diff --git a/README.md b/README.md
index 1049764..e8ea673 100644
--- a/README.md
+++ b/README.md
@@ -29,7 +29,8 @@ Physilinks is a browser-based physics linking game built with Matter.js. Match a
 - `src/ui.js`: DOM access, HUD updates, overlays, popups, and control/selector wiring.
 - `src/spawn.js`: Spawner utilities (intervals, batch/column/grid spawns), ball creation (shapes/blobs), radius scaling, and blob cleanup.
 - `src/goals.js`: Goal computation and messaging (timer/score/clear/color goals, milestone announcements, intro message).
-- `src/main.js`: Physics setup, state machine, chain interaction, scene application, and pause/restart logic; delegates spawn duties to `src/spawn.js` and goal handling to `src/goals.js`.
+- `src/input.js`: Pointer/touch handling, drag constraints, chain linking/undo flow, and input event wiring.
+- `src/main.js`: Physics setup, state machine, chain interaction, scene application, and pause/restart logic; delegates spawn duties to `src/spawn.js`, goal handling to `src/goals.js`, and input/chain interactions to `src/input.js`.
 
 ## Development quick start
 - No build step. Open `index.html` directly in the browser.
diff --git a/index.html b/index.html
index 7e6b777..5e07223 100644
--- a/index.html
+++ b/index.html
@@ -109,6 +109,7 @@
         <script src="./src/storage.js"></script>
         <script src="./src/spawn.js"></script>
         <script src="./src/goals.js"></script>
+        <script src="./src/input.js"></script>
         <script src="./src/main.js"></script>
     </body>
 </html>
diff --git a/src/input.js b/src/input.js
new file mode 100644
index 0000000..4c74e8d
--- /dev/null
+++ b/src/input.js
@@ -0,0 +1,167 @@
+(() => {
+  const { Query, Constraint, World, Vector } = Matter;
+
+  const create = ({
+    render,
+    world,
+    balls,
+    boundaries,
+    chain,
+    config,
+    getCurrentScene,
+    isPaused,
+    isLevelWon,
+    isGameOver,
+    getMaxLinkDistance,
+    setHighlight,
+    removeLastFromChain,
+    addToChain,
+    finishChain,
+    updateHud,
+  }) => {
+    let dragConstraint = null;
+
+    const getPointerPosition = (evt) => {
+      const rect = render.canvas.getBoundingClientRect();
+      const clientX = evt.touches ? evt.touches[0].clientX : evt.clientX;
+      const clientY = evt.touches ? evt.touches[0].clientY : evt.clientY;
+      return {
+        x: clientX - rect.left,
+        y: clientY - rect.top,
+      };
+    };
+
+    const getDraggableBody = (point) => {
+      const draggables = [
+        ...boundaries.filter((b) => b.plugin?.draggable),
+        ...balls.filter((b) => b.plugin?.draggable),
+      ];
+      const hits = Query.point(draggables, point);
+      return hits[0];
+    };
+
+    const pickBody = (point) => {
+      const hits = Query.point(balls, point);
+      return hits[0];
+    };
+
+    const startDrag = (body, point) => {
+      endDrag();
+      dragConstraint = Constraint.create({
+        pointA: point,
+        bodyB: body,
+        stiffness: 0.2,
+        damping: 0.3,
+        render: { visible: false },
+      });
+      World.add(world, dragConstraint);
+    };
+
+    const updateDrag = (point) => {
+      if (!dragConstraint) return;
+      dragConstraint.pointA = point;
+    };
+
+    const endDrag = () => {
+      if (dragConstraint) {
+        World.remove(world, dragConstraint);
+        dragConstraint = null;
+      }
+    };
+
+    const handlePointerDown = (evt) => {
+      if (isGameOver() || isPaused() || isLevelWon()) return;
+      const point = getPointerPosition(evt);
+      const dragTarget = getDraggableBody(point);
+      if (dragTarget) {
+        startDrag(dragTarget, point);
+        return;
+      }
+      const body = pickBody(point);
+      if (!body) return;
+      const scene = getCurrentScene();
+      if (!scene?.config?.relaxMode) {
+        chain.color = body.plugin.color;
+      } else {
+        chain.color = body.plugin.color;
+      }
+      chain.active = true;
+      chain.bodies = [body];
+      chain.constraints = [];
+      chain.pointer = point;
+      setHighlight(body, true);
+      updateHud();
+    };
+
+    const handlePointerMove = (evt) => {
+      if (dragConstraint) {
+        updateDrag(getPointerPosition(evt));
+        return;
+      }
+      if (!chain.active) return;
+      if (isGameOver() || isPaused() || isLevelWon()) return;
+      const point = getPointerPosition(evt);
+      chain.pointer = point;
+      const body = pickBody(point);
+      if (!body) return;
+      const alreadyInChain = chain.bodies.includes(body);
+      if (alreadyInChain) {
+        const targetIndex = chain.bodies.indexOf(body);
+        if (chain.bodies.length > 1 && targetIndex === chain.bodies.length - 2) {
+          removeLastFromChain();
+        }
+        return;
+      }
+      const scene = getCurrentScene();
+      if (!scene?.config?.relaxMode && body.plugin.color !== chain.color) return;
+      const maxLinkDist = getMaxLinkDistance();
+      const dist = Vector.magnitude(
+        Vector.sub(chain.bodies[chain.bodies.length - 1].position, body.position),
+      );
+      if (dist > maxLinkDist) return;
+      addToChain(body);
+    };
+
+    const handlePointerUp = () => {
+      if (dragConstraint) {
+        endDrag();
+        return;
+      }
+      finishChain(chain.pointer);
+    };
+
+    render.canvas.addEventListener("mousedown", handlePointerDown);
+    render.canvas.addEventListener("mousemove", handlePointerMove);
+    window.addEventListener("mouseup", handlePointerUp);
+    render.canvas.addEventListener(
+      "touchstart",
+      (e) => {
+        e.preventDefault();
+        handlePointerDown(e);
+      },
+      { passive: false },
+    );
+    render.canvas.addEventListener(
+      "touchmove",
+      (e) => {
+        e.preventDefault();
+        handlePointerMove(e);
+      },
+      { passive: false },
+    );
+    render.canvas.addEventListener(
+      "touchend",
+      (e) => {
+        e.preventDefault();
+        handlePointerUp(e);
+      },
+      { passive: false },
+    );
+
+    return {
+      endDrag,
+    };
+  };
+
+  window.PhysilinksInput = { create };
+})();
diff --git a/src/main.js b/src/main.js
index 8f41dc5..74497a4 100644
--- a/src/main.js
+++ b/src/main.js
@@ -1,15 +1,6 @@
 (() => {
-  const {
-    Engine,
-    Render,
-    Runner,
-    World,
-    Body,
-    Constraint,
-    Events,
-    Query,
-    Vector,
-  } = Matter;
+  const { Engine, Render, Runner, World, Body, Constraint, Events, Vector } =
+    Matter;
 
   const { scenes = [], defaultSceneId } = window.PhysilinksScenes || {};
   const getSceneById = (sceneId) =>
@@ -143,8 +134,8 @@
   let levelWon = false;
   let timerEndMs = null;
   let lastTimerDisplay = null;
-  let dragConstraint = null;
   let spawnSystem = null;
+  let input = null;
 
   const {
     loadHighScore = () => 0,
@@ -303,7 +294,7 @@
     clearedCount = 0;
     clearedByColor = {};
     goals.resetMilestones();
-    endDrag();
+    input?.endDrag();
     const winCond = currentScene?.config?.winCondition;
     if (winCond?.type === "timer") {
       const duration = winCond.durationSec ?? 120;
@@ -571,143 +562,6 @@
     checkWinCondition();
   };
 
-  const pickBody = (point) => {
-    const hits = Query.point(balls, point);
-    return hits[0];
-  };
-
-  const getDraggableBody = (point) => {
-    const draggables = [
-      ...boundaries.filter((b) => b.plugin?.draggable),
-      ...balls.filter((b) => b.plugin?.draggable),
-    ];
-    const hits = Query.point(draggables, point);
-    return hits[0];
-  };
-
-  const startDrag = (body, point) => {
-    endDrag();
-    dragConstraint = Constraint.create({
-      pointA: point,
-      bodyB: body,
-      stiffness: 0.2,
-      damping: 0.3,
-      render: { visible: false },
-    });
-    World.add(world, dragConstraint);
-  };
-
-  const updateDrag = (point) => {
-    if (!dragConstraint) return;
-    dragConstraint.pointA = point;
-  };
-
-  const endDrag = () => {
-    if (dragConstraint) {
-      World.remove(world, dragConstraint);
-      dragConstraint = null;
-    }
-  };
-
-  const getPointerPosition = (evt) => {
-    const rect = render.canvas.getBoundingClientRect();
-    const clientX = evt.touches ? evt.touches[0].clientX : evt.clientX;
-    const clientY = evt.touches ? evt.touches[0].clientY : evt.clientY;
-    return {
-      x: clientX - rect.left,
-      y: clientY - rect.top,
-    };
-  };
-
-  const handlePointerDown = (evt) => {
-    if (gameOver || isPaused || levelWon) return;
-    const point = getPointerPosition(evt);
-    const dragTarget = getDraggableBody(point);
-    if (dragTarget) {
-      startDrag(dragTarget, point);
-      return;
-    }
-    const body = pickBody(point);
-    if (!body) return;
-    if (!currentScene?.config?.relaxMode) {
-      // Only allow linking same colors unless relax mode explicitly opts out.
-      chain.color = body.plugin.color;
-    } else {
-      chain.color = body.plugin.color;
-    }
-    chain.active = true;
-    chain.bodies = [body];
-    chain.constraints = [];
-    chain.pointer = point;
-    setHighlight(body, true);
-    updateHud();
-  };
-
-  const handlePointerMove = (evt) => {
-    if (dragConstraint) {
-      updateDrag(getPointerPosition(evt));
-      return;
-    }
-    if (!chain.active) return;
-    if (gameOver || isPaused || levelWon) return;
-    const point = getPointerPosition(evt);
-    chain.pointer = point;
-    const body = pickBody(point);
-    if (!body) return;
-    const alreadyInChain = chain.bodies.includes(body);
-    if (alreadyInChain) {
-      const targetIndex = chain.bodies.indexOf(body);
-      if (chain.bodies.length > 1 && targetIndex === chain.bodies.length - 2) {
-        removeLastFromChain();
-      }
-      return;
-    }
-    if (!currentScene?.config?.relaxMode && body.plugin.color !== chain.color)
-      return;
-    const maxLinkDist = getMaxLinkDistance();
-    const dist = Vector.magnitude(
-      Vector.sub(chain.bodies[chain.bodies.length - 1].position, body.position),
-    );
-    if (dist > maxLinkDist) return;
-    addToChain(body);
-  };
-
-  const handlePointerUp = () => {
-    if (dragConstraint) {
-      endDrag();
-      return;
-    }
-    finishChain(chain.pointer);
-  };
-
-  render.canvas.addEventListener("mousedown", handlePointerDown);
-  render.canvas.addEventListener("mousemove", handlePointerMove);
-  window.addEventListener("mouseup", handlePointerUp);
-  render.canvas.addEventListener(
-    "touchstart",
-    (e) => {
-      e.preventDefault();
-      handlePointerDown(e);
-    },
-    { passive: false },
-  );
-  render.canvas.addEventListener(
-    "touchmove",
-    (e) => {
-      e.preventDefault();
-      handlePointerMove(e);
-    },
-    { passive: false },
-  );
-  render.canvas.addEventListener(
-    "touchend",
-    (e) => {
-      e.preventDefault();
-      handlePointerUp(e);
-    },
-    { passive: false },
-  );
-
   const updateHud = () => {
     ui.updateHud({
       spawnIntervalMs: config.spawnIntervalMs,
@@ -722,6 +576,25 @@
     goals.maybeAnnounceGoalProgress(goal);
   };
 
+  input = window.PhysilinksInput.create({
+    render,
+    world,
+    balls,
+    boundaries,
+    chain,
+    config,
+    getCurrentScene: () => currentScene,
+    isPaused: () => isPaused,
+    isLevelWon: () => levelWon,
+    isGameOver: () => gameOver,
+    getMaxLinkDistance,
+    setHighlight,
+    removeLastFromChain,
+    addToChain,
+    finishChain,
+    updateHud,
+  });
+
   const buildLegend = () => {
     ui.buildLegend(config.palette);
   };
@@ -743,7 +616,7 @@
       Body.setVelocity(ball, { x: 0, y: 0 });
     });
     resetChainVisuals();
-    endDrag();
+    input?.endDrag();
   };
 
   const handleResize = () => {