fix: disable manifest for commit-engine URIs on default connect

Connecting to an external commit-engine URI (e.g. `s3+ddb://...`) went
through the directory namespace with manifest listing enabled by default.
That opens a `__manifest` table under the root, whose URI has no
`ddbTableName` query, so building its commit handler fails with
"`s3+ddb://` scheme and expects exactly one query `ddbTableName`".

Lance v8 silently swallowed that error and fell back to directory
listing, so the connect succeeded. Lance v9's directory namespace only
falls back on not-found errors and propagates everything else, turning
the pre-existing incompatibility into a hard failure (surfaced by
`test_concurrent_dynamodb_commit`).

Disable the manifest namespace when a commit engine is in use, matching
the explicit `manifest_enabled(true)` path which already rejects these
URIs.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

rust/lancedb/src/connection.rs

@@ -1472,6 +1472,33 @@ mod tests {
         );
     }
 
+    // A default connection to a commit-engine URI must disable the manifest
+    // namespace: the `__manifest` table under the root has no `ddbTableName`
+    // query, so building its commit handler would fail. See the DynamoDB
+    // regression fixed alongside the Lance v9 bump.
+    #[cfg(feature = "dynamodb")]
+    #[tokio::test]
+    async fn test_default_connect_disables_manifest_for_commit_engine() {
+        for uri in [
+            "s3+ddb://bucket/db?ddbTableName=manifest",
+            "s3://bucket/db?engine=ddb&ddbTableName=manifest",
+        ] {
+            let db = connect(uri)
+                .storage_option("region", "us-east-1")
+                .execute()
+                .await
+                .unwrap_or_else(|e| panic!("expected {uri} to connect, got {e:?}"));
+
+            let (ns_impl, properties) = db.namespace_client_config().await.unwrap();
+            assert_eq!(ns_impl, "dir");
+            assert_eq!(
+                properties.get("manifest_enabled"),
+                Some(&"false".to_string()),
+                "manifest should be disabled for commit-engine URI {uri}"
+            );
+        }
+    }
+
     #[tokio::test]
     async fn test_manifest_enabled_connection_migrates_root_listing_table() {
         let tmp_dir = tempdir().unwrap();

rust/lancedb/src/database/listing.rs

@@ -323,12 +323,21 @@ impl ListingDatabase {
         namespace_client_properties: HashMap<String, String>,
         read_consistency_interval: Option<std::time::Duration>,
         session: Arc<lance::session::Session>,
+        uses_commit_engine: bool,
     ) -> Result<Arc<LanceNamespaceDatabase>> {
-        let ns_properties = Self::build_namespace_client_properties(
+        let mut ns_properties = Self::build_namespace_client_properties(
             uri,
             &storage_options,
             namespace_client_properties,
         );
+        // The directory namespace enables manifest-based listing by default, which
+        // opens a `__manifest` table under the root. That is incompatible with an
+        // external commit engine (e.g. `s3+ddb://`): the manifest table URI has no
+        // `ddbTableName` query, so building its commit handler fails. Disable the
+        // manifest so these connections fall back to directory listing.
+        if uses_commit_engine {
+            ns_properties.insert("manifest_enabled".to_string(), "false".to_string());
+        }
         Ok(Arc::new(
             LanceNamespaceDatabase::connect(
                 "dir",
@@ -503,6 +512,12 @@ impl ListingDatabase {
                     }
                 }
 
+                // A commit engine is in use either via an explicit `engine=` query
+                // param or a `<scheme>+<engine>` URI scheme (e.g. `s3+ddb`). The
+                // manifest namespace is incompatible with these, so track it to
+                // disable the manifest below.
+                let uses_commit_engine = engine.is_some() || url.scheme().contains('+');
+
                 // Filter out the commit store query param -- it's a lancedb param
                 url.query_pairs_mut().clear();
                 url.query_pairs_mut().extend_pairs(filtered_querys);
@@ -575,6 +590,7 @@ impl ListingDatabase {
                     request.namespace_client_properties.clone(),
                     request.read_consistency_interval,
                     session.clone(),
+                    uses_commit_engine,
                 )
                 .await?;
 
@@ -629,6 +645,7 @@ impl ListingDatabase {
             namespace_client_properties,
             read_consistency_interval,
             session.clone(),
+            false,
         )
         .await?;