Fix heightmap arc segmentation and G-code modal state bug

- segmentArc: prepend start point so push() generates the
  first chord correctly (arc points exclude start by convention)
- generateGCodeLine: emit explicit G0/G1 for motion/rapid moves
  to prevent G2/G3 modal state from carrying over to linearized
  segments after arc conversion
- simplifyViewTransform: replace cumulative-length threshold with
  perpendicular-distance (Ramer-Douglas-Peucker style) for
  geometrically correct simplification; break early on arcs
- applyLoaderGCode: allow program reload in Alarm state

Author: etet100

src/gpilot/core/gcode/converter/applyheightmap.cpp

@@ -225,6 +225,10 @@ QList<QVector3D> ApplyHeightmap::segmentArc(const QVector3D &start, const QVecto
                                             bool clockwise, PointSegment::planes plane)
 {
     QList<QVector3D> points;
+    // Include the raw start so the loop in push() generates the first chord
+    // (startPoint → arc[0]) correctly, matching segmentLine's convention.
+    // generatePointsAlongArcBDring does NOT include the start point.
+    points.append(start);
 
     QList<QVector3D> arcPoints = GcodePreprocessorUtils::generatePointsAlongArcBDring(
         plane, start, end, center, clockwise, radius,
@@ -330,11 +334,20 @@ QString ApplyHeightmap::generateGCodeLine(const QVector3D &start, const QVector3
     if (!commandOverride.isEmpty()) {
         command = commandOverride;
     } else {
-        // Take only the G/M code prefix (first token) because later we append
-        // fresh X/Y/Z/F values; the original args would duplicate coordinates.
-        const QString full = originalItem.command();
-        const int sp = full.indexOf(' ');
-        command = (sp < 0) ? full : full.left(sp);
+        // Always emit an explicit motion code so that the machine's modal state
+        // from a preceding G2/G3 (preserved arc) does not carry over into what
+        // should be a G1/G0 move. A modal G1 line ("X10 Y5" without a G-word)
+        // would otherwise be interpreted as G2/G3 by the controller.
+        switch (originalItem.group) {
+            case GCodeItemGroup::Movement:      command = "G1"; break;
+            case GCodeItemGroup::RapidMovement: command = "G0"; break;
+            default: {
+                const QString full = originalItem.command();
+                const int sp = full.indexOf(' ');
+                command = (sp < 0) ? full : full.left(sp);
+                break;
+            }
+        }
     }
     if (command.isEmpty() && !originalItem.args.empty()) {
         command = QString::fromStdString(originalItem.args.front());

src/gpilot/core/gcode/parser/viewtransform/simplifyviewtransform.cpp

@@ -23,6 +23,17 @@ bool areCollinear(const QVector3D& refDir, const LineSegment& s, float tolerance
     return cross.lengthSquared() < tolerance * tolerance;
 }
 
+float perpendicularDistance(const QVector3D& p, const QVector3D& lineStart, const QVector3D& lineEnd)
+{
+    QVector3D chord = lineEnd - lineStart;
+    float chordLen = chord.length();
+    if (chordLen < 1e-7f) {
+        return (p - lineStart).length();
+    }
+
+    return QVector3D::crossProduct(p - lineStart, chord / chordLen).length();
+}
+
 }
 
 SimplifyViewTransform::SimplifyViewTransform(double precision, double collinearTolerance)
@@ -48,19 +59,25 @@ QList<LineSegment> SimplifyViewTransform::apply(const QList<LineSegment>& input)
             float refLen = refVec.length();
             QVector3D refDir = (refLen > 1e-7f) ? (refVec / refLen) : QVector3D();
             bool hasRefDir = refLen > 1e-7f && !input[j].isArc();
-            double length = refLen;
 
             while (i < input.count() - 1
                    && segmentType(input[i + 1]) == segmentType(input[j])) {
-                bool collinear = hasRefDir && !input[i + 1].isArc()
-                                 && areCollinear(refDir, input[i + 1], (float)m_collinearTolerance);
-                bool withinPrecision = length < m_precision;
+                if (input[i + 1].isArc() || !hasRefDir) {
+                    break;
+                }
+
+                bool collinear = areCollinear(refDir, input[i + 1], (float)m_collinearTolerance);
+                bool withinDeviation = m_precision > 0.0
+                                       && perpendicularDistance(
+                                              input[i].getEnd(),
+                                              input[j].getStart(),
+                                              input[i + 1].getEnd()
+                                          ) <= (float)m_precision;
 
-                if (!collinear && !withinPrecision) {
+                if (!collinear && !withinDeviation) {
                     break;
                 }
 
-                length += (input[i + 1].getEnd() - input[i + 1].getStart()).length();
                 i++;
             }
         }

src/gpilot/ui/forms/frmmain.cpp

@@ -2683,7 +2683,7 @@ void FrmMain::applyLoaderGCode(GCodeLoaderData *data)
     // pendant or scripted actions could still push the machine into Running
     // between load start and load finish. Replacing program() while the
     // RunningBehavior is iterating it crashes the sender.
-    if (!communicator()->stateBehavior()->is(AbstractStateBehavior::Type::Idle)) {
+    if (!communicator()->stateBehavior()->isOneOf(AbstractStateBehavior::Type::Idle, AbstractStateBehavior::Type::Alarm)) {
         qWarning() << "[FrmMain] applyLoaderGCode: machine is not idle, discarding loaded data";
         ui->console->appendSystem(tr("Cannot replace program: machine is not idle"));
         return;