Fix #8756 parse enum values in federation reference resolver

[michaelstaib]

Fixes #8756

Summary

• add a focused regression test that reproduces enum argument binding from _entities representations where the enum arrives as a string value
• update federation ArgumentParser to resolve string values against EnumType before scalar coercion
• keep existing scalar coercion behavior unchanged

Reproduction Code

var representations = new List<Representation>
{
    new(
        nameof(Issue8756Entity),
        new ObjectValueNode(
            new ObjectFieldNode("id", "1"),
            new ObjectFieldNode("enumValue", "B")))
};

var result = await EntitiesResolver.ResolveAsync(schema, representations, context);
var entity = Assert.IsType<Issue8756Entity>(result[0]);
Assert.Equal(Issue8756Enum.B, entity.EnumValue);

[github-actions]

Fusion Gateway Performance Results

Progress: 0/6 benchmarks completed — this report updates as each job finishes.

Simple Composite Query

	Req/s	Err%
Constant 2 (50 VUs)	pending	pending
Ramping 2 (0-500-0 VUs)	pending	pending

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	pending	pending	pending	pending	pending	pending
Ramping 2	pending	pending	pending	pending	pending	pending

---

Deep Recursion Query

	Req/s	Err%
Constant 2 (50 VUs)	pending	pending
Ramping 2 (0-500-0 VUs)	pending	pending

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	pending	pending	pending	pending	pending	pending
Ramping 2	pending	pending	pending	pending	pending	pending

---

Variable Batching Throughput

	Req/s	Err%
Constant 2 (50 VUs)	pending	pending
Ramping 2 (0-500-0 VUs)	pending	pending

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	pending	pending	pending	pending	pending	pending
Ramping 2	pending	pending	pending	pending	pending	pending

---

Runner 2 = benchmarking-2

Run 22506886204 • Commit 3c0391a • Fri, 27 Feb 2026 22:50:25 GMT