[Bug]: `A2A-Version` validation ignores minor versions and the query parameter

[lkk7]

What happened?

The specification says:

“Agents MUST process requests using the semantics of the requested A2A-Version (matching Major.Minor).”

and

“Clients MAY provide the A2A-Version as a request parameter instead of a header.”

The implementation seems to miss both points.

1. The code compares only major:

return actual_v.major == expected_v.major

2. The query parameter is ignored.

            actual_version = headers.get(
                constants.VERSION_HEADER
            ) or headers.get(constants.VERSION_HEADER.lower())

            if not actual_version:
                return constants.PROTOCOL_VERSION_0_3

            return str(actual_version)

A similar issue existed: #856 but it was not fully fixed.

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