath.Join(target, "package.json"))
	if err != nil {
		return false
	}
	var pkg struct {
		Pi       any               `json:"pi"`
		Keywords []string          `json:"keywords"`
		Deps     map[string]string `json:"dependencies"`
		Peers    map[string]string `json:"peerDependencies"`
	}
	if json.Unmarshal(b, &pkg) != nil {
		return false
	}
	if _, ok := pkg.Pi.(map[string]any); ok || slices.Contains(pkg.Keywords, "pi-package") {
		return true
	}
	for _, d := range []map[string]string{pkg.Deps, pkg.Peers} {
		if _, ok := d[piAgent]; ok {
			return true
		}
		if _, ok := d["@mariozechner/pi-coding-agent"]; ok {
			return true
		}
	}
	return false
}

// ensurePi installs pi for a pi plugin that came without it (one that
// doesn't name it among what it depends on, or one on disk), as pi itself
// is what loads it.
func ensurePi(ctx context.Context, target string) error {
	if !IsPi(target) {
		return nil
	}
	if _, err := os.Stat(filepath.Join(Dir(), "node_modules", piAgent, "package.json")); err == nil {
		return nil
	}
	if _, err := os.Stat(filepath.Join(target, "node_modules", piAgent, "package.json")); err == nil {
		return nil
	}
	return install(ctx, piAgent)
}

// reinstall installs spec again: an npm one with bun add, a git one with
// bun update, which fetches its branch's (or tag's) commit now where bun
// add keeps the one bun.lock has.
func reinstall(ctx context.Context, spec string) error {
	name := Name(spec)
	if !IsGit(spec) || name == spec {
		return install(ctx, spec)
	}
	bun, err := Bun(ctx)
	if err != nil {
		return err
	}
	out, err := bunCommand(ctx, bun, Dir(), "update", "--ignore-scripts", name).CombinedOutput()
	if err != nil {
		return fmt.Errorf("bun update %s: %v: %s", name, err, lastLines(string(out), 6))
	}
	return nil
}

func lastLines(s string, n int) string {
	ls := strings.Split(strings.TrimSpace(s), "\n")
	if len(ls) > n {
		ls = ls[len(ls)-n:]
	}
	return strings.Join(ls, "\n")
}

func command(ctx context.Context, name string, args ...string) *exec.Cmd {
	return proc.CommandContext(ctx, name, args...)
}

// env is the plugins' environment: magpie's, with its proxy.
func env() []string { return netproxy.Env(os.Environ()) }

// Version is the version of the package spec installed (or checked out
// at its path), "" when there is none.
func Version(spec string) string {
	dir := Target(spec)
	if fi, err := os.Stat(dir); err == nil && !fi.IsDir() {
		dir = filepath.Dir(dir)
	}
	var pj struct {
		Version string `json:"version"`
	}
	if b, err := os.ReadFile(filepath.Join(dir, "package.json")); err == nil && json.Unmarshal(b, &pj) == nil {
		return pj.Version
	}
	return ""
}

// PackageName is the npm package spec is: its name, or, for a plugin added
// from a folder or file (a checkout of it), the name its package.json gives.
func PackageName(spec string) string {
	if !IsPath(spec) {
		return Name(spec)
	}
	dir := Target(spec)
	if fi, err := os.Stat(dir); err == nil && !fi.IsDir() {
		dir = filepath.Dir(dir)
	}
	var pj struct {
		Name string `json:"name"`
	}
	if b, err := os.ReadFile(filepath.Join(dir, "package.json")); err == nil && json.Unmarshal(b, &pj) == nil && pj.Name != "" {
		return pj.Name
	}
	return spec
}