A strap serial hidden in a hex payload walks past every redaction rule #1833

The gap

redactStrapLogPii scrubs identifiers written as text:

private val PII_WHOOP_SERIAL_RE = Regex("WHOOP (\\d[0-9A-Za-z]{5,})")

It cannot see an identifier that arrives as hex, because it is reading hex digits rather than the
ASCII those bytes decode to.

That is not theoretical. On a WHOOP 5/MG, event 0x6D(109) carries the strap serial as plain ASCII
inside its payload:

payload=142e1c0001d36e3d1c12a35742423541503035333938353 20000
        \x14.\x1c\x00\x01\xd3n=\x1c\x12\xa3WBB5AP0539852\x00\x00
                                           ^^^^^^^^^^^^^ serial

Any diagnostic that dumps that payload puts the serial into the strap log — the file people are asked to
attach to a public issue. The MAC rule works (device=FD:••:••:••:••:4A in a real capture), so the log
looks redacted while an identifier passes through in a different encoding.

Where this already applies

• The event census on test centre: log every pushed strap EVENT under the Connection domain #1825 dumps payload=<hex> for every pushed event. Caught in review; that PR now
  carries the fix below.
• Apple logs hex too — commandResponsePayloadHex for the alarm readback, and the frame=<full frame hex> added for the clock diagnostic on diag(clock): read the strap's answer instead of asserting it (#1823) #1824. LiveState.redactPii has the same text-only shape, so
  the same blind spot exists there and is not fixed by this issue's change.

The fix taken

Decode each payload=/frame= hex run, find printable ASCII stretches, and mask the bytes of any run
shaped like a serial — leaving the rest of the dump intact. Blanket-truncating the payload would defeat
the reason these dumps exist: the payload is exactly where an undocumented field would be found.

Landed on Android with the event census. The Apple twin is still open — LiveState.redactPii needs
the same treatment before another hex-dumping diagnostic is added there.

Worth noting

The serial in the example above is real, and it reached a public PR description through exactly this
route before anyone noticed. The redaction is not optional decoration; it is the thing that makes "please
attach your strap log" a safe request.