fix(auto-update): revert config pin on install failure to prevent version mismatch

When bun install fails after updating the config pin, the config now shows the
new version but the actual package is the old one. Add revertPinnedVersion() to
roll back the config entry on install failure, keeping config and installed
version in sync.

Ref #1472

src/hooks/auto-update-checker/hook/background-update-check.ts

@@ -4,7 +4,7 @@ import { log } from "../../../shared/logger"
 import { invalidatePackage } from "../cache"
 import { PACKAGE_NAME } from "../constants"
 import { extractChannel } from "../version-channel"
-import { findPluginEntry, getCachedVersion, getLatestVersion, updatePinnedVersion } from "../checker"
+import { findPluginEntry, getCachedVersion, getLatestVersion, updatePinnedVersion, revertPinnedVersion } from "../checker"
 import { showAutoUpdatedToast, showUpdateAvailableToast } from "./update-toasts"
 
 async function runBunInstallSafe(): Promise<boolean> {
@@ -72,8 +72,14 @@ export async function runBackgroundUpdateCheck(
   if (installSuccess) {
     await showAutoUpdatedToast(ctx, currentVersion, latestVersion)
     log(`[auto-update-checker] Update installed: ${currentVersion} → ${latestVersion}`)
-  } else {
-    await showUpdateAvailableToast(ctx, latestVersion, getToastMessage)
-    log("[auto-update-checker] bun install failed; update not installed (falling back to notification-only)")
+    return
   }
+
+  if (pluginInfo.isPinned) {
+    revertPinnedVersion(pluginInfo.configPath, latestVersion, pluginInfo.entry)
+    log("[auto-update-checker] Config reverted due to install failure")
+  }
+
+  await showUpdateAvailableToast(ctx, latestVersion, getToastMessage)
+  log("[auto-update-checker] bun install failed; update not installed (falling back to notification-only)")
 }