fix(auto-update-checker): use OpenCode cache paths for updates

Align version lookup, invalidation, and bun install with OpenCode's cache directory so updates target the loaded plugin location. Keep dependency declarations intact during invalidation so auto-update can reinstall instead of converging to uninstall.

src/cli/config-manager/bun-install.test.ts

@@ -0,0 +1,39 @@
+import { beforeEach, afterEach, describe, expect, it, mock, spyOn } from "bun:test"
+import * as dataPath from "../../shared/data-path"
+import * as logger from "../../shared/logger"
+import * as spawnHelpers from "../../shared/spawn-with-windows-hide"
+import { runBunInstallWithDetails } from "./bun-install"
+
+describe("runBunInstallWithDetails", () => {
+  let getOpenCodeCacheDirSpy: ReturnType<typeof spyOn>
+  let logSpy: ReturnType<typeof spyOn>
+  let spawnWithWindowsHideSpy: ReturnType<typeof spyOn>
+
+  beforeEach(() => {
+    getOpenCodeCacheDirSpy = spyOn(dataPath, "getOpenCodeCacheDir").mockReturnValue("/tmp/opencode-cache")
+    logSpy = spyOn(logger, "log").mockImplementation(() => {})
+    spawnWithWindowsHideSpy = spyOn(spawnHelpers, "spawnWithWindowsHide").mockReturnValue({
+      exited: Promise.resolve(0),
+      exitCode: 0,
+      kill: mock(() => {}),
+    } as ReturnType<typeof spawnHelpers.spawnWithWindowsHide>)
+  })
+
+  afterEach(() => {
+    getOpenCodeCacheDirSpy.mockRestore()
+    logSpy.mockRestore()
+    spawnWithWindowsHideSpy.mockRestore()
+  })
+
+  it("runs bun install in the OpenCode cache directory", async () => {
+    const result = await runBunInstallWithDetails()
+
+    expect(result).toEqual({ success: true })
+    expect(getOpenCodeCacheDirSpy).toHaveBeenCalledTimes(1)
+    expect(spawnWithWindowsHideSpy).toHaveBeenCalledWith(["bun", "install"], {
+      cwd: "/tmp/opencode-cache",
+      stdout: "inherit",
+      stderr: "inherit",
+    })
+  })
+})