扩大原始图片文本字段上限

multipart 文本字段改为 chunk 流式读取并限制 16KB。

统一 UTF-8 校验和超限错误，避免先完整分配超长 prompt。

server-rs/crates/api-server/src/raw_image.rs

@@ -58,7 +58,7 @@ pub(crate) struct RawImageEditResponse {
     pub(crate) data: Vec<RawImageEditItem>,
 }
 
-const RAW_IMAGE_MAX_PROMPT_BYTES: usize = 4 * 1024;
+const RAW_IMAGE_MAX_TEXT_FIELD_BYTES: usize = 16 * 1024;
 
 pub(crate) async fn edit_raw_image(
     State(state): State<AppState>,
@@ -244,15 +244,32 @@ async fn read_multipart_image(
 
 async fn set_text_field(
     target: &mut Option<String>,
-    field: axum::extract::multipart::Field<'_>,
+    mut field: axum::extract::multipart::Field<'_>,
     name: &str,
 ) -> Result<(), AppError> {
     if target.is_some() {
         return Err(bad_request(format!("{name} 字段不能重复")));
     }
-    *target = Some(field.text().await.map_err(|error| {
+    let mut bytes = Vec::new();
+    while let Some(chunk) = field.chunk().await.map_err(|error| {
         tracing::warn!(field = name, error = %error, "raw image multipart 文本读取失败");
         bad_request(format!("{name} 字段读取失败"))
+    })? {
+        if bytes.len().saturating_add(chunk.len()) > RAW_IMAGE_MAX_TEXT_FIELD_BYTES {
+            tracing::warn!(
+                field = name,
+                limit_bytes = RAW_IMAGE_MAX_TEXT_FIELD_BYTES,
+                "raw image multipart 文本字段超过大小限制"
+            );
+            return Err(bad_request(format!(
+                "{name} 字段不能超过 {RAW_IMAGE_MAX_TEXT_FIELD_BYTES} 字节"
+            )));
+        }
+        bytes.extend_from_slice(&chunk);
+    }
+    *target = Some(String::from_utf8(bytes).map_err(|error| {
+        tracing::warn!(field = name, error = %error, "raw image multipart 文本字段不是有效 UTF-8");
+        bad_request(format!("{name} 字段必须为有效 UTF-8 文本"))
     })?);
     Ok(())
 }
@@ -269,9 +286,9 @@ fn prepare_request(payload: RawImageEditRequest) -> Result<PreparedRawImageEdit,
     if payload.prompt.trim().is_empty() {
         return Err(bad_request("prompt 不能为空"));
     }
-    if payload.prompt.len() > RAW_IMAGE_MAX_PROMPT_BYTES {
+    if payload.prompt.len() > RAW_IMAGE_MAX_TEXT_FIELD_BYTES {
         return Err(bad_request(format!(
-            "prompt 不能超过 {RAW_IMAGE_MAX_PROMPT_BYTES} 字节"
+            "prompt 不能超过 {RAW_IMAGE_MAX_TEXT_FIELD_BYTES} 字节"
         )));
     }
     validate_raw_image_edit_dimensions(payload.width, payload.height)
@@ -567,12 +584,12 @@ mod tests {
     #[test]
     fn prompt_uses_raw_utf8_byte_limit() {
         let mut parsed = request(png_bytes(1, 1), None);
-        parsed.prompt = "a".repeat(RAW_IMAGE_MAX_PROMPT_BYTES + 1);
+        parsed.prompt = "a".repeat(RAW_IMAGE_MAX_TEXT_FIELD_BYTES + 1);
         let error = match prepare_request(parsed) {
             Ok(_) => panic!("oversized prompt should fail before image decode and billing"),
             Err(error) => error,
         };
 
-        assert!(format!("{error:?}").contains("prompt 不能超过 4096 字节"));
+        assert!(format!("{error:?}").contains("prompt 不能超过 16384 字节"));
     }
 }