First hardware run (fmu-v6xrt over USB, macOS) surfaced three issues:
- param_torture consumed PARAM_VALUE echoes positionally; one duplicate
broadcast desynced every subsequent check. Drain stale messages before
each set and match the echo against the expected value, reporting all
observed values so a genuine wrong-echo bug remains visible.
- the shell sentinel's second safety echo leaked into the next command's
captured output; strip any sentinel line, not just the current one.
- pymavlink 2.4.49 add_message() intermittently crashes with TypeError
when the first message of an instanced type arrives with its instance
field unset; wrap it defensively until fixed upstream.
Full suite now passes 5/5 against fmu-v6xrt.
Signed-off-by: Ramon Roche <mrpollo@gmail.com>