fix(stream): payload-length cap, quiet-port resync, main-thread error teardown

tests/test_session_controller.py

@@ -96,6 +96,45 @@ def test_leaving_live_mode_stops_stream(controller):
     assert not controller._repaint_timer.isActive()
 
 
+def test_binary_frame_decode_bounded_to_loaded_layout(controller, monkeypatch):
+    """Regression for phantom sensor #239 polluting MIN/MAX/AVG: the wire
+    payload carries a fixed-width channel array (up to 244 slots) wider than
+    any single wafer family's real sensor count. Family "A" (aepwafer.yaml)
+    has 48 real sensors — everything past that in the payload is an
+    unpopulated hardware slot and must never reach Frame.values."""
+    fake_transport = MagicMock()
+    fake_transport.read.return_value = b""
+    monkeypatch.setattr(
+        "pygui.serialcomm.serial_port.SerialPort.open_port",
+        lambda *a, **k: fake_transport,
+    )
+
+    controller.startStream("COM_FAKE", "A")
+    try:
+        assert len(controller._sensors) == 48  # sanity: aepwafer.yaml loaded
+        parse = controller._reader._parse
+        payload = bytes(244 * 2)  # full-width wire payload, well beyond the real 48
+        frame = parse(payload, seq=1)
+        assert len(frame.values) == 48
+    finally:
+        controller.stopStream()
+
+
+def test_live_error_surfaces_message_and_stops_stream(controller):
+    """A fatal StreamReader error must reach QML with its message (for the
+    Activity Log) and must tear the stream down cleanly."""
+    controller.setMode("live")
+    controller._reader = MagicMock()
+
+    error_seen = MagicMock()
+    controller.liveError.connect(error_seen)
+
+    controller._on_live_error("Binary stream resync failed: no sync marker")
+
+    error_seen.assert_called_once_with("Binary stream resync failed: no sync marker")
+    assert controller._reader is None
+
+
 def test_compare_files_integration(controller):
     # Mock the comparisonResult signal
     mock_slot = MagicMock()