fix(tomo_params): block submit/queue-add when Fermat scan is below minimum

The estimated Fermat-scan point count was only ever flagged with an
orange label -- Submit and Add-to-queue would both happily accept a
configuration that's guaranteed to abort when actually run. Enforce
the same minimum in _validate(), shared by both actions, so it's now a
hard block instead of a cosmetic warning.

csaxs_bec/bec_widgets/widgets/tomo_params/tomo_params.py

@@ -848,6 +848,13 @@ class TomoParamsWidget(BECWidget, QWidget):
             rshift = params.get("single_point_random_shift_max", 0.0)
             if not 0 <= rshift <= 10:
                 return "single_point_random_shift_max must be between 0 and 10 µm"
+        count, min_positions = self._profile["compute_fermat_positions"](params)
+        if count < min_positions:
+            return (
+                f"Estimated Fermat scan points ({count}) is below the minimum of "
+                f"{min_positions} required for the scan to run -- increase FOV, "
+                "reduce step size, or adjust stitch/piezo range before submitting."
+            )
         return None
 
     # ── type visibility ───────────────────────────────────────────────────────
@@ -911,8 +918,10 @@ class TomoParamsWidget(BECWidget, QWidget):
         edited fov/step/stitch/piezo-range fields (see
         self._profile["compute_fermat_positions"], which calls the real
         scan class's own position-generation algorithm -- not a
-        reimplementation). Warning-only: flags orange below the scan
-        server's own minimum, never blocks Submit/Add-to-queue."""
+        reimplementation). This is just the live preview cue (flags orange
+        below the scan server's own minimum); the actual minimum is
+        enforced as a hard block in _validate(), shared by both
+        submit_params() and add_edited_to_queue()."""
         params = {}
         for key in self._profile["fermat_position_fields"]:
             widget = self._pw.get(key)