perf: async parallel cache initialization and remove deepcopy

Problem: first completion request blocked the UI with three sequential
synchronous vim.system():wait() calls (man page, command names,
command list), and every subsequent completion unnecessarily
deep-copied the entire cache.

Solution: run all three system calls concurrently via vim.system
callbacks, merging results when all complete. Queue pending completion
requests during loading. Return cached items directly instead of
deep-copying.

lua/blink-cmp-tmux.lua

@@ -3,6 +3,9 @@ local M = {}
 
 ---@type blink.cmp.CompletionItem[]?
 local cache = nil
+local loading = false
+---@type {ctx: blink.cmp.Context, callback: fun(response: blink.cmp.CompletionResponse)}[]
+local pending = {}
 
 function M.new()
   return setmetatable({}, { __index = M })
@@ -13,18 +16,17 @@ function M.enabled()
   return vim.bo.filetype == 'tmux'
 end
 
+---@param man_stdout string
+---@param names_stdout string
 ---@return table<string, string>
-local function parse_descriptions()
-  local result = vim.system({ 'bash', '-c', 'MANWIDTH=80 man -P cat tmux 2>/dev/null' }):wait()
-  local stdout = result.stdout or ''
+local function parse_descriptions(man_stdout, names_stdout)
   local lines = {}
-  for line in (stdout .. '\n'):gmatch('(.-)\n') do
+  for line in (man_stdout .. '\n'):gmatch('(.-)\n') do
     lines[#lines + 1] = line
   end
 
-  local cmd_result = vim.system({ 'tmux', 'list-commands', '-F', '#{command_list_name}' }):wait()
   local cmds = {}
-  for name in (cmd_result.stdout or ''):gmatch('[^\n]+') do
+  for name in names_stdout:gmatch('[^\n]+') do
     cmds[name] = true
   end
 
@@ -128,27 +130,66 @@ end
 
 ---@param ctx blink.cmp.Context
 ---@param callback fun(response: blink.cmp.CompletionResponse)
----@return fun()
-function M:get_completions(ctx, callback)
-  if not cache then
-    local ok, descs = pcall(parse_descriptions)
-    if not ok then
-      descs = {}
-    end
-    local result = vim.system({ 'tmux', 'list-commands' }):wait()
-    cache = parse(result.stdout or '', descs)
-  end
-
+local function respond(ctx, callback)
   local before = ctx.line:sub(1, ctx.cursor[2])
   if before:match('^%s*[a-z-]*$') then
     callback({
       is_incomplete_forward = false,
       is_incomplete_backward = false,
-      items = vim.deepcopy(cache),
+      items = cache,
     })
   else
     callback({ items = {} })
   end
+end
+
+---@param ctx blink.cmp.Context
+---@param callback fun(response: blink.cmp.CompletionResponse)
+---@return fun()
+function M:get_completions(ctx, callback)
+  if cache then
+    respond(ctx, callback)
+    return function() end
+  end
+
+  pending[#pending + 1] = { ctx = ctx, callback = callback }
+  if not loading then
+    loading = true
+    local man_out, names_out, cmds_out
+    local remaining = 3
+
+    local function on_all_done()
+      remaining = remaining - 1
+      if remaining > 0 then
+        return
+      end
+      vim.schedule(function()
+        local ok, descs = pcall(parse_descriptions, man_out, names_out)
+        if not ok then
+          descs = {}
+        end
+        cache = parse(cmds_out, descs)
+        loading = false
+        for _, p in ipairs(pending) do
+          respond(p.ctx, p.callback)
+        end
+        pending = {}
+      end)
+    end
+
+    vim.system({ 'bash', '-c', 'MANWIDTH=80 man -P cat tmux 2>/dev/null' }, {}, function(result)
+      man_out = result.stdout or ''
+      on_all_done()
+    end)
+    vim.system({ 'tmux', 'list-commands', '-F', '#{command_list_name}' }, {}, function(result)
+      names_out = result.stdout or ''
+      on_all_done()
+    end)
+    vim.system({ 'tmux', 'list-commands' }, {}, function(result)
+      cmds_out = result.stdout or ''
+      on_all_done()
+    end)
+  end
   return function() end
 end