feat(#73): IMP-44 u1~u5 layout override unknown-key guard + frontend zone_geometries validation

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Front/client/src/pages/Home.tsx

@@ -19,6 +19,7 @@ import {
   deriveUserOverridesKey,
   applyPersistedNonFrameOverrides,
   remapPersistedFramesToZoneFrames,
+  validateZoneGeometriesAgainstLayout,
 } from "../utils/slidePlanUtils";
 import {
   parseMdxFile,
@@ -154,6 +155,21 @@ export default function Home() {
         }
         carriedZoneSections[targetPos].push(...zone.section_ids);
       });
+      // IMP-44 (#73) u4 — clear in-memory zone_geometries on layout flip.
+      // The persisted keys were valid for the *prior* preset; carrying them
+      // forward into the new preset would either trip the u1/u2 backend
+      // [override-warning] guards (foreign keys dropped, override_applied
+      // forced back to None) or partially apply on shared keys. Drop them
+      // up-front so the new layout starts from a clean even-split baseline,
+      // and persist a clear sentinel (null) so a subsequent reopen does not
+      // resurrect the stale snapshot from user_overrides.json.
+      const priorGeoms = p.userSelection.overrides.zone_geometries;
+      const hadPriorGeoms =
+        priorGeoms && typeof priorGeoms === "object" && Object.keys(priorGeoms).length > 0;
+      if (p.uploadedFile && hadPriorGeoms) {
+        const key = deriveUserOverridesKey(p.uploadedFile.name);
+        void saveUserOverrides(key, { zone_geometries: null });
+      }
       return {
         ...p,
         userSelection: {
@@ -162,6 +178,7 @@ export default function Home() {
             ...p.userSelection.overrides,
             layout_preset: layoutId,
             zone_sections: carriedZoneSections,
+            zone_geometries: {},
           },
           selectedZoneId: null,
           selectedRegionId: null,
@@ -329,9 +346,28 @@ export default function Home() {
 
       // zone-geometry override — backend 의 build_layout_css 에 전달 (horizontal-2 /
       // vertical-2 만 적용). zone_id (top/bottom/...) → slide-body 내부 0~1 비율.
+      // IMP-44 (#73) u4 — validate against the active layout *before* the
+      // round-trip so foreign-preset keys never reach the backend. Mirrors
+      // the u1/u2 WARN+DROP guards on the frontend side: dropped keys surface
+      // as a toast (so the user knows why their resize "vanished"), and only
+      // the `kept` subset is forwarded. The active layout = the layout the
+      // backend will use, which is `overrides.layout` when the user has set
+      // one, else the default slidePlan preset (mirrors backend resolution).
       const zoneGeometries = state.userSelection.overrides.zone_geometries;
       if (zoneGeometries && Object.keys(zoneGeometries).length > 0) {
-        overrides.zoneGeometries = zoneGeometries;
+        const activeLayout = overrides.layout ?? sourcePlan.layout_preset;
+        const validation = validateZoneGeometriesAgainstLayout(
+          zoneGeometries,
+          activeLayout,
+        );
+        if (Object.keys(validation.dropped).length > 0) {
+          toast.error(
+            `zone_geometries layout-mismatch: dropped ${Object.keys(validation.dropped).join(", ")} (expected ${validation.expectedPositions.join(", ") || "—"}; layout=${activeLayout}).`,
+          );
+        }
+        if (Object.keys(validation.kept).length > 0) {
+          overrides.zoneGeometries = validation.kept;
+        }
       }
 
       // 2026-05-22 — IMP-08 B-3 원래 동작 (sameAsDefault with effectiveSlidePlan) 복귀.