Preserve placement during drag compile updates

frontend/app.js

@@ -364,11 +364,12 @@ function defaultProject() {
   };
 }
 
-function compileOptions() {
+function compileOptions(extra = {}) {
   return {
     render_mode: state.renderMode,
     show_labels: state.showLabels,
-    generic_symbols: true
+    generic_symbols: true,
+    ...extra
   };
 }
 
@@ -1807,12 +1808,21 @@ async function compileModel(model, opts = {}) {
   const source = opts.source ?? "manual";
   const fit = opts.fit ?? false;
   const keepView = opts.keepView ?? false;
+  const preservePlacement = opts.preservePlacement ?? false;
 
   setStatus(source === "drag" ? "Compiling after drag..." : "Compiling...");
   try {
     const result = await apiPost("/compile", {
       payload: model,
-      options: compileOptions()
+      options: compileOptions(
+        preservePlacement
+          ? {
+              preserve_placement: true,
+              auto_rotate: false,
+              respect_locks: true
+            }
+          : {}
+      )
     });
 
     state.model = applyCompileLayoutToModel(model, result);
@@ -3316,7 +3326,7 @@ function setupEvents() {
           inst.placement.locked = true;
         }
       }
-      await compileModel(state.model, { source: "drag", keepView: true });
+      await compileModel(state.model, { source: "drag", keepView: true, preservePlacement: true });
     }
   });
 

src/layout.js

@@ -118,6 +118,41 @@ function rotateSide(side, rotation) {
   return order[(idx + steps) % 4];
 }
 
+function hasValidPlacement(inst) {
+  return Number.isFinite(inst?.placement?.x) && Number.isFinite(inst?.placement?.y);
+}
+
+function preservePlacedInstances(model, options = {}) {
+  const respectLocks = options.respectLocks ?? true;
+  const autoRotate = options.autoRotate ?? false;
+  const fallback = placeInstances(model, { respectLocks, autoRotate });
+  const fallbackByRef = new Map((fallback?.placed ?? []).map((inst) => [inst.ref, inst]));
+  const instances = [...model.instances].sort((a, b) => a.ref.localeCompare(b.ref));
+
+  return instances.map((inst) => {
+    if (hasValidPlacement(inst)) {
+      return {
+        ...inst,
+        placement: {
+          x: toGrid(Number(inst.placement.x)),
+          y: toGrid(Number(inst.placement.y)),
+          rotation: normalizeRotation(inst.placement.rotation ?? 0),
+          locked: respectLocks ? Boolean(inst.placement.locked) : false
+        }
+      };
+    }
+    return fallbackByRef.get(inst.ref) ?? {
+      ...inst,
+      placement: {
+        x: toGrid(MARGIN_X),
+        y: toGrid(MARGIN_Y),
+        rotation: normalizeRotation(inst.placement?.rotation ?? 0),
+        locked: respectLocks ? Boolean(inst.placement?.locked) : false
+      }
+    };
+  });
+}
+
 function getNodePin(model, placedMap, node) {
   const inst = placedMap.get(node.ref);
   if (!inst) {
@@ -2358,8 +2393,11 @@ export function layoutAndRoute(model, options = {}) {
   const renderMode = options.render_mode === "explicit" ? "explicit" : DEFAULT_RENDER_MODE;
   const respectLocks = options.respect_locks ?? true;
   const autoRotate = options.auto_rotate ?? true;
-
+  const preservePlacement = options.preserve_placement === true;
-  const { placed, placedMap } = placeInstances(model, { respectLocks, autoRotate });
+  const placed = preservePlacement
+    ? preservePlacedInstances(model, { respectLocks, autoRotate: false })
+    : placeInstances(model, { respectLocks, autoRotate }).placed;
+  const placedMap = new Map(placed.map((inst) => [inst.ref, inst]));
   const bounds = buildBounds(model, placed);
   const { routed, busGroups } = routeAllNets(model, placed, placedMap, bounds, {
     renderMode