test(dynamodb): fence the local-replica-only GSI read-capacity derivation (#1452)

A live CloudFormation probe (stack Cdkd1452ProbeXRegionRead, us-east-1 + us-west-2, 2026-08-10) disproved the CapacityAutoScalingSettings doc sentence that motivated the issue. A GlobalTable whose local replica GSI carried SeedCapacity 10 (MinCapacity 1) and whose remote replica GSI carried a fixed ReadCapacityUnits 20 came up with ReadCapacityUnits 1 in us-east-1 and a ProvisionedThroughputOverride of 20 on the us-west-2 replica -- no cross-region max, and the remote value scoped to the remote replica.

So deriving read capacity from the LOCAL replica alone is CORRECT and cdkd needs no source change. This adds the probe shape as a regression fence so a future reader who finds the same doc sentence cannot turn it into a cross-region max, with the transcript inlined in the test comment. The same run independently re-confirmed issue #1435's MinCapacity-on-create finding on a new template shape.

Author: go-to-k

tests/unit/provisioning/dynamodb-globaltable-provider-gsi-throughput.test.ts

@@ -361,6 +361,81 @@ describe('DynamoDBGlobalTable GSI throughput translation (issue #1387)', () => {
       expect(gsi!.OnDemandThroughput).toBeUndefined();
     });
 
+    // Issue #1452 FENCE. The CFn docs for CapacityAutoScalingSettings claim a
+    // CROSS-REGION max: "if your global secondary index myGSI has a
+    // SeedCapacity of 10 in us-east-1 and a fixed ReadCapacityUnits of 20 in
+    // eu-west-1, CloudFormation will initially set the read capacity for myGSI
+    // to 20." A live probe DISPROVED that sentence, so deriving read capacity
+    // from the LOCAL replica alone is CORRECT and must stay that way.
+    //
+    // Probe (stack Cdkd1452ProbeXRegionRead, us-east-1 + us-west-2, 2026-08-10):
+    // an AWS::DynamoDB::GlobalTable whose local (us-east-1) replica GSI carried
+    // ReadCapacityAutoScalingSettings{MinCapacity 1, MaxCapacity 100,
+    // SeedCapacity 10} and whose remote (us-west-2) replica GSI carried a fixed
+    // ReadCapacityUnits 20 reached CREATE_COMPLETE with:
+    //   us-east-1 myGSI ProvisionedThroughput.ReadCapacityUnits = 1
+    //   us-west-2 myGSI ProvisionedThroughputOverride.ReadCapacityUnits = 20
+    // So CloudFormation took the LOCAL replica's MinCapacity (1) and applied
+    // the remote's 20 only as that replica's own override. It took neither the
+    // remote's higher value NOR the local SeedCapacity — the latter
+    // independently re-confirming issue #1435's 'min'-on-create finding.
+    //
+    // Taking a max across replicas here would OVER-provision every such table
+    // and diverge from CloudFormation. This is the same failure mode as #1427,
+    // whose doc-derived premise the same probe family also disproved.
+    it('does NOT raise the local read capacity to a higher REMOTE replica value (issue #1452)', () => {
+      const [gsi] = toSdkGlobalSecondaryIndexes(
+        {
+          BillingMode: 'PROVISIONED',
+          GlobalSecondaryIndexes: [
+            {
+              IndexName: 'myGSI',
+              KeySchema: [{ AttributeName: 'gsipk', KeyType: 'HASH' }],
+              Projection: { ProjectionType: 'KEYS_ONLY' },
+              WriteProvisionedThroughputSettings: {
+                WriteCapacityAutoScalingSettings: { MinCapacity: 1, MaxCapacity: 10 },
+              },
+            },
+          ],
+          Replicas: [
+            {
+              Region: 'us-east-1',
+              GlobalSecondaryIndexes: [
+                {
+                  IndexName: 'myGSI',
+                  ReadProvisionedThroughputSettings: {
+                    ReadCapacityAutoScalingSettings: {
+                      MinCapacity: 1,
+                      MaxCapacity: 100,
+                      SeedCapacity: 10,
+                    },
+                  },
+                },
+              ],
+            },
+            {
+              Region: 'us-west-2',
+              GlobalSecondaryIndexes: [
+                {
+                  IndexName: 'myGSI',
+                  ReadProvisionedThroughputSettings: { ReadCapacityUnits: 20 },
+                },
+              ],
+            },
+          ],
+        },
+        'us-east-1',
+        'PROVISIONED'
+      );
+      // 1 = the LOCAL replica's MinCapacity. NOT 20 (the remote replica's
+      // fixed value) and NOT 10 (the local SeedCapacity) — both were rejected
+      // by the live probe above.
+      expect(gsi!.ProvisionedThroughput).toEqual({
+        ReadCapacityUnits: 1,
+        WriteCapacityUnits: 1,
+      });
+    });
+
     it('maps the on-demand CDK shape to SDK OnDemandThroughput (both directions)', () => {
       const [gsi] = toSdkGlobalSecondaryIndexes(
         ON_DEMAND_TABLE_PROPS,