feat(#93): IMP-55 u1~u12 frontend manual section swap detection (manual_section_assignment bool axis + drag-only marker gate + dual-axis persistence + backend manual-true gate)

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

Front/client/src/pages/Home.tsx

@@ -170,6 +170,16 @@ export default function Home() {
         const key = deriveUserOverridesKey(p.uploadedFile.name);
         void saveUserOverrides(key, { zone_geometries: null });
       }
+      // IMP-55 (#93) u12 — persist the marker reset to disk so a stale
+      // `manual_section_assignment: true` from a prior drag (written via
+      // u6's co-PUT) cannot survive the layout apply. The in-memory reset
+      // on line 192 protects the current session, but a page reload would
+      // re-seed from disk via u3's restore branch and re-arm the u7 gate.
+      // Unconditional — apply always resets, independent of hadPriorGeoms.
+      if (p.uploadedFile) {
+        const key = deriveUserOverridesKey(p.uploadedFile.name);
+        void saveUserOverrides(key, { manual_section_assignment: false });
+      }
       return {
         ...p,
         userSelection: {
@@ -179,6 +189,17 @@ export default function Home() {
             layout_preset: layoutId,
             zone_sections: carriedZoneSections,
             zone_geometries: {},
+            // IMP-55 (#93) u5 — reset the bool intent marker to `false` on
+            // layout apply. `carriedZoneSections` above is auto-carry (old
+            // zone.section_ids → new layout positions), NOT user drag-drop
+            // intent. Without this explicit reset the spread of
+            // `...p.userSelection.overrides` would carry a prior-drag `true`
+            // into the new layout, causing handleGenerate (u7) to forward
+            // auto-carried assignments as user overrides and re-trigger the
+            // PARTIAL_COVERAGE regression. The marker flips back to `true`
+            // only when the user actually drag-drops a section in the new
+            // layout (u6 handleSectionDrop).
+            manual_section_assignment: false,
           },
           selectedZoneId: null,
           selectedRegionId: null,
@@ -193,10 +214,27 @@ export default function Home() {
   // pending 모드 취소 → 평소 (final.html iframe) 모드 복귀.
   const handleCancelPendingLayout = useCallback(() => {
     setPendingLayout(null);
-    setState((p) => ({
-      ...p,
-      userSelection: createInitialUserSelection(p.slidePlan),
-    }));
+    setState((p) => {
+      // IMP-55 (#93) u12 — persist marker=false to disk on cancel. In-memory
+      // the u3 seed via createInitialUserSelection already pins false (u5
+      // contract), but if a prior drag-drop wrote `true` to disk via u6's
+      // co-PUT, that value would survive a reopen and re-arm the u7
+      // forwarding gate on the next page load. Symmetric with the apply
+      // path's disk PUT above.
+      if (p.uploadedFile) {
+        const key = deriveUserOverridesKey(p.uploadedFile.name);
+        void saveUserOverrides(key, { manual_section_assignment: false });
+      }
+      return {
+        ...p,
+        // IMP-55 (#93) u5 — cancel discards all pending overrides via
+        // `createInitialUserSelection`, whose u3 seed pins
+        // `manual_section_assignment: false`. In-memory reset is implicit
+        // via the seed; u12 adds the disk-side PUT above to keep persisted
+        // state consistent so a reopen does not re-arm the marker.
+        userSelection: createInitialUserSelection(p.slidePlan),
+      };
+    });
     setHasPendingChanges(false);
   }, []);
 
@@ -354,29 +392,45 @@ export default function Home() {
         }
       }
 
-      // 2026-05-22 — IMP-08 B-3 원래 동작 (sameAsDefault with effectiveSlidePlan) 복귀.
-      // 시연 안정성 우선. section swap 은 별 path (수동 drag detection) 로 풀어야 함.
-      // 임시 over-aggressive fix 가 default flow 깨뜨려 PARTIAL_COVERAGE 발생했음.
-      const userZoneSections = state.userSelection.overrides.zone_sections;
-      if (userZoneSections) {
-        const defaultByZone = new Map<string, string[]>();
-        sourcePlan.zones.forEach((z) => {
-          defaultByZone.set(z.zone_id, z.section_ids);
-        });
-        const zoneSectionsDiff: Record<string, string[]> = {};
-        for (const [zoneId, sids] of Object.entries(userZoneSections)) {
-          if (!Array.isArray(sids)) continue;
-          const cleaned = sids.filter((s) => typeof s === "string" && s.trim());
-          const defaults = defaultByZone.get(zoneId) ?? [];
-          const sameAsDefault =
-            cleaned.length === defaults.length &&
-            cleaned.every((sid, i) => sid === defaults[i]);
-          if (!sameAsDefault) {
-            zoneSectionsDiff[zoneId] = cleaned;
+      // IMP-55 (#93) u7 — Replace the IMP-08 B-3 self-compare with the bool
+      // `manual_section_assignment` intent marker gate. The prior code built
+      // `defaultByZone` from `sourcePlan.zones` and compared against the
+      // user's `overrides.zone_sections`, but `sourcePlan === effectiveSlidePlan`
+      // (Home.tsx:305) and `effectiveSlidePlan.zones === pendingZones`
+      // (Home.tsx:649), which is itself derived from
+      // `state.userSelection.overrides.zone_sections` via slidePlanUtils.ts.
+      // The comparison was degenerate (user input vs itself), so real drag-drop
+      // swaps were classified `sameAsDefault` and silently dropped from
+      // `overrides.zoneSections` — the exact regression IMP-55 fixes.
+      //   - true  → forward `zone_sections` filtered to zone_ids that exist in
+      //     `sourcePlan.zones` (cross-layout safety so foreign zone keys from a
+      //     stale persisted layout never reach backend `--override-section-
+      //     assignment`). u6 is the SOLE setter of true (real drag-drop).
+      //   - false → skip. Backend determines assignment from its own default
+      //     policy. u3 seeds false on first load, u5 resets false on layout
+      //     apply auto-carry, u12 persists false so a stale disk `true` cannot
+      //     survive a reopen-after-apply window.
+      // No `sameAsDefault` heuristic — the marker is the source of intent.
+      const manualMarker =
+        state.userSelection.overrides.manual_section_assignment;
+      if (manualMarker === true) {
+        const userZoneSections = state.userSelection.overrides.zone_sections;
+        if (userZoneSections) {
+          const validZoneIds = new Set(
+            sourcePlan.zones.map((z) => z.zone_id),
+          );
+          const zoneSectionsForward: Record<string, string[]> = {};
+          for (const [zoneId, sids] of Object.entries(userZoneSections)) {
+            if (!validZoneIds.has(zoneId)) continue;
+            if (!Array.isArray(sids)) continue;
+            const cleaned = sids.filter(
+              (s) => typeof s === "string" && s.trim(),
+            );
+            zoneSectionsForward[zoneId] = cleaned;
+          }
+          if (Object.keys(zoneSectionsForward).length > 0) {
+            overrides.zoneSections = zoneSectionsForward;
           }
-        }
-        if (Object.keys(zoneSectionsDiff).length > 0) {
-          overrides.zoneSections = zoneSectionsDiff;
         }
       }
     }
@@ -478,7 +532,21 @@ export default function Home() {
   const handleSectionDrop = useCallback((sectionId: string, zoneId: string) => {
     setState((p) => {
       const newSelection = moveSectionToZone(p.userSelection, sectionId, zoneId);
-      const finalSelection = selectZone(newSelection, zoneId); // 이동된 존 자동 선택
+      const zoneSelected = selectZone(newSelection, zoneId); // 이동된 존 자동 선택
+      // IMP-55 (#93) u6 — flip the bool intent marker to `true` on real
+      // user drag-drop. Inverse of the u5 reset (layout apply/cancel
+      // auto-carry → false). handleGenerate (u7) gates `overrides.zoneSections`
+      // forwarding on this marker, so an unflipped drop would never reach
+      // the backend (the IMP-55 self-compare regression). The marker is
+      // flipped BEFORE persistence so the in-memory selection and the
+      // co-PUT body stay in sync atomically.
+      const finalSelection = {
+        ...zoneSelected,
+        overrides: {
+          ...zoneSelected.overrides,
+          manual_section_assignment: true,
+        },
+      };
       // IMP-52 u7 — persist the post-drop zone_sections snapshot. The on-disk
       // schema axis (`zone_sections`) shares the in-memory shape (zone_id →
       // section_ids), so we forward the full mutated value; the u4 PUT path
@@ -486,10 +554,15 @@ export default function Home() {
       // p.uploadedFile gate skips persistence before any MDX is loaded —
       // the demo-mode initial render path would otherwise PUT to the empty
       // key. saveUserOverrides is debounced (300ms) and per-key coalesced.
+      // IMP-55 (#93) u6 — co-PUT `manual_section_assignment: true` in the
+      // SAME body so the disk file never has the post-drop zone_sections
+      // without the marker (would otherwise look like an unmotivated
+      // IMP-52 zone_sections write to the u9 backend fallback).
       if (p.uploadedFile) {
         const key = deriveUserOverridesKey(p.uploadedFile.name);
         void saveUserOverrides(key, {
           zone_sections: finalSelection.overrides.zone_sections,
+          manual_section_assignment: true,
         });
       }
       return { ...p, userSelection: finalSelection };