fix: Ensure we drop user after tool messages

lua/codecompanion/adapters/http/mistral.lua

@@ -61,6 +61,33 @@ return {
       return openai.handlers.form_parameters(self, params, messages)
     end,
     form_messages = function(self, messages)
+      local pending_messages = self.pending_messages or {}
+      local is_previous_tool = false
+      for k, msg in ipairs(messages) do
+        local is_tool = msg.role == "tool"
+        local is_user = msg.role == "user"
+        -- Mistral does not like user after tool messages, those should always be assistant
+        if is_previous_tool and is_user then
+          table.insert(pending_messages, msg)
+          messages[k] = nil
+          -- message was dropped, so for the next message, the previous one
+          -- is still a tool
+          is_tool = true
+        else
+          if not is_previous_tool then
+            -- Flush pending messages whenever we can
+            for i, m in ipairs(pending_messages) do
+              table.insert(messages, m)
+            end
+            pending_messages = {}
+          end
+        end
+        is_previous_tool = is_tool
+      end
+
+      -- Keep the pending messages for next round
+      self.pending_messages = pending_messages
+
       return openai.handlers.form_messages(self, messages)
     end,
     chat_output = function(self, data, tools)

tests/adapters/http/test_mistral.lua

@@ -50,6 +50,8 @@ T["Mistral adapter"]["form_messages"]["it can form messages with tools"] = funct
         },
       },
     },
+    { role = "tool", content = "ok" },
+    { role = "assistant", content = "that works" },
   }
 
   local expected = {
@@ -83,6 +85,56 @@ T["Mistral adapter"]["form_messages"]["it can form messages with tools"] = funct
           },
         },
       },
+      { role = "tool", content = "ok" },
+      { role = "assistant", content = "that works" },
+    },
+  }
+
+  h.eq(expected, adapter.handlers.form_messages(adapter, input))
+end
+
+T["Mistral adapter"]["form_messages"]["it skips messages when user follows tools"] = function()
+  local input = {
+    { role = "user", content = "User1" },
+    {
+      role = "llm",
+      tools = {
+        calls = {
+          {
+            ["function"] = {
+              arguments = '{"location":"London, UK","units":"fahrenheit"}',
+              name = "weather",
+            },
+            id = "call_1_a460d461-60a7-468c-a699-ef9e2dced125",
+            type = "function",
+          },
+        },
+      },
+    },
+    { role = "tool", content = "ok" },
+    { role = "user", content = "my message" },
+  }
+
+  local expected = {
+    messages = {
+      {
+        content = "User1",
+        role = "user",
+      },
+      {
+        role = "llm",
+        tool_calls = {
+          {
+            ["function"] = {
+              arguments = '{"location":"London, UK","units":"fahrenheit"}',
+              name = "weather",
+            },
+            id = "call_1_a460d461-60a7-468c-a699-ef9e2dced125",
+            type = "function",
+          },
+        },
+      },
+      { role = "tool", content = "ok" },
     },
   }