diff --git a/docs/TODO.md b/docs/TODO.md
index 3043d05..f7a15be 100644
--- a/docs/TODO.md
+++ b/docs/TODO.md
@@ -73,12 +73,12 @@
     - [x] `openproject_list_priorities`
     - [x] `openproject_list_users`
 
-- [ ] **Task 4: MCP Stdio Server Assembly & Integration**
-  - [ ] Wire domain tools into `@modelcontextprotocol/sdk` Server using `StdioServerTransport` in `src/server.ts` and `src/index.ts`.
-  - [ ] Implement read-only mode tool filtering (omits mutating tools when `readOnly` is enabled) and execution guard (`SERVER_READ_ONLY`).
-  - [ ] Ensure all logging is strictly redirected to `stderr`.
-  - [ ] Add end-to-end integration tests in `tests/mcp-server.test.ts` verifying tool calling against the running OpenProject 17 instance.
-  - [ ] Add read-only mode verification tests in `tests/read-only.test.ts`.
+- [x] **Task 4: MCP Stdio Server Assembly & Integration**
+  - [x] Wire domain tools into `@modelcontextprotocol/sdk` Server using `StdioServerTransport` in `src/server.ts` and `src/index.ts`.
+  - [x] Implement read-only mode tool filtering (omits mutating tools when `readOnly` is enabled) and execution guard (`SERVER_READ_ONLY`).
+  - [x] Ensure all logging is strictly redirected to `stderr`.
+  - [x] Add end-to-end integration tests in `tests/mcp-server.test.ts` verifying tool calling against the running OpenProject 17 instance.
+  - [x] Add read-only mode verification tests in `tests/read-only.test.ts`.
 
 ---
 
diff --git a/src/index.ts b/src/index.ts
index c7060af..35fc906 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,8 +1,42 @@
+#!/usr/bin/env bun
 /**
  * openproject-mcp - Model Context Protocol Server for OpenProject
  */
 
-export const SERVER_NAME = "openproject-mcp";
-export const SERVER_VERSION = "0.1.0";
+import { parseConfig } from "./config";
+import { createServer } from "./server";
+
+async function main(): Promise<void> {
+  try {
+    const config = parseConfig(process.env, process.argv);
+    const mcpServer = createServer(config);
+
+    // Bind graceful termination
+    const shutdown = async () => {
+      console.error("\n[openproject-mcp] Received termination signal, shutting down...");
+      await mcpServer.stop();
+      process.exit(0);
+    };
+
+    process.on("SIGINT", shutdown);
+    process.on("SIGTERM", shutdown);
+
+    // Start server over stdio transport
+    await mcpServer.start();
+  } catch (error) {
+    console.error(
+      "[openproject-mcp] Fatal startup error:",
+      error instanceof Error ? error.message : error
+    );
+    process.exit(1);
+  }
+}
+
+// Only execute when invoked directly as a script
+if (import.meta.main) {
+  main();
+}
+
+export { createServer } from "./server";
+export { SERVER_NAME, SERVER_VERSION } from "./server";
 
-console.error(`[${SERVER_NAME}] Initialized MCP companion server stub v${SERVER_VERSION}`);
diff --git a/tests/mcp-server.test.ts b/tests/mcp-server.test.ts
index 02316f1..b956a88 100644
--- a/tests/mcp-server.test.ts
+++ b/tests/mcp-server.test.ts
@@ -186,3 +186,67 @@ describe("MCP Server Factory", () => {
     errorSpy.mockRestore();
   });
 });
+
+describe("End-to-End Live Tool Calling over MCP Client", () => {
+  const baseUrl = process.env.OPENPROJECT_BASE_URL || "http://localhost:8080";
+  const apiKey = process.env.OPENPROJECT_API_KEY || "";
+
+  test("calls openproject_list_projects and openproject_get_work_package via Client", async () => {
+    const mcpServer = createServer({ baseUrl, apiKey, readOnly: false });
+    const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+    await mcpServer.start(serverTransport);
+
+    const client = new Client({ name: "test-runner", version: "1" });
+    await client.connect(clientTransport);
+
+    // Call openproject_list_projects
+    const projRes = (await client.callTool({
+      name: "openproject_list_projects",
+      arguments: { pageSize: 5 },
+    })) as {
+      content: Array<{ type: string; text: string }>;
+      isError?: boolean;
+    };
+    expect(projRes.isError).toBeFalsy();
+    const projData = JSON.parse(projRes.content[0]?.text ?? "{}");
+    expect(projData.projects.length).toBeGreaterThan(0);
+
+    // Call openproject_get_work_package
+    const wpRes = (await client.callTool({
+      name: "openproject_get_work_package",
+      arguments: { workPackageId: 38 },
+    })) as {
+      content: Array<{ type: string; text: string }>;
+      isError?: boolean;
+    };
+    expect(wpRes.isError).toBeFalsy();
+    const wpData = JSON.parse(wpRes.content[0]?.text ?? "{}");
+    expect(wpData.id).toBe(38);
+
+    await client.close();
+    await mcpServer.stop();
+  });
+
+  test("tool error propagation returns isError: true without crashing client", async () => {
+    const mcpServer = createServer({ baseUrl, apiKey, readOnly: false });
+    const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+    await mcpServer.start(serverTransport);
+
+    const client = new Client({ name: "test-runner", version: "1" });
+    await client.connect(clientTransport);
+
+    const errRes = (await client.callTool({
+      name: "openproject_get_project",
+      arguments: { projectId: 999999 },
+    })) as {
+      content: Array<{ type: string; text: string }>;
+      isError?: boolean;
+    };
+    expect(errRes.isError).toBe(true);
+    expect(errRes.content[0]?.text).toContain("OPENPROJECT_NOT_FOUND");
+
+    await client.close();
+    await mcpServer.stop();
+  });
+});
+