Add MCP provider feature discovery (#910)

Refs #835

packages/server/src/server/agent/mcp-parity.e2e.test.ts

@@ -390,6 +390,26 @@ describe("Suite A: Core Fixes", () => {
     }
   });
 
+  test("list_provider_features returns draft provider features over MCP", async () => {
+    const payload = await callToolStructured(topLevelClient, "list_provider_features", {
+      provider: "claude",
+      cwd: parentAgentCwd,
+      model: "claude-test-model",
+      featureValues: { test_feature: true },
+    });
+
+    expect(payload.provider).toBe("claude");
+    expect(recordArr(payload.features)).toEqual(
+      expect.arrayContaining([
+        expect.objectContaining({
+          type: "toggle",
+          id: "test_feature",
+          value: true,
+        }),
+      ]),
+    );
+  });
+
   test("create_agent accepts labels param", async () => {
     let agentId: string | null = null;
     try {

packages/server/src/server/agent/mcp-server.test.ts

@@ -133,6 +133,7 @@ function buildAgentManagerSpies() {
     cancelAgentRun: vi.fn(),
     getPendingPermissions: vi.fn(),
     getRegisteredProviderIds: vi.fn().mockReturnValue(["claude"]),
+    listDraftFeatures: vi.fn(),
   };
 }
 
@@ -1793,6 +1794,57 @@ describe("provider listing MCP tool", () => {
 describe("model listing MCP tool", () => {
   const logger = createTestLogger();
 
+  it("lists provider features for a draft agent configuration", async () => {
+    const { agentManager, agentStorage, spies } = createTestDeps();
+    spies.agentManager.listDraftFeatures.mockResolvedValue([
+      {
+        type: "toggle",
+        id: "fast_mode",
+        label: "Fast mode",
+        value: false,
+      },
+    ]);
+    const server = await createAgentMcpServer({
+      agentManager,
+      agentStorage,
+      logger,
+    });
+    const tool = registeredTool(server, "list_provider_features");
+    const input = {
+      provider: "codex",
+      cwd: "~/repo",
+      modeId: "full-access",
+      model: "gpt-5.4",
+      thinkingOptionId: "high",
+      featureValues: { fast_mode: true },
+    };
+
+    const parsed = await tool.inputSchema.safeParseAsync(input);
+    expect(parsed.success).toBe(true);
+
+    const response = await tool.handler(input);
+
+    expect(spies.agentManager.listDraftFeatures).toHaveBeenCalledWith({
+      provider: "codex",
+      cwd: expect.stringContaining("repo"),
+      modeId: "full-access",
+      model: "gpt-5.4",
+      thinkingOptionId: "high",
+      featureValues: { fast_mode: true },
+    });
+    expect(response.structuredContent).toEqual({
+      provider: "codex",
+      features: [
+        {
+          type: "toggle",
+          id: "fast_mode",
+          label: "Fast mode",
+          value: false,
+        },
+      ],
+    });
+  });
+
   it("rejects disabled providers without fetching models", async () => {
     const { agentManager, agentStorage } = createTestDeps();
     const fetchModels = vi.fn().mockResolvedValue([

packages/server/src/server/agent/mcp-server.ts

@@ -8,6 +8,7 @@ import type { ServerNotification, ServerRequest } from "@modelcontextprotocol/sd
 import type { AgentProvider } from "./agent-sdk-types.js";
 import type { AgentManager, WaitForAgentResult } from "./agent-manager.js";
 import {
+  AgentFeatureSchema,
   AgentPermissionRequestPayloadSchema,
   AgentListItemPayloadSchema,
   AgentPermissionResponseSchema,
@@ -587,6 +588,14 @@ export async function createAgentMcpServer(options: AgentMcpServerOptions): Prom
   const createAgentInputSchema = callerAgentId ? agentToAgentInputSchema : topLevelInputSchema;
   const agentToAgentCreateAgentArgsSchema = z.object(agentToAgentInputSchema).strict();
   const topLevelCreateAgentArgsSchema = z.object(topLevelInputSchema).strict();
+  const listProviderFeaturesInputSchema = {
+    provider: AgentProviderEnum,
+    cwd: z.string().describe("Working directory used to resolve provider feature availability."),
+    modeId: z.string().optional(),
+    model: z.string().optional(),
+    thinkingOptionId: z.string().optional(),
+    featureValues: z.record(z.unknown()).optional(),
+  };
 
   if (options.voiceOnly || options.enableVoiceTools || callerContext?.enableVoiceTools) {
     server.registerTool(
@@ -1813,6 +1822,37 @@ export async function createAgentMcpServer(options: AgentMcpServerOptions): Prom
     },
   );
 
+  server.registerTool(
+    "list_provider_features",
+    {
+      title: "List provider features",
+      description:
+        "List provider-specific features available for a draft agent configuration, such as Codex fast_mode.",
+      inputSchema: listProviderFeaturesInputSchema,
+      outputSchema: {
+        provider: AgentProviderEnum,
+        features: z.array(AgentFeatureSchema),
+      },
+    },
+    async ({ provider, cwd, modeId, model, thinkingOptionId, featureValues }) => {
+      const features = await agentManager.listDraftFeatures({
+        provider,
+        cwd: expandUserPath(cwd),
+        ...(modeId ? { modeId } : {}),
+        ...(model ? { model } : {}),
+        ...(thinkingOptionId ? { thinkingOptionId } : {}),
+        ...(featureValues ? { featureValues } : {}),
+      });
+      return {
+        content: [],
+        structuredContent: ensureValidJson({
+          provider,
+          features,
+        }),
+      };
+    },
+  );
+
   server.registerTool(
     "list_worktrees",
     {

public-docs/mcp.md

@@ -53,10 +53,11 @@ The MCP server itself is controlled by `daemon.mcp.enabled`. Existing agents may
 
 ### Providers
 
-| Tool             | Function                                                  |
+| Tool                     | Function                                                                                    |
-| ---------------- | --------------------------------------------------------- |
+| ------------------------ | ------------------------------------------------------------------------------------------- |
-| `list_providers` | List configured agent providers, availability, and modes. |
+| `list_providers`         | List configured agent providers, availability, and modes.                                   |
-| `list_models`    | List models for an agent provider.                        |
+| `list_models`            | List models for an agent provider.                                                          |
+| `list_provider_features` | List provider-specific features for a draft agent configuration, such as Codex `fast_mode`. |
 
 ### Worktrees
 

skills/paseo/SKILL.md

@@ -34,6 +34,12 @@ Compose: call `create_worktree` first, then `create_agent` with `cwd` set to the
 
 **`archive_agent`** — `{ agentId }`. Interrupts if running, removes from active list.
 
+## Provider features
+
+**`list_provider_features`** — query provider-specific features before setting them. Required: `provider`, `cwd`. Optional: `model`, `modeId`, `thinkingOptionId`, `featureValues`.
+
+Only set feature IDs returned by `list_provider_features`. For Codex fast mode, look for `fast_mode` and pass `features: { "fast_mode": true }` to `create_agent`.
+
 ## Heartbeats
 
 **`create_schedule`** — required: `prompt`. Pick one of `cron` or `every` (`"5m"`, `"1h"`). Optional: `name`, `target` (`self` | `new-agent`), `provider`, `maxRuns`, `expiresIn`. Use for periodic checks on long-running work or recurring maintenance.