Use more strict type guards in ai package

Turned on type-checked linting and fixed the low-hanging fruit of issues
that arose. We can't yet add these lint rules in more places, but I
wanted to at least get the benefit of these refactors before abandoning
them for a while until we have time to address the issues.

Author: scotttrinh

packages/ai/src/core.ts

@@ -1,7 +1,6 @@
 import type { Client } from "gel";
 import { EventSourceParserStream } from "eventsource-parser/stream";
 
-import type { ResolvedConnectConfig } from "gel/dist/conUtils.js";
 import {
   getAuthenticatedFetch,
   type AuthenticatedFetch,
@@ -46,9 +45,7 @@ export class RAGClient {
   }
 
   private static async getAuthenticatedFetch(client: Client) {
-    const connectConfig: ResolvedConnectConfig = (
-      await (client as any).pool._getNormalizedConnectConfig()
-    ).connectionParams;
+    const connectConfig = await client.resolveConnectionParams();
 
     return getAuthenticatedFetch(connectConfig, httpSCRAMAuth, "ext/ai/");
   }
@@ -110,7 +107,7 @@ export class RAGClient {
             !providedPrompt && {
               name: "builtin::rag-default",
             }),
-          custom: [...(this.options.prompt?.custom || []), ...messages],
+          custom: [...(this.options.prompt?.custom ?? []), ...messages],
         },
         query: [...messages].reverse().find((msg) => msg.role === "user")!
           .content[0].text,
@@ -139,18 +136,9 @@ export class RAGClient {
       );
     }
 
-    const data = await res.json();
+    const data: unknown = await res.json();
 
-    if (
-      !data ||
-      typeof data !== "object" ||
-      typeof data.response !== "string"
-    ) {
-      throw new Error(
-        "Expected response to be an object with response key of type string",
-      );
-    }
-    return data.response;
+    return parseResponse(data);
   }
 
   streamRag(
@@ -190,6 +178,7 @@ export class RAGClient {
         }
       },
       then<TResult1 = Response, TResult2 = never>(
+        /* eslint-disable @typescript-eslint/no-duplicate-type-constituents */
         onfulfilled?:
           | ((value: Response) => TResult1 | PromiseLike<TResult1>)
           | undefined
@@ -198,6 +187,7 @@ export class RAGClient {
           | ((reason: any) => TResult2 | PromiseLike<TResult2>)
           | undefined
           | null,
+        /* eslint-enable @typescript-eslint/no-duplicate-type-constituents */
       ): Promise<TResult1 | TResult2> {
         return fetchRag(
           {
@@ -225,7 +215,43 @@ export class RAGClient {
       await handleResponseError(response);
     }
 
-    const data: { data: { embedding: number[] }[] } = await response.json();
-    return data.data[0].embedding;
+    const data: unknown = await response.json();
+    return parseEmbeddingResponse(data);
+  }
+}
+
+function parseResponse(data: unknown): string {
+  if (
+    typeof data === "object" &&
+    data != null &&
+    "response" in data &&
+    typeof data.response === "string"
+  ) {
+    return data.response;
+  }
+
+  throw new Error(
+    "Expected response to be an object with response key of type string",
+  );
+}
+
+function parseEmbeddingResponse(responseData: unknown): number[] {
+  if (
+    typeof responseData === "object" &&
+    responseData != null &&
+    "data" in responseData &&
+    Array.isArray(responseData.data)
+  ) {
+    const firstItem: unknown = responseData.data[0];
+    if (
+      typeof firstItem === "object" &&
+      firstItem != null &&
+      "embedding" in firstItem
+    ) {
+      return firstItem.embedding as number[];
+    }
   }
+  throw new Error(
+    "Expected response to be an object with data key of type array of objects with embedding key of type number[]",
+  );
 }