diff --git a/tests/connection-heartbeat-failures.test.ts b/tests/connection-heartbeat-failures.test.ts
new file mode 100644
index 0000000..659e16f
--- /dev/null
+++ b/tests/connection-heartbeat-failures.test.ts
@@ -0,0 +1,196 @@
+import { describe, expect, it, vi, beforeEach, afterEach } from "vitest";
+
+import { buildHeartbeat, decodeBuiltin, encodeBuiltin } from "../../Yonexus.Protocol/src/index.js";
+import { createYonexusServerRuntime } from "../plugin/core/runtime.js";
+import { createClientRecord, type ClientRecord } from "../plugin/core/persistence.js";
+import type { YonexusServerStore } from "../plugin/core/store.js";
+import type { ClientConnection, ServerTransport } from "../plugin/core/transport.js";
+
+function createMockSocket() {
+  return { close: vi.fn() } as unknown as ClientConnection["ws"];
+}
+
+function createConnection(identifier: string | null = null): ClientConnection {
+  return {
+    identifier,
+    ws: createMockSocket(),
+    connectedAt: 1_710_000_000,
+    isAuthenticated: false
+  };
+}
+
+function createMockStore(initialClients: ClientRecord[] = []): YonexusServerStore {
+  const persisted = new Map(initialClients.map((record) => [record.identifier, record]));
+
+  return {
+    filePath: "/tmp/yonexus-server-connection-heartbeat-failures.json",
+    load: vi.fn(async () => ({
+      version: 1,
+      persistedAt: 1_710_000_000,
+      clients: new Map(persisted)
+    })),
+    save: vi.fn(async (clients: Iterable<ClientRecord>) => {
+      persisted.clear();
+      for (const client of clients) {
+        persisted.set(client.identifier, client);
+      }
+    })
+  };
+}
+
+function createMockTransport() {
+  const sent: Array<{ connection: ClientConnection; message: string }> = [];
+
+  const transport: ServerTransport = {
+    isRunning: false,
+    connections: new Map(),
+    start: vi.fn(),
+    stop: vi.fn(),
+    send: vi.fn(),
+    sendToConnection: vi.fn((connection: ClientConnection, message: string) => {
+      sent.push({ connection, message });
+      return true;
+    }),
+    broadcast: vi.fn(),
+    closeConnection: vi.fn(),
+    promoteToAuthenticated: vi.fn(),
+    removeTempConnection: vi.fn(),
+    assignIdentifierToTemp: vi.fn()
+  };
+
+  return { transport, sent };
+}
+
+describe("YNX-1105d: Connection & Heartbeat Failure Paths", () => {
+  let now = 1_710_000_000;
+
+  beforeEach(() => {
+    now = 1_710_000_000;
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+  });
+
+  it("CF-06: unauthenticated rule message closes connection", async () => {
+    const record = createClientRecord("client-a");
+    const store = createMockStore([record]);
+    const { transport } = createMockTransport();
+
+    const runtime = createYonexusServerRuntime({
+      config: {
+        followerIdentifiers: ["client-a"],
+        notifyBotToken: "stub-token",
+        adminUserId: "admin-user",
+        listenHost: "127.0.0.1",
+        listenPort: 8787
+      },
+      store,
+      transport,
+      now: () => now
+    });
+
+    await runtime.start();
+
+    const connection = createConnection("client-a");
+    runtime.state.registry.sessions.set("client-a", {
+      identifier: "client-a",
+      socket: connection.ws,
+      isAuthenticated: false,
+      connectedAt: now,
+      lastActivityAt: now,
+      publicKey: undefined
+    });
+
+    await runtime.handleMessage(connection, "chat::hello");
+
+    expect(connection.ws.close).toHaveBeenCalledWith(1008, "Not authenticated");
+  });
+
+  it("HF-03: heartbeat before auth returns error", async () => {
+    const record = createClientRecord("client-a");
+    const store = createMockStore([record]);
+    const { transport, sent } = createMockTransport();
+
+    const runtime = createYonexusServerRuntime({
+      config: {
+        followerIdentifiers: ["client-a"],
+        notifyBotToken: "stub-token",
+        adminUserId: "admin-user",
+        listenHost: "127.0.0.1",
+        listenPort: 8787
+      },
+      store,
+      transport,
+      now: () => now
+    });
+
+    await runtime.start();
+
+    const connection = createConnection("client-a");
+    runtime.state.registry.sessions.set("client-a", {
+      identifier: "client-a",
+      socket: connection.ws,
+      isAuthenticated: false,
+      connectedAt: now,
+      lastActivityAt: now,
+      publicKey: undefined
+    });
+
+    await runtime.handleMessage(
+      connection,
+      encodeBuiltin(
+        buildHeartbeat(
+          { identifier: "client-a", status: "alive" },
+          { requestId: "req-hb-early", timestamp: now }
+        )
+      )
+    );
+
+    const lastMessage = decodeBuiltin(sent.at(-1)!.message);
+    expect(lastMessage.type).toBe("error");
+    expect(lastMessage.payload).toMatchObject({
+      code: "AUTH_FAILED"
+    });
+  });
+
+  it("HF-04: heartbeat without session returns error", async () => {
+    const record = createClientRecord("client-a");
+    const store = createMockStore([record]);
+    const { transport, sent } = createMockTransport();
+
+    const runtime = createYonexusServerRuntime({
+      config: {
+        followerIdentifiers: ["client-a"],
+        notifyBotToken: "stub-token",
+        adminUserId: "admin-user",
+        listenHost: "127.0.0.1",
+        listenPort: 8787
+      },
+      store,
+      transport,
+      now: () => now
+    });
+
+    await runtime.start();
+
+    const connection = createConnection("client-a");
+
+    await runtime.handleMessage(
+      connection,
+      encodeBuiltin(
+        buildHeartbeat(
+          { identifier: "client-a", status: "alive" },
+          { requestId: "req-hb-unauth", timestamp: now }
+        )
+      )
+    );
+
+    const lastMessage = decodeBuiltin(sent.at(-1)!.message);
+    expect(lastMessage.type).toBe("error");
+    expect(lastMessage.payload).toMatchObject({
+      code: "AUTH_FAILED"
+    });
+  });
+});