refactor(multipart): replace co-busboy with @eggjs/co-busboy

- Update multipart plugin to use the new @eggjs/co-busboy package
- Import Part type for proper type narrowing
- Add truncated property to FileStream interface
- Fix type assertions for AsyncIterable return

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: fengmk2

packages/co-busboy/src/index.ts

@@ -28,6 +28,10 @@ export interface FileStream extends Readable {
   transferEncoding: string;
   mime: string;
   mimeType: string;
+  /**
+   * Set by busboy when file size limit is reached
+   */
+  truncated?: boolean;
 }
 
 /**
@@ -94,6 +98,10 @@ export interface Parts {
   (): Promise<Part | null>;
   field: Record<string, string | string[]>;
   fields: FieldTuple[];
+  /**
+   * Allow adding async iterator at runtime for for-await-of support
+   */
+  [Symbol.asyncIterator]?: () => AsyncIterator<Part>;
 }
 
 /**

plugins/multipart/package.json

@@ -59,9 +59,9 @@
     "typecheck": "tsgo --noEmit"
   },
   "dependencies": {
+    "@eggjs/co-busboy": "workspace:*",
     "@eggjs/path-matching": "workspace:*",
     "bytes": "catalog:",
-    "co-busboy": "catalog:",
     "dayjs": "catalog:"
   },
   "devDependencies": {

plugins/multipart/src/app/extend/context.ts

@@ -6,8 +6,7 @@ import path from 'node:path';
 import { Readable, PassThrough } from 'node:stream';
 import { pipeline } from 'node:stream/promises';
 
-// @ts-expect-error no types
-import parse from 'co-busboy';
+import { parse, type Part } from '@eggjs/co-busboy';
 import dayjs from 'dayjs';
 import { Context } from 'egg';
 
@@ -120,7 +119,7 @@ export default class MultipartContext extends Context {
     // mount asyncIterator, so we can use `for await` to get parts
     const parts = parse(this, parseOptions);
     parts[Symbol.asyncIterator] = async function* () {
-      let part: MultipartFileStream | undefined;
+      let part: Part | null;
       do {
         part = await parts();
 
@@ -157,10 +156,10 @@ export default class MultipartContext extends Context {
         }
 
         // dispatch part to outter logic such as for-await-of
-        yield part;
-      } while (part !== undefined);
+        yield part as MultipartFileStream;
+      } while (part !== null);
     };
-    return parts;
+    return parts as unknown as AsyncIterable<MultipartFileStream>;
   }
 
   /**