fix(core): small delay on open

Caused by vim.system():wait() delay when checking opencode version.

Fixed by adding Promise.system() which wraps vim.system in a promise
(using vim.system's callback mechanism)

Author: cameronr

lua/opencode/core.lua

@@ -296,7 +296,7 @@ M.cancel = Promise.async(function()
   end
 end)
 
-function M.opencode_ok()
+M.opencode_ok = Promise.async(function()
   if vim.fn.executable('opencode') == 0 then
     vim.notify(
       'opencode command not found - please install and configure opencode before using this plugin',
@@ -306,7 +306,7 @@ function M.opencode_ok()
   end
 
   if not state.opencode_cli_version or state.opencode_cli_version == '' then
-    local result = vim.system({ 'opencode', '--version' }):wait()
+    local result = Promise.system({ 'opencode', '--version' }):await()
     local out = (result and result.stdout or ''):gsub('%s+$', '')
     state.opencode_cli_version = out:match('(%d+%%.%d+%%.%d+)') or out
   end
@@ -328,7 +328,7 @@ function M.opencode_ok()
   end
 
   return true
-end
+end)
 
 local function on_opencode_server()
   state.current_permission = nil

lua/opencode/promise.lua

@@ -22,6 +22,7 @@
 ---@field wrap fun(obj: T | Promise<T>): Promise<T>
 ---@field spawn fun(fn: fun(): T|nil): Promise<T>
 ---@field async fun(fn: fun(...): T?): fun(...): Promise<T>
+---@field system fun()
 local Promise = {}
 Promise.__index = Promise
 
@@ -336,4 +337,23 @@ function Promise.async(fn)
   end
 end
 
+---Wrap vim.system in a promise
+---@generic T
+---@param cmd table vim.system cmd options
+---@param opts table|nil vim.system opts
+---@return Promise<T>
+function Promise.system(cmd, opts)
+  local p = Promise.new()
+
+  vim.system(cmd, opts or {}, function(result)
+    if result.code == 0 then
+      p:resolve(result)
+    else
+      p:reject(result)
+    end
+  end)
+
+  return p
+end
+
 return Promise