fix(cursor): discover models via Cursor ACP client

Fixes #925

packages/server/src/server/agent/provider-registry.test.ts

@@ -13,6 +13,10 @@ const mockState = vi.hoisted(() => {
       claude: [] as ConstructorEntry[],
       codex: [] as ConstructorEntry[],
       copilot: [] as ConstructorEntry[],
+      cursor: [] as Array<{
+        command: string[];
+        env?: Record<string, string>;
+      }>,
       pi: [] as ConstructorEntry[],
       genericAcp: [] as Array<{
         command: string[];
@@ -27,6 +31,7 @@ const mockState = vi.hoisted(() => {
       this.constructorArgs.claude = [];
       this.constructorArgs.codex = [];
       this.constructorArgs.copilot = [];
+      this.constructorArgs.cursor = [];
       this.constructorArgs.pi = [];
       this.constructorArgs.genericAcp = [];
       this.isCommandAvailable.mockReset();
@@ -286,6 +291,55 @@ vi.mock("./providers/generic-acp-agent.js", () => ({
   },
 }));
 
+vi.mock("./providers/cursor-acp-agent.js", () => ({
+  CursorACPAgentClient: class CursorACPAgentClient {
+    readonly capabilities = {
+      supportsStreaming: true,
+      supportsSessionPersistence: true,
+      supportsDynamicModes: true,
+      supportsMcpServers: true,
+      supportsReasoningStream: true,
+      supportsToolInvocations: true,
+    };
+    readonly provider = "acp";
+    readonly runtimeSettings?: unknown;
+
+    constructor(options: { command: string[]; env?: Record<string, string> }) {
+      this.runtimeSettings = {
+        command: {
+          mode: "replace",
+          argv: options.command,
+        },
+        env: options.env,
+      };
+      mockState.constructorArgs.cursor.push({
+        command: options.command,
+        env: options.env,
+      });
+    }
+
+    async createSession(): Promise<never> {
+      throw new Error("not implemented");
+    }
+
+    async resumeSession(): Promise<never> {
+      throw new Error("not implemented");
+    }
+
+    async listModels(): Promise<AgentModelDefinition[]> {
+      return mockState.runtimeModels.get(this.provider) ?? [];
+    }
+
+    async listModes(): Promise<[]> {
+      return [];
+    }
+
+    async isAvailable(): Promise<boolean> {
+      return true;
+    }
+  },
+}));
+
 import {
   AGENT_PROVIDER_DEFINITIONS,
   buildProviderRegistry,
@@ -410,6 +464,38 @@ test("new provider extending acp uses GenericACPAgentClient", () => {
   ]);
 });
 
+test("cursor provider extending acp uses CursorACPAgentClient", () => {
+  const registry = buildProviderRegistry(logger, {
+    providerOverrides: {
+      cursor: {
+        extends: "acp",
+        label: "Cursor",
+        command: ["cursor-agent", "acp"],
+        env: {
+          CURSOR_AGENT_LOG: "debug",
+        },
+      },
+    },
+  });
+
+  expect(registry.cursor.createClient(logger).provider).toBe("cursor");
+  expect(mockState.constructorArgs.cursor).toEqual([
+    {
+      command: ["cursor-agent", "acp"],
+      env: {
+        CURSOR_AGENT_LOG: "debug",
+      },
+    },
+    {
+      command: ["cursor-agent", "acp"],
+      env: {
+        CURSOR_AGENT_LOG: "debug",
+      },
+    },
+  ]);
+  expect(mockState.constructorArgs.genericAcp).toEqual([]);
+});
+
 test('extends: "acp" without command throws', () => {
   expect(() =>
     buildProviderRegistry(logger, {

packages/server/src/server/agent/provider-registry.ts

@@ -24,6 +24,7 @@ import type {
 import { ClaudeAgentClient } from "./providers/claude/agent.js";
 import { CodexAppServerAgentClient } from "./providers/codex-app-server-agent.js";
 import { CopilotACPAgentClient } from "./providers/copilot-acp-agent.js";
+import { CursorACPAgentClient } from "./providers/cursor-acp-agent.js";
 import { GenericACPAgentClient } from "./providers/generic-acp-agent.js";
 import { OpenCodeAgentClient } from "./providers/opencode-agent.js";
 import { OpenCodeServerManager } from "./providers/opencode/server-manager.js";
@@ -110,6 +111,12 @@ const PROVIDER_CLIENT_FACTORIES: Record<string, ProviderClientFactory> = {
       logger,
       runtimeSettings,
     }),
+  cursor: (logger, runtimeSettings) =>
+    new CursorACPAgentClient({
+      logger,
+      command: getCursorACPCommand(runtimeSettings),
+      env: runtimeSettings?.env,
+    }),
   opencode: (logger, runtimeSettings) => new OpenCodeAgentClient(logger, runtimeSettings),
   pi: (logger, runtimeSettings) =>
     new PiDirectAgentClient({
@@ -119,6 +126,19 @@ const PROVIDER_CLIENT_FACTORIES: Record<string, ProviderClientFactory> = {
   mock: (logger) => new MockLoadTestAgentClient(logger),
 };
 
+function getCursorACPCommand(
+  runtimeSettings: ProviderRuntimeSettings | undefined,
+): [string, ...string[]] {
+  if (
+    runtimeSettings?.command?.mode === "replace" &&
+    isNonEmptyStringArray(runtimeSettings.command.argv)
+  ) {
+    return runtimeSettings.command.argv;
+  }
+
+  return ["cursor-agent", "acp"];
+}
+
 function getProviderClientFactory(provider: string): ProviderClientFactory {
   const factory = PROVIDER_CLIENT_FACTORIES[provider];
   if (!factory) {
@@ -513,13 +533,21 @@ function addDerivedProviders(
         enabled: override.enabled !== false,
         derivedFromProviderId: null,
         createBaseClient: (logger) =>
-          new GenericACPAgentClient({
-            logger,
-            command,
-            env: override.env,
-            providerId,
-            label: override.label ?? providerId,
-          }),
+          providerId === "cursor"
+            ? new CursorACPAgentClient({
+                logger,
+                command,
+                env: override.env,
+                providerId,
+                label: override.label ?? providerId,
+              })
+            : new GenericACPAgentClient({
+                logger,
+                command,
+                env: override.env,
+                providerId,
+                label: override.label ?? providerId,
+              }),
       });
       continue;
     }

packages/server/src/server/agent/providers/cursor-acp-agent.test.ts

@@ -0,0 +1,193 @@
+import { afterEach, describe, expect, test, vi } from "vitest";
+
+import type { SpawnedACPProcess, SessionStateResponse } from "./acp-agent.js";
+import { CursorACPAgentClient, parseCursorAgentModelsOutput } from "./cursor-acp-agent.js";
+import { createTestLogger } from "../../../test-utils/test-logger.js";
+import * as spawnUtils from "../../../utils/spawn.js";
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+describe("parseCursorAgentModelsOutput", () => {
+  test("parses Cursor model list output and marks default model", () => {
+    expect(
+      parseCursorAgentModelsOutput(`
+Available models
+
+auto - Auto
+composer-2-fast - Composer 2 Fast (default)
+gpt-5.5-low - GPT-5.5 1M Low (current)
+
+Tip: use --model <id> (or /model <id> in interactive mode) to switch.
+`),
+    ).toEqual([
+      { provider: "acp", id: "auto", label: "Auto", isDefault: false },
+      {
+        provider: "acp",
+        id: "composer-2-fast",
+        label: "Composer 2 Fast",
+        isDefault: true,
+      },
+      {
+        provider: "acp",
+        id: "gpt-5.5-low",
+        label: "GPT-5.5 1M Low",
+        isDefault: false,
+      },
+    ]);
+  });
+
+  test("falls back to first model as default when Cursor marks none", () => {
+    expect(
+      parseCursorAgentModelsOutput(`
+Available models
+composer-2 - Composer 2
+gpt-5.5-low - GPT-5.5 1M Low
+`),
+    ).toEqual([
+      { provider: "acp", id: "composer-2", label: "Composer 2", isDefault: true },
+      { provider: "acp", id: "gpt-5.5-low", label: "GPT-5.5 1M Low", isDefault: false },
+    ]);
+  });
+});
+
+describe("CursorACPAgentClient model fallback", () => {
+  class TestCursorACPAgentClient extends CursorACPAgentClient {
+    constructor(options: {
+      command?: [string, ...string[]];
+      env?: Record<string, string>;
+      response: SessionStateResponse;
+    }) {
+      super({
+        logger: createTestLogger(),
+        command: options.command ?? ["cursor-agent", "acp"],
+        env: options.env,
+      });
+      this.response = options.response;
+    }
+
+    private readonly response: SessionStateResponse;
+
+    protected override async spawnProcess(): Promise<SpawnedACPProcess> {
+      return {
+        child: { kill: vi.fn(), exitCode: 0, signalCode: null, once: vi.fn() },
+        connection: {
+          newSession: vi.fn().mockResolvedValue(this.response),
+        },
+        initialize: { agentCapabilities: {} },
+      } as SpawnedACPProcess;
+    }
+
+    protected override async closeProbe(): Promise<void> {}
+  }
+
+  test("uses cursor-agent models when Cursor ACP reports zero models", async () => {
+    const execCommand = vi.spyOn(spawnUtils, "execCommand").mockResolvedValue({
+      stdout: "Available models\ncomposer-2-fast - Composer 2 Fast (default)\n",
+      stderr: "",
+    });
+    const client = new TestCursorACPAgentClient({
+      response: { sessionId: "session-1", models: null, configOptions: [] },
+    });
+
+    const models = await client.listModels({ cwd: "/tmp/cursor", force: false });
+
+    expect(models).toEqual([
+      {
+        provider: "acp",
+        id: "composer-2-fast",
+        label: "Composer 2 Fast",
+        isDefault: true,
+      },
+    ]);
+    expect(execCommand).toHaveBeenCalledWith(
+      "cursor-agent",
+      ["models"],
+      expect.objectContaining({ timeout: expect.any(Number) }),
+    );
+  });
+
+  test("uses cursor-agent models for absolute cursor-agent commands", async () => {
+    const execCommand = vi.spyOn(spawnUtils, "execCommand").mockResolvedValue({
+      stdout: "Available models\ncomposer-2-fast - Composer 2 Fast (default)\n",
+      stderr: "",
+    });
+    const client = new TestCursorACPAgentClient({
+      command: ["/opt/cursor/bin/cursor-agent", "acp"],
+      response: { sessionId: "session-1", models: null, configOptions: [] },
+    });
+
+    await expect(client.listModels({ cwd: "/tmp/cursor", force: false })).resolves.toEqual([
+      {
+        provider: "acp",
+        id: "composer-2-fast",
+        label: "Composer 2 Fast",
+        isDefault: true,
+      },
+    ]);
+    expect(execCommand).toHaveBeenCalledWith(
+      "/opt/cursor/bin/cursor-agent",
+      ["models"],
+      expect.objectContaining({ timeout: expect.any(Number) }),
+    );
+  });
+
+  test("passes Cursor provider env to cursor-agent models fallback", async () => {
+    const execCommand = vi.spyOn(spawnUtils, "execCommand").mockResolvedValue({
+      stdout: "Available models\ncomposer-2-fast - Composer 2 Fast (default)\n",
+      stderr: "",
+    });
+    const env = { CURSOR_AGENT_LOG: "debug" };
+    const client = new TestCursorACPAgentClient({
+      env,
+      response: { sessionId: "session-1", models: null, configOptions: [] },
+    });
+
+    await client.listModels({ cwd: "/tmp/cursor", force: false });
+
+    expect(execCommand).toHaveBeenCalledWith(
+      "cursor-agent",
+      ["models"],
+      expect.objectContaining({ envOverlay: env }),
+    );
+  });
+
+  test("does not run fallback when ACP returns models", async () => {
+    const execCommand = vi.spyOn(spawnUtils, "execCommand");
+    const client = new TestCursorACPAgentClient({
+      response: {
+        sessionId: "session-1",
+        models: {
+          currentModelId: "acp-model",
+          availableModels: [{ modelId: "acp-model", name: "ACP Model", description: null }],
+        },
+        configOptions: [],
+      },
+    });
+
+    await expect(client.listModels({ cwd: "/tmp/cursor", force: false })).resolves.toEqual([
+      {
+        provider: "acp",
+        id: "acp-model",
+        label: "ACP Model",
+        description: undefined,
+        isDefault: true,
+        thinkingOptions: undefined,
+        defaultThinkingOptionId: undefined,
+      },
+    ]);
+    expect(execCommand).not.toHaveBeenCalled();
+  });
+
+  test("does not run fallback when command is not cursor-agent", async () => {
+    const execCommand = vi.spyOn(spawnUtils, "execCommand");
+    const client = new TestCursorACPAgentClient({
+      command: ["other-agent", "acp"],
+      response: { sessionId: "session-1", models: null, configOptions: [] },
+    });
+
+    await expect(client.listModels({ cwd: "/tmp/cursor", force: false })).resolves.toEqual([]);
+    expect(execCommand).not.toHaveBeenCalled();
+  });
+});

packages/server/src/server/agent/providers/cursor-acp-agent.ts

@@ -0,0 +1,125 @@
+import { basename } from "node:path";
+import type { Logger } from "pino";
+
+import type { AgentModelDefinition, ListModelsOptions } from "../agent-sdk-types.js";
+import * as spawnUtils from "../../../utils/spawn.js";
+import { GenericACPAgentClient } from "./generic-acp-agent.js";
+
+interface CursorACPAgentClientOptions {
+  logger: Logger;
+  command: [string, ...string[]];
+  env?: Record<string, string>;
+  providerId?: string;
+  label?: string;
+}
+
+const CURSOR_MODELS_TIMEOUT_MS = 10_000;
+const CURSOR_MODEL_MARKER_PATTERN = /\s+\((?:default|current)\)$/;
+
+export class CursorACPAgentClient extends GenericACPAgentClient {
+  private readonly cursorCommand: [string, ...string[]];
+  private readonly env?: Record<string, string>;
+
+  constructor(options: CursorACPAgentClientOptions) {
+    super(options);
+    this.cursorCommand = options.command;
+    this.env = options.env;
+  }
+
+  override async listModels(options: ListModelsOptions): Promise<AgentModelDefinition[]> {
+    const acpModels = await super.listModels(options);
+    if (acpModels.length > 0) {
+      return acpModels;
+    }
+
+    if (this.canUseCursorModelsFallback()) {
+      return this.listCursorModelsFallback(acpModels);
+    }
+
+    return acpModels;
+  }
+
+  private canUseCursorModelsFallback(): boolean {
+    return basename(this.cursorCommand[0]) === "cursor-agent";
+  }
+
+  private async listCursorModelsFallback(
+    acpModels: AgentModelDefinition[],
+  ): Promise<AgentModelDefinition[]> {
+    try {
+      const { stdout } = await spawnUtils.execCommand(this.cursorCommand[0], ["models"], {
+        envOverlay: this.env,
+        timeout: CURSOR_MODELS_TIMEOUT_MS,
+        maxBuffer: 1024 * 1024,
+      });
+      const fallbackModels = parseCursorAgentModelsOutput(stdout);
+      if (fallbackModels.length === 0) {
+        this.logger.warn(
+          { provider: "cursor" },
+          "Cursor ACP model fallback returned no parseable models",
+        );
+        return acpModels;
+      }
+      return fallbackModels;
+    } catch (error) {
+      this.logger.warn(
+        { err: error, provider: "cursor" },
+        "Failed to list Cursor models via cursor-agent models fallback",
+      );
+      return acpModels;
+    }
+  }
+}
+
+interface ParsedCursorModel {
+  provider: "acp";
+  id: string;
+  label: string;
+  marker: "default" | "current" | null;
+}
+
+export function parseCursorAgentModelsOutput(output: string): AgentModelDefinition[] {
+  const parsed = output
+    .split(/\r?\n/)
+    .map((line) => line.trim())
+    .filter((line) => line && line !== "Available models" && !line.startsWith("Tip:"))
+    .map((line) => {
+      const separatorIndex = line.indexOf(" - ");
+      if (separatorIndex <= 0) {
+        return null;
+      }
+
+      const id = line.slice(0, separatorIndex).trim();
+      const rawLabel = line.slice(separatorIndex + 3).trim();
+      if (!id || !rawLabel) {
+        return null;
+      }
+
+      let marker: "default" | "current" | null = null;
+      if (rawLabel.endsWith(" (default)")) {
+        marker = "default";
+      } else if (rawLabel.endsWith(" (current)")) {
+        marker = "current";
+      }
+
+      return {
+        provider: "acp",
+        id,
+        label: rawLabel.replace(CURSOR_MODEL_MARKER_PATTERN, ""),
+        marker,
+      };
+    })
+    .filter((model): model is ParsedCursorModel => model !== null);
+
+  const defaultModelId =
+    parsed.find((model) => model.marker === "default")?.id ??
+    parsed.find((model) => model.marker === "current")?.id ??
+    parsed[0]?.id;
+
+  return parsed.map((model) => ({
+    provider: model.provider,
+    id: model.id,
+    label: model.label,
+    isDefault: model.id === defaultModelId,
+  }));
+}