fix(acp): cancel prompt and tools (#3024)

Closes #3011

Author: olimorris

lua/codecompanion/acp/init.lua

@@ -639,7 +639,7 @@ function Connection:handle_rpc_message(line)
   if message.id and not message.method then
     self:store_rpc_response(message)
     if message.result and message.result ~= vim.NIL and message.result.stopReason then
-      if self._active_prompt and self._active_prompt.handle_done then
+      if self._active_prompt and self._active_prompt._request_id == message.id and self._active_prompt.handle_done then
         self._active_prompt:handle_done(message.result.stopReason)
       end
     end

lua/codecompanion/acp/prompt_builder.lua

@@ -70,6 +70,10 @@ function PromptBuilder:on_error(fn)
   self.handlers.error = fn
   return self
 end
+function PromptBuilder:on_cancel(fn)
+  self.handlers.cancel = fn
+  return self
+end
 function PromptBuilder:with_options(opts)
   self.options = vim.tbl_extend("force", self.options, opts or {})
   return self
@@ -105,6 +109,7 @@ function PromptBuilder:send()
   -- Send the prompt
   local jsonrpc = require("codecompanion.utils.jsonrpc")
   local id = self.connection._state.id_gen:next()
+  self._request_id = id
   local req = jsonrpc.request(id, self.connection.METHODS.SESSION_PROMPT, {
     sessionId = self.connection.session_id,
     prompt = self.messages,
@@ -213,9 +218,9 @@ function PromptBuilder:handle_permission_request(id, params)
     session_id = params.sessionId,
     tool_call = tool_call,
     options = options,
-    respond = function(option_id, canceled)
-      if canceled or not option_id then
-        respond({ outcome = "canceled" })
+    respond = function(option_id, cancelled)
+      if cancelled or not option_id then
+        respond({ outcome = "cancelled" })
       else
         respond({ outcome = "selected", optionId = option_id })
       end
@@ -297,6 +302,13 @@ function PromptBuilder:cancel()
       utils.fire("RequestFinished", self.options)
     end
   end
+
+  -- Handler MUST respond to all requests with "cancelled"
+  -- Ref: https://agentclientprotocol.com/protocol/prompt-turn#cancellation
+  if self.handlers.cancel then
+    pcall(self.handlers.cancel)
+  end
+
   self.connection._active_prompt = nil
 end
 

lua/codecompanion/interactions/chat/acp/handler.lua

@@ -12,7 +12,7 @@ local watch = require("codecompanion.interactions.shared.watch")
 ---@field reasoning table Reasoning output from the Agent
 ---@field tools table<string, table> Cache of tool calls by their ID
 ---@field ui_state table<string, table> Cache of tool call UI states (line_number, icon_id) by tool call ID
----@field _permission { queue: CodeCompanion.Queue, active: boolean } Internal state for managing permission requests
+---@field _permission { queue: CodeCompanion.Queue, active: boolean, respond: function|nil } Internal state for managing permission requests
 local ACPHandler = {}
 
 ---@param chat CodeCompanion.Chat
@@ -27,6 +27,7 @@ function ACPHandler.new(chat)
     _permission = {
       active = false,
       queue = Queue.new(),
+      respond = nil,
     },
   }, { __index = ACPHandler })
 
@@ -196,6 +197,9 @@ function ACPHandler:create_and_send_prompt(payload)
     :on_error(function(error)
       self:handle_error(error)
     end)
+    :on_cancel(function()
+      self:_clear_permission_queue()
+    end)
     :with_options({ bufnr = self.chat.bufnr, interaction = "chat" })
     :send()
 end
@@ -330,11 +334,18 @@ function ACPHandler:_process_next_permission()
     end, request.options or {}))
   )
 
+  -- The original respond function is stored so that if the user cancels the request, we can respond as per the spec
+  self._permission.respond = request.respond
+
   -- Ensure that the next item in the queue is processed after the user's response
   local send_response = request.respond
-  request.respond = function(option_id, canceled)
-    send_response(option_id, canceled)
+  request.respond = function(option_id, cancelled)
+    if not self._permission.respond then
+      return
+    end
+    send_response(option_id, cancelled)
     self._permission.active = false
+    self._permission.respond = nil
     self:_process_next_permission()
   end
 
@@ -344,11 +355,24 @@ end
 ---Clear any requests in the queue
 ---@return nil
 function ACPHandler:_clear_permission_queue()
+  local had_pending = self._permission.respond ~= nil or not self._permission.queue:is_empty()
+
+  -- Cancel the currently active permission request (if any)
+  if self._permission.respond then
+    pcall(self._permission.respond, nil, true)
+    self._permission.respond = nil
+  end
+
+  -- Cancel all queued permission requests
   while not self._permission.queue:is_empty() do
     local request = self._permission.queue:pop()
     pcall(request.respond, nil, true)
   end
   self._permission.active = false
+
+  if had_pending then
+    utils.fire("ToolApprovalFinished", { bufnr = self.chat.bufnr, choice = "cancelled" })
+  end
 end
 
 ---Handle the prompt response when it's complete

tests/acp/test_acp.lua

@@ -405,6 +405,7 @@ T["ACP Responses"]["_handle_done when stopReason present"] = function()
     local connection = create_test_connection()
     local seen
     connection._active_prompt = {
+      _request_id = 1,
       handle_done = function(_, sr) seen = sr end
     }
     connection:handle_rpc_message('{"jsonrpc":"2.0","id":1,"result":{"stopReason":"end_turn"}}')

tests/acp/test_prompt_builder.lua

@@ -306,7 +306,7 @@ T["Prompt Builder"]["Auto-cancels when no handler is registered"] = function()
   ]])
 
   h.eq(13, result.id)
-  h.eq("canceled", result.outcome)
+  h.eq("cancelled", result.outcome)
   h.eq(false, result.has_optionId)
 end
 

tests/interactions/chat/acp/test_handler.lua

@@ -69,6 +69,11 @@ T = new_set({
                 return self
               end,
 
+              on_cancel = function(self, handler)
+                self.handlers.cancel = handler
+                return self
+              end,
+
               with_options = function(self, opts)
                 self.options = opts
                 return self
@@ -846,7 +851,7 @@ T["ACPHandler"]["Permission Queue"]["clears queue on completion"] = function()
 
   h.is_true(result.queue_empty)
   h.is_false(result.active)
-  h.eq({ "tool_2", "tool_3" }, result.rejected)
+  h.eq({ "tool_1", "tool_2", "tool_3" }, result.rejected)
 end
 
 T["ACPHandler"]["Permission Queue"]["clears queue on error"] = function()
@@ -904,7 +909,7 @@ T["ACPHandler"]["Permission Queue"]["clears queue on error"] = function()
 
   h.is_true(result.queue_empty)
   h.is_false(result.active)
-  h.eq({ "tool_2" }, result.rejected)
+  h.eq({ "tool_1", "tool_2" }, result.rejected)
 end
 
 T["ACPHandler"]["Config Options"] = new_set()