diff --git a/apps/ai-game-creator-shell/src-tauri/src/agent/direct_tool_bridge.rs b/apps/ai-game-creator-shell/src-tauri/src/agent/direct_tool_bridge.rs
index 399bc45cd..b13078c13 100644
--- a/apps/ai-game-creator-shell/src-tauri/src/agent/direct_tool_bridge.rs
+++ b/apps/ai-game-creator-shell/src-tauri/src/agent/direct_tool_bridge.rs
@@ -1930,20 +1930,15 @@ async fn bridge_remove_background(state: &DirectToolBridgeState, arguments: &Val
         );
         let (_operation_id, idempotency_key) = state.resource_request_ids(&fingerprint)?;
         let route = access.api_route("/api/external/v1/editor/images/background-removals");
-        let mut request_body = json!({
-            "sourceImageSrc": source_resource_id,
-            "projectId": manifest.project_id,
-            "assetKind": source_asset.kind,
-            "assetFolderId": context.asset_folder_id,
-            "assetLabel": asset_name,
-            "sourceResourceId": source_resource_id,
-        });
-        if background_mode == Some("flat") {
-            request_body["backgroundMode"] = json!("flat");
-        }
-        if let Some(color) = screen_color {
-            request_body["screenColor"] = json!(color);
-        }
+        let request_body = background_removal_request_body(
+            &source_resource_id,
+            &context.project_id,
+            &source_asset.kind,
+            &context.asset_folder_id,
+            &asset_name,
+            background_mode,
+            screen_color,
+        );
         let response = crate::http_client::with_agc_main_site_marker(
             client
                 .post(format!("{}{}", api_base_url, route))
@@ -1971,7 +1966,7 @@ async fn bridge_remove_background(state: &DirectToolBridgeState, arguments: &Val
             "status": "queued",
             "sourceLocalAssetId": source_asset_id,
             "assetName": asset_name,
-            "projectId": manifest.project_id,
+            "projectId": context.project_id,
             "assetFolderId": context.asset_folder_id,
             "queueState": bridge_safe_queue_state(queue_state),
         }))
@@ -2001,6 +1996,32 @@ fn background_removal_request_fingerprint(
     }
 }
 
+fn background_removal_request_body(
+    source_resource_id: &str,
+    remote_project_id: &str,
+    asset_kind: &str,
+    asset_folder_id: &str,
+    asset_name: &str,
+    background_mode: Option<&str>,
+    screen_color: Option<&str>,
+) -> Value {
+    let mut body = json!({
+        "sourceImageSrc": source_resource_id,
+        "projectId": remote_project_id,
+        "assetKind": asset_kind,
+        "assetFolderId": asset_folder_id,
+        "assetLabel": asset_name,
+        "sourceResourceId": source_resource_id,
+    });
+    if background_mode == Some("flat") {
+        body["backgroundMode"] = json!("flat");
+    }
+    if let Some(color) = screen_color {
+        body["screenColor"] = json!(color);
+    }
+    body
+}
+
 fn background_removal_queue_state(
     payload: &Value,
     platform_account_route: bool,
@@ -3652,4 +3673,20 @@ mod tests {
             })
         );
     }
+
+    #[test]
+    fn background_removal_request_uses_bound_remote_project_id() {
+        let body = background_removal_request_body(
+            "editor-resource-source",
+            "remote-project-1",
+            "character",
+            "remote-folder-1",
+            "雄狮-透明底",
+            Some("complex"),
+            None,
+        );
+        assert_eq!(body["projectId"], "remote-project-1");
+        assert_ne!(body["projectId"], "local-project-1");
+        assert_eq!(body["assetFolderId"], "remote-folder-1");
+    }
 }
diff --git a/docs/project-memory/shared-memory/decision-log.md b/docs/project-memory/shared-memory/decision-log.md
index 598f4a991..2afd9c0f5 100644
--- a/docs/project-memory/shared-memory/decision-log.md
+++ b/docs/project-memory/shared-memory/decision-log.md
@@ -2,6 +2,13 @@
 
 > 用途：记录已经确认、会影响后续开发的长期技术/产品/协作决策。短期讨论不要写在这里。
 > 当前口径：历史条目的旧路径、旧版本和已退役对象只用于追溯，不构成现行实现依据；如与当前代码或 `docs/README.md` 冲突，以当前代码和最新专题文档为准。
+
+## 2026-09-17 AGC 抠图提交使用远端画布项目身份
+
+- 背景：AGC 已通过本地项目 ID 建立并持久化本地项目到主站远端画布项目的绑定，但 `agc_remove_background` 提交请求仍把本地 `manifest.project_id` 放入 `projectId`；`assetFolderId` 已使用远端素材目录 ID。主站因此按项目不存在或不属于当前账号返回 404，主站抠图和 BgFilter 本身均正常。
+- 决策：抠图请求及工具回执统一使用 `prepare_external_canvas_generation_context` 返回的远端 `context.project_id`；本地 manifest 项目 ID 只用于绑定键和本地状态，不得作为主站业务请求的 `projectId`。
+- 验证：客户端定向 Rust 测试、格式、编码和 diff 检查通过；未修改主站路由或 BgFilter。
+
 ## 2026-09-16 抠图模式与背景色契约
 
 - External v1 抠图和 AGC `agc_remove_background` 支持 `complex`（语义分割识别前景）与 `flat`（纯色背景抠图）；明确纯色背景优先 flat，模式缺省仍为 complex，主站前端保持现有行为。
diff --git a/docs/technical/【技术方案】AGC抠图模式与背景色透传-2026-09-16.md b/docs/technical/【技术方案】AGC抠图模式与背景色透传-2026-09-16.md
index a7e9525fd..cef2b2850 100644
--- a/docs/technical/【技术方案】AGC抠图模式与背景色透传-2026-09-16.md
+++ b/docs/technical/【技术方案】AGC抠图模式与背景色透传-2026-09-16.md
@@ -65,6 +65,8 @@ OpenAPI 与客户端工具的对外说明只描述模式用途、参数约束和
 
 工具 schema、桥接参数校验和随包 `agc-client-projection` Skill/契约说明必须保持一致。模式与颜色属于请求意图，必须参与客户端幂等指纹；同一图片与名称的不同模式不能复用同一次请求。缺省 complex 且没有颜色时保留既有指纹。主站在默认值归一化之前计算 External 请求指纹，缺失的新字段不序列化，避免旧请求重放发生冲突。
 
+客户端提交前建立的本地项目绑定会返回主站远端 `projectId` 与 `assetFolderId`，抠图请求必须使用这两个远端身份；本地 manifest `projectId` 仅用于绑定和本地状态，不能直接提交给主站。
+
 ## 实施任务
 
 ### 任务一：冻结 BgFilter 契约