refactor(cua-driver-rs): cross-platform dedup audit — image_utils + Spring + ArgsExt (#A + #1b + #C)

libs/cua-driver-rs/crates/cursor-overlay/src/lib.rs

@@ -15,12 +15,14 @@ pub mod path_planner;
 pub mod shape;
 pub mod capture_utils;
 pub mod util;
+pub mod render_state;
 
 pub use palette::Palette;
-pub use motion::MotionConfig;
+pub use motion::{MotionConfig, Spring};
 pub use bezier::CubicBezier;
 pub use path_planner::{PathPlanner, PlannedPath, PathState};
 pub use shape::CursorShape;
+pub use render_state::{RenderStateCore, FocusRect, render_frame, draw_default_arrow};
 
 /// Configuration assembled from CLI arguments and passed to every
 /// platform backend when it initialises the overlay window.

libs/cua-driver-rs/crates/cursor-overlay/src/motion.rs

@@ -82,3 +82,20 @@ impl MotionConfig {
         }
     }
 }
+
+/// Post-arrival spring physics state.
+///
+/// When the cursor reaches the end of a planned path the engine
+/// hands control to a spring-damper that overshoots a touch and
+/// settles to the target. This struct holds the spring's mutable
+/// state across ticks. Identical across all platform crates — was
+/// duplicated 3× before the 2026-05 dedup audit.
+///
+/// `(ox, oy)` = offset from the spring target; `(vx, vy)` = velocity.
+#[derive(Clone, Copy, Default)]
+pub struct Spring {
+    pub ox: f64,
+    pub oy: f64,
+    pub vx: f64,
+    pub vy: f64,
+}