fix(tests): resolve 5 cross-file test isolation failures

- model-fallback hook: mock selectFallbackProvider and add _resetForTesting()
  to test-setup.ts to clear module-level state between files
- fallback-retry-handler: add afterAll(mock.restore) and use mockReturnValueOnce
  to prevent connected-providers mock leaking to subsequent test files
- opencode-config-dir: use win32.join for Windows APPDATA path construction
  so tests pass on macOS (path.join uses POSIX semantics regardless of
  process.platform override)
- system-loaded-version: use resolveSymlink from file-utils instead of
  realpathSync to handle macOS /var -> /private/var symlink consistently

All 4456 tests pass (0 failures) on full bun test suite.

src/cli/doctor/checks/system-loaded-version.test.ts

@@ -1,9 +1,10 @@
 import { afterEach, describe, expect, it } from "bun:test"
-import { mkdirSync, mkdtempSync, realpathSync, rmSync, symlinkSync, writeFileSync } from "node:fs"
+import { mkdirSync, mkdtempSync, rmSync, symlinkSync, writeFileSync } from "node:fs"
 import { tmpdir } from "node:os"
 import { dirname, join } from "node:path"
 
 import { PACKAGE_NAME } from "../constants"
+import { resolveSymlink } from "../../../shared/file-utils"
 
 const systemLoadedVersionModulePath = "./system-loaded-version?system-loaded-version-test"
 
@@ -125,7 +126,7 @@ describe("system loaded version", () => {
       const loadedVersion = getLoadedPluginVersion()
 
       //#then
-      expect(loadedVersion.cacheDir).toBe(realpathSync(symlinkConfigDir))
+      expect(loadedVersion.cacheDir).toBe(resolveSymlink(symlinkConfigDir))
       expect(loadedVersion.expectedVersion).toBe("4.5.6")
       expect(loadedVersion.loadedVersion).toBe("4.5.6")
     })

src/cli/doctor/checks/system-loaded-version.ts

@@ -1,7 +1,7 @@
-import { existsSync, readFileSync, realpathSync } from "node:fs"
+import { existsSync, readFileSync } from "node:fs"
 import { homedir } from "node:os"
 import { join } from "node:path"
-
+import { resolveSymlink } from "../../../shared/file-utils"
 import { getLatestVersion } from "../../../hooks/auto-update-checker/checker"
 import { extractChannel } from "../../../hooks/auto-update-checker"
 import { PACKAGE_NAME } from "../constants"
@@ -38,12 +38,7 @@ function resolveOpenCodeCacheDir(): string {
 
 function resolveExistingDir(dirPath: string): string {
   if (!existsSync(dirPath)) return dirPath
-
+  return resolveSymlink(dirPath)
-  try {
-    return realpathSync(dirPath)
-  } catch {
-    return dirPath
-  }
 }
 
 function readPackageJson(filePath: string): PackageJsonShape | null {

src/features/background-agent/fallback-retry-handler.test.ts

@@ -1,4 +1,4 @@
-import { describe, test, expect, mock, beforeEach } from "bun:test"
+import { afterAll, beforeEach, describe, expect, mock, test } from "bun:test"
 
 mock.module("../../shared", () => ({
   log: mock(() => {}),
@@ -82,6 +82,10 @@ function createDefaultArgs(taskOverrides: Partial<BackgroundTask> = {}) {
 }
 
 describe("tryFallbackRetry", () => {
+  afterAll(() => {
+    mock.restore()
+  })
+
   beforeEach(() => {
     ;(shouldRetryError as any).mockImplementation(() => true)
     ;(selectFallbackProvider as any).mockImplementation((providers: string[]) => providers[0])
@@ -274,8 +278,8 @@ describe("tryFallbackRetry", () => {
 
   describe("#given disconnected fallback providers with connected preferred provider", () => {
     test("keeps fallback entry and selects connected preferred provider", () => {
-      ;(readProviderModelsCache as any).mockReturnValue({ connected: ["provider-a"] })
+      ;(readProviderModelsCache as any).mockReturnValueOnce({ connected: ["provider-a"] })
-      ;(selectFallbackProvider as any).mockImplementation(
+      ;(selectFallbackProvider as any).mockImplementationOnce(
         (_providers: string[], preferredProviderID?: string) => preferredProviderID ?? "provider-b",
       )
 

src/hooks/model-fallback/hook.test.ts

@@ -3,6 +3,24 @@ const { beforeEach, describe, expect, mock, test } = require("bun:test")
 
 const readConnectedProvidersCacheMock = mock(() => null)
 const readProviderModelsCacheMock = mock(() => null)
+const selectFallbackProviderMock = mock((providers: string[], preferredProviderID?: string) => {
+  const connectedProviders = readConnectedProvidersCacheMock()
+  if (connectedProviders) {
+    const connectedSet = new Set(connectedProviders.map((provider: string) => provider.toLowerCase()))
+
+    for (const provider of providers) {
+      if (connectedSet.has(provider.toLowerCase())) {
+        return provider
+      }
+    }
+
+    if (preferredProviderID && connectedSet.has(preferredProviderID.toLowerCase())) {
+      return preferredProviderID
+    }
+  }
+
+  return providers[0] || preferredProviderID || "opencode"
+})
 const transformModelForProviderMock = mock((provider: string, model: string) => {
   if (provider === "github-copilot") {
     return model
@@ -31,6 +49,10 @@ mock.module("../../shared/provider-model-id-transform", () => ({
   transformModelForProvider: transformModelForProviderMock,
 }))
 
+mock.module("../../shared/model-error-classifier", () => ({
+  selectFallbackProvider: selectFallbackProviderMock,
+}))
+
 import {
   clearPendingModelFallback,
   createModelFallbackHook,
@@ -44,6 +66,7 @@ describe("model fallback hook", () => {
     readProviderModelsCacheMock.mockReturnValue(null)
     readConnectedProvidersCacheMock.mockClear()
     readProviderModelsCacheMock.mockClear()
+    selectFallbackProviderMock.mockClear()
 
     clearPendingModelFallback("ses_model_fallback_main")
     clearPendingModelFallback("ses_model_fallback_ghcp")

src/hooks/model-fallback/hook.ts

@@ -274,3 +274,13 @@ export function createModelFallbackHook(args?: { toast?: FallbackToast; onApplie
     },
   }
 }
+
+/**
+ * Resets all module-global state for testing.
+ * Clears pending fallbacks, toast keys, and session chains.
+ */
+export function _resetForTesting(): void {
+  pendingModelFallbacks.clear()
+  lastToastKey.clear()
+  sessionFallbackChains.clear()
+}

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

@@ -1,6 +1,6 @@
 import { describe, test, expect, beforeEach, afterEach } from "bun:test"
 import { homedir } from "node:os"
-import { join, resolve } from "node:path"
+import { join, resolve, win32 } from "node:path"
 import {
   getOpenCodeConfigDir,
   getOpenCodeConfigPaths,
@@ -241,9 +241,10 @@ describe("opencode-config-dir", () => {
         // when getOpenCodeConfigDir is called with binary="opencode-desktop"
         const result = getOpenCodeConfigDir({ binary: "opencode-desktop", version: "1.0.200", checkExisting: false })
 
-        // then returns %APPDATA%/ai.opencode.desktop
+        // then returns %APPDATA%/ai.opencode.desktop using Windows path semantics
-        expect(result).toBe(join("C:\\Users\\TestUser\\AppData\\Roaming", TAURI_APP_IDENTIFIER))
+        expect(result).toBe(win32.join("C:\\Users\\TestUser\\AppData\\Roaming", TAURI_APP_IDENTIFIER))
       })
+
     })
 
     describe("dev build detection", () => {

src/shared/opencode-config-dir.ts

@@ -1,6 +1,6 @@
 import { existsSync, realpathSync } from "node:fs"
 import { homedir } from "node:os"
-import { join, resolve } from "node:path"
+import { join, resolve, win32 } from "node:path"
 
 import type {
   OpenCodeBinaryType,
@@ -31,7 +31,7 @@ function getTauriConfigDir(identifier: string): string {
 
     case "win32": {
       const appData = process.env.APPDATA || join(homedir(), "AppData", "Roaming")
-      return join(appData, identifier)
+      return win32.join(appData, identifier)
     }
 
     case "linux":
@@ -71,7 +71,10 @@ export function getOpenCodeConfigDir(options: OpenCodeConfigDirOptions): string
   }
 
   const identifier = isDevBuild(version) ? TAURI_APP_IDENTIFIER_DEV : TAURI_APP_IDENTIFIER
-  const tauriDir = resolveConfigPath(getTauriConfigDir(identifier))
+  const tauriDirBase = getTauriConfigDir(identifier)
+  const tauriDir = process.platform === "win32"
+    ? (win32.isAbsolute(tauriDirBase) ? win32.normalize(tauriDirBase) : win32.resolve(tauriDirBase))
+    : resolveConfigPath(tauriDirBase)
 
   if (checkExisting) {
     const legacyDir = getCliConfigDir()

test-setup.ts

@@ -1,6 +1,8 @@
 import { beforeEach } from "bun:test"
-import { _resetForTesting } from "./src/features/claude-code-session-state/state"
+import { _resetForTesting as resetClaudeSessionState } from "./src/features/claude-code-session-state/state"
+import { _resetForTesting as resetModelFallbackState } from "./src/hooks/model-fallback/hook"
 
 beforeEach(() => {
-  _resetForTesting()
+  resetClaudeSessionState()
+  resetModelFallbackState()
 })