fix(sockets): a board a hair off the seat is still plugged in

frontend/src/components/simulator/SimulatorCanvas.tsx

@@ -50,7 +50,7 @@ import {
   seatOnDrop,
   snapPositionToBreadboard,
 } from '../../utils/breadboardSnap';
-import { snapBoardToSocket } from '../../utils/socketSnap';
+import { snapBoardToSocket, isBoardSeated } from '../../utils/socketSnap';
 import {
   findWireNearPoint,
   findSegmentNearPoint,
@@ -138,8 +138,7 @@ function carrySeatedBoards(
   for (const b of st.boards) {
     // Restricting the candidate list to the dragged component asks the
     // narrow question: is this board seated on THIS socket?
-    const seat = snapBoardToSocket(b.id, b.boardKind, b.x, b.y, [dragged]);
-    if (seat && Math.hypot(seat.x - b.x, seat.y - b.y) < 0.5) {
+    if (isBoardSeated(b.id, b.boardKind, b.x, b.y, [dragged])) {
       st.setBoardPosition({ x: b.x + dx, y: b.y + dy }, b.id);
     }
   }
@@ -949,10 +948,7 @@ export const SimulatorCanvas = ({ headerSlot }: SimulatorCanvasProps = {}) => {
             const boardRunning = !!(b && (b.running || st.running));
             const seatedOn =
               boardRunning && b
-                ? st.components.find((c) => {
-                    const seat = snapBoardToSocket(b.id, b.boardKind, b.x, b.y, [c]);
-                    return !!seat && Math.hypot(seat.x - b.x, seat.y - b.y) < 0.5;
-                  })
+                ? st.components.find((c) => isBoardSeated(b.id, b.boardKind, b.x, b.y, [c]))
                 : undefined;
             carriedSocketRef.current = { dragId: touchId, sockId: seatedOn?.id ?? '' };
           }
@@ -1628,10 +1624,7 @@ export const SimulatorCanvas = ({ headerSlot }: SimulatorCanvasProps = {}) => {
             const boardRunning = !!(b && (b.running || st.running));
             const seatedOn =
               boardRunning && b
-                ? st.components.find((c) => {
-                    const seat = snapBoardToSocket(b.id, b.boardKind, b.x, b.y, [c]);
-                    return !!seat && Math.hypot(seat.x - b.x, seat.y - b.y) < 0.5;
-                  })
+                ? st.components.find((c) => isBoardSeated(b.id, b.boardKind, b.x, b.y, [c]))
                 : undefined;
             carriedSocketRef.current = {
               dragId: draggedComponentId,

frontend/src/store/useSimulatorStore.ts

@@ -52,7 +52,7 @@ import {
   collectWireSegments,
 } from '../utils/wireAutoRoute';
 import { isBreadboard } from '../utils/breadboardNets';
-import { snapBoardToSocket } from '../utils/socketSnap';
+import { isBoardSeated } from '../utils/socketSnap';
 import { computeSeating } from '../utils/breadboardSnap';
 import { createSerialBatcher } from './serialBatcher';
 import {
@@ -3169,16 +3169,9 @@ export const useSimulatorStore = create<SimulatorState>((set, get) => {
       // above — raising the socket alone buried its own seated board, and a
       // buried board cannot be grabbed to unplug it.
       const seatedOnIt = s.components.some((c) => c.id === id)
-        ? s.boards.filter((b) => {
-            const seat = snapBoardToSocket(
-              b.id,
-              b.boardKind,
-              b.x,
-              b.y,
-              s.components.filter((c) => c.id === id),
-            );
-            return !!seat && Math.hypot(seat.x - b.x, seat.y - b.y) < 0.5;
-          })
+        ? s.boards.filter((b) =>
+            isBoardSeated(b.id, b.boardKind, b.x, b.y, s.components.filter((c) => c.id === id)),
+          )
         : [];
       let top = s.zTop;
       const zOrders = { ...s.zOrders, [id]: ++top };

frontend/src/utils/socketSnap.ts

@@ -95,12 +95,24 @@ export function snapBoardToSocket(
 }
 
 /**
- * True when the board's CURRENT position IS a socket seat (within half a
- * pixel). This is the z-order question, not the drag question: a seated
- * board must paint above its socket component, an unseated one must stay
- * below components like every other board — the blanket zIndex bump that
- * preceded this check hid a resistor behind an Arduino in every ordinary
- * example.
+ * How far off the exact seat a board may sit and still count as plugged in.
+ * Not zero, and deliberately far below SOCKET_SNAP_TOLERANCE: a stack the
+ * magnet built lands exact, but one an EXAMPLE declares (or a project saved
+ * before a socket's art was nudged) can be a fraction of a pixel out. At the
+ * old half-pixel bar such a board looked seated on screen while every seat
+ * test said otherwise — so it got no electrical connection and its socket
+ * did not travel with it. A couple of pixels is invisible to the eye and
+ * still nowhere near the next hole.
+ */
+const SEATED_EPSILON = 2;
+
+/**
+ * True when the board's CURRENT position IS a socket seat. This is the
+ * "is it plugged in?" question, asked by z-order (a seated board must paint
+ * above its socket, an unseated one stays below components like every other
+ * board — a blanket zIndex bump once hid a resistor behind an Arduino),
+ * by the electrical hop that makes seating mean connection, and by the drag
+ * rules that keep a plugged stack together.
  */
 export function isBoardSeated(
   boardId: string,
@@ -110,5 +122,5 @@ export function isBoardSeated(
   components: ComponentLike[],
 ): boolean {
   const seat = snapBoardToSocket(boardId, boardKind, x, y, components);
-  return !!seat && Math.hypot(seat.x - x, seat.y - y) < 0.5;
+  return !!seat && Math.hypot(seat.x - x, seat.y - y) <= SEATED_EPSILON;
 }