number stimulus outputs in device stage order

The output index now equals the device stage, so outputs follow the order the
device measures them: master port 1 through its switch positions, then port 2.
The previous position-major numbering permuted the middle two against the
physical order, so data captured before this needs its calibration re-captured.

python_app/tests/test_librevna_multidevice.py

@@ -399,20 +399,32 @@ class PerPointStimulusSwitchingTest(unittest.TestCase):
 
     def test_two_positions_give_four_outputs(self) -> None:
         channels = build_output_channels((1, 2), 2)
-        # Outputs are switch-position-major, so outputs 0/1 stay exactly what they are
-        # without switching; stages are port-major, matching the bitstream taking the
-        # port from the stage counter's UPPER bits.
+        # Port-major in BOTH numbers: the output index is the device stage, so outputs
+        # come in the order the device measures them — port 1 through its switch
+        # positions, then port 2. Verified against a scope on the switch line.
         self.assertEqual(
             [(c.index, c.stimulus_port, c.stage_index) for c in channels],
-            [(0, 1, 0), (1, 2, 2), (2, 1, 1), (3, 2, 3)],
+            [(0, 1, 0), (1, 1, 1), (2, 2, 2), (3, 2, 3)],
         )
 
+    def test_output_index_is_the_device_stage(self) -> None:
+        # The whole point of the 2026-09-17 renumbering: an operator hanging antennas
+        # sees stage order on a scope, and the output numbering must not permute it.
+        for substage_count in (1, 2, 4):
+            channels = build_output_channels((1, 2), substage_count)
+            self.assertEqual(
+                [c.index for c in channels],
+                [c.stage_index for c in channels],
+                msg=f"substages={substage_count}",
+            )
+            self.assertEqual([c.index for c in channels], list(range(len(channels))))
+
     def test_switch_position_is_the_low_stage_bit(self) -> None:
         # This is what lets the controller just invert its pin on every trigger cycle
         # instead of tracking an absolute stage number.
         channels = build_output_channels((1, 2), 2)
         for channel in channels:
-            expected_position = channel.index // 2  # switch-position-major output order
+            expected_position = channel.index & 1
             self.assertEqual(channel.stage_index & 1, expected_position)
 
     def test_stage_budget_is_enforced(self) -> None: