[exim] Pipe transports, environment, and transport_filter

For a pipe transport where the "transport_filter" option is specified, are
the environment items listed in section 29.4 of the spec, plus the
additional items given with the "environment" private option, also in
place for the transport_filter program?

If not, is there some other way to pass information (such as the
envelope sender, connecting ip, etc.) from exim to the filter program,
other than command line args? I'd like to avoid command line args
because they're publicly visible in the /proc filesystem.

If yes, can this fact be documented please?

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