Fix UseProjection with JsonDocument nested field selection

[michaelstaib]

Overview

• fix projection field handling to keep the original nested value when a nested scope has no projectable members
• avoid creating invalid member-init expressions for read-only nested types such as JsonDocument
• add regression coverage for issue JsonDocument problem when using [UseProjection] #5893 ([UseProjection] + JsonDocument + nested rootElement selection)

Verification

• dotnet test src/HotChocolate/Data/test/Data.Tests/HotChocolate.Data.Tests.csproj --filter "FullyQualifiedName~Issue5893Tests"
• dotnet test src/HotChocolate/Data/test/Data.Tests/HotChocolate.Data.Tests.csproj --filter "FullyQualifiedName~IntegrationTests" --framework net10.0

Fixes #5893

[github-actions]

Fusion Gateway Performance Results

Simple Composite Query

	Req/s	Err%
Constant 2 (50 VUs)	4045.48	0.00%
Ramping 2 (0-500-0 VUs)	3858.74	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	1.01ms	9.72ms	12.14ms	20.39ms	28.47ms	243.52ms
Ramping 2	1.28ms	51.61ms	56.73ms	98.01ms	139.80ms	288.33ms

---

Deep Recursion Query

	Req/s	Err%
Constant 2 (50 VUs)	673.39	0.00%
Ramping 2 (0-500-0 VUs)	775.82	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	7.91ms	64.24ms	71.65ms	91.36ms	111.29ms	862.94ms
Ramping 2	3.26ms	238.60ms	264.41ms	555.99ms	621.39ms	985.01ms

---

Variable Batching Throughput

	Req/s	Err%
Constant 2 (50 VUs)	5438.47	0.00%
Ramping 2 (0-500-0 VUs)	5387.53	0.00%

Response Times

	Min	Med	Avg	P90	P95	Max
Constant 2	0.16ms	8.59ms	9.08ms	15.24ms	18.12ms	58.46ms
Ramping 2	0.19ms	38.16ms	42.64ms	79.67ms	102.64ms	211.97ms

---

Runner 2 = benchmarking-2

Run 22414006389 • Commit 9140f41 • Wed, 25 Feb 2026 20:22:47 GMT

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (6a3b7a3) to head (ffeb7b0).
⚠️ Report is 815 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #9210       +/-   ##
==========================================
- Coverage   74.16%       0   -74.17%     
==========================================
  Files        2677       0     -2677     
  Lines      140790       0   -140790     
  Branches    16371       0    -16371     
==========================================
- Hits       104421       0   -104421     
+ Misses      30774       0    -30774     
+ Partials     5595       0     -5595     

Flag	Coverage Δ
unittests	?

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.