apps/api/src/app.module.ts

@@ -57,6 +57,7 @@ import { ContainerLifecycleModule } from "./container-lifecycle/container-lifecy
 import { ContainerReaperModule } from "./container-reaper/container-reaper.module";
 import { FleetSettingsModule } from "./fleet-settings/fleet-settings.module";
 import { OnboardingModule } from "./onboarding/onboarding.module";
+import { ChatProxyModule } from "./chat-proxy/chat-proxy.module";
 
 @Module({
   imports: [
@@ -135,6 +136,7 @@ import { OnboardingModule } from "./onboarding/onboarding.module";
     ContainerReaperModule,
     FleetSettingsModule,
     OnboardingModule,
+    ChatProxyModule,
   ],
   controllers: [AppController, CsrfController],
   providers: [

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();
+      }
+    }
+  }
+}

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

@@ -0,0 +1,25 @@
+import { Type } from "class-transformer";
+import { ArrayMinSize, IsArray, IsNotEmpty, IsString, ValidateNested } from "class-validator";
+
+export interface ChatMessage {
+  role: string;
+  content: string;
+}
+
+export class ChatMessageDto implements ChatMessage {
+  @IsString({ message: "role must be a string" })
+  @IsNotEmpty({ message: "role is required" })
+  role!: string;
+
+  @IsString({ message: "content must be a string" })
+  @IsNotEmpty({ message: "content is required" })
+  content!: string;
+}
+
+export class ChatStreamDto {
+  @IsArray({ message: "messages must be an array" })
+  @ArrayMinSize(1, { message: "messages must contain at least one message" })
+  @ValidateNested({ each: true })
+  @Type(() => ChatMessageDto)
+  messages!: ChatMessageDto[];
+}

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

@@ -0,0 +1,14 @@
+import { Module } from "@nestjs/common";
+import { AgentConfigModule } from "../agent-config/agent-config.module";
+import { ContainerLifecycleModule } from "../container-lifecycle/container-lifecycle.module";
+import { PrismaModule } from "../prisma/prisma.module";
+import { ChatProxyController } from "./chat-proxy.controller";
+import { ChatProxyService } from "./chat-proxy.service";
+
+@Module({
+  imports: [PrismaModule, ContainerLifecycleModule, AgentConfigModule],
+  controllers: [ChatProxyController],
+  providers: [ChatProxyService],
+  exports: [ChatProxyService],
+})
+export class ChatProxyModule {}

apps/api/src/chat-proxy/chat-proxy.service.spec.ts

@@ -0,0 +1,107 @@
+import { ServiceUnavailableException } from "@nestjs/common";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { ChatProxyService } from "./chat-proxy.service";
+
+describe("ChatProxyService", () => {
+  const userId = "user-123";
+
+  const prisma = {
+    userAgentConfig: {
+      findUnique: vi.fn(),
+    },
+  };
+
+  const containerLifecycle = {
+    ensureRunning: vi.fn(),
+    touch: vi.fn(),
+  };
+
+  let service: ChatProxyService;
+  let fetchMock: ReturnType<typeof vi.fn>;
+
+  beforeEach(() => {
+    fetchMock = vi.fn();
+    vi.stubGlobal("fetch", fetchMock);
+    service = new ChatProxyService(prisma as never, containerLifecycle as never);
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+    vi.clearAllMocks();
+  });
+
+  describe("getContainerUrl", () => {
+    it("calls ensureRunning and touch for the user", async () => {
+      containerLifecycle.ensureRunning.mockResolvedValue({
+        url: "http://mosaic-user-user-123:19000",
+        token: "gateway-token",
+      });
+      containerLifecycle.touch.mockResolvedValue(undefined);
+
+      const url = await service.getContainerUrl(userId);
+
+      expect(url).toBe("http://mosaic-user-user-123:19000");
+      expect(containerLifecycle.ensureRunning).toHaveBeenCalledWith(userId);
+      expect(containerLifecycle.touch).toHaveBeenCalledWith(userId);
+    });
+  });
+
+  describe("proxyChat", () => {
+    it("forwards the request to the user's OpenClaw container", async () => {
+      containerLifecycle.ensureRunning.mockResolvedValue({
+        url: "http://mosaic-user-user-123:19000",
+        token: "gateway-token",
+      });
+      containerLifecycle.touch.mockResolvedValue(undefined);
+      fetchMock.mockResolvedValue(new Response("event: token\ndata: hello\n\n"));
+
+      const messages = [{ role: "user", content: "Hello from Mosaic" }];
+      const response = await service.proxyChat(userId, messages);
+
+      expect(response).toBeInstanceOf(Response);
+      expect(fetchMock).toHaveBeenCalledWith(
+        "http://mosaic-user-user-123:19000/v1/chat/completions",
+        expect.objectContaining({
+          method: "POST",
+          headers: {
+            "Content-Type": "application/json",
+          },
+        })
+      );
+
+      const [, request] = fetchMock.mock.calls[0] as [string, RequestInit];
+      const parsedBody = JSON.parse(String(request.body));
+      expect(parsedBody).toEqual({
+        messages,
+        model: "openclaw:default",
+        stream: true,
+      });
+    });
+
+    it("throws ServiceUnavailableException on connection refused errors", async () => {
+      containerLifecycle.ensureRunning.mockResolvedValue({
+        url: "http://mosaic-user-user-123:19000",
+        token: "gateway-token",
+      });
+      containerLifecycle.touch.mockResolvedValue(undefined);
+      fetchMock.mockRejectedValue(new Error("connect ECONNREFUSED 127.0.0.1:19000"));
+
+      await expect(service.proxyChat(userId, [])).rejects.toBeInstanceOf(
+        ServiceUnavailableException
+      );
+    });
+
+    it("throws ServiceUnavailableException on timeout errors", async () => {
+      containerLifecycle.ensureRunning.mockResolvedValue({
+        url: "http://mosaic-user-user-123:19000",
+        token: "gateway-token",
+      });
+      containerLifecycle.touch.mockResolvedValue(undefined);
+      fetchMock.mockRejectedValue(new Error("The operation was aborted due to timeout"));
+
+      await expect(service.proxyChat(userId, [])).rejects.toBeInstanceOf(
+        ServiceUnavailableException
+      );
+    });
+  });
+});

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

@@ -0,0 +1,89 @@
+import { BadGatewayException, Injectable, ServiceUnavailableException } from "@nestjs/common";
+import { ContainerLifecycleService } from "../container-lifecycle/container-lifecycle.service";
+import { PrismaService } from "../prisma/prisma.service";
+import type { ChatMessage } from "./chat-proxy.dto";
+
+const DEFAULT_OPENCLAW_MODEL = "openclaw:default";
+
+@Injectable()
+export class ChatProxyService {
+  constructor(
+    private readonly prisma: PrismaService,
+    private readonly containerLifecycle: ContainerLifecycleService
+  ) {}
+
+  // Get the user's OpenClaw container URL and mark it active.
+  async getContainerUrl(userId: string): Promise<string> {
+    const { url } = await this.containerLifecycle.ensureRunning(userId);
+    await this.containerLifecycle.touch(userId);
+    return url;
+  }
+
+  // Proxy chat request to OpenClaw.
+  async proxyChat(
+    userId: string,
+    messages: ChatMessage[],
+    signal?: AbortSignal
+  ): Promise<Response> {
+    const containerUrl = await this.getContainerUrl(userId);
+    const model = await this.getPreferredModel(userId);
+    const requestInit: RequestInit = {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({
+        messages,
+        model,
+        stream: true,
+      }),
+    };
+
+    if (signal) {
+      requestInit.signal = signal;
+    }
+
+    try {
+      const response = await fetch(`${containerUrl}/v1/chat/completions`, requestInit);
+
+      if (!response.ok) {
+        const detail = await this.readResponseText(response);
+        const status = `${String(response.status)} ${response.statusText}`.trim();
+        const message = detail
+          ? `OpenClaw returned ${status}: ${detail}`
+          : `OpenClaw returned ${status}`;
+        throw new BadGatewayException(message);
+      }
+
+      return response;
+    } catch (error: unknown) {
+      if (error instanceof BadGatewayException) {
+        throw error;
+      }
+
+      const message = error instanceof Error ? error.message : String(error);
+      throw new ServiceUnavailableException(`Failed to proxy chat to OpenClaw: ${message}`);
+    }
+  }
+
+  private async getPreferredModel(userId: string): Promise<string> {
+    const config = await this.prisma.userAgentConfig.findUnique({
+      where: { userId },
+      select: { primaryModel: true },
+    });
+
+    const primaryModel = config?.primaryModel?.trim();
+    if (!primaryModel) {
+      return DEFAULT_OPENCLAW_MODEL;
+    }
+
+    return primaryModel;
+  }
+
+  private async readResponseText(response: Response): Promise<string | null> {
+    try {
+      const text = (await response.text()).trim();
+      return text.length > 0 ? text : null;
+    } catch {
+      return null;
+    }
+  }
+}