P2: Fix S3 multipart route - use query param for action

- Change route from /s3/multipart/:bucket/*key/init to /s3/multipart/:bucket/*key?action=init
- Add multipart_handler to unify all multipart operations
- Use Response type instead of impl IntoResponse for type compatibility

markbase-core/src/s3.rs

@@ -1027,3 +1027,79 @@ fn extract_user_from_auth(headers: &HeaderMap) -> Option<String> {
         None
     }
 }
+
+/// Unified multipart handler using query param for action
+#[derive(serde::Deserialize)]
+pub struct MultipartActionQuery {
+    action: Option<String>,  // init, part, complete, abort
+    upload_id: Option<String>,
+    part_number: Option<u32>,
+}
+
+pub async fn multipart_handler(
+    method: axum::http::Method,
+    Path((bucket, key)): Path<(String, String)>,
+    State(state): State<crate::server::AppState>,
+    query: axum::extract::Query<MultipartActionQuery>,
+    headers: HeaderMap,
+    body: Body,
+) -> axum::response::Response {
+    let action = query.action.as_deref().unwrap_or("");
+    
+    match action {
+        "init" => {
+            initiate_multipart_upload(
+                Path((bucket, key)),
+                State(state),
+                headers,
+            ).await.into_response()
+        }
+        "part" => {
+            let upload_query = axum::extract::Query(UploadPartQuery {
+                upload_id: query.upload_id.clone().unwrap_or_default(),
+                part_number: query.part_number.unwrap_or(1),
+            });
+            upload_part(
+                Path((bucket, key)),
+                State(state),
+                upload_query,
+                headers,
+                body,
+            ).await.into_response()
+        }
+        "complete" => {
+            let complete_query = axum::extract::Query(CompleteMultipartQuery {
+                upload_id: query.upload_id.clone().unwrap_or_default(),
+            });
+            complete_multipart_upload(
+                Path((bucket, key)),
+                State(state),
+                complete_query,
+                headers,
+                body,
+            ).await.into_response()
+        }
+        "abort" => {
+            let abort_query = axum::extract::Query(AbortMultipartQuery {
+                upload_id: query.upload_id.clone().unwrap_or_default(),
+            });
+            abort_multipart_upload(
+                Path((bucket, key)),
+                State(state),
+                abort_query,
+                headers,
+            ).await.into_response()
+        }
+        _ => {
+            if method == axum::http::Method::POST {
+                initiate_multipart_upload(
+                    Path((bucket, key)),
+                    State(state),
+                    headers,
+                ).await.into_response()
+            } else {
+                (StatusCode::BAD_REQUEST, "Missing action parameter").into_response()
+            }
+        }
+    }
+}

markbase-core/src/server.rs

@@ -245,11 +245,12 @@ pub async fn run(port: u16, file: Option<String>) -> anyhow::Result<()> {
             .post(crate::s3::put_object)  // POST for uploads (same handler handles multipart detection)
             .delete(crate::s3::delete_object)
         )
-        // Multipart upload endpoints
-        .route("/s3/multipart/:bucket/*key/init", post(crate::s3::initiate_multipart_upload))
-        .route("/s3/multipart/:bucket/*key/part", put(crate::s3::upload_part))
-        .route("/s3/multipart/:bucket/*key/complete", post(crate::s3::complete_multipart_upload))
-        .route("/s3/multipart/:bucket/*key/abort", delete(crate::s3::abort_multipart_upload))
+        // Multipart upload endpoints (use query param for action)
+        .route("/s3/multipart/:bucket/*key", 
+            post(crate::s3::multipart_handler)
+            .put(crate::s3::multipart_handler)
+            .delete(crate::s3::multipart_handler)
+        )
         // Bucket policy endpoints
         .route("/s3/policy/:bucket", get(crate::s3::get_bucket_policy))
         .route("/s3/policy/:bucket", put(crate::s3::put_bucket_policy))