fix(pack): install missing plugins asynchronously without startup updates

lua/plugins/pack.lua

@@ -1,4 +1,5 @@
 local M = {}
+local async_install_started = false
 
 local function has_valid_head(path)
     if vim.fn.isdirectory(path .. "/.git") == 0 then
@@ -31,6 +32,45 @@ local function to_src(value)
     return "https://github.com/" .. value
 end
 
+local function plugin_name(spec)
+    if type(spec) == "table" and type(spec.name) == "string" and spec.name ~= "" then
+        return spec.name
+    end
+
+    local src = type(spec) == "string" and spec or spec.src
+    local name = src:gsub("/$", ""):match("([^/]+)$") or src
+    return name:gsub("%.git$", "")
+end
+
+local function plugin_installed(spec)
+    local root = vim.fn.stdpath("data") .. "/site/pack/core/opt"
+    local path = root .. "/" .. plugin_name(spec)
+    return vim.fn.isdirectory(path) == 1
+end
+
+local function install_missing_async(specs)
+    if async_install_started or #specs == 0 then
+        return
+    end
+
+    async_install_started = true
+
+    local specs_json = vim.json.encode(specs)
+    local lua_expr = string.format(
+        "local s=vim.json.decode(%q); vim.pack.add(s,{confirm=false,load=false})",
+        specs_json
+    )
+
+    vim.system({
+        vim.v.progpath,
+        "--headless",
+        "-u",
+        "NONE",
+        "+lua " .. lua_expr,
+        "+qall",
+    }, { detach = true })
+end
+
 function M.add(specs)
     local resolved = {}
 
@@ -44,17 +84,42 @@ function M.add(specs)
         end
     end
 
-    local ok, err = pcall(vim.pack.add, resolved, { confirm = false, load = true })
+    local installed = {}
+    local missing = {}
+
+    for _, spec in ipairs(resolved) do
+        if plugin_installed(spec) then
+            table.insert(installed, spec)
+        else
+            table.insert(missing, spec)
+        end
+    end
+
+    if #missing > 0 then
+        install_missing_async(missing)
+        vim.schedule(function()
+            vim.notify(
+                "Missing plugins detected. Started background install; restart Neovim when it finishes.",
+                vim.log.levels.WARN
+            )
+        end)
+    end
+
+    if #installed == 0 then
+        return false
+    end
+
+    local ok, err = pcall(vim.pack.add, installed, { confirm = false, load = true })
 
     if not ok and tostring(err):find("ambiguous argument 'HEAD'", 1, true) then
         prune_broken_pack_repos()
         vim.fn.delete(vim.fn.stdpath("config") .. "/nvim-pack-lock.json")
-        ok, err = pcall(vim.pack.add, resolved, { confirm = false, load = true })
+        ok, err = pcall(vim.pack.add, installed, { confirm = false, load = true })
     end
 
     if not ok then
         vim.schedule(function()
-            local msg = "vim.pack failed to install/load plugins. Check network and run :lua vim.pack.update()."
+            local msg = "vim.pack failed to load installed plugins."
             vim.notify(msg .. "\n" .. tostring(err), vim.log.levels.WARN)
         end)
         return false