feat(upload): 支持 Agent 本地图片安全上传

.agents/skills/upload-delivery-desk-work/references/api-contract.md

@@ -51,7 +51,7 @@ Returns current work content, project identity, images, and rounds. Use `?round=
 
 ### `POST /api/projects/:projectId/works`
 
-JSON body:
+URL mode uses a JSON body:
 
 ```json
 {
@@ -72,6 +72,15 @@ Constraints:
 - Cross-origin images must be supported image responses no larger than 20 MB. Local, private, reserved, and non-standard-port targets are rejected.
 - Repeating the same `projectId + externalId` returns the existing work with `idempotent: true`.
 
+Local-file mode uses `multipart/form-data` with text fields `externalId`, `title`, `description`, `tags` and repeated file field `images`.
+
+- Send `tags` as a JSON array string.
+- Send 1-30 JPEG, PNG, GIF, WebP, or AVIF files, each no larger than 20 MB.
+- File order is display order; file 1 is the cover.
+- The server validates actual image content instead of trusting only the filename or declared MIME.
+- With active Tencent COS configuration, accepted files are streamed from server temporary storage into COS.
+- Do not send Base64 in JSON. The agent script reads local files directly into the multipart request; binary bytes never belong in the plan or conversation.
+
 ### `POST /api/works/:workId/rounds`
 
 JSON body:
@@ -87,6 +96,7 @@ JSON body:
 
 This endpoint is not idempotent. One successful call creates exactly one new round. Never blindly retry after a timeout.
 It applies the same COS reuse/import rules as work creation.
+It also accepts the same local-file multipart fields, except `externalId` is omitted.
 
 ## State guards