feat(#79): IMP-51 image_overrides axis (u1~u11 backend stamp+CLI+CSS inject + frontend drag/resize+persistence + tests)

Front/client/src/utils/slidePlanUtils.ts

@@ -72,6 +72,18 @@ export function applyPersistedNonFrameOverrides(
   ) {
     next.zone_sections = { ...persisted.zone_sections };
   }
+  // IMP-51 (#79) u11 — layer the 5th persisted axis (`image_overrides`) by
+  // the same array / non-object guard the zone_geometries branch uses. The
+  // u3 typed client (services/userOverridesApi.ts) shape and the on-disk
+  // KNOWN_AXES entry (src/user_overrides_io.py u1) are both flat dicts
+  // (image_id → {x,y,w,h} percent-of-slide), so a shallow copy is enough.
+  if (
+    persisted.image_overrides &&
+    typeof persisted.image_overrides === "object" &&
+    !Array.isArray(persisted.image_overrides)
+  ) {
+    next.image_overrides = { ...persisted.image_overrides };
+  }
   return { ...selection, overrides: next };
 }
 
@@ -143,13 +155,17 @@ export function createInitialUserSelection(slidePlan?: SlidePlan | null): UserSe
       zone_sections: initialSections,
       zone_sizes: {},
       zone_geometries: {},
+      // IMP-51 (#79) u11 — image_overrides axis starts empty; entries land
+      // here via `saveImageOverride` (SlideCanvas drag/resize handler) and
+      // are seeded on reopen via `applyPersistedNonFrameOverrides`.
+      image_overrides: {},
     },
   };
 }
 
 export function saveZoneGeometry(
-  selection: UserSelection, 
-  zoneId: string, 
+  selection: UserSelection,
+  zoneId: string,
   geometry: { x: number; y: number; w: number; h: number }
 ): UserSelection {
   return {
@@ -164,6 +180,32 @@ export function saveZoneGeometry(
   };
 }
 
+/**
+ * IMP-51 (#79) u11 — record a single `image_id` → slide-absolute percent
+ * geometry on the in-memory selection. Mirrors `saveZoneGeometry` but on
+ * the 5th persisted axis (`image_overrides`); the SlideCanvas drag/resize
+ * handler (u8) emits one entry per pointer move, and u10's Home wiring
+ * funnels each emit through this helper before scheduling the debounced
+ * PUT. Pure / immutable — returns a fresh `UserSelection`; the input is
+ * never mutated. Existing entries for the same `imageId` are replaced.
+ */
+export function saveImageOverride(
+  selection: UserSelection,
+  imageId: string,
+  geometry: { x: number; y: number; w: number; h: number },
+): UserSelection {
+  return {
+    ...selection,
+    overrides: {
+      ...selection.overrides,
+      image_overrides: {
+        ...selection.overrides.image_overrides,
+        [imageId]: geometry,
+      },
+    },
+  };
+}
+
 export function saveZoneSizes(selection: UserSelection, groupId: string, sizes: number[]): UserSelection {
   return {
     ...selection,