Total, bounded validator for the pinned Open Responses HTTP/SSE event profile.

Schemas are compiled into OpenResponsesSchema.Generated; validation never reads a file, resolves an external reference, parses a schema, or performs network I/O at runtime. Each schema/instance evaluation consumes the frozen event budget, including union branches. Draft 2020-12 integer semantics include decoded integral floats such as 1.0 and -0.0; local policy may constrain their value after schema validation. Diagnostics are fixed atoms and never retain Provider values.