test(shared): cover loadOpencodePlugins memoization

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/load-opencode-plugins.test.ts

@@ -0,0 +1,89 @@
+/// <reference path="../../bun-test.d.ts" />
+
+import { afterEach, beforeEach, describe, expect, it, mock } from "bun:test"
+import * as fs from "node:fs"
+
+type LoadOpencodePluginsModule = {
+  loadOpencodePlugins: (directory: string) => string[]
+  clearOpencodePluginsCache?: () => void
+}
+
+const existsSyncMock = mock((_path: string) => true)
+const readFileSyncMock = mock((_path: string, _encoding?: string) => `{
+  "plugin": ["plugin-a", "plugin-b"]
+}`)
+
+async function importFreshLoadOpencodePluginsModule(): Promise<LoadOpencodePluginsModule> {
+  const modulePath = `${new URL("./load-opencode-plugins.ts", import.meta.url).pathname}?test=${Date.now()}-${Math.random()}`
+  return import(modulePath)
+}
+
+describe("loadOpencodePlugins", () => {
+  beforeEach(() => {
+    existsSyncMock.mockReset()
+    existsSyncMock.mockImplementation((_path: string) => true)
+    readFileSyncMock.mockReset()
+    readFileSyncMock.mockImplementation((_path: string, _encoding?: string) => `{
+  "plugin": ["plugin-a", "plugin-b"]
+}`)
+
+    mock.module("node:fs", () => ({
+      ...fs,
+      existsSync: existsSyncMock,
+      readFileSync: readFileSyncMock,
+    }))
+  })
+
+  afterEach(() => {
+    mock.restore()
+  })
+
+  describe("#given the same directory is loaded twice", () => {
+    describe("#when loading plugins repeatedly", () => {
+      it("#then does not call readFileSync on the second load", async () => {
+        // given
+        const { loadOpencodePlugins } = await importFreshLoadOpencodePluginsModule()
+
+        // when
+        const firstResult = loadOpencodePlugins("/some/fake/dir")
+        const readCountAfterFirstLoad = readFileSyncMock.mock.calls.length
+        const secondResult = loadOpencodePlugins("/some/fake/dir")
+        const readCountAfterSecondLoad = readFileSyncMock.mock.calls.length
+
+        // then
+        expect(firstResult).toEqual(["plugin-a", "plugin-b"])
+        expect(secondResult).toEqual(["plugin-a", "plugin-b"])
+        expect(readCountAfterFirstLoad).toBeGreaterThan(0)
+        expect(readCountAfterSecondLoad - readCountAfterFirstLoad).toBe(0)
+      })
+    })
+  })
+
+  describe("#given the plugin cache was cleared", () => {
+    describe("#when loading the same directory again", () => {
+      it("#then re-reads plugin config files from disk", async () => {
+        // given
+        const { loadOpencodePlugins, clearOpencodePluginsCache } = await importFreshLoadOpencodePluginsModule()
+
+        if (typeof clearOpencodePluginsCache !== "function") {
+          throw new Error("clearOpencodePluginsCache export is missing")
+        }
+
+        // when
+        const firstResult = loadOpencodePlugins("/some/fake/dir")
+        const readCountAfterFirstLoad = readFileSyncMock.mock.calls.length
+        loadOpencodePlugins("/some/fake/dir")
+        const readCountAfterSecondLoad = readFileSyncMock.mock.calls.length
+        clearOpencodePluginsCache()
+        const thirdResult = loadOpencodePlugins("/some/fake/dir")
+        const readCountAfterThirdLoad = readFileSyncMock.mock.calls.length
+
+        // then
+        expect(firstResult).toEqual(["plugin-a", "plugin-b"])
+        expect(thirdResult).toEqual(["plugin-a", "plugin-b"])
+        expect(readCountAfterSecondLoad - readCountAfterFirstLoad).toBe(0)
+        expect(readCountAfterThirdLoad - readCountAfterSecondLoad).toBeGreaterThan(0)
+      })
+    })
+  })
+})