fix: s3parser now looks for bare ETX, not DLE+ETX.

minimateplus/framing.py

@@ -155,8 +155,16 @@ class S3FrameParser:
     State machine:
         IDLE             — scanning for DLE (0x10)
         SEEN_DLE         — saw DLE, waiting for STX (0x02) to start a frame
-        IN_FRAME         — collecting de-stuffed payload bytes
-        IN_FRAME_DLE     — inside frame, saw DLE; ETX ends frame, DLE continues stuffing
+        IN_FRAME         — collecting de-stuffed payload bytes; bare ETX ends frame
+        IN_FRAME_DLE     — inside frame, saw DLE; DLE continues stuffing;
+                           DLE+ETX is treated as literal data (NOT a frame end),
+                           which lets inner-frame terminators pass through intact
+
+    Wire format confirmed from captures:
+        [DLE=0x10] [STX=0x02] [stuffed payload+chk] [bare ETX=0x03]
+    The ETX is NOT preceded by a DLE on the wire.  DLE+ETX sequences that
+    appear inside the payload are inner-frame terminators and must be
+    treated as literal data.
 
     ACK (0x41) bytes and arbitrary non-DLE bytes in IDLE state are silently
     discarded (covers device boot string "Operating System" and keepalive ACKs).
@@ -210,6 +218,11 @@ class S3FrameParser:
         elif self._state == self._IN_FRAME:
             if b == DLE:
                 self._state = self._IN_FRAME_DLE
+            elif b == ETX:
+                # Bare ETX = real frame terminator (confirmed from captures)
+                frame = self._finalise()
+                self._state = self._IDLE
+                return frame
             else:
                 self._body.append(b)
 
@@ -219,10 +232,11 @@ class S3FrameParser:
                 self._body.append(DLE)
                 self._state = self._IN_FRAME
             elif b == ETX:
-                # End of frame
-                frame = self._finalise()
-                self._state = self._IDLE
-                return frame
+                # DLE+ETX inside a frame is an inner-frame terminator, NOT
+                # the outer frame end.  Treat as literal data and continue.
+                self._body.append(DLE)
+                self._body.append(ETX)
+                self._state = self._IN_FRAME
             else:
                 # Unexpected DLE + byte — treat both as literal data and continue
                 self._body.append(DLE)