Return a copy projected to the negotiated protocol version. Per-content
_meta was introduced by 2025-06-18 ("Add _meta to additional interface
types"), so it is dropped for an older peer. uri/mimeType/text/blob
all existed in 2024-11-05 and are preserved unchanged. Mirrors the
content-level _meta stripping in Content.forVersion.
Return a copy projected to the negotiated protocol version. Per-content _meta was introduced by 2025-06-18 ("Add _meta to additional interface types"), so it is dropped for an older peer. uri/mimeType/text/blob all existed in 2024-11-05 and are preserved unchanged. Mirrors the content-level _meta stripping in Content.forVersion.