ui-trace: add holddrag, a press-hold-then-drag gesture

Neither existing action can produce "hold stationary for LONG_PRESS,
then move without lifting, then release": tap has no hold at all, and
swipe X1 Y1 X2 Y2 MS interpolates motion across its whole duration
starting at t=0, so a long swipe with a short first segment is still
continuous motion throughout, never a hold followed by a drag.

holddrag X1 Y1 X2 Y2 HOLD_MS MOVE_MS extends the same
MotionEvent/injectInputEvent mechanism swipe already uses: DOWN, sleep
HOLD_MS, then MOVE at the same fixed 10ms cadence swipe uses over
MOVE_MS, then UP -- one continuous touch. Additive; existing commands
unchanged.

Verified against a real device (this repo has no unit test harness, so
verification is driving a device, matching its existing posture):
`ui-trace record --do "holddrag 300 1850 300 2050 600 300"` against
ai-app-2's iris transcript screen produced a real long-press-then-drag
selection (confirmed by the app's own logcat and a screenshot showing
the resulting highlighted selection) that neither tap nor swipe could
reach. javac --release 17 -Xlint:all -Werror clean.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

bin/ui-trace

@@ -367,7 +367,8 @@ def main():
     rec.add_argument("-i", "--interval", type=int, default=16,
                      help="ms between samples (0 = as fast as possible)")
     rec.add_argument("--do", action="append", default=[], metavar="ACTION",
-                     help="'wait MS' | 'tap X Y' | 'swipe X1 Y1 X2 Y2 [MS]', repeatable")
+                     help="'wait MS' | 'tap X Y' | 'swipe X1 Y1 X2 Y2 [MS]' | "
+                          "'holddrag X1 Y1 X2 Y2 HOLD_MS MOVE_MS', repeatable")
     rec.add_argument("-o", "--out", help="where to save the trace")
     rec.add_argument("-m", "--match", help="show a timeline for these afterwards")
     rec.add_argument("--field", default="top",

share/ui-trace/UiTrace.java

@@ -221,6 +221,9 @@ public final class UiTrace {
             case "swipe" -> swipe(Integer.parseInt(step[1]), Integer.parseInt(step[2]),
                     Integer.parseInt(step[3]), Integer.parseInt(step[4]),
                     step.length > 5 ? Long.parseLong(step[5]) : 300);
+            case "holddrag" -> holdDrag(Integer.parseInt(step[1]), Integer.parseInt(step[2]),
+                    Integer.parseInt(step[3]), Integer.parseInt(step[4]),
+                    Long.parseLong(step[5]), Long.parseLong(step[6]));
             default -> throw new IllegalArgumentException("unknown action: " + step[0]);
         }
     }
@@ -345,4 +348,36 @@ public final class UiTrace {
         }
         send(MotionEvent.ACTION_UP, down, x2, y2);
     }
+
+    /**
+     * A press held stationary for `holdMs`, then moved to `(x2, y2)` over `moveMs`, then
+     * released -- one continuous touch, never lifted between the hold and the move.
+     *
+     * Neither existing action can produce this. `tap` has no hold at all, and `swipe`
+     * interpolates motion across its *whole* duration starting at t=0, so a long `swipe` with a
+     * short first segment is still continuous motion throughout, never a hold followed by a
+     * drag. That gap matters for anything that decides pan-vs-select the way Android itself
+     * does -- a stationary press held past `LONG_PRESS` (500ms) starts a selection, which
+     * further drag then extends -- because neither of the other two actions can reach the
+     * "starts a selection" branch at all.
+     *
+     * The move phase reuses `swipe`'s own fixed 10ms cadence for the same reason: a velocity
+     * tracker needs a real sequence of points, not two.
+     */
+    private void holdDrag(int x1, int y1, int x2, int y2, long holdMs, long moveMs) {
+        long down = SystemClock.uptimeMillis();
+        send(MotionEvent.ACTION_DOWN, down, x1, y1);
+        SystemClock.sleep(holdMs);
+        int steps = (int) Math.max(2, moveMs / 10);
+        long moveStart = SystemClock.uptimeMillis();
+        for (int i = 1; i <= steps; i++) {
+            float part = (float) i / steps;
+            long due = moveStart + (long) (moveMs * part);
+            long slack = due - SystemClock.uptimeMillis();
+            if (slack > 0) SystemClock.sleep(slack);
+            send(MotionEvent.ACTION_MOVE, down, Math.round(x1 + (x2 - x1) * part),
+                    Math.round(y1 + (y2 - y1) * part));
+        }
+        send(MotionEvent.ACTION_UP, down, x2, y2);
+    }
 }