fix: add new helper (_recv_5a_batch()) that helps with assembling chunks over TCP

sfm/server.py

@@ -886,17 +886,14 @@ def device_event_blastware_file(
             with _build_client(port, baud, host, tcp_port, timeout=120.0) as client:
                 info = client.connect()
                 # Use stop_after_metadata=True (full_waveform=False) with 1 extra
-                # chunk after "Project:".  The extra chunk is required to prime the
-                # device over TCP: termination at term_counter=metadata_counter+0x0400
-                # returns only ~90 bytes (no useful footer) over TCP/cellular, but
-                # termination at metadata_counter+0x0800 (one chunk later) returns
-                # the full 737-byte frame containing the footer.
+                # chunk after "Project:".  The extra chunk primes the device so that
+                # the termination response carries the full waveform footer bytes.
+                # Without it the terminator returns only ~90 bytes (no useful footer).
                 #
-                # Confirmed from 4-26-26 BW RS-232 capture: BW terminates at 0x1800
-                # without an extra chunk (works on RS-232 but not TCP).
-                # write_blastware_file() automatically skips the extra chunk's
-                # contribution — only the probe+ADC+metadata+terminator bytes appear
-                # in the output file.
+                # The extra chunk's ADC data IS part of the Blastware file body —
+                # confirmed from 4-27-26 TCP capture: all 14 A5 frames (including the
+                # extra chunk's 2 TCP sub-frames) contribute to the correct 6864-byte
+                # output.  write_blastware_file() includes all frames unconditionally.
                 #
                 # full_waveform=True (natural end-of-stream) downloads ALL chunks
                 # including post-event silence (35+ chunks for a 9-sec event at