fix(05-04): use ghost rect for field placement, canvas offset for overlays

- Replace cursor+delta calculation with active.rect.current.translated (ghost bounding rect)
- Measure coordinates relative to the inner <canvas> element, not the DroppableZone wrapper
- Add canvasOffset state + useLayoutEffect to offset field overlays by canvas position within wrapper
- Inline PDF coordinate math in handleDragEnd; clamp uses field pixel dimensions

teressa-copeland-homes/src/app/portal/(protected)/documents/[docId]/_components/FieldPlacer.tsx

@@ -130,6 +130,8 @@ export function FieldPlacer({ docId, pageInfo, currentPage, children }: FieldPla
   const containerRef = useRef<HTMLDivElement | null>(null);
   // Track rendered canvas dimensions in state so renderFields re-runs when they change
   const [containerSize, setContainerSize] = useState<{ w: number; h: number } | null>(null);
+  // Offset of the <canvas> element relative to the DroppableZone wrapper div
+  const [canvasOffset, setCanvasOffset] = useState({ x: 0, y: 0 });
 
   // Configure sensors: require a minimum drag distance so clicks on delete buttons
   // are not intercepted as drag starts
@@ -162,65 +164,67 @@ export function FieldPlacer({ docId, pageInfo, currentPage, children }: FieldPla
     setContainerSize({ w: pageInfo.width, h: pageInfo.height });
   }, [pageInfo]);
 
+  // Track the canvas element's offset within the DroppableZone wrapper div so that
+  // field overlays (position: absolute relative to the wrapper) are placed correctly.
+  useLayoutEffect(() => {
+    if (!pageInfo || !containerRef.current) return;
+    const canvas = containerRef.current.querySelector('canvas');
+    if (!canvas) return;
+    const canvasRect = canvas.getBoundingClientRect();
+    const containerRect = containerRef.current.getBoundingClientRect();
+    setCanvasOffset({
+      x: canvasRect.left - containerRect.left,
+      y: canvasRect.top - containerRect.top,
+    });
+  }, [pageInfo]);
+
   const handleDragEnd = useCallback(
     (event: DragEndEvent) => {
       setIsDraggingToken(false);
 
-      const { over, activatorEvent, delta } = event;
-
-      // Only process if dropped onto the PDF zone
+      const { over, active } = event;
       if (!over || over.id !== 'pdf-drop-zone') return;
       if (!pageInfo) return;
 
-      const containerRect = containerRef.current?.getBoundingClientRect();
-      if (!containerRect) return;
+      // Use the ghost's final bounding rect so the field appears exactly where
+      // the ghost was — not at cursor, which is offset by the grab point.
+      const ghostRect = active.rect.current.translated;
+      if (!ghostRect) return;
+
+      // Use the actual <canvas> element as the coordinate reference to avoid any
+      // offset between the DroppableZone wrapper div and the inner canvas.
+      const canvas = containerRef.current?.querySelector('canvas');
+      const refRect = (canvas ?? containerRef.current)?.getBoundingClientRect();
+      if (!refRect) return;
 
-      // Use pageInfo.width/height as the authoritative rendered canvas size —
-      // containerRect.width/height could be slightly off if the wrapper div has
-      // any extra decoration that doesn't match the canvas exactly.
       const renderedW = pageInfo.width;
       const renderedH = pageInfo.height;
 
-      // Compute the final screen position relative to the container
-      // activatorEvent is the initial MouseEvent/TouchEvent at drag start
-      // delta is the displacement from drag start to drop
-      let clientX: number;
-      let clientY: number;
+      // Ghost's top-left position relative to the canvas
+      const rawX = ghostRect.left - refRect.left;
+      const rawY = ghostRect.top - refRect.top;
 
-      if (activatorEvent instanceof MouseEvent) {
-        clientX = activatorEvent.clientX;
-        clientY = activatorEvent.clientY;
-      } else if (activatorEvent instanceof TouchEvent && activatorEvent.touches.length > 0) {
-        clientX = activatorEvent.touches[0].clientX;
-        clientY = activatorEvent.touches[0].clientY;
-      } else {
-        // Fallback: use center of container
-        clientX = containerRect.left + renderedW / 2;
-        clientY = containerRect.top + renderedH / 2;
-      }
+      // Field dimensions in screen pixels (for clamping)
+      const fieldWpx = (144 / pageInfo.originalWidth) * renderedW;
+      const fieldHpx = (36 / pageInfo.originalHeight) * renderedH;
 
-      // finalClient = activatorClient + delta (displacement during drag)
-      const finalClientX = clientX + delta.x;
-      const finalClientY = clientY + delta.y;
+      // Clamp so field stays within canvas bounds
+      const clampedX = Math.max(0, Math.min(rawX, renderedW - fieldWpx));
+      const clampedY = Math.max(0, Math.min(rawY, renderedH - fieldHpx));
 
-      // Convert to coordinates relative to the container's top-left corner
-      const screenX = finalClientX - containerRect.left;
-      const screenY = finalClientY - containerRect.top;
-
-      // Clamp to canvas bounds
-      const clampedX = Math.max(0, Math.min(screenX, renderedW));
-      const clampedY = Math.max(0, Math.min(screenY, renderedH));
-
-      // Convert screen coords to PDF user-space (Y-flip applied)
-      const { x: pdfX, y: pdfY } = screenToPdfCoords(clampedX, clampedY, renderedW, renderedH, pageInfo);
+      // Convert to PDF user-space coordinates.
+      // pdfX = left edge (X increases right in both screen and PDF).
+      // pdfY = bottom edge (PDF Y=0 is bottom, increases upward).
+      const pdfX = (clampedX / renderedW) * pageInfo.originalWidth;
+      const pdfY = ((renderedH - (clampedY + fieldHpx)) / renderedH) * pageInfo.originalHeight;
 
       const newField: SignatureFieldData = {
         id: crypto.randomUUID(),
         page: currentPage,
         x: pdfX,
         y: pdfY,
-        width: 144, // 2 inches at 72 DPI
-        height: 36, // 0.5 inches at 72 DPI
+        width: 144,
+        height: 36,
       };
 
       const next = [...fields, newField];
@@ -250,8 +254,8 @@ export function FieldPlacer({ docId, pageInfo, currentPage, children }: FieldPla
             key={field.id}
             style={{
               position: 'absolute',
-              left,
-              top: top - heightPx, // top is y of bottom-left corner; shift up by height
+              left: left + canvasOffset.x,
+              top: top - heightPx + canvasOffset.y, // top is y of bottom-left corner; shift up by height
               width: widthPx,
               height: heightPx,
               border: '2px solid #2563eb',