fix(todo): make Todo id field optional for OpenCode beta compatibility

- Make id field optional in all Todo interfaces (TodoInfo, Todo, TodoItem)
- Fix null-unsafe comparisons in todo-sync.ts to handle missing ids
- Add test case for todos without id field preservation
- All tests pass and typecheck clean

src/shared/opencode-message-dir.test.ts

@@ -0,0 +1,99 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest"
+import { existsSync, readdirSync } from "node:fs"
+import { join } from "node:path"
+import { getMessageDir } from "./opencode-message-dir"
+
+// Mock the constants
+vi.mock("../tools/session-manager/constants", () => ({
+  MESSAGE_STORAGE: "/mock/message/storage",
+}))
+
+vi.mock("node:fs", () => ({
+  existsSync: vi.fn(),
+  readdirSync: vi.fn(),
+}))
+
+vi.mock("node:path", () => ({
+  join: vi.fn(),
+}))
+
+const mockExistsSync = vi.mocked(existsSync)
+const mockReaddirSync = vi.mocked(readdirSync)
+const mockJoin = vi.mocked(join)
+
+describe("getMessageDir", () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+    mockJoin.mockImplementation((...args) => args.join("/"))
+  })
+
+  afterEach(() => {
+    vi.restoreAllMocks()
+  })
+
+  it("returns null when MESSAGE_STORAGE does not exist", () => {
+    // given
+    mockExistsSync.mockReturnValue(false)
+
+    // when
+    const result = getMessageDir("session123")
+
+    // then
+    expect(result).toBe(null)
+    expect(mockExistsSync).toHaveBeenCalledWith("/mock/message/storage")
+  })
+
+  it("returns direct path when session exists directly", () => {
+    // given
+    mockExistsSync.mockImplementation((path) => path === "/mock/message/storage" || path === "/mock/message/storage/session123")
+
+    // when
+    const result = getMessageDir("session123")
+
+    // then
+    expect(result).toBe("/mock/message/storage/session123")
+    expect(mockExistsSync).toHaveBeenCalledWith("/mock/message/storage")
+    expect(mockExistsSync).toHaveBeenCalledWith("/mock/message/storage/session123")
+  })
+
+  it("returns subdirectory path when session exists in subdirectory", () => {
+    // given
+    mockExistsSync.mockImplementation((path) => {
+      return path === "/mock/message/storage" || path === "/mock/message/storage/subdir/session123"
+    })
+    mockReaddirSync.mockReturnValue(["subdir"])
+
+    // when
+    const result = getMessageDir("session123")
+
+    // then
+    expect(result).toBe("/mock/message/storage/subdir/session123")
+    expect(mockReaddirSync).toHaveBeenCalledWith("/mock/message/storage")
+  })
+
+  it("returns null when session not found anywhere", () => {
+    // given
+    mockExistsSync.mockImplementation((path) => path === "/mock/message/storage")
+    mockReaddirSync.mockReturnValue(["subdir1", "subdir2"])
+
+    // when
+    const result = getMessageDir("session123")
+
+    // then
+    expect(result).toBe(null)
+  })
+
+  it("returns null when readdirSync throws", () => {
+    // given
+    mockExistsSync.mockImplementation((path) => path === "/mock/message/storage")
+    mockReaddirSync.mockImplementation(() => {
+      throw new Error("Permission denied")
+    })
+
+    // when
+    const result = getMessageDir("session123")
+
+    // then
+    expect(result).toBe(null)
+  })
+})