[tobias-tengler]

The gateway forwarded string and enum variables to source schemas through UTF-16 strings: variable coercion called JsonElement.GetString() for every value, and FetchResultStore transcoded those strings back to UTF-8 when writing the source schema request.

This PR keeps forwarded variables in UTF-8. JsonVariableCoercion copies the raw UTF-8 bytes of string and enum values into the request's Utf8MemoryBuilder (unescaping them when the JSON string contains escape sequences) and creates segment-backed StringValueNode and EnumValueNode literals. FetchResultStore writes string, enum, int and float literals from their UTF-8 spans, so no strings are created for forwarded variables.

Benchmarks

Enums (21 enum values)

Method	Version	Mean	Ratio	Allocated	Alloc Ratio
Gateway request	main	20.04 μs	1.00	31.55 KB	1.00
Gateway request	PR	19.47 μs	0.97	31.03 KB	0.98
Variable coercion	main	1.310 μs	1.00	2.59 KB	1.00
Variable coercion	PR	1.215 μs	0.93	2.04 KB	0.79

256 character strings (21 values)

Method	Version	Mean	Ratio	Allocated	Alloc Ratio
Gateway request	main	21.84 μs	1.00	41.91 KB	1.00
Gateway request	PR	21.70 μs	0.99	36.25 KB	0.86
Variable coercion	main	2.279 μs	1.00	13.03 KB	1.00
Variable coercion	PR	2.308 μs	1.01	7.34 KB	0.56

16 KB lorem ipsum string (1 value)

Method	Version	Mean	Ratio	Allocated	Alloc Ratio
Gateway request	main	23.82 μs	1.00	61.35 KB	1.00
Gateway request	PR	22.33 μs	0.94	45.38 KB	0.74
Variable coercion	main	2.294 μs	1.00	32.48 KB	1.00
Variable coercion	PR	2.165 μs	0.94	16.51 KB	0.51

Gateway requests allocate 2% less with enum variables, 14% less with 256 character strings and 26% less with a 16 KB string, because each forwarded string value is no longer held as a UTF-16 string. With the 16 KB string, the gateway request is also 6% faster. The other time differences are within the measurement error (about ±0.2 to ±0.5 μs for gateway requests).

[github-actions]

Patch coverage

77.8% of changed lines covered (35/45)

File	Covered	Changed	Patch %
…/src/Fusion.Execution/Execution/JsonVariableCoercion.cs	31	41	75.6% 🔴
…/src/Fusion.Execution/Execution/Results/FetchResultStore.cs	4	4	100.0% 🟢

Uncovered changed lines (JSON)

{
  "sha": "7e7e55ef636f9b001713427c67693958eb5815bc",
  "files": [
    { "path": "src/HotChocolate/Fusion/src/Fusion.Execution/Execution/JsonVariableCoercion.cs", "ranges": [[477, 477], [479, 487]] }
  ]
}

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Project coverage: 58.6% (314214/536401 lines)

[Copilot]

🟡 Changes recommended

An unused import will fail CI, and forwarded UTF-8 serialization lacks direct regression coverage.

2 open findings

• Remove unused System.Text import · New
• Add execution test for forwarded value JSON serialization · New

What changed in this PR

Updates Fusion to preserve forwarded variable literals as UTF-8 through coercion and serialization.

Changes:

• Stores coerced strings and enums as UTF-8.
• Writes value-node spans directly to JSON.
• Adds escape-sequence coercion tests.

File	Description
VariableCoercionHelperTests.cs	Tests escaped strings and enums.
FetchResultStore.cs	Serializes value nodes directly from UTF-8 spans.
JsonVariableCoercion.cs	Coerces JSON strings and enums into UTF-8-backed nodes.

🧠 Review effort: Balanced

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