fix(selection): a fast press-drag starts the selection window at once

A left drag only became a lasso/window after the button had been held
150 ms, however far the cursor had moved. A fast flick released inside
that delay read as a click and armed a click-click box instead. A press
that has moved more than 12 px is now a drag at once; the delay still
keeps small movements of a click from becoming one. (#1808)

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/mod.rs

@@ -378,6 +378,9 @@ use iced::{mouse, Point, Task, Theme};
 use std::sync::Arc;
 
 pub(super) const POLY_START_DELAY_MS: u128 = 150;
+/// Squared screen distance (12 px) past which a left press is a drag
+/// without waiting for `POLY_START_DELAY_MS`.
+pub(super) const DRAG_START_FAST_PX2: f32 = 144.0;
 pub(super) const VARIES_LABEL: &str = "*VARIES*";
 
 // ── File-open progress ─────────────────────────────────────────────────────

src/app/update/viewport.rs

@@ -8,7 +8,7 @@ use crate::app::helpers::{
     polar_constrain_if_near, polar_constrain_near, ucs_rotate_vec, ucs_to_wcs, ucs_z_axis,
     CoordKind,
 };
-use crate::app::{Message, OpenCADStudio, POLY_START_DELAY_MS};
+use crate::app::{Message, OpenCADStudio, DRAG_START_FAST_PX2, POLY_START_DELAY_MS};
 use crate::modules::ModuleEvent;
 use crate::scene::model::object::GripApply;
 use crate::scene::pick::grip::{
@@ -1323,7 +1323,13 @@ impl OpenCADStudio {
                 .left_press_time
                 .map(|t| Instant::now().duration_since(t).as_millis())
                 .unwrap_or(u128::MAX);
-            if !sel.input.left_dragging && elapsed_ms >= POLY_START_DELAY_MS && dist2 > 9.0 {
+            // The delay keeps a click made while the mouse is still moving
+            // from turning into a drag; a press that has already travelled
+            // well past click jitter is a drag at once, or a fast flick
+            // released inside the delay read as a click. (#1808)
+            let dragged =
+                dist2 > 9.0 && (elapsed_ms >= POLY_START_DELAY_MS || dist2 > DRAG_START_FAST_PX2);
+            if !sel.input.left_dragging && dragged {
                 sel.input.left_dragging = true;
                 if self.pick_drag_rect {
                     // PICKDRAG 1 (#226): press-drag spans a RECTANGLE