Allow creating a fine-tuning datasplit with a tag. Need this more now…

… that we have evals. Cooool.

app/web_ui/src/routes/(app)/fine_tune/[project_id]/[task_id]/create_finetune/+page.svelte

@@ -26,6 +26,7 @@
   let dataset_id = disabled_header
   let new_dataset_split = disabled_header
   let new_dataset_filter = disabled_header
+  let custom_dataset_tag = ""
   let automatic_validation = disabled_header
   let data_strategy: FinetuneDataStrategy = "final_only"
   let finetune_custom_system_prompt = ""
@@ -285,6 +286,12 @@
     try {
       create_dataset_split_loading = true
       create_dataset_split_error = null
+
+      let dataset_filter_id = new_dataset_filter
+      if (dataset_filter_id === "custom_tag") {
+        dataset_filter_id = "tag::" + custom_dataset_tag
+      }
+
       const { data: create_dataset_split_response, error: post_error } =
         await client.POST(
           "/api/projects/{project_id}/tasks/{task_id}/dataset_splits",
@@ -298,7 +305,7 @@
             body: {
               // @ts-expect-error types are validated by the server
               dataset_split_type: new_dataset_split,
-              filter_id: new_dataset_filter,
+              filter_id: dataset_filter_id,
             },
           },
         )
@@ -798,9 +805,20 @@
               "thinking_model_high_rated",
               "Thinking + High Rated (4+ stars and thinking)",
             ],
+            ["custom_tag", "Custom Dataset Tag (eg 'training_set_v2')"],
           ]}
           bind:value={new_dataset_filter}
         />
+        {#if new_dataset_filter === "custom_tag"}
+          <FormElement
+            label="Custom Dataset Tag Filter"
+            description="The dataset split will only include examples with this tag."
+            inputType="input"
+            id="custom_dataset_tag"
+            bind:value={custom_dataset_tag}
+          />
+        {/if}
+
         <FormElement
           label="Dataset Splits"
           description="Select a splitting strategy for your dataset."