Fix QueryableOffsetPagingProvider.CanHandle for executable lists

[michaelstaib]

What

• implement QueryableOffsetPagingProvider.CanHandle instead of throwing NotImplementedException
• return support for array/list sources and guard null input
• add regression coverage for executable fields with .AddQueryableOffsetPagingProvider()

Why

This reproduces and fixes #5082 where schema initialization could fail because CanHandle threw while probing paging providers.

Closes #5082

[github-actions]

Fusion Gateway Performance Results

Simple Composite Query

	Req/s	Err%
Constant (50 VUs)	6906.58	0.00%
Ramping (0-500-0 VUs)	7404.46	0.00%

Response Times & Query

	Min	Med	Avg	P90	P95	Max
Constant	0.58ms	5.95ms	7.10ms	11.05ms	15.81ms	177.83ms
Ramping	0.57ms	24.09ms	29.81ms	63.48ms	75.87ms	177.81ms

query TestQuery {
  topProducts(first: 5) {
    inStock
    name
    price
    shippingEstimate
    upc
    weight
    reviews {
      id
      body
      author {
        id
        username
        name
      }
    }
  }
}

---

Deep Recursion Query

	Req/s	Err%
Constant (50 VUs)	1294.96	0.00%
Ramping (0-500-0 VUs)	1353.04	0.00%

Response Times & Query

	Min	Med	Avg	P90	P95	Max
Constant	4.39ms	34.08ms	37.46ms	51.04ms	59.66ms	384.92ms
Ramping	1.83ms	135.13ms	157.15ms	338.02ms	383.71ms	683.45ms

query TestQuery {
  users {
    id
    username
    name
    reviews {
      id
      body
      product {
        inStock
        name
        price
        shippingEstimate
        upc
        weight
        reviews {
          id
          body
          author {
            id
            username
            name
            reviews {
              id
              body
              product {
                inStock
                name
                price
                shippingEstimate
                upc
                weight
              }
            }
          }
        }
      }
    }
  }
  topProducts(first: 5) {
    inStock
    name
    price
    shippingEstimate
    upc
    weight
    reviews {
      id
      body
      author {
        id
        username
        name
        reviews {
          id
          body
          product {
            inStock
            name
            price
            shippingEstimate
            upc
            weight
          }
        }
      }
    }
  }
}

---

Variable Batching Throughput

	Req/s	Err%
Constant (50 VUs)	23589.00	0.00%
Ramping (0-500-0 VUs)	18388.27	0.00%

Response Times & Query

	Min	Med	Avg	P90	P95	Max
Constant	0.08ms	1.72ms	2.07ms	3.98ms	4.82ms	45.96ms
Ramping	0.08ms	9.32ms	11.44ms	23.73ms	28.53ms	108.89ms

query TestQuery($upc: ID!, $price: Long!, $weight: Long!) {
  productByUpc(upc: $upc) {
    inStock
    shippingEstimate(weight: $weight, price: $price)
  }
}

Variables (5 sets batched per request)

[
  { "upc": "1", "price": 899, "weight": 100 },
  { "upc": "2", "price": 1299, "weight": 1000 },
  { "upc": "3", "price": 15, "weight": 20 },
  { "upc": "4", "price": 499, "weight": 100 },
  { "upc": "5", "price": 1299, "weight": 1000 }
]

---

Run 22394542715 • Commit be59491 • Wed, 25 Feb 2026 11:38:43 GMT