Generator can crash the consuming build on unrelated additional files

[YVbakker]

The AdditionalTextsProvider filter matches any .yaml/.yml/.json file marked as AdditionalFiles in the consuming project, not just OpenAPI specs:

var provider = context.AdditionalTextsProvider
    .Where(file => file.Path.EndsWith(".yaml", StringComparison.OrdinalIgnoreCase) ||
                   file.Path.EndsWith(".yml", StringComparison.OrdinalIgnoreCase) ||
                   file.Path.EndsWith(".json", StringComparison.OrdinalIgnoreCase))
    .Collect();

Combined with OpenApiDocumentProcessor.ProcessDocument:

return (document.Components?.Schemas ?? throw new InvalidOperationException("Document has no schemas"))

Any unrelated JSON/YAML additional file (e.g. appsettings.json) picked up by a consumer will throw and surface as a generator-crash diagnostic (CS8785), breaking their build.

Suggested fix:

• Require an explicit opt-in (filename convention, e.g. *.openapi.yaml, or MSBuild item metadata) instead of matching by extension alone.
• Replace thrown exceptions with context.ReportDiagnostic(...) using a proper DiagnosticDescriptor so a single bad/unrelated file doesn't take down the whole build.