refactor: refactor TODO handling to context messages

- Refactor TODOs handling: move logic to `context_messages` instead of using `template_opts`
- Improve todo message filtering by using more precise tags (`<todos>...</todos>`)
- Append TODOs after history messages
- Remove the TODOs section from `_task-guidelines.avanterules` template

Signed-off-by: doodleEsc <cinuor@gmail.com>

lua/avante/llm.lua

@@ -309,10 +309,7 @@ function M.generate_prompts(opts)
     memory = opts.memory,
   }
 
-  if opts.get_todos then
-    local todos = opts.get_todos()
-    if todos and #todos > 0 then template_opts.todos = vim.json.encode(todos) end
-  end
+  -- Removed the original todos processing logic, now handled in context_messages
 
   local system_prompt
   if opts.prompt_opts and opts.prompt_opts.system_prompt then
@@ -418,6 +415,30 @@ function M.generate_prompts(opts)
     messages = vim.list_extend(messages, { { role = "user", content = opts.instructions } })
   end
 
+  if opts.get_todos then
+    local todos = opts.get_todos()
+    if todos and #todos > 0 then
+      -- Remove existing todos-related messages - use more precise <todos> tag matching
+      messages = vim
+        .iter(messages)
+        :filter(function(msg)
+          if not msg.content or type(msg.content) ~= "string" then return true end
+          -- Only filter out messages that start with <todos> and end with </todos> to avoid accidentally deleting other messages
+          return not msg.content:match("^<todos>.*</todos>$")
+        end)
+        :totable()
+
+      -- Add the latest todos to the end of messages, wrapped in <todos> tags
+      local todos_content = vim.json.encode(todos)
+      table.insert(messages, {
+        role = "user",
+        content = "<todos>\n" .. todos_content .. "\n</todos>",
+        visible = false,
+        is_context = true,
+      })
+    end
+  end
+
   opts.session_ctx = opts.session_ctx or {}
   opts.session_ctx.system_prompt = system_prompt
   opts.session_ctx.messages = messages

lua/avante/templates/_task-guidelines.avanterules

@@ -1,13 +1,3 @@
-{% if todos -%}
-====
-
-# Task TODOs
-
-{{todos}}
-
-====
-{%- endif %}
-
 # Task Management
 You have access to the add_todos and update_todo_status tools to help you manage and plan tasks. Use these tools VERY frequently to ensure that you are tracking your tasks and giving the user visibility into your progress.
 These tools are also EXTREMELY helpful for planning tasks, and for breaking down larger complex tasks into smaller steps. If you do not use this tool when planning, you may forget to do important tasks - and that is unacceptable.