feat(copilot): optimize copilot quota usage for tool calling

* update: new function in copilot provider for agent initiator

* refactor: remove initiator into prepare_input function

Author: pxwg

lua/CopilotChat/client.lua

@@ -511,7 +511,14 @@ function Client:ask(opts)
   end
 
   local headers = self:authenticate(provider_name)
-  local request = provider.prepare_input(generate_ask_request(opts.system_prompt, history, generated_messages), options)
+
+  local request, extra_headers =
+    provider.prepare_input(generate_ask_request(opts.system_prompt, history, generated_messages), options)
+
+  if extra_headers then
+    headers = vim.tbl_extend('force', headers, extra_headers)
+  end
+
   local is_stream = request.stream
 
   local args = {

lua/CopilotChat/config/providers.lua

@@ -641,10 +641,21 @@ M.copilot = {
   end,
 
   prepare_input = function(inputs, opts)
+    local request
     if opts.model.use_responses then
-      return prepare_responses_input(inputs, opts)
+      request = prepare_responses_input(inputs, opts)
+    else
+      request = prepare_chat_input(inputs, opts)
     end
-    return prepare_chat_input(inputs, opts)
+
+    if inputs and #inputs > 0 then
+      local last_msg = inputs[#inputs]
+      if last_msg.role == constants.ROLE.TOOL then
+        return request, { ['x-initiator'] = 'agent' }
+      end
+    end
+
+    return request
   end,
 
   prepare_output = function(output, opts)