Fix deepseek v4 reasoning inject thoughts (#5527)

* Fix deepseek v4 injectReasoning error
resolves #5509

* comment

server/utils/agents/aibitat/providers/deepseek.js

@@ -54,8 +54,20 @@ class DeepSeekProvider extends InheritMultiple([Provider, UnTooled]) {
     return rest;
   }
 
+  /**
+   * Check if the model is a thinking model
+   * because we need to inject reasoning content into the messages
+   * or else the DeepSeek API will return an error for specific models.
+   * There is no official way to predetect if a model will require this
+   * so we have to hardcode the list of thinking models.
+   * @returns {boolean}
+   */
   get #isThinkingModel() {
-    return this.model === "deepseek-reasoner";
+    return [
+      "deepseek-reasoner",
+      "deepseek-v4-flash",
+      "deepseek-v4-pro",
+    ].includes(this.model);
   }
 
   get #tooledOptions() {