cli: shared skill install for global skill install

README.md

@@ -159,6 +159,7 @@ The `shared` binary talks to the server over HTTP (`--server`, default
 
 ```sh
 shared init [dir]                 # scaffold index.html + a shared-sites agent skill
+shared skill install [--force]    # install the shared-sites skill into ~/.claude/skills
 shared deploy [dir] --name NAME   # pack a directory and deploy it (--force skips
                                   # the overwrite check)
 shared list                       # deployed sites with size, views, last deployer
@@ -171,7 +172,10 @@ shared backup [file]              # download a gzipped tarball of all server dat
 
 `shared init` writes a minimal `index.html` and
 `.claude/skills/shared-sites/SKILL.md` (an agent skill documenting the client
-API), refusing to overwrite existing files. `shared backup` defaults to
+API) into a site directory, refusing to overwrite existing files. `shared skill
+install` writes that same skill to `~/.claude/skills/shared-sites/SKILL.md` so
+it is available to agents in every project, not just a scaffolded one; it skips
+an existing file unless `--force` is given. `shared backup` defaults to
 `shared-backup-<yyyymmdd-hhmmss>.tar.gz` in the current directory.
 
 ## Subdomain routing

cmd/shared/main.go

@@ -37,6 +37,7 @@ commands:
   versions NAME [--server URL]                list a site's saved versions
   backup [file] [--server URL]                download a tarball of all server data
   init [dir]                                  scaffold a new site directory
+  skill install [--force]                     install the shared-sites skill into ~/.claude/skills
 `
 
 func main() {
@@ -61,6 +62,8 @@ func main() {
 		cmdBackup(os.Args[2:])
 	case "init":
 		cmdInit(os.Args[2:])
+	case "skill":
+		cmdSkill(os.Args[2:])
 	case "-h", "--help", "help":
 		fmt.Print(usage)
 	default:
@@ -643,6 +646,35 @@ func cmdInit(args []string) {
 	}
 }
 
+func cmdSkill(args []string) {
+	if len(args) < 1 || args[0] != "install" {
+		fmt.Fprintln(os.Stderr, "usage: shared skill install [--force]")
+		os.Exit(2)
+	}
+	fs := flag.NewFlagSet("skill install", flag.ExitOnError)
+	force := fs.Bool("force", false, "overwrite an existing skill file")
+	fs.Parse(args[1:])
+
+	home, err := os.UserHomeDir()
+	if err != nil {
+		fatal("%v", err)
+	}
+	dest := filepath.Join(home, ".claude", "skills", "shared-sites", "SKILL.md")
+	if _, err := os.Stat(dest); err == nil && !*force {
+		fmt.Printf("skip %s (exists; --force to overwrite)\n", dest)
+		return
+	} else if err != nil && !os.IsNotExist(err) {
+		fatal("%v", err)
+	}
+	if err := os.MkdirAll(filepath.Dir(dest), 0o755); err != nil {
+		fatal("%v", err)
+	}
+	if err := os.WriteFile(dest, web.InitSkillMD, 0o644); err != nil {
+		fatal("writing %s: %v", dest, err)
+	}
+	fmt.Printf("wrote %s\n", dest)
+}
+
 func humanSize(n int64) string {
 	const unit = 1024
 	if n < unit {