fix(cli): add backup and crash recovery to auth-plugins config write

Creates .bak before writeFileSync; on failure restores from backup
and returns a descriptive error instead of corrupting the config.

src/cli/config-manager/auth-plugins.ts

@@ -1,4 +1,4 @@
-import { readFileSync, writeFileSync, copyFileSync } from "node:fs"
+import { readFileSync, writeFileSync, copyFileSync, existsSync } from "node:fs"
 import { modify, applyEdits } from "jsonc-parser"
 import type { ConfigMergeResult, InstallConfig } from "../types"
 import { getConfigDir } from "./config-context"
@@ -31,6 +31,7 @@ export async function addAuthPlugins(config: InstallConfig): Promise<ConfigMerge
   }
 
   const { format, path } = detectConfigFormat()
+  const backupPath = `${path}.bak`
 
   try {
     let existingConfig: OpenCodeConfig | null = null
@@ -59,11 +60,13 @@ export async function addAuthPlugins(config: InstallConfig): Promise<ConfigMerge
 
     const newConfig = { ...(existingConfig ?? {}), plugin: plugins }
 
+    if (format !== "none" && existsSync(path)) {
+      copyFileSync(path, backupPath)
+    }
+
     if (format === "jsonc") {
       const content = readFileSync(path, "utf-8")
 
-      copyFileSync(path, `${path}.bak`)
-
       const newContent = applyEdits(
         content,
         modify(content, ["plugin"], plugins, {
@@ -74,13 +77,62 @@ export async function addAuthPlugins(config: InstallConfig): Promise<ConfigMerge
       try {
         parseJsonc(newContent)
       } catch (error) {
-        copyFileSync(`${path}.bak`, path)
+        if (existsSync(backupPath)) {
+          copyFileSync(backupPath, path)
+        }
         throw new Error(`Generated JSONC is invalid: ${error instanceof Error ? error.message : String(error)}`)
       }
 
-      writeFileSync(path, newContent)
+      try {
+        writeFileSync(path, newContent)
+      } catch (error) {
+        const hasBackup = existsSync(backupPath)
+        try {
+          if (hasBackup) {
+            copyFileSync(backupPath, path)
+          }
+        } catch (restoreError) {
+          return {
+            success: false,
+            configPath: path,
+            error: `Failed to write config file, and restore from backup failed: ${String(error)}; restore error: ${String(restoreError)}`,
+          }
+        }
+
+        return {
+          success: false,
+          configPath: path,
+          error: hasBackup
+            ? `Failed to write config file. Restored from backup: ${String(error)}`
+            : `Failed to write config file. No backup was available: ${String(error)}`,
+        }
+      }
     } else {
-      writeFileSync(path, JSON.stringify(newConfig, null, 2) + "\n")
+      const nextContent = JSON.stringify(newConfig, null, 2) + "\n"
+      try {
+        writeFileSync(path, nextContent)
+      } catch (error) {
+        const hasBackup = existsSync(backupPath)
+        try {
+          if (hasBackup) {
+            copyFileSync(backupPath, path)
+          }
+        } catch (restoreError) {
+          return {
+            success: false,
+            configPath: path,
+            error: `Failed to write config file, and restore from backup failed: ${String(error)}; restore error: ${String(restoreError)}`,
+          }
+        }
+
+        return {
+          success: false,
+          configPath: path,
+          error: hasBackup
+            ? `Failed to write config file. Restored from backup: ${String(error)}`
+            : `Failed to write config file. No backup was available: ${String(error)}`,
+        }
+      }
     }
     return { success: true, configPath: path }
   } catch (err) {