Make it so you can't delete the last prompt or scenario

No reason for an experiment to have 0 prompts or 0 scenarios and it makes the UI look bad.

src/server/api/routers/experiments.router.ts

@@ -74,15 +74,23 @@ export const experimentsRouter = createTRPCRouter({
           constructFn: dedent`prompt = {
             model: "gpt-3.5-turbo-0613",
             stream: true,
-            messages: [{ role: "system", content: "Return 'Ready to go!'" }],
+            messages: [{ role: "system", content: ${"`Return '${scenario.text}'`"} }],
           }`,
           model: "gpt-3.5-turbo-0613",
         },
       }),
+      prisma.templateVariable.create({
+        data: {
+          experimentId: exp.id,
+          label: "text",
+        },
+      }),
       prisma.testScenario.create({
         data: {
           experimentId: exp.id,
-          variableValues: {},
+          variableValues: {
+            text: "This is a test scenario.",
+          },
         },
       }),
     ]);

src/server/api/routers/promptVariants.router.ts

@@ -1,3 +1,4 @@
+import dedent from "dedent";
 import { isObject } from "lodash";
 import { z } from "zod";
 import { createTRPCRouter, publicProcedure } from "~/server/api/trpc";
@@ -113,7 +114,18 @@ export const promptVariantsRouter = createTRPCRouter({
           experimentId: input.experimentId,
           label: `Prompt Variant ${largestSortIndex + 2}`,
           sortIndex: (lastVariant?.sortIndex ?? 0) + 1,
-          constructFn: lastVariant?.constructFn ?? "",
+          constructFn:
+            lastVariant?.constructFn ??
+            dedent`
+          prompt = {
+            model: "gpt-3.5-turbo",
+            messages: [
+              {
+                role: "system",
+                content: "Return 'Hello, world!'",
+              }
+            ]
+          }`,
           model: lastVariant?.model ?? "gpt-3.5-turbo",
         },
       });

src/server/utils/constructPrompt.ts

@@ -9,7 +9,7 @@ export async function constructPrompt(
   scenario: TestScenario["variableValues"],
 ): Promise<JSONSerializable> {
   const code = `
-      const scenario = ${JSON.stringify(scenario, null, 2)};
+      const scenario = ${JSON.stringify(scenario ?? {}, null, 2)};
       let prompt
 
       ${variant.constructFn}