feat(api): chat proxy (MS22-P1i) (#615)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/api/src/chat-proxy/chat-proxy.controller.ts

@@ -0,0 +1,72 @@
+import { Body, Controller, Post, Req, Res, UnauthorizedException, UseGuards } from "@nestjs/common";
+import type { Response } from "express";
+import { AuthGuard } from "../auth/guards/auth.guard";
+import type { MaybeAuthenticatedRequest } from "../auth/types/better-auth-request.interface";
+import { ChatStreamDto } from "./chat-proxy.dto";
+import { ChatProxyService } from "./chat-proxy.service";
+
+@Controller("chat")
+@UseGuards(AuthGuard)
+export class ChatProxyController {
+  constructor(private readonly chatProxyService: ChatProxyService) {}
+
+  // POST /api/chat/stream
+  // Request: { messages: Array<{role, content}> }
+  // Response: SSE stream of chat completion events
+  @Post("stream")
+  async streamChat(
+    @Body() body: ChatStreamDto,
+    @Req() req: MaybeAuthenticatedRequest,
+    @Res() res: Response
+  ): Promise<void> {
+    const userId = req.user?.id;
+    if (!userId) {
+      throw new UnauthorizedException("No authenticated user found on request");
+    }
+
+    const abortController = new AbortController();
+    req.once("close", () => {
+      abortController.abort();
+    });
+
+    res.setHeader("Content-Type", "text/event-stream");
+    res.setHeader("Cache-Control", "no-cache");
+    res.setHeader("Connection", "keep-alive");
+    res.setHeader("X-Accel-Buffering", "no");
+
+    try {
+      const upstreamResponse = await this.chatProxyService.proxyChat(
+        userId,
+        body.messages,
+        abortController.signal
+      );
+
+      const upstreamContentType = upstreamResponse.headers.get("content-type");
+      if (upstreamContentType) {
+        res.setHeader("Content-Type", upstreamContentType);
+      }
+
+      if (!upstreamResponse.body) {
+        throw new Error("OpenClaw response did not include a stream body");
+      }
+
+      for await (const chunk of upstreamResponse.body as unknown as AsyncIterable<Uint8Array>) {
+        if (res.writableEnded || res.destroyed) {
+          break;
+        }
+
+        res.write(Buffer.from(chunk));
+      }
+    } catch (error: unknown) {
+      if (!res.writableEnded && !res.destroyed) {
+        const message = error instanceof Error ? error.message : String(error);
+        res.write("event: error\n");
+        res.write(`data: ${JSON.stringify({ error: message })}\n\n`);
+      }
+    } finally {
+      if (!res.writableEnded && !res.destroyed) {
+        res.end();
+      }
+    }
+  }
+}