refactor(shared): unify MESSAGE_STORAGE/PART_STORAGE constants into single source

- Add src/shared/opencode-storage-paths.ts with consolidated constants

- Update imports in hook-message-injector and session-manager

- Add src/shared/opencode-storage-detection.ts with isSqliteBackend()

- Add OPENCODE_SQLITE_VERSION constant

- Export all from shared/index.ts

src/shared/opencode-storage-detection.test.ts

@@ -0,0 +1,94 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from "bun:test"
+import { existsSync } from "node:fs"
+import { join } from "node:path"
+import { isSqliteBackend, resetSqliteBackendCache } from "./opencode-storage-detection"
+import { getDataDir } from "./data-path"
+import { isOpenCodeVersionAtLeast, OPENCODE_SQLITE_VERSION } from "./opencode-version"
+
+// Mock the dependencies
+const mockExistsSync = vi.fn()
+const mockGetDataDir = vi.fn()
+const mockIsOpenCodeVersionAtLeast = vi.fn()
+
+vi.mock("node:fs", () => ({
+  existsSync: mockExistsSync,
+}))
+
+vi.mock("./data-path", () => ({
+  getDataDir: mockGetDataDir,
+}))
+
+vi.mock("./opencode-version", () => ({
+  isOpenCodeVersionAtLeast: mockIsOpenCodeVersionAtLeast,
+  OPENCODE_SQLITE_VERSION: "1.1.53",
+}))
+
+describe("isSqliteBackend", () => {
+  beforeEach(() => {
+    // Reset the cached result
+    resetSqliteBackendCache()
+  })
+
+  afterEach(() => {
+    vi.clearAllMocks()
+  })
+
+  it("returns false when version is below threshold", () => {
+    // given
+    mockIsOpenCodeVersionAtLeast.mockReturnValue(false)
+    mockGetDataDir.mockReturnValue("/home/user/.local/share")
+    mockExistsSync.mockReturnValue(true)
+
+    // when
+    const result = isSqliteBackend()
+
+    // then
+    expect(result).toBe(false)
+    expect(mockIsOpenCodeVersionAtLeast).toHaveBeenCalledWith(OPENCODE_SQLITE_VERSION)
+  })
+
+  it("returns false when DB file does not exist", () => {
+    // given
+    mockIsOpenCodeVersionAtLeast.mockReturnValue(true)
+    mockGetDataDir.mockReturnValue("/home/user/.local/share")
+    mockExistsSync.mockReturnValue(false)
+
+    // when
+    const result = isSqliteBackend()
+
+    // then
+    expect(result).toBe(false)
+    expect(mockExistsSync).toHaveBeenCalledWith(join("/home/user/.local/share", "opencode", "opencode.db"))
+  })
+
+  it("returns true when version is at or above threshold and DB exists", () => {
+    // given
+    mockIsOpenCodeVersionAtLeast.mockReturnValue(true)
+    mockGetDataDir.mockReturnValue("/home/user/.local/share")
+    mockExistsSync.mockReturnValue(true)
+
+    // when
+    const result = isSqliteBackend()
+
+    // then
+    expect(result).toBe(true)
+    expect(mockIsOpenCodeVersionAtLeast).toHaveBeenCalledWith(OPENCODE_SQLITE_VERSION)
+    expect(mockExistsSync).toHaveBeenCalledWith(join("/home/user/.local/share", "opencode", "opencode.db"))
+  })
+
+  it("caches the result and does not re-check on subsequent calls", () => {
+    // given
+    mockIsOpenCodeVersionAtLeast.mockReturnValue(true)
+    mockGetDataDir.mockReturnValue("/home/user/.local/share")
+    mockExistsSync.mockReturnValue(true)
+
+    // when
+    isSqliteBackend()
+    isSqliteBackend()
+    isSqliteBackend()
+
+    // then
+    expect(mockIsOpenCodeVersionAtLeast).toHaveBeenCalledTimes(1)
+    expect(mockExistsSync).toHaveBeenCalledTimes(1)
+  })
+})