The PFS register-and-walk path now serves the annual IPPS/LTCH and
OPPS/ASC rules and DMEPOS payment rules: title-filtered FR discovery
(discover-*-rules) and docket registration + comment walks
(fetch-*-comments). Correction documents (C1-...) parse, a null FR
abstract no longer becomes 'None', and the store waits out the mail
poller's write bursts (busy_timeout) instead of failing SQLITE_BUSY.