feat(nushell): add auto-bootstrapped completion registry flow

- generate cache registry module from command list and load it at startup

- add pj completion sync (-s) with optional help and restart behavior

- keep missing-cache fallback via noop module and preserve cache ignore rules

.gitignore

@@ -1,4 +1,2 @@
 .zed
 .vscode
-nushell/cache/*
-!nushell/cache/.gitignore

nushell/cache/.gitignore

@@ -1,2 +1,3 @@
 *
 !.gitignore
+!noop.nu

nushell/cache/noop.nu

@@ -0,0 +1 @@
+# Fallback completion module intentionally exports nothing.

nushell/modules/pj_completions.nu

@@ -1,6 +1,14 @@
 const pj_module_dir = (path self | path dirname)
-const pj_completion_base_dir = ($pj_module_dir | path join '..' 'cache' 'nu_scripts' 'custom-completions')
-const pj_completion_commands = [git ssh cargo uv rustup make pytest rg tar fzf vscode winget zig]
+const pj_cache_dir = ($pj_module_dir | path join '..' 'cache')
+const pj_completion_base_dir = ($pj_cache_dir | path join 'nu_scripts' 'custom-completions')
+const pj_completion_commands = [git ssh cargo uv rustup make pytest rg tar vscode winget zig]
+const pj_completion_noop_module = ($pj_cache_dir | path join 'noop.nu')
+const pj_completion_registry_module = ($pj_cache_dir | path join 'pj_completions_registry.nu')
+const pj_completion_bootstrap_module = if ($pj_completion_registry_module | path exists) {
+    $pj_completion_registry_module
+} else {
+    $pj_completion_noop_module
+}
 
 def _pj_completion_script_path [name: string] {
     ($pj_completion_base_dir | path join $name $"($name)-completions.nu")
@@ -15,10 +23,78 @@ def _pj_required_completion_files [] {
     }
 }
 
+def _pj_completion_registry_lines [] {
+    let header = [
+        "# Auto-generated by `pj completion sync`."
+        "# Edit pj_completion_commands in pj_completions.nu, then re-run sync."
+        "const pj_registry_dir = (path self | path dirname)"
+        "const pj_completion_base_dir = ($pj_registry_dir | path join 'nu_scripts' 'custom-completions')"
+        "const pj_completion_noop_module = ($pj_registry_dir | path join 'noop.nu')"
+        ""
+    ]
+
+    let lines = ($pj_completion_commands | each {|name|
+        [
+            (
+                "export use (if ((($pj_completion_base_dir | path join '"
+                + $name
+                + "' '"
+                + $name
+                + "-completions.nu') | path exists)) { ($pj_completion_base_dir | path join '"
+                + $name
+                + "' '"
+                + $name
+                + "-completions.nu') } else { $pj_completion_noop_module }) *"
+            )
+            ""
+        ]
+    } | flatten)
+
+    ($header | append $lines)
+}
+
+def _pj_completion_help [] {
+    print "pj completion commands:"
+    print "  pj completion             Clone/update cache and check required completion files."
+    print "  pj completion -u          Update cached nu_scripts repository."
+    print "  pj completion -f          Force re-clone cached nu_scripts repository."
+    print "  pj completion sync        Regenerate cache registry and restart Nushell."
+    print "  pj completion -s          Same as `pj completion sync`."
+    print "  pj completion -h          Show this help message."
+}
+
+export def "pj completion sync" [
+    --help(-h)
+] {
+    if $help {
+        _pj_completion_help
+        return
+    }
+
+    mkdir $pj_cache_dir
+    let content = ((_pj_completion_registry_lines) | str join "\n")
+    $content | save -f $pj_completion_registry_module
+    print $"[pj completion] synced: ($pj_completion_registry_module)"
+    print "[pj completion] restarting Nushell..."
+    exec nu
+}
+
 export def "pj completion" [
     --update(-u) # Pull latest changes when repo already exists.
     --force(-f) # Re-clone even when repo already exists.
+    --sync(-s) # Regenerate static registry and restart Nushell.
+    --help(-h) # Show help.
 ] {
+    if $help {
+        _pj_completion_help
+        return
+    }
+
+    if $sync {
+        pj completion sync
+        return
+    }
+
     let repo_url = "https://github.com/nushell/nu_scripts.git"
     let cache_dir = if ('NU_POLYJUICE_PATH' in $env) {
         ($env.NU_POLYJUICE_PATH | path join 'cache')
@@ -94,18 +170,19 @@ export-env {
             }
         }
     }
+
+    if not ($pj_completion_registry_module | path exists) {
+        mkdir $pj_cache_dir
+        let content = ((_pj_completion_registry_lines) | str join "\n")
+        $content | save -f $pj_completion_registry_module
+
+        if (($env.PJ_COMPLETION_BOOTSTRAPPED? | default "0") != "1") {
+            load-env { PJ_COMPLETION_BOOTSTRAPPED: "1" }
+            print "[pj completion] generated cache registry, restarting Nushell..."
+            exec nu
+        }
+    }
 }
 
-# Re-export imported extern signatures so they are visible when this module is `use`d.
-export use ($pj_completion_base_dir | path join 'git' 'git-completions.nu') *
-export use ($pj_completion_base_dir | path join 'ssh' 'ssh-completions.nu') *
-export use ($pj_completion_base_dir | path join 'cargo' 'cargo-completions.nu') *
-export use ($pj_completion_base_dir | path join 'uv' 'uv-completions.nu') *
-export use ($pj_completion_base_dir | path join 'rustup' 'rustup-completions.nu') *
-export use ($pj_completion_base_dir | path join 'make' 'make-completions.nu') *
-export use ($pj_completion_base_dir | path join 'pytest' 'pytest-completions.nu') *
-export use ($pj_completion_base_dir | path join 'rg' 'rg-completions.nu') *
-export use ($pj_completion_base_dir | path join 'tar' 'tar-completions.nu') *
-export use ($pj_completion_base_dir | path join 'vscode' 'vscode-completions.nu') *
-export use ($pj_completion_base_dir | path join 'winget' 'winget-completions.nu') *
-export use ($pj_completion_base_dir | path join 'zig' 'zig-completions.nu') *
+# Re-export completion externs from generated static registry.
+export use $pj_completion_bootstrap_module *