feat: discreet ghost mark at the cursor's previous position

When you move the highlight start (click/drag the timeline), leave a single
faint dashed line at where it was, so an accidental move is easy to undo by
eye. Only the most recent prior position is kept, it's suppressed when leaving
an already-exported spot (it has a marker), and it clears on a new file.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main.py

@@ -1860,6 +1860,8 @@ class TimelineWidget(QWidget):
         self._scan_mode = False
         self._play_pos: float | None = None  # current playback position (seconds)
         self._last_play_x = -1               # last painted playhead pixel (repaint coalescing)
+        self._ghost_cursor: float | None = None  # previous cursor pos (undo-by-eye after a move)
+        self._gesture_cursor: float | None = None  # cursor at the start of a mouse gesture
         self._locked = False                 # when True, clicks scrub playback, not cursor
         self._crop_keyframes: list[tuple[float, float, str | None, bool, bool]] = []
         self._markers: list[tuple[float, int, str, float]] = []
@@ -1916,6 +1918,7 @@ class TimelineWidget(QWidget):
         self._c_mlabel = QColor(200, 50, 50)
         self._c_white = QColor(255, 255, 255)
         self._c_black = QColor(0, 0, 0)
+        self._pen_ghost = QPen(QColor(120, 170, 230, 90), 1, Qt.PenStyle.DashLine)
         self._other_colors = (
             QColor(220, 190, 50), QColor(60, 190, 100), QColor(80, 160, 220),
             QColor(200, 120, 220), QColor(220, 140, 60),
@@ -1937,6 +1940,8 @@ class TimelineWidget(QWidget):
         self._duration = duration
         self._cursor = 0.0
         self._play_pos = None
+        self._ghost_cursor = None
+        self._gesture_cursor = None
         self._view_start = 0.0
         self._view_span = 0.0
         self._other_markers = []
@@ -2252,6 +2257,14 @@ class TimelineWidget(QWidget):
                 p.drawLine(x_start, rh, x_start, h)
                 p.drawLine(x_end,   rh, x_end,   h)
 
+            # ── ghost of the previous cursor position (undo-by-eye) ──────────
+            if (not self._scan_mode and self._ghost_cursor is not None
+                    and abs(self._ghost_cursor - self._cursor) > 0.05):
+                gx = int(self._time_to_x(self._ghost_cursor))
+                if -2 <= gx <= w + 2:
+                    p.setPen(self._pen_ghost)
+                    p.drawLine(gx, rh, gx, h)
+
             # ── scan regions ──────────────────────────────────────────────
             if self._scan_regions and self._duration > 0:
                 for (start, end, score, os_, oe) in self._scan_regions:
@@ -2464,6 +2477,8 @@ class TimelineWidget(QWidget):
                 self._drag_start_val = r[0]
                 self._drag_end_val = r[1]
                 return
+        # Remember where the highlight started, to ghost it on release.
+        self._gesture_cursor = self._cursor
         self._seek(x)
 
     def mouseDoubleClickEvent(self, event):
@@ -2579,6 +2594,21 @@ class TimelineWidget(QWidget):
         # On release, flush any pending debounced seek immediately.
         self._seek_timer.stop()
         self._emit_seek()
+        self._commit_ghost()
+
+    def _at_export_marker(self, t: float) -> bool:
+        """True if *t* sits on an existing export marker (already marked)."""
+        return any(abs(t - mt) < 0.15 for mt, _n, _p, _s in self._markers)
+
+    def _commit_ghost(self) -> None:
+        """After a move, leave a single discreet mark at the prior position —
+        unless that spot was an exported area (it already has a marker)."""
+        g = self._gesture_cursor
+        self._gesture_cursor = None
+        if g is None or abs(self._cursor - g) < 0.05:
+            return
+        self._ghost_cursor = None if self._at_export_marker(g) else g
+        self.update()
 
     def wheelEvent(self, event):
         """Ctrl+wheel zooms the view around the mouse; plain wheel adds/removes