Extract buildChatRequest out of ChatInterface (#21)

Pulls the inline ChatRequest assembly into a stateless helper in src/chat/.
Snapshots messages on build so post-send mutations by the caller don't
leak into the in-flight request. Unit tests cover field passthrough, uuid
generation, and the snapshot guarantee.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/chat/__tests__/request-builder.test.ts

@@ -0,0 +1,64 @@
+import { describe, it, expect } from "vitest";
+import { buildChatRequest } from "@/chat/request-builder";
+import type { Model, ModelChatMessage } from "@/types";
+
+const model: Model = {
+    id: "openai:gpt-4-turbo",
+    provider: "openai",
+    name: "GPT-4 Turbo",
+    renaming: false,
+    toggleWebSearch: true,
+    streaming: true,
+};
+
+const messages: ModelChatMessage[] = [
+    { role: "user", content: "hello" },
+    { role: "assistant", content: "hi" },
+];
+
+describe("buildChatRequest", () => {
+    it("populates modelId from the supplied model", () => {
+        const request = buildChatRequest({ model, messages });
+        expect(request.modelId).toBe(model.id);
+    });
+
+    it("assigns a uuid-shaped requestID", () => {
+        const request = buildChatRequest({ model, messages });
+        expect(request.requestID).toMatch(
+            /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/,
+        );
+    });
+
+    it("issues a fresh requestID for each call", () => {
+        const a = buildChatRequest({ model, messages });
+        const b = buildChatRequest({ model, messages });
+        expect(a.requestID).not.toBe(b.requestID);
+    });
+
+    it("snapshots the messages array so caller mutations don't leak", () => {
+        const local = [...messages];
+        const request = buildChatRequest({ model, messages: local });
+        local.push({ role: "user", content: "mutated after build" });
+        expect(request.messages).toHaveLength(2);
+    });
+
+    it("passes through optional fields", () => {
+        const request = buildChatRequest({
+            model,
+            messages,
+            context: [{ title: "note", content: "body" }],
+            webSearch: true,
+            systemPrompt: "be terse",
+        });
+        expect(request.context).toEqual([{ title: "note", content: "body" }]);
+        expect(request.webSearch).toBe(true);
+        expect(request.systemPrompt).toBe("be terse");
+    });
+
+    it("leaves optional fields undefined when omitted", () => {
+        const request = buildChatRequest({ model, messages });
+        expect(request.context).toBeUndefined();
+        expect(request.webSearch).toBeUndefined();
+        expect(request.systemPrompt).toBeUndefined();
+    });
+});

src/chat/request-builder.ts

@@ -0,0 +1,29 @@
+import {
+    ChatRequest,
+    ContextItemContent,
+    Model,
+    ModelChatMessage,
+} from "@/types";
+
+export interface BuildChatRequestParams {
+    model: Model;
+    messages: ModelChatMessage[];
+    context?: ContextItemContent[];
+    webSearch?: boolean;
+    systemPrompt?: string;
+}
+
+/**
+ * Assembles a {@link ChatRequest} from its inputs. Snapshots the messages array
+ * so later mutations by the caller don't leak into the in-flight request.
+ */
+export function buildChatRequest(params: BuildChatRequestParams): ChatRequest {
+    return {
+        requestID: crypto.randomUUID(),
+        modelId: params.model.id,
+        messages: [...params.messages],
+        context: params.context,
+        webSearch: params.webSearch,
+        systemPrompt: params.systemPrompt,
+    };
+}

src/components/ChatInterface.tsx

@@ -18,6 +18,7 @@ import { SourceList } from "@/components/SourceList";
 
 import { getContext } from "@/utils/model-context";
 import { ensureSourceTitle } from "@/utils/url";
+import { buildChatRequest } from "@/chat/request-builder";
 import { loadSystemPrompt } from "@/chat/system-prompt-loader";
 import { HandleChatChangeProps } from "@/ChatView";
 
@@ -140,14 +141,13 @@ export const ChatInterface = ({
             );
         }
 
-        const request: ChatRequest = {
-            requestID: crypto.randomUUID(),
-            modelId: requestModel.id,
-            messages: [...messages()],
+        const request = buildChatRequest({
+            model: requestModel,
+            messages: messages(),
             context: parsedContext,
             webSearch: webSearchEnabled,
-            systemPrompt: systemPrompt,
-        };
+            systemPrompt,
+        });
         setCurrentRequest(request);
 
         try {