feat(protocol): enhance raw capture functionality and documentation updates

- Update `s3_bridge.py` to default raw capture file paths to "auto" for timestamped naming.
- Modify `gui_bridge.py` to pre-check raw capture options and streamline path handling.
- Extend `ach_server.py` to save both incoming and outgoing raw bytes for analysis.
- Revise `CHANGELOG.md` and `instantel_protocol_reference.md` to reflect changes in recording mode handling and compliance data encoding.

bridges/ach_server.py

@@ -35,6 +35,7 @@ Output per session
     device_info.json   — serial number, firmware version, calibration date, etc.
     events.json        — all events: timestamp, PPV per channel, peaks, metadata
     raw_rx_<ts>.bin    — raw bytes from the device (S3 side) for Analyzer
+    raw_tx_<ts>.bin    — raw bytes we sent to the device (BW side) for Analyzer
     session_<ts>.log   — detailed protocol log
 
 What to look for
@@ -172,16 +173,24 @@ class AchSession:
         transport = SocketTransport(self.sock, peer=self.peer)
 
         # Collect raw bytes in memory until startup succeeds, then flush to disk.
-        raw_buf: list[bytes] = []
-        _orig_read = transport.read
+        raw_rx_buf: list[bytes] = []   # device → us  (S3 side)
+        raw_tx_buf: list[bytes] = []   # us → device  (BW side)
+        _orig_read  = transport.read
+        _orig_write = transport.write
 
         def tapped_read(n: int) -> bytes:
             data = _orig_read(n)
             if data:
-                raw_buf.append(data)
+                raw_rx_buf.append(data)
             return data
 
-        transport.read = tapped_read  # type: ignore[method-assign]
+        def tapped_write(data: bytes) -> None:
+            _orig_write(data)
+            if data:
+                raw_tx_buf.append(data)
+
+        transport.read  = tapped_read   # type: ignore[method-assign]
+        transport.write = tapped_write  # type: ignore[method-assign]
 
         serial: Optional[str] = None
 
@@ -201,23 +210,35 @@ class AchSession:
         # Startup succeeded — this is a real unit.  Create session dir now.
         session_dir = self.output_dir / f"ach_inbound_{ts}"
         session_dir.mkdir(parents=True, exist_ok=True)
-        log_path = session_dir / f"session_{ts}.log"
-        raw_path = session_dir / f"raw_rx_{ts}.bin"
+        log_path   = session_dir / f"session_{ts}.log"
+        raw_rx_path = session_dir / f"raw_rx_{ts}.bin"   # device → us  (S3 side)
+        raw_tx_path = session_dir / f"raw_tx_{ts}.bin"   # us → device  (BW side)
 
-        # Flush buffered raw bytes to file and switch to direct file writes.
-        raw_fh = open(raw_path, "wb")
-        for chunk in raw_buf:
-            raw_fh.write(chunk)
-        raw_buf.clear()
+        # Flush buffered bytes to files and switch to direct file writes.
+        raw_rx_fh = open(raw_rx_path, "wb")
+        raw_tx_fh = open(raw_tx_path, "wb")
+        for chunk in raw_rx_buf:
+            raw_rx_fh.write(chunk)
+        for chunk in raw_tx_buf:
+            raw_tx_fh.write(chunk)
+        raw_rx_buf.clear()
+        raw_tx_buf.clear()
 
         def tapped_read_file(n: int) -> bytes:
             data = _orig_read(n)
             if data:
-                raw_fh.write(data)
-                raw_fh.flush()
+                raw_rx_fh.write(data)
+                raw_rx_fh.flush()
             return data
 
-        transport.read = tapped_read_file  # type: ignore[method-assign]
+        def tapped_write_file(data: bytes) -> None:
+            _orig_write(data)
+            if data:
+                raw_tx_fh.write(data)
+                raw_tx_fh.flush()
+
+        transport.read  = tapped_read_file   # type: ignore[method-assign]
+        transport.write = tapped_write_file  # type: ignore[method-assign]
 
         # Wire up file handler now that the session dir exists.
         fh = logging.FileHandler(log_path, encoding="utf-8")
@@ -530,7 +551,8 @@ class AchSession:
                     log.warning("  [WARN] Failed to restart monitoring: %s", exc)
 
         finally:
-            raw_fh.close()
+            raw_rx_fh.close()
+            raw_tx_fh.close()
             client.close()  # closes transport / socket cleanly
             root_logger.removeHandler(fh)
             fh.close()