fix(select): add the validation prefix to the ALL_PROJECTED_ATTRIBUTES refusal

crates/core/src/validation/mod.rs

@@ -1661,7 +1661,7 @@ pub fn validate_select_projection(
     }
     if matches!(select, Some(Select::AllProjectedAttributes)) && !has_index_name {
         return Err(DynamoDbError::ValidationException(
-            "ALL_PROJECTED_ATTRIBUTES can be used only when Querying using an IndexName".to_owned(),
+            "1 validation error detected: ALL_PROJECTED_ATTRIBUTES can be used only when Querying using an IndexName".to_owned(),
         ));
     }
     Ok(())
@@ -3457,7 +3457,7 @@ mod tests {
         .unwrap_err();
         assert_eq!(
             err.to_string(),
-            "ALL_PROJECTED_ATTRIBUTES can be used only when Querying using an IndexName"
+            "1 validation error detected: ALL_PROJECTED_ATTRIBUTES can be used only when Querying using an IndexName"
         );
         assert!(
             validate_select_projection(

crates/engine/src/scan.rs

@@ -377,7 +377,8 @@ pub async fn handle_scan(
         && index_info.is_none()
     {
         return Err(DynamoDbError::ValidationException(
-            "ALL_PROJECTED_ATTRIBUTES can be used only when Querying using an IndexName".to_owned(),
+            "1 validation error detected: ALL_PROJECTED_ATTRIBUTES can be used only when Querying using an IndexName"
+                .to_owned(),
         ));
     }
     if let Some(Select::Count) = input.select

tests/test_select_all_projected_attributes.py

@@ -0,0 +1,83 @@
+# Copyright 2026 ExtendDB contributors
+# SPDX-License-Identifier: Apache-2.0
+
+"""Select=ALL_PROJECTED_ATTRIBUTES without an IndexName.
+
+Amazon DynamoDB answers ``1 validation error detected:
+ALL_PROJECTED_ATTRIBUTES can be used only when Querying using an IndexName``
+on Query, with a KeyConditionExpression or legacy KeyConditions and with
+ConsistentRead, and on Scan (measured 2026-10-25 at 21:13 UTC, us-east-1,
+each request twice).
+
+Dual-target against Amazon DynamoDB and extenddb.
+"""
+
+from __future__ import annotations
+
+import pytest
+from botocore.exceptions import ClientError
+
+from conftest import scoped_table
+
+MESSAGE = (
+    "1 validation error detected: "
+    "ALL_PROJECTED_ATTRIBUTES can be used only when Querying using an IndexName"
+)
+
+
+@pytest.fixture(scope="module")
+def table(dynamodb_client):
+    with scoped_table(
+        dynamodb_client,
+        attribute_definitions=[
+            {"AttributeName": "pk", "AttributeType": "S"},
+            {"AttributeName": "sk", "AttributeType": "S"},
+        ],
+        key_schema=[
+            {"AttributeName": "pk", "KeyType": "HASH"},
+            {"AttributeName": "sk", "KeyType": "RANGE"},
+        ],
+    ) as name:
+        yield name
+
+
+def _message(func) -> str:
+    with pytest.raises(ClientError) as exc_info:
+        func()
+    err = exc_info.value.response["Error"]
+    assert err["Code"] == "ValidationException", err
+    return err["Message"]
+
+
+@pytest.mark.parametrize("consistent", [False, True])
+def test_query_key_condition_expression(dynamodb_client, table, consistent):
+    msg = _message(
+        lambda: dynamodb_client.query(
+            TableName=table,
+            KeyConditionExpression="pk = :p",
+            ExpressionAttributeValues={":p": {"S": "absent"}},
+            Select="ALL_PROJECTED_ATTRIBUTES",
+            ConsistentRead=consistent,
+        )
+    )
+    assert msg == MESSAGE
+
+
+def test_query_legacy_key_conditions(dynamodb_client, table):
+    msg = _message(
+        lambda: dynamodb_client.query(
+            TableName=table,
+            KeyConditions={
+                "pk": {"ComparisonOperator": "EQ", "AttributeValueList": [{"S": "absent"}]}
+            },
+            Select="ALL_PROJECTED_ATTRIBUTES",
+        )
+    )
+    assert msg == MESSAGE
+
+
+def test_scan(dynamodb_client, table):
+    msg = _message(
+        lambda: dynamodb_client.scan(TableName=table, Select="ALL_PROJECTED_ATTRIBUTES")
+    )
+    assert msg == MESSAGE