Merge same-named fields across fragments in MCP tool output schemas

[glen-84]

Summary

• OperationToolFactory threw ArgumentException while building a tool's output schema whenever two selections shared a response name — inline fragments on different types selecting the same field (the shape any interface/union with implementation-declared fields forces), fragment spreads doing the same, or a plain duplicate field selection. Because the throw happened during warmup, one such operation took down the whole tool catalogue.
• Colliding response names now merge into a single property: object schemas union their properties, only sub-fields selected in every branch stay required, and array schemas merge their item schemas the same way. A field reached only through a type condition was already optional and stays that way.

Test plan

• New OperationToolFactory snapshot tests cover same-named fields via inline fragments (identical and diverging sub-selections), via fragment spreads, and via duplicate field selections; each previously failed with the reported ArgumentException.
• Full Adapters.Mcp.Tests suite passes (241 tests).

Closes #10321

[Copilot]

Pull request overview

Fixes OperationToolFactory output-schema generation to tolerate duplicate response names (e.g., same-named fields selected across fragments) by merging colliding JSON Schema properties instead of throwing during tool warmup, and adds snapshot coverage for the previously failing selection shapes.

Changes:

• Replace Dictionary.Add with collision-aware TryAdd + schema merge for same response-name fields in output schema generation.
• Introduce MergeProperties to union object properties / array item schemas and intersect required sets across branches.
• Add new snapshot tests covering inline fragments, fragment spreads, and duplicate field selections.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/HotChocolate/Adapters/src/Adapters.Mcp.Core/OperationToolFactory.cs	Merges colliding response-name properties and adds recursive schema-merge helper.
src/HotChocolate/Adapters/test/Adapters.Mcp.Tests/OperationToolFactoryTests.cs	Adds new snapshot tests and a small schema to reproduce same-named-field scenarios.
src/HotChocolate/Adapters/test/Adapters.Mcp.Tests/snapshots/OperationToolFactoryTests.CreateTool_InlineFragmentsOnDifferentTypesSelectSameField_MergesIntoSingleProperty.json	New snapshot for identical sub-selections across inline fragments.
src/HotChocolate/Adapters/test/Adapters.Mcp.Tests/snapshots/OperationToolFactoryTests.CreateTool_InlineFragmentsWithDivergingSubSelections_UnionsSubSelections.json	New snapshot for diverging sub-selections merged into a unified schema.
src/HotChocolate/Adapters/test/Adapters.Mcp.Tests/snapshots/OperationToolFactoryTests.CreateTool_FragmentSpreadsSelectSameField_MergesIntoSingleProperty.json	New snapshot for same field selected via multiple fragment spreads.
src/HotChocolate/Adapters/test/Adapters.Mcp.Tests/snapshots/OperationToolFactoryTests.CreateTool_DuplicateFieldSelection_MergesIntoSingleProperty.json	New snapshot for duplicate field selections in the same selection set.

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[github-actions]

Patch coverage

100.0% of changed lines covered (43/43)

File	Covered	Changed	Patch %
…/Adapters/src/Adapters.Mcp.Core/OperationToolFactory.cs	43	43	100.0% 🟢

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Project coverage: 57.7% (286110/495834 lines)