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A Deck client asking for 'steamdeck' on a Windows host resolved to Xbox360, whose apply_rich is a no-op — gyro and both trackpads silently discarded. Windows already ships a full DualSense backend (UMDF driver, touchpad + motion, wire units 1:1), so pick_gamepad now folds SteamDeck -> DualSense there. The three near-identical DualSense-family appliers (Linux UHID, Windows DualSense, Windows DS4) are hoisted into one shared dualsense_proto::DsState::apply_rich, with two mapping upgrades for Steam dual-pad clients everywhere: * the Deck's two pads SPLIT the single DualSense touchpad — left pad -> contact 0 on the left half, right pad -> contact 1 on the right half — mirroring the physical thumb layout and the split-pad zones games and Steam Input already use (the left pad was previously dropped outright) * TouchpadEx pad clicks now press the touchpad-click button (persisted in DsState::touch_click, OR-ed in by both serializers; previously dropped by every DualSense-family backend, Linux included) Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>