fix: improve metadata frame detection and update version to v0.12.1

CHANGELOG.md

@@ -4,6 +4,29 @@ All notable changes to seismo-relay are documented here.
 
 ---
 
+## v0.12.1 — 2026-04-15
+
+### Fixed
+
+- **Metadata frame not detected when compliance fields are unconfigured** — the
+  5A bulk waveform stream contains one metadata frame carrying ASCII compliance
+  strings.  The decoder skipped it only if `b"Project:"` appeared in the frame
+  payload.  On devices where Project/Client/User Name/Seis Loc are all blank, the
+  device omits those label strings entirely, so the check returned False and the
+  frame was decoded as ADC waveform samples.  The serial number bytes (`"BE11529\0"`)
+  appeared at sample ~929 followed by `0xFF 0xFF` fill, truncating the second half
+  of every waveform and producing a flat-line at 0 in/s after ~660 ms.
+
+  Fix: `_decode_a5_waveform` now checks a tuple of needles (`_METADATA_FRAME_NEEDLES`)
+  against the full frame bytes (`db`, not `db[7:]`): `b"Project:"`, `b"Client:"`,
+  `b"User Name:"`, `b"Seis Loc:"`, `b"Extended Notes"`, and `b"Geo: "`.  The geo
+  threshold label is always present (monitoring cannot operate without a configured
+  geo trigger level) and is the reliable universal anchor.  The same tuple is used
+  in `read_bulk_waveform_stream` for the `stop_after_metadata` early-exit path.
+  The log records which needle matched, aiding future diagnosis.
+
+---
+
 ## v0.12.0 — 2026-04-13
 
 ### Added