feat: preserve and encode raw 0C record in sidecar extensions for offline analysis

minimateplus/event_file_io.py

@@ -15,6 +15,7 @@ declared in `event_to_sidecar_dict()`.
 
 from __future__ import annotations
 
+import base64
 import datetime
 import hashlib
 import json
@@ -135,6 +136,20 @@ def event_to_sidecar_dict(
 
     captured_at = captured_at or datetime.datetime.utcnow()
 
+    # Stash raw 0C record bytes in `extensions.raw_records` so future
+    # field-decoding work (Peak Acceleration, ZC Freq, Time of Peak,
+    # sensor self-check results, etc.) can run offline against committed
+    # sidecars without a live device.  Cheap (~280 bytes base64) and
+    # forward-compatible (older readers ignore unknown extensions keys).
+    ext_dict: dict = dict(extensions) if extensions else {}
+    raw_0c = getattr(event, "_raw_record", None)
+    if raw_0c:
+        rr = ext_dict.setdefault("raw_records", {})
+        # Don't clobber a raw_0c that callers explicitly passed in via
+        # `extensions=...` (e.g. round-trip preservation in patch_sidecar).
+        rr.setdefault("waveform_record_b64", base64.b64encode(raw_0c).decode("ascii"))
+        rr.setdefault("waveform_record_len", len(raw_0c))
+
     return {
         "schema_version": SCHEMA_VERSION,
         "kind":           SIDECAR_KIND,
@@ -174,7 +189,7 @@ def event_to_sidecar_dict(
             "notes":         "",
         },
 
-        "extensions": extensions or {},
+        "extensions": ext_dict,
     }