fix(aerotech): limit abort explains the run-up separately from the scan range

The message now says whether the scan range itself is outside the limits or
only the extra run-up travel for acceleration and settling, by how much, and
what to do about it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M8zoDzDfsCTY2o5bT3J7Wv

csaxs_bec/scans/scans_v4/aerotech_cont_grid.py

@@ -506,14 +506,27 @@ class AerotechContGrid(ScanBase):
     def _check_line_limits(self):
         """The lines including run-up / run-out and the step axis range must fit the limits."""
         line = self._line
+        name = self.fast_axis.name
         low, high = self.fast_axis.limits
-        if low < high and (line["line_start"] < low or line["line_end"] > high):
-            run_up = line["trigger_low"] - line["line_start"]
+        if low < high and (self.fast_start < low or self.fast_end > high):
             raise ScanAbortion(
-                f"{self.fast_axis.name} range {line['line_start']:.4f} .. {line['line_end']:.4f}"
-                f" (including {run_up:.4f} run-up / run-out on each side at"
-                f" {line['target_velocity']} / s, acceleration {line['acceleration']} / s^2)"
-                f" is outside the limits ({low}, {high})."
+                f"Scan range of {name} {self.fast_start:.4f} .. {self.fast_end:.4f} is outside"
+                f" the limits ({low}, {high})."
+            )
+        if low < high and (line["line_start"] < low or line["line_end"] > high):
+            extra = self.fast_start - line["line_start"]
+            if line["line_end"] > high:
+                beyond = f"beyond the high limit {high} by {line['line_end'] - high:.4f}"
+            else:
+                beyond = f"beyond the low limit {low} by {low - line['line_start']:.4f}"
+            raise ScanAbortion(
+                f"The scan range of {name} {self.fast_start:.4f} .. {self.fast_end:.4f} is"
+                f" within the limits, but {name} needs {extra:.4f} extra travel on each side"
+                f" to accelerate to the scan velocity {line['target_velocity']:g} / s and"
+                f" settle (acceleration {line['acceleration']:g} / s^2, settle_time"
+                f" {self.settle_time:g} s). It would travel {line['line_start']:.4f} .."
+                f" {line['line_end']:.4f}, {beyond}. Move the scan away from the limit or"
+                " scan slower (larger exp_time or smaller fast_step_size)."
             )
         low, high = self.stepper_axis.limits
         stepper_range = sorted((self.stepper_start, self.stepper_stop))

tests/tests_scans/test_aerotech_cont_grid_scan.py

@@ -207,7 +207,16 @@ def test_run_up_outside_limits_aborts(v4_scan_assembler, device_manager):
     scan = v4_scan_assembler(
         "aerotech_cont_grid", "aerox", -4.0, 4.0, 0.1, "aeroy", -2.0, 2.0, 2, exp_time=0.005
     )
-    with pytest.raises(ScanAbortion, match="run-up"):
+    with pytest.raises(ScanAbortion, match="within the limits, but aerox needs .* extra travel"):
+        scan.prepare_scan()
+
+
+def test_scan_range_outside_limits_aborts(v4_scan_assembler, device_manager):
+    _add_devices(device_manager)
+    scan = v4_scan_assembler(
+        "aerotech_cont_grid", "aerox", -1.0, 11.0, 0.5, "aeroy", -2.0, 2.0, 2, exp_time=0.1
+    )
+    with pytest.raises(ScanAbortion, match="Scan range of aerox"):
         scan.prepare_scan()