fix(pi): declare properties on MCP tool schemas that omit them

packages/provider-pi/src/server/mcpBridge.testkit.ts

@@ -44,6 +44,7 @@ export async function loadMcpBridge(
     readonly toolSearchDisabled?: boolean;
     readonly allowsTool?: (name: string) => boolean;
     readonly runtimeMode?: string;
+    readonly inputSchema?: Record<string, unknown>;
   } = {},
 ) {
   const handlers = new Map<string, AgentStartHook>();
@@ -72,7 +73,7 @@ export async function loadMcpBridge(
     { name: "preview_snapshot", description: "Inspect the collaborative browser." },
   ].map((tool) => ({
     ...tool,
-    inputSchema: { type: "object", properties: {} },
+    inputSchema: options.inputSchema ?? { type: "object", properties: {} },
     outputSchema: { type: "object", properties: { count: { type: "number" } } },
   }));
   const source = NodeModule.stripTypeScriptTypes(

packages/provider-pi/src/server/mcpExtensionSource.test.ts

@@ -286,6 +286,32 @@ describe("Pi MCP tool exposure", () => {
   );
 });
 
+describe("Pi MCP tool schemas", () => {
+  it.each([{ type: "object" }, {}])(
+    "declares empty properties on object schemas that omit them: %j",
+    async (inputSchema) => {
+      const bridge = await loadMcpBridge({ inputSchema });
+      assert.isAbove(bridge.tools.length, 0);
+      for (const tool of bridge.tools) {
+        assert.deepEqual(tool.parameters, { type: "object", properties: {} });
+      }
+    },
+  );
+
+  it("keeps declared properties and other schema keywords", async () => {
+    const inputSchema = {
+      type: "object",
+      properties: { depth: { type: "number" } },
+      required: ["depth"],
+      additionalProperties: false,
+    };
+    const bridge = await loadMcpBridge({ inputSchema });
+    for (const tool of bridge.tools) {
+      assert.deepEqual(tool.parameters, inputSchema);
+    }
+  });
+});
+
 describe("Pi tool discovery permissions", () => {
   it.each(["approval-required", "auto-accept-edits", "auto"])(
     "allows annotated T3 reads in %s while gating mutations and replacements",

packages/provider-pi/src/server/mcpExtensionSource.ts

@@ -91,7 +91,13 @@ function parseSseOrJson(body: string, contentType: string): JsonRpcResponse {
 function jsonSchemaToTypebox(schema: Record<string, unknown> | undefined) {
   const unsafe = (Type as { Unsafe?: (value: unknown) => unknown }).Unsafe;
   if (typeof unsafe === "function" && schema !== undefined) {
-    return unsafe(schema);
+    // Zero-argument MCP tools may omit "properties", which some OpenAI-compatible
+    // servers reject. Declare it, as Pi does for its own MCP tools.
+    return unsafe({
+      ...schema,
+      type: schema.type ?? "object",
+      ...(schema.properties === undefined ? { properties: {} } : {}),
+    });
   }
   return Type.Object({}, { additionalProperties: true });
 }