fix(protocol): remove auto-detection of frame mode and ensure extra chunks are always used for valid waveform footer

CLAUDE.md

@@ -350,14 +350,20 @@ Do NOT use fixed absolute offsets for sample_rate or record_time.
 **SUB 5A (bulk waveform) TCP frame splitting — confirmed 2026-04-27:**
 
 Over TCP via cellular modem, each 5A chunk request that produces a single ~1100-byte
-A5 response over direct RS-232 arrives as **two separate, complete S3 frames** of
+A5 response over direct RS-232 may arrive as **two separate, complete S3 frames** of
-~550 bytes each.  This is because the device sends its RS-232 response as multiple
+~550 bytes each ("2-frame mode").  The modem's Data Forwarding Timeout (~100-150 ms)
-frames, and the modem's Data Forwarding Timeout (~100-150 ms) delivers them to us
+can split the RS-232 response into two TCP segments, each parsed as a complete S3 frame.
-as separate TCP segments, each parsed as a complete S3 frame.
+Under different modem/timing conditions the full ~1100-byte response arrives as **one
+S3 frame** ("1-frame mode").
+
+**Both modes require `extra_chunks_after_metadata=1`** (the extra chunk at metadata_counter
++ 0x0400).  The device's waveform footer data lives at circular-buffer address 0x1C00 for
+this event; the terminator frame must be sent at 0x1C00 (not 0x1800) to receive it.
 
 Example for a 2-second Continuous event (BE11529, key=01110000) via TCP:
-- 1 probe frame (554 B) + 5 chunks × 2 frames (556-573 B) + 1 extra chunk × 2 frames + 1 terminator (208 B) = **14 A5 frames**
+- **2-frame mode:** 1 probe frame (554 B) + 5 chunks × 2 frames (556-573 B) + 1 extra chunk × 2 frames + 1 terminator (208 B) = **14 A5 frames** → 6864-byte file
-- All 14 frames contribute body data; using all of them gives the correct 6864-byte file.
+- **1-frame mode:** 1 probe frame (~1097 B) + 5 chunks × 1 frame (~1079-1113 B) + 1 extra chunk × 1 frame (smaller, tail of event) + 1 terminator → **8 A5 frames** → 6864-byte file
+- All frames contribute body data; using all of them gives the correct file.
 
 **Fix (confirmed 2026-04-27):**  `_recv_5a_batch()` in `protocol.py` collects ALL
 A5 frames per chunk request before the next request is sent, using a 0.5 s batch
@@ -365,6 +371,12 @@ timeout after the first frame to catch the ~150 ms delayed second frame.  `write
 includes ALL body frames without skipping — the extra chunk's frames are part of the
 body data, NOT padding to be discarded.
 
+**WRONG earlier hypothesis (do not re-introduce):** An attempt was made to auto-detect
+1-frame vs 2-frame mode from the probe frame size and skip the extra chunk when
+`probe_data_len >= 700`.  This was wrong — the extra chunk is always needed to advance
+the device's internal state to the footer address.  The `_probe_is_large` branch was
+removed 2026-04-27.
+
 ### Required ACEmanager settings (Sierra Wireless RV50/RV55)
 
 | Setting | Value | Why |

minimateplus/protocol.py

@@ -614,31 +614,14 @@ class MiniMateProtocol:
             [f"0x{f.page_key:04X}" for f in probe_batch],
         )
 
-        # Auto-detect frame mode from probe response size.
+        # Log probe frame size for diagnostics.
-        #
+        # The device always needs extra_chunks_after_metadata chunks after the
-        # Two observed TCP modes (confirmed from 4-26-26 and 4-27-26 captures):
+        # metadata frame before termination to prime the valid waveform footer.
-        #
+        # This holds regardless of TCP frame size (1-frame vs 2-frame mode).
-        #   1-frame mode (RS-232 / fast TCP): probe returns 1 large frame (~1100 B).
+        _effective_extra_chunks = extra_chunks_after_metadata
-        #     Each subsequent chunk also returns 1 large frame.  The probe contributes
-        #     ~999 bytes of ADC body data.  The correct term_counter = metadata_counter
-        #     + 0x0400, which returns ~702 bytes of tail+footer — NO extra chunk needed.
-        #
-        #   2-frame mode (TCP frame-splitting): probe returns 1 smaller frame (~554 B).
-        #     Each subsequent chunk returns 2 smaller frames (~550 B each).  The probe
-        #     contributes only ~487 bytes.  The missing ~512 bytes of body data must come
-        #     from an extra chunk after metadata, terminating at metadata_counter+0x0800.
-        #     The caller's extra_chunks_after_metadata value (default 1) covers this.
-        #
-        # Threshold 700 B sits comfortably between the two observed probe sizes (554 vs
-        # 1097 bytes) and is robust to minor variation.
-        _probe_is_large = (
-            len(probe_batch) == 1 and len(probe_batch[0].data) >= 700
-        )
-        _effective_extra_chunks = 0 if _probe_is_large else extra_chunks_after_metadata
         log.warning(
-            "5A probe data_len=%d  _probe_is_large=%s  effective_extra_chunks=%d",
+            "5A probe data_len=%d  effective_extra_chunks=%d",
             len(probe_batch[0].data),
-            _probe_is_large,
             _effective_extra_chunks,
         )