fix: fail fast on missing host IPC dir for task runtimes

runners/agent-runner/test/ipc-paths.test.ts

@@ -0,0 +1,45 @@
+import { describe, expect, it } from 'vitest';
+
+import {
+  isTaskScopedIpcDir,
+  resolveIpcDirectories,
+} from '../src/ipc-paths.js';
+
+describe('ipc path helpers', () => {
+  it('detects task-scoped IPC directories', () => {
+    expect(isTaskScopedIpcDir('/data/ipc/group/tasks/task-123')).toBe(true);
+    expect(isTaskScopedIpcDir('C:\\ipc\\group\\tasks\\task-123')).toBe(true);
+    expect(isTaskScopedIpcDir('/data/ipc/group')).toBe(false);
+  });
+
+  it('fails fast when task-scoped IPC is missing host IPC dir', () => {
+    expect(() =>
+      resolveIpcDirectories({
+        EJCLAW_IPC_DIR: '/data/ipc/group/tasks/task-123',
+      }),
+    ).toThrow(/EJCLAW_HOST_IPC_DIR is required/i);
+  });
+
+  it('allows group-scoped IPC to fall back to the local IPC dir', () => {
+    expect(
+      resolveIpcDirectories({
+        EJCLAW_IPC_DIR: '/data/ipc/group',
+      }),
+    ).toEqual({
+      ipcDir: '/data/ipc/group',
+      hostIpcDir: '/data/ipc/group',
+    });
+  });
+
+  it('keeps host and task IPC dirs distinct when both are provided', () => {
+    expect(
+      resolveIpcDirectories({
+        EJCLAW_IPC_DIR: '/data/ipc/group/tasks/task-123',
+        EJCLAW_HOST_IPC_DIR: '/data/ipc/group',
+      }),
+    ).toEqual({
+      ipcDir: '/data/ipc/group/tasks/task-123',
+      hostIpcDir: '/data/ipc/group',
+    });
+  });
+});