[Fusion] Prune unreachable types from source schemas after preprocessing

[tobias-tengler]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (1f0b160) to head (2255b20).

Additional details and impacted files

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##   main   #9767   +/-   ##
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[Copilot]

Pull request overview

This PR updates Fusion composition to prune unreachable type system definitions from source schemas after preprocessing/enrichment, preventing validation/merge failures caused by orphaned types (e.g., when ExcludeByTag removes an entry-point and leaves a now-unreachable type behind).

Changes:

• Prunes unreferenced definitions from each source schema prior to source schema validation.
• Adds a regression test ensuring tag-based exclusion doesn’t accidentally trigger InvalidFieldSharing due to an orphaned type collision.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/HotChocolate/Fusion/src/Fusion.Composition/SchemaComposer.cs	Adds a pruning pass over source schemas before validation to drop unreachable definitions.
src/HotChocolate/Fusion/test/Fusion.Composition.Tests/SchemaComposerTests.cs	Adds a test case reproducing an orphaned-type collision scenario after tag exclusion.

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