How to verify this evidence package
===================================

ledger.jsonl holds every record this walk added to the account's hash chain.
For each line:  hash == SHA-256(prev_hash + record)   (hex strings, UTF-8)
and each line's prev_hash equals the previous line's hash (entries from other
walks may sit in between; the account-wide chain is checked by the server and
its head hash is printed in report.html).

Spectrum files sweeps/NNNNNN_pk.i16 / _pw.i16 are little-endian int16 tenths of
a dB, one value per channel; their SHA-256 must equal pk_sha256 / pw_sha256 in
the matching sweep record. Audio files must match audio_sha256 of their mark.

Python:
    import hashlib, json
    for line in open('ledger.jsonl'):
        e = json.loads(line)
        assert hashlib.sha256((e['prev_hash'] + e['record']).encode()).hexdigest() == e['hash']
