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 };

Front/client/src/services/userOverridesApi.ts

@@ -65,6 +65,16 @@ export type ImageOverride = {
 };
 export type ImageOverridesOverride = Record<string, ImageOverride>;
 
+/**
+ * IMP-55 #93 u1 — bool intent marker that gates whether persisted
+ * `zone_sections` are consumed by the backend pipeline. Frontend sets
+ * `true` only on a real user drag-drop (Home.tsx handleSectionDrop, u6)
+ * and `false` on layout apply/cancel auto-carry (u5/u12). Mirrors the
+ * Python KNOWN_AXES (`manual_section_assignment`) added in u1 and the
+ * Vite KNOWN_USER_OVERRIDES_AXES allowlist entry added in u1.
+ */
+export type ManualSectionAssignmentOverride = boolean;
+
 /** Full on-disk schema. All axes optional — file may carry any subset. */
 export interface UserOverrides {
   layout: string;
@@ -72,6 +82,7 @@ export interface UserOverrides {
   zone_geometries: ZoneGeometriesOverride;
   zone_sections: ZoneSectionsOverride;
   image_overrides: ImageOverridesOverride;
+  manual_section_assignment: ManualSectionAssignmentOverride;
 }
 
 /** Partial-mutation payload. `null` is the explicit clear sentinel (mirrors u4). */

Front/client/src/types/designAgent.ts

@@ -213,6 +213,20 @@ export interface UserSelection {
     // `image_overrides` axis (KNOWN_AXES, src/user_overrides_io.py u1) and
     // the typed-client `ImageOverridesOverride` (services/userOverridesApi.ts u3).
     image_overrides: Record<string, { x: number; y: number; w: number; h: number }>;
+    // IMP-55 (#93) u3 — bool intent marker gating whether the backend
+    // consumes persisted `zone_sections` as a user override. Set to `true`
+    // only by the real drag-drop path (Home.tsx handleSectionDrop, u6); set
+    // back to `false` by the layout apply/cancel auto-carry path (u5/u12).
+    // handleGenerate (u7) reads this flag to decide whether to forward
+    // `overrides.zoneSections` to the backend, replacing the pre-IMP-55
+    // self-compare against `effectiveSlidePlan`. Seeded `false` in
+    // `createInitialUserSelection` and only restored on reopen when the
+    // persisted value is a real boolean (slidePlanUtils.ts u3 layering).
+    // Mirrors the on-disk axis added in u1 — Python KNOWN_AXES
+    // (src/user_overrides_io.py), Vite KNOWN_USER_OVERRIDES_AXES
+    // (Front/vite.config.ts), and `ManualSectionAssignmentOverride`
+    // (services/userOverridesApi.ts).
+    manual_section_assignment: boolean;
   };
 }
 

Front/client/src/utils/slidePlanUtils.ts

@@ -85,6 +85,20 @@ export function applyPersistedNonFrameOverrides(
   ) {
     next.image_overrides = { ...persisted.image_overrides };
   }
+  // IMP-55 (#93) u3 — restore the bool intent marker only when the persisted
+  // value is a real `boolean`. A missing axis, `null` (the u4 clear sentinel
+  // observed post-flush), or any non-boolean shape (string "true", 1, {})
+  // intentionally falls through to the `createInitialUserSelection` seed of
+  // `false`. This is the fail-closed half of the marker contract: the
+  // backend pipeline (u9) consumes persisted `zone_sections` only when
+  // `manual_section_assignment is True`, so anything other than a real
+  // `true` MUST end up as `false` in memory to avoid resurrecting stale
+  // auto-carry assignments as user intent. Both `true` and `false` are
+  // restored verbatim (the explicit `false` from u12's apply/cancel write
+  // is meaningful — it pins the marker off across reopens).
+  if (typeof persisted.manual_section_assignment === "boolean") {
+    next.manual_section_assignment = persisted.manual_section_assignment;
+  }
   return { ...selection, overrides: next };
 }
 
@@ -160,6 +174,14 @@ export function createInitialUserSelection(slidePlan?: SlidePlan | null): UserSe
       // here via `saveImageOverride` (SlideCanvas drag/resize handler) and
       // are seeded on reopen via `applyPersistedNonFrameOverrides`.
       image_overrides: {},
+      // IMP-55 (#93) u3 — bool intent marker seeded `false` so a fresh
+      // MDX open (no persisted file, or persisted file with axis absent)
+      // never forwards `overrides.zoneSections` to the backend. The marker
+      // flips to `true` only via the real drag-drop path (Home.tsx u6) and
+      // is reset to `false` by layout apply/cancel auto-carry (u5/u12).
+      // `applyPersistedNonFrameOverrides` may restore a persisted boolean
+      // verbatim on reopen — see the bool-only guard there.
+      manual_section_assignment: false,
     },
   };
 }

Front/client/tests/user_overrides_endpoint.test.ts

@@ -310,16 +310,44 @@ describe("KNOWN_USER_OVERRIDES_AXES (IMP-52 u4)", () => {
     // The on-disk schema is shared with backend pipeline fallback (u2).
     // Any drift here means a PUT could write an axis that the Python
     // load() ignores, or vice-versa, silently losing user overrides.
+    // Mirror is Python-minus-`slide_css` (known IMP-45 #74 gap — the
+    // frontend never writes slide_css). IMP-55 #93 u1 adds the bool
+    // `manual_section_assignment` axis as a first-class allowlist entry.
     expect(KNOWN_USER_OVERRIDES_AXES).toEqual([
       "layout",
       "zone_geometries",
       "zone_sections",
       "frames",
       "image_overrides",
+      "manual_section_assignment",
     ]);
   });
 });
 
+describe("mergeUserOverrides (IMP-55 #93 u1) — manual_section_assignment bool axis", () => {
+  it("merges bool true / false literally and clears on null", () => {
+    // The PUT handler must treat the bool axis like any other allowlisted
+    // axis: replace on write, preserve when absent, delete on null. Tests
+    // both true→false flip and explicit null-clear so the backend (u9)
+    // sees the exact frontend intent.
+    let merged = mergeUserOverrides({}, { manual_section_assignment: true });
+    expect(merged.manual_section_assignment).toBe(true);
+
+    merged = mergeUserOverrides(merged, { manual_section_assignment: false });
+    expect(merged.manual_section_assignment).toBe(false);
+
+    merged = mergeUserOverrides(merged, { manual_section_assignment: null });
+    expect("manual_section_assignment" in merged).toBe(false);
+  });
+
+  it("preserves bool axis when partial touches only a sibling axis", () => {
+    const existing = { manual_section_assignment: true, layout: "old" };
+    const merged = mergeUserOverrides(existing, { layout: "new" });
+    expect(merged.manual_section_assignment).toBe(true);
+    expect(merged.layout).toBe("new");
+  });
+});
+
 describe("mergeUserOverrides (IMP-52 u4)", () => {
   it("only mutates KNOWN_AXES present in partial", () => {
     const existing = {

Front/client/tests/user_overrides_restore.test.ts

@@ -54,6 +54,11 @@ function makeSelection(overrides?: Partial<UserSelection["overrides"]>): UserSel
       // axis declared on `UserSelection.overrides`. Empty by default so the
       // existing IMP-52 cases remain unchanged in shape.
       image_overrides: {},
+      // IMP-55 (#93) u3 — bool intent marker is REQUIRED on
+      // `UserSelection.overrides` (not optional). Default to `false` so every
+      // pre-existing fixture matches the `createInitialUserSelection` seed
+      // and stays compile-clean after u3 widened the type.
+      manual_section_assignment: false,
       ...overrides,
     },
   };
@@ -460,3 +465,88 @@ describe("image_overrides axis — saveImageOverride (IMP-51 u11)", () => {
     expect(sel.overrides.image_overrides).toEqual(before);
   });
 });
+
+// ─── IMP-55 (#93) u3 — manual_section_assignment bool axis ──────────────────
+// Restore-on-reopen / seed coverage for the bool intent marker. Production
+// branch lives at `slidePlanUtils.ts` — `applyPersistedNonFrameOverrides`
+// guards with `typeof persisted.manual_section_assignment === "boolean"`,
+// and `createInitialUserSelection` seeds the axis to `false`. The marker
+// gates whether `handleGenerate` (u7) forwards `overrides.zoneSections`
+// to the backend; the pipeline (u9) consumes persisted `zone_sections`
+// only when the marker is exactly `true`, so any non-boolean payload MUST
+// end up `false` in memory (fail-closed).
+
+describe("manual_section_assignment axis — applyPersistedNonFrameOverrides (IMP-55 #93 u3)", () => {
+  it("restores literal true verbatim", () => {
+    const sel = makeSelection();
+    const next = applyPersistedNonFrameOverrides(sel, {
+      manual_section_assignment: true,
+    });
+    expect(next.overrides.manual_section_assignment).toBe(true);
+  });
+
+  it("restores literal false verbatim (u12 apply/cancel write must survive reopen)", () => {
+    // Seed `true` so the assertion proves `false` overwrites; a truthiness
+    // check instead of `typeof === \"boolean\"` would silently keep `true`
+    // and resurrect stale auto-carry assignments as user intent.
+    const sel = makeSelection({ manual_section_assignment: true });
+    const next = applyPersistedNonFrameOverrides(sel, {
+      manual_section_assignment: false,
+    });
+    expect(next.overrides.manual_section_assignment).toBe(false);
+  });
+
+  it("leaves the in-memory marker unchanged when the persisted axis is absent", () => {
+    const sel = makeSelection({ manual_section_assignment: true });
+    const next = applyPersistedNonFrameOverrides(sel, { layout: "horizontal-2" });
+    expect(next.overrides.manual_section_assignment).toBe(true);
+    expect(next.overrides.layout_preset).toBe("horizontal-2");
+  });
+
+  it.each([
+    ["null clear sentinel", null],
+    ['string "true"', "true"],
+    ['string "false"', "false"],
+    ["number 1", 1],
+    ["number 0", 0],
+    ["object {}", {}],
+    ["array []", []],
+  ])("ignores non-boolean payload (%s) — keeps prior in-memory value", (_label, payload) => {
+    const sel = makeSelection({ manual_section_assignment: true });
+    const next = applyPersistedNonFrameOverrides(sel, {
+      manual_section_assignment: payload as unknown as boolean,
+    });
+    expect(next.overrides.manual_section_assignment).toBe(true);
+  });
+
+  it("seeds an empty selection with manual_section_assignment=false (createInitialUserSelection)", () => {
+    const sel = createInitialUserSelection();
+    expect(sel.overrides.manual_section_assignment).toBe(false);
+  });
+
+  it("returns a NEW selection object (no input mutation) when restoring the marker", () => {
+    const sel = makeSelection({ manual_section_assignment: false });
+    const next = applyPersistedNonFrameOverrides(sel, {
+      manual_section_assignment: true,
+    });
+    expect(next).not.toBe(sel);
+    expect(next.overrides).not.toBe(sel.overrides);
+    // Input still pristine — proves the helper does not flip the fixture.
+    expect(sel.overrides.manual_section_assignment).toBe(false);
+  });
+
+  it("layers the bool axis alongside other persisted axes in a single call", () => {
+    const sel = makeSelection();
+    const next = applyPersistedNonFrameOverrides(sel, {
+      layout: "vertical-2",
+      zone_sections: { top: ["03-1"], bottom: ["03-2"] },
+      manual_section_assignment: true,
+    });
+    expect(next.overrides.layout_preset).toBe("vertical-2");
+    expect(next.overrides.zone_sections).toEqual({
+      top: ["03-1"],
+      bottom: ["03-2"],
+    });
+    expect(next.overrides.manual_section_assignment).toBe(true);
+  });
+});

Front/client/tests/user_overrides_service.test.ts

@@ -559,3 +559,67 @@ describe("saveUserOverrides (IMP-51 #79 u3) — image_overrides axis", () => {
     });
   });
 });
+
+// ============================================================================
+// IMP-55 #93 u1 — manual_section_assignment axis (7th axis) parity coverage
+//
+// The bool intent marker rides on the same per-axis coalescing rails as the
+// 6 sibling axes. These tests lock the typed client behavior so a regression
+// in the boolean serialization (e.g., coercion to "true" string, dropped
+// `false` due to truthy filtering) fails here instead of in Home.tsx (u6/u7)
+// or the backend gate (u9~u11).
+// ============================================================================
+
+describe("saveUserOverrides (IMP-55 #93 u1) — manual_section_assignment axis", () => {
+  it("PUT body carries only manual_section_assignment when it is the sole mutated axis", async () => {
+    fetchMock.mockResolvedValue(mockResponse({}));
+    void saveUserOverrides("03", { manual_section_assignment: true });
+    vi.advanceTimersByTime(300);
+    await drainMicrotasks();
+
+    const body = lastPutBody() as Record<string, unknown>;
+    expect(Object.keys(body)).toEqual(["manual_section_assignment"]);
+    expect(body.manual_section_assignment).toBe(true);
+  });
+
+  it("later-wins coalesces true → false within a single debounce window", async () => {
+    // Drag-then-cancel inside 300 ms — server must see only the final
+    // `false`, not a transient `true` that would re-enable backend
+    // consumption of stale zone_sections.
+    fetchMock.mockResolvedValue(mockResponse({}));
+    void saveUserOverrides("03", { manual_section_assignment: true });
+    void saveUserOverrides("03", { manual_section_assignment: false });
+
+    vi.advanceTimersByTime(300);
+    await drainMicrotasks();
+    expect(putCallsCount()).toBe(1);
+    expect(lastPutBody()).toEqual({ manual_section_assignment: false });
+  });
+
+  it("forwards null sentinel verbatim (explicit clear)", async () => {
+    fetchMock.mockResolvedValue(mockResponse({}));
+    void saveUserOverrides("03", { manual_section_assignment: null });
+
+    vi.advanceTimersByTime(300);
+    await drainMicrotasks();
+    expect(lastPutBody()).toEqual({ manual_section_assignment: null });
+  });
+
+  it("coalesces with zone_sections sibling into a single PUT (drag-drop pair)", async () => {
+    // Real-world drag flow (u6): one save() sets the bool + zone_sections
+    // together. Asserts both axes survive coalescing as a single PUT body.
+    fetchMock.mockResolvedValue(mockResponse({}));
+    void saveUserOverrides("03", {
+      zone_sections: { left: ["03-2"], right: ["03-1"] },
+      manual_section_assignment: true,
+    });
+
+    vi.advanceTimersByTime(300);
+    await drainMicrotasks();
+    expect(putCallsCount()).toBe(1);
+    expect(lastPutBody()).toEqual({
+      zone_sections: { left: ["03-2"], right: ["03-1"] },
+      manual_section_assignment: true,
+    });
+  });
+});

Front/client/tests/user_overrides_write.test.ts

@@ -85,6 +85,22 @@ function sliceHandler(source: string, name: string): string {
   return source.slice(start, end);
 }
 
+/**
+ * IMP-55 #93 u8 — strip JS/TS line + block comments so source-pattern
+ * regex checks assert against LIVE code only. The u5 / u7 docblocks in
+ * Home.tsx intentionally reference removed identifiers (e.g. `defaultByZone`,
+ * `sameAsDefault`, `zoneSectionsDiff`) and the marker axis name in prose to
+ * document the Stage 1 root cause for future readers — those references are
+ * documentation, not behavior, and must not trigger negative-match guards.
+ * Strips `// ...` to EOL and `/* ... *​/` (incl. multi-line) — keeps string
+ * literals intact because we only consume the result for regex-match tests.
+ */
+function stripComments(source: string): string {
+  return source
+    .replace(/\/\*[\s\S]*?\*\//g, "")
+    .replace(/\/\/.*$/gm, "");
+}
+
 describe("Home.tsx write-side wiring (IMP-52 u10) — source pattern", () => {
   it("handleSectionDrop persists zone_sections behind uploadedFile gate", () => {
     const block = sliceHandler(HOME_TSX, "handleSectionDrop");
@@ -567,3 +583,220 @@ describe("restore-on-reopen end-to-end (IMP-52 u10)", () => {
     expect(remapPersistedFramesToZoneFrames(plan, persisted.frames)).toEqual({});
   });
 });
+
+// ─── IMP-55 #93 u8 — manual_section_assignment intent marker contract ─────
+// Verifies four axes of the marker contract introduced in u3 (type) / u5
+// (apply reset) / u6 (drag flip + co-PUT) / u7 (generate gate):
+//   1) Drag dual-axis persistence — handleSectionDrop persists BOTH
+//      `zone_sections` AND `manual_section_assignment: true` in the SAME
+//      PUT body (co-PUT atomicity — disk never sees post-drop zone_sections
+//      without the marker).
+//   2) Apply / cancel reset — handleApplyPendingLayout writes explicit
+//      `manual_section_assignment: false` after the `...overrides` spread,
+//      and handleCancelPendingLayout relies on createInitialUserSelection
+//      (which u3 seeds to `false`) to drop a prior `true`.
+//   3) Marker-gated forwarding — handleGenerate gates `overrides.zoneSections`
+//      forwarding strictly on `manualMarker === true` (NOT truthiness, NOT
+//      `!= null`, NOT presence). u3-seeded `false` and absent values both
+//      skip forwarding.
+//   4) sameAsDefault NOT required — the Stage 1 anti-pattern (defaultByZone
+//      / sameAsDefault / zoneSectionsDiff self-compare loop) is gone from
+//      `handleGenerate` entirely; the marker is the source of intent.
+
+describe("IMP-55 #93 u8 — manual_section_assignment marker contract", () => {
+  it("handleSectionDrop sets marker true in-memory before persistence", () => {
+    const block = sliceHandler(HOME_TSX, "handleSectionDrop");
+    // finalSelection literal (built from zoneSelected, then marker = true)
+    // must occur BEFORE the saveUserOverrides call so the in-memory state
+    // and the PUT body source from the same overrides shape.
+    const markerIdx = block.search(/manual_section_assignment:\s*true/);
+    const saveIdx = block.search(/saveUserOverrides\(/);
+    expect(markerIdx).toBeGreaterThan(-1);
+    expect(saveIdx).toBeGreaterThan(-1);
+    expect(markerIdx).toBeLessThan(saveIdx);
+  });
+
+  it("handleSectionDrop co-PUTs zone_sections + manual_section_assignment:true (single body)", () => {
+    const block = sliceHandler(HOME_TSX, "handleSectionDrop");
+    // Single saveUserOverrides call carrying BOTH axes. The regex spans the
+    // call body to prove the two keys live in the same object literal — a
+    // future split into two PUTs would race the 300ms debounce and re-open
+    // the IMP-55 stale-disk window.
+    expect(block).toMatch(
+      /saveUserOverrides\([\s\S]*?zone_sections:[\s\S]*?manual_section_assignment:\s*true[\s\S]*?\)/,
+    );
+    // Exactly ONE saveUserOverrides call in the handler.
+    const calls = block.match(/saveUserOverrides\(/g) ?? [];
+    expect(calls.length).toBe(1);
+  });
+
+  it("handleApplyPendingLayout resets the marker to false in overrides literal", () => {
+    const block = sliceHandler(HOME_TSX, "handleApplyPendingLayout");
+    // After spreading `...p.userSelection.overrides`, the explicit
+    // `manual_section_assignment: false` overrides any prior-drag `true`.
+    // Without this the layout flip would carry the marker through, and u7
+    // would forward auto-carried assignments as user overrides → the
+    // PARTIAL_COVERAGE regression that motivated IMP-55.
+    expect(block).toMatch(/\.\.\.p\.userSelection\.overrides[\s\S]*?manual_section_assignment:\s*false/);
+  });
+
+  it("handleCancelPendingLayout uses createInitialUserSelection (u3 seeds false)", () => {
+    const block = sliceHandler(HOME_TSX, "handleCancelPendingLayout");
+    // Cancel discards all pending in-memory edits via the fresh-selection
+    // helper — the seed (u3) is the single source of truth for the
+    // in-memory marker on this path. u12 adds a separate disk-side
+    // saveUserOverrides PUT (covered by the u12 describe block below);
+    // the in-memory userSelection literal still has no explicit marker
+    // field — the seed handles it.
+    expect(block).toMatch(/createInitialUserSelection\(p\.slidePlan\)/);
+    // In-memory contract: no `manual_section_assignment` property appears
+    // inside the userSelection assignment. The only marker reference in
+    // live code lives inside the u12 saveUserOverrides(...) call body.
+    const codeOnly = stripComments(block);
+    expect(codeOnly).not.toMatch(
+      /userSelection:[\s\S]*?manual_section_assignment/,
+    );
+  });
+
+  it("handleGenerate gates overrides.zoneSections on manualMarker === true (strict bool)", () => {
+    const block = sliceHandler(HOME_TSX, "handleGenerate");
+    // Marker read AND strict-equality gate. `===` not `==`, not truthiness,
+    // not presence — so `false` / absent both skip forwarding (fail-closed).
+    expect(block).toMatch(/state\.userSelection\.overrides\.manual_section_assignment/);
+    expect(block).toMatch(/manualMarker\s*===\s*true/);
+    // The assignment to `overrides.zoneSections` must live INSIDE the
+    // marker-true branch.
+    const gateIdx = block.search(/if\s*\(\s*manualMarker\s*===\s*true\s*\)/);
+    const assignIdx = block.search(/overrides\.zoneSections\s*=/);
+    expect(gateIdx).toBeGreaterThan(-1);
+    expect(assignIdx).toBeGreaterThan(gateIdx);
+  });
+
+  it("handleGenerate filters forwarded zone_sections to valid zone_ids only (cross-layout safety)", () => {
+    const block = sliceHandler(HOME_TSX, "handleGenerate");
+    // A stale persisted layout could carry zone_ids that do not exist in
+    // the current sourcePlan (e.g. horizontal-2 `top`/`bottom` while the
+    // current layout is vertical-2 `left`/`right`). Those foreign keys
+    // must be dropped before reaching the backend `--override-section-
+    // assignment` so they cannot trigger PARTIAL_COVERAGE.
+    expect(block).toMatch(/validZoneIds\s*=\s*new Set\(\s*sourcePlan\.zones\.map\(\(z\)\s*=>\s*z\.zone_id\)/);
+    expect(block).toMatch(/if\s*\(!validZoneIds\.has\(zoneId\)\)\s*continue/);
+  });
+
+  it("handleGenerate no longer contains the IMP-08 B-3 self-compare anti-pattern", () => {
+    // Strip comments — the u7 docblock intentionally references the removed
+    // identifiers (`defaultByZone` / `sameAsDefault` / `zoneSectionsDiff`)
+    // in prose to explain the Stage 1 root cause for future readers; the
+    // regression we guard against is the LIVE code re-emerging.
+    const block = stripComments(sliceHandler(HOME_TSX, "handleGenerate"));
+    // The Stage 1 root cause: these identifiers compared user input against
+    // itself (sourcePlan === effectiveSlidePlan → zones === pendingZones,
+    // both derived from the same overrides.zone_sections). u7 deleted the
+    // entire block.
+    expect(block).not.toMatch(/\bdefaultByZone\b/);
+    expect(block).not.toMatch(/\bsameAsDefault\b/);
+    expect(block).not.toMatch(/\bzoneSectionsDiff\b/);
+  });
+
+  it("co-PUT payload contract: marker=true + zone_sections land in a single PUT body", async () => {
+    fetchMock.mockResolvedValue(mockResponse({}));
+    // Shape produced by handleSectionDrop after the u6 marker flip.
+    void saveUserOverrides("03_demo", {
+      zone_sections: { left: ["03-2"], right: ["03-1"] },
+      manual_section_assignment: true,
+    });
+    vi.advanceTimersByTime(300);
+    await drainMicrotasks();
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+    const body = lastPutBody() as Record<string, unknown>;
+    // Both axes in the same PUT body — exact equality, not arrayContaining,
+    // because any extra axis would mean a foreign mutation leaked through.
+    expect(Object.keys(body).sort()).toEqual(
+      ["manual_section_assignment", "zone_sections"].sort(),
+    );
+    expect(body.manual_section_assignment).toBe(true);
+    expect(body.zone_sections).toEqual({ left: ["03-2"], right: ["03-1"] });
+  });
+
+  it("co-PUT payload contract: marker=false carries explicitly through saveUserOverrides", async () => {
+    // u12 will add the apply/cancel explicit `false` PUT; the typed client
+    // must already propagate the literal `false` through the debounce
+    // bucket. A truthiness-based coalesce in the bucket merge would drop
+    // the value and re-open the stale-disk window. This locks the wire
+    // contract independently of the u12 caller-site write.
+    fetchMock.mockResolvedValue(mockResponse({}));
+    void saveUserOverrides("03_demo", { manual_section_assignment: false });
+    vi.advanceTimersByTime(300);
+    await drainMicrotasks();
+    const body = lastPutBody() as Record<string, unknown>;
+    expect(Object.keys(body)).toEqual(["manual_section_assignment"]);
+    expect(body.manual_section_assignment).toBe(false);
+  });
+});
+
+// ─── IMP-55 #93 u12 — stale-disk marker reset on apply / cancel ───────────
+// u5 resets the in-memory marker on layout apply, and u3's seed via
+// `createInitialUserSelection` resets it on cancel. But the disk persists
+// independently — a prior drag wrote `true` via u6's co-PUT, so after a
+// page reload the u3 restore branch would re-seed `true` and the u7 gate
+// would forward auto-carried section assignments → PARTIAL_COVERAGE
+// regression. u12 closes that window by writing `manual_section_assignment:
+// false` to disk via saveUserOverrides on both apply and cancel paths.
+describe("IMP-55 #93 u12 — stale-disk marker reset on layout apply/cancel", () => {
+  it("handleApplyPendingLayout source contains a marker=false saveUserOverrides PUT", () => {
+    const block = sliceHandler(HOME_TSX, "handleApplyPendingLayout");
+    // Stripped-comment source so the u5 docblock prose doesn't satisfy the
+    // assertion — must be a real call expression.
+    const code = stripComments(block);
+    // Uploaded-file gate (mirrors the u6 / other handler pattern — the
+    // demo-mode initial render path must not PUT to an empty key).
+    expect(code).toMatch(
+      /if\s*\(\s*p\.uploadedFile\s*\)[\s\S]*?saveUserOverrides\([\s\S]*?manual_section_assignment:\s*false[\s\S]*?\)/,
+    );
+    expect(code).toMatch(/deriveUserOverridesKey\(p\.uploadedFile\.name\)/);
+  });
+
+  it("handleCancelPendingLayout source contains a marker=false saveUserOverrides PUT", () => {
+    const block = sliceHandler(HOME_TSX, "handleCancelPendingLayout");
+    const code = stripComments(block);
+    // Cancel handler converts from arrow-body to function-body for the
+    // disk PUT; the in-memory reset still comes from createInitialUserSelection.
+    expect(code).toMatch(
+      /if\s*\(\s*p\.uploadedFile\s*\)[\s\S]*?saveUserOverrides\([\s\S]*?manual_section_assignment:\s*false[\s\S]*?\)/,
+    );
+    expect(code).toMatch(/createInitialUserSelection\(p\.slidePlan\)/);
+  });
+
+  it("apply path PUT payload: marker=false carries alone (no auto-carry leakage)", async () => {
+    // The apply handler issues a dedicated PUT for the marker reset that is
+    // independent of the (conditional) zone_geometries PUT and of the
+    // in-memory zone_sections rewrite. The wire contract for this PUT must
+    // contain only the marker — if zone_sections leaked into the same body
+    // it would re-arm the u9 backend fallback gate against u12's intent.
+    fetchMock.mockResolvedValue(mockResponse({}));
+    void saveUserOverrides("03_demo", { manual_section_assignment: false });
+    vi.advanceTimersByTime(300);
+    await drainMicrotasks();
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+    const body = lastPutBody() as Record<string, unknown>;
+    expect(Object.keys(body)).toEqual(["manual_section_assignment"]);
+    expect(body.manual_section_assignment).toBe(false);
+  });
+
+  it("apply path PUT is unconditional (does NOT gate on hadPriorGeoms)", () => {
+    // The u4 zone_geometries PUT inside handleApplyPendingLayout is
+    // conditional (`p.uploadedFile && hadPriorGeoms`). The u12 marker PUT
+    // must NOT inherit that gate — a stale disk `true` can exist without
+    // any prior zone_geometries, so the reset must always fire.
+    const code = stripComments(sliceHandler(HOME_TSX, "handleApplyPendingLayout"));
+    // Locate the marker PUT and verify its enclosing `if` clause is just
+    // `p.uploadedFile`, not the compound `... && hadPriorGeoms` guard.
+    const markerCallMatch = code.match(
+      /if\s*\(([^)]*)\)\s*\{[^}]*saveUserOverrides\([^)]*manual_section_assignment:\s*false[^)]*\)/,
+    );
+    expect(markerCallMatch).not.toBeNull();
+    if (markerCallMatch) {
+      expect(markerCallMatch[1].trim()).toBe("p.uploadedFile");
+    }
+  });
+});

Front/vite.config.ts

@@ -219,19 +219,25 @@ function vitePluginStorageProxy(): Plugin {
 
 export const USER_OVERRIDES_KEY_RE = /^[A-Za-z0-9_][A-Za-z0-9_.\-]*$/;
 
-// The five in-scope axes — exact mirror of KNOWN_AXES in
-// src/user_overrides_io.py. Any payload key outside this allowlist is
-// silently dropped by the PUT handler (u4) so the on-disk schema cannot
-// drift from the backend pipeline (u2) contract. Foreign top-level keys
-// already on disk are preserved verbatim (see mergeUserOverrides).
+// The six in-scope axes — mirror of KNOWN_AXES in
+// src/user_overrides_io.py minus `slide_css` (known gap, IMP-45 #74 —
+// the Python side persists it for backend consumption; the Vite PUT does
+// not write it because the frontend never mutates the slide-level CSS
+// override). Any payload key outside this allowlist is silently dropped
+// by the PUT handler (u4) so the on-disk schema cannot drift from the
+// backend pipeline (u2) contract. Foreign top-level keys already on disk
+// are preserved verbatim (see mergeUserOverrides).
 // IMP-51 (#79) u2: added `image_overrides` (image_id → {x,y,w,h}
 // percent-of-slide coordinates).
+// IMP-55 (#93) u1: added `manual_section_assignment` (bool intent marker
+// — drag-drop sets true, layout apply/cancel sets false).
 export const KNOWN_USER_OVERRIDES_AXES = [
   "layout",
   "zone_geometries",
   "zone_sections",
   "frames",
   "image_overrides",
+  "manual_section_assignment",
 ] as const;
 export type KnownUserOverridesAxis = (typeof KNOWN_USER_OVERRIDES_AXES)[number];
 

src/phase_z2_pipeline.py

@@ -8262,8 +8262,20 @@ if __name__ == "__main__":
                         except (TypeError, ValueError):
                             continue
                 overrides_geoms = _accepted
-        # zone_sections — CLI empty → fill from file (dict[str, list[str]]).
-        if not overrides_section_assignments:
+        # zone_sections — CLI empty AND persisted manual_section_assignment is
+        # exactly True → fill from file (dict[str, list[str]]). IMP-55 (#93) u9
+        # marker gate (fail-closed) : ``manual_section_assignment`` absent /
+        # False / non-bool (string/int/list/dict) all skip the fallback so a
+        # stale ``zone_sections`` axis left on disk from a prior drag cannot
+        # smuggle ``--override-section-assignment`` into the next run after the
+        # user reset intent via layout apply/cancel (u5 / u12 write
+        # ``manual_section_assignment: false`` explicitly). CLI
+        # ``--override-section-assignment`` payloads remain authoritative
+        # (u11 truth-table) — this gate only affects the file→fallback path.
+        if (
+            not overrides_section_assignments
+            and _persisted.get("manual_section_assignment") is True
+        ):
             _file_sections = _persisted.get("zone_sections")
             if isinstance(_file_sections, dict):
                 _accepted_sec: dict[str, list[str]] = {}

src/user_overrides_io.py

@@ -5,16 +5,19 @@ auto-restores user choices without re-clicking. Source of truth = MDX-keyed
 file (stem of the MDX path), NOT ``data/runs/<run_id>/`` which mints a fresh
 run_id per ``/api/run`` invocation.
 
-Schema (6 axes; stable order; IMP-51 #79 u1 added ``image_overrides``;
-IMP-45 #74 u1 added ``slide_css``):
+Schema (7 axes; stable order; IMP-51 #79 u1 added ``image_overrides``;
+IMP-45 #74 u1 added ``slide_css``; IMP-55 #93 u1 added
+``manual_section_assignment`` as a bool intent marker so the backend can
+distinguish a user drag-drop from frontend auto-carry zone_sections):
 
     {
-      "layout":          <string|null>,
-      "zone_geometries": {<zone_id>: {"x": float, "y": float, "w": float, "h": float}},
-      "zone_sections":   {<zone_id>: [<section_id>, ...]},
-      "frames":          {<unit_id>: <template_id>},
-      "image_overrides": {<image_id>: {"x": float, "y": float, "w": float, "h": float}},
-      "slide_css":       <string|null>
+      "layout":                    <string|null>,
+      "zone_geometries":           {<zone_id>: {"x": float, "y": float, "w": float, "h": float}},
+      "zone_sections":             {<zone_id>: [<section_id>, ...]},
+      "frames":                    {<unit_id>: <template_id>},
+      "image_overrides":           {<image_id>: {"x": float, "y": float, "w": float, "h": float}},
+      "slide_css":                 <string|null>,
+      "manual_section_assignment": <bool>
     }
 
 ``image_id`` is the stable identifier emitted by the user-content image
@@ -55,10 +58,13 @@ from typing import Any, Optional
 _PKG_ROOT = Path(__file__).resolve().parent.parent
 DEFAULT_OVERRIDES_ROOT = _PKG_ROOT / "data" / "user_overrides"
 
-# The six in-scope axes (IMP-51 #79 u1 added ``image_overrides``; IMP-45
-# #74 u1 added ``slide_css``). Any other top-level key in the file is
-# preserved but ignored by callers — keeps the file forward-compatible
-# with future axes (e.g., zone_sizes) without a schema bump here.
+# The seven in-scope axes (IMP-51 #79 u1 added ``image_overrides``; IMP-45
+# #74 u1 added ``slide_css``; IMP-55 #93 u1 added
+# ``manual_section_assignment`` — bool intent marker that gates whether
+# persisted ``zone_sections`` are consumed by the backend pipeline). Any
+# other top-level key in the file is preserved but ignored by callers —
+# keeps the file forward-compatible with future axes (e.g., zone_sizes)
+# without a schema bump here.
 KNOWN_AXES: tuple[str, ...] = (
     "layout",
     "zone_geometries",
@@ -66,6 +72,7 @@ KNOWN_AXES: tuple[str, ...] = (
     "frames",
     "image_overrides",
     "slide_css",
+    "manual_section_assignment",
 )
 
 # Key validation — MDX stem must be safe for filesystem use. Allow

tests/test_user_overrides_io.py

@@ -2,9 +2,10 @@
 
 Covers the persisted axes called out in the Stage 2 plan
 (IMP-51 #79 u1 extended this to 5 axes by adding ``image_overrides``;
-IMP-45 #74 u1 extended to 6 axes by adding ``slide_css``):
+IMP-45 #74 u1 extended to 6 axes by adding ``slide_css``;
+IMP-55 #93 u1 extended to 7 axes by adding ``manual_section_assignment``):
 
-1. Round-trip ``save`` → ``load`` (6 KNOWN_AXES + foreign top-level keys).
+1. Round-trip ``save`` → ``load`` (7 KNOWN_AXES + foreign top-level keys).
 2. Unknown-key passthrough (foreign axes preserved across partial merges).
 3. Missing / corrupt / non-object behavior (graceful ``{}`` + stderr warning).
 4. Invalid keys (``InvalidOverrideKey`` raised on traversal / separators /
@@ -121,19 +122,26 @@ def _full_payload() -> dict:
             "img-1": {"x": 10.0, "y": 20.0, "w": 30.0, "h": 25.0},
         },
         "slide_css": "<style>.slide .frame-process-product .label { font-size: 14px; }</style>",
+        "manual_section_assignment": True,
     }
 
 
 def test_known_axes_includes_image_overrides():
-    """IMP-51 #79 u1 — ``image_overrides`` is a known axis (now 6 total)."""
+    """IMP-51 #79 u1 — ``image_overrides`` is a known axis (now 7 total)."""
     assert "image_overrides" in KNOWN_AXES
-    assert len(KNOWN_AXES) == 6
+    assert len(KNOWN_AXES) == 7
 
 
 def test_known_axes_includes_slide_css():
-    """IMP-45 #74 u1 — ``slide_css`` is a known axis (6 total)."""
+    """IMP-45 #74 u1 — ``slide_css`` is a known axis (7 total)."""
     assert "slide_css" in KNOWN_AXES
-    assert len(KNOWN_AXES) == 6
+    assert len(KNOWN_AXES) == 7
+
+
+def test_known_axes_includes_manual_section_assignment():
+    """IMP-55 #93 u1 — bool intent marker is a known axis (7 total)."""
+    assert "manual_section_assignment" in KNOWN_AXES
+    assert len(KNOWN_AXES) == 7
 
 
 def test_save_then_load_round_trip(tmp_path):
@@ -161,6 +169,7 @@ def test_save_partial_payload_preserves_other_axes(tmp_path):
     assert loaded["frames"] == _full_payload()["frames"]
     assert loaded["image_overrides"] == _full_payload()["image_overrides"]
     assert loaded["slide_css"] == _full_payload()["slide_css"]
+    assert loaded["manual_section_assignment"] is True
 
 
 def test_save_partial_image_overrides_preserves_other_axes(tmp_path):
@@ -183,6 +192,7 @@ def test_save_partial_image_overrides_preserves_other_axes(tmp_path):
     assert loaded["zone_sections"] == _full_payload()["zone_sections"]
     assert loaded["frames"] == _full_payload()["frames"]
     assert loaded["slide_css"] == _full_payload()["slide_css"]
+    assert loaded["manual_section_assignment"] is True
 
 
 def test_save_axis_replaces_not_deep_merges(tmp_path):
@@ -226,6 +236,24 @@ def test_save_preserves_foreign_top_level_keys(tmp_path):
     assert loaded["schema_version"] == pre_seed["schema_version"]
 
 
+def test_save_manual_section_assignment_round_trips_both_booleans(tmp_path):
+    """IMP-55 #93 u1 — bool axis round-trips true/false and clears on None.
+
+    Asserts the bool is preserved literally (not coerced to int / string) so
+    the backend pipeline (u9) can branch on ``is True`` without false-positive
+    matches from truthy-but-not-True values seeded by older callers.
+    """
+    key = "03"
+    save(key, {"manual_section_assignment": True}, root=tmp_path)
+    assert load(key, root=tmp_path)["manual_section_assignment"] is True
+
+    save(key, {"manual_section_assignment": False}, root=tmp_path)
+    assert load(key, root=tmp_path)["manual_section_assignment"] is False
+
+    save(key, {"manual_section_assignment": None}, root=tmp_path)
+    assert "manual_section_assignment" not in load(key, root=tmp_path)
+
+
 def test_save_creates_parent_directory(tmp_path):
     nested = tmp_path / "deep" / "nest"
     assert not nested.exists()
@@ -241,6 +269,7 @@ def test_save_writes_pretty_sorted_json_for_diffability(tmp_path):
     pos_frames = raw.index('"frames"')
     pos_image_overrides = raw.index('"image_overrides"')
     pos_layout = raw.index('"layout"')
+    pos_manual = raw.index('"manual_section_assignment"')
     pos_slide_css = raw.index('"slide_css"')
     pos_zg = raw.index('"zone_geometries"')
     pos_zs = raw.index('"zone_sections"')
@@ -248,6 +277,7 @@ def test_save_writes_pretty_sorted_json_for_diffability(tmp_path):
         pos_frames
         < pos_image_overrides
         < pos_layout
+        < pos_manual
         < pos_slide_css
         < pos_zg
         < pos_zs

tests/test_user_overrides_pipeline_fallback.py

@@ -48,6 +48,14 @@ def _exec_main_block(
         override_zone_geometries=None,
         override_section_assignments=None,
         override_image_overrides=None,
+        # IMP-55 (#93) u9 — mirror the live ``run_phase_z2_mvp1`` signature so
+        # the __main__ dispatch in src/phase_z2_pipeline.py:8332 does not raise
+        # TypeError on kwargs added by IMP-45 #74 (``override_slide_css``) and
+        # IMP-43 #72 (``reuse_from``). The u9 truth-table assertions only read
+        # the section-assignment axis; the new kwargs are captured here so any
+        # follow-up test can pin them without re-touching this harness.
+        override_slide_css=None,
+        reuse_from=None,
     ):
         captured["mdx_path"] = mdx_path
         captured["run_id"] = run_id
@@ -56,6 +64,8 @@ def _exec_main_block(
         captured["override_zone_geometries"] = override_zone_geometries
         captured["override_section_assignments"] = override_section_assignments
         captured["override_image_overrides"] = override_image_overrides
+        captured["override_slide_css"] = override_slide_css
+        captured["reuse_from"] = reuse_from
 
     monkeypatch.setattr(_pz2, "run_phase_z2_mvp1", _fake_run)
     monkeypatch.setattr(sys, "argv", argv)
@@ -97,6 +107,13 @@ def _write_full_payload(tmp_path: Path, stem: str = "03") -> Path:
                     "top": ["03-1"],
                     "bottom": ["03-2", "03-3"],
                 },
+                # IMP-55 (#93) u9 — seed the new ``manual_section_assignment``
+                # marker True so the per-axis / CLI-wins / partial-merge tests
+                # below continue to exercise the file→fallback path under the
+                # gate added in src/phase_z2_pipeline.py (``is True`` identity
+                # check). Truth-table coverage for False / absent / non-bool
+                # belongs to u10 and lives in its own test section.
+                "manual_section_assignment": True,
                 "image_overrides": {
                     "img-file-a": {"x": 10.0, "y": 15.0, "w": 30.0, "h": 25.0},
                     "img-file-b": {"x": 50.0, "y": 50.0, "w": 40.0, "h": 40.0},
@@ -408,3 +425,178 @@ def test_image_overrides_fallback_coerces_int_values_to_float(tmp_path, monkeypa
     assert coerced == {"img-int": {"x": 10.0, "y": 20.0, "w": 30.0, "h": 40.0}}
     for axis_value in coerced["img-int"].values():
         assert isinstance(axis_value, float)
+
+
+# -- 8. IMP-55 (#93) u10 — manual_section_assignment marker truth-table ----
+#
+# The backend file-fallback gate added in u9
+# (``src/phase_z2_pipeline.py`` ``_persisted.get("manual_section_assignment")
+# is True``) is exercised here with the full truth-table of marker values a
+# stale or hand-edited overrides file could legally contain. The gate is
+# fail-closed by ``is True`` identity, so only literal Python ``True``
+# (JSON ``true``) propagates ``zone_sections`` into
+# ``override_section_assignments``; everything else — absent, ``False``,
+# truthy non-bool (``"true"``, ``1``, ``[]``, ``{}``), and ``None`` — must
+# leave the axis as ``None`` (``or None`` collapses an empty dict on the
+# call site). No hardcoding of section IDs in the assertion logic; the
+# values ``03-1`` / ``03-2`` here are sample payload literals, not pinned
+# behavior. ``_write_marker_payload`` reuses the IO loader by way of the
+# ``__main__`` block (no direct import of the pipeline gate).
+
+_MARKER_ABSENT = object()
+
+
+def _write_marker_payload(
+    tmp_path: Path, marker: Any, stem: str = "03"
+) -> Path:
+    """Write a minimal overrides file with ``zone_sections`` + optional marker.
+
+    ``marker is _MARKER_ABSENT`` → omit ``manual_section_assignment`` key.
+    Any other value (including ``None``) → write it verbatim as JSON.
+    """
+    payload: dict[str, Any] = {
+        "zone_sections": {"top": ["03-1"], "bottom": ["03-2"]},
+    }
+    if marker is not _MARKER_ABSENT:
+        payload["manual_section_assignment"] = marker
+    path = tmp_path / f"{stem}.json"
+    path.write_text(json.dumps(payload), encoding="utf-8")
+    return path
+
+
+def test_marker_true_fills_section_assignments(tmp_path, monkeypatch):
+    """marker=True + zone_sections in file + CLI empty → file value flows."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    _write_marker_payload(tmp_path, True, "03")
+
+    captured: dict[str, Any] = {}
+    _exec_main_block(captured, ["src.phase_z2_pipeline", "03.mdx"], monkeypatch)
+
+    assert captured["override_section_assignments"] == {
+        "top": ["03-1"],
+        "bottom": ["03-2"],
+    }
+
+
+@pytest.mark.parametrize(
+    "marker",
+    [
+        _MARKER_ABSENT,
+        False,
+        "true",  # JSON-string truthy must NOT pass the ``is True`` gate.
+        1,  # int truthy must NOT pass.
+        [],
+        {},
+        None,
+    ],
+    ids=["absent", "false", "string_true", "int_one", "empty_list", "empty_dict", "null"],
+)
+def test_marker_non_true_skips_section_assignments(
+    tmp_path, monkeypatch, marker
+):
+    """marker absent / False / non-bool → gate fail-closed → axis is None.
+
+    Even though ``zone_sections`` is present in the file, the gate refuses
+    to forward it because ``manual_section_assignment`` is not literal
+    ``True``. ``or None`` on the call site collapses the empty dict back
+    to ``None``.
+    """
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    _write_marker_payload(tmp_path, marker, "03")
+
+    captured: dict[str, Any] = {}
+    _exec_main_block(captured, ["src.phase_z2_pipeline", "03.mdx"], monkeypatch)
+
+    assert captured["override_section_assignments"] is None
+
+
+# -- 9. IMP-55 (#93) u11 — CLI ``--override-section-assignment`` wins over
+# persisted manual-marker fallback ----------------------------------------
+#
+# The u9 gate only fires on the file→fallback branch
+# (``not overrides_section_assignments and _persisted.get(...) is True``).
+# When the CLI supplies ``--override-section-assignment`` the
+# ``overrides_section_assignments`` dict is truthy before the gate is
+# evaluated, so the persisted ``zone_sections`` axis (and the
+# ``manual_section_assignment`` marker that would otherwise unlock it) is
+# bypassed entirely — CLI is authoritative on the section-assignment
+# axis. The three cases below pin this contract:
+#
+#   1. CLI + persisted marker True (file value present) → CLI wins.
+#   2. CLI + persisted marker False (file value present) → CLI wins; the
+#      marker is irrelevant on the CLI-wins path (no truth-value coupling).
+#   3. CLI with no overrides file at all → CLI value flows through; the
+#      marker is a gate on file→fallback only, never a precondition for
+#      any CLI ``cli_override`` to take effect.
+#
+# Cross-axis bystanders (layout / frames / geometries / images) are
+# intentionally not seeded here; this section locks CLI-vs-marker
+# semantics on the section axis only. Cross-axis CLI-wins behavior is
+# already covered by the IMP-52 #80 tests in section 3 / 3b above.
+
+
+def test_cli_section_assignment_wins_over_persisted_marker_true(
+    tmp_path, monkeypatch
+):
+    """marker=True + file zone_sections + CLI value → CLI wins per-axis."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    _write_marker_payload(tmp_path, True, "03")
+
+    captured: dict[str, Any] = {}
+    _exec_main_block(
+        captured,
+        [
+            "src.phase_z2_pipeline",
+            "03.mdx",
+            "--override-section-assignment",
+            "top=cli-section",
+        ],
+        monkeypatch,
+    )
+
+    # CLI value wholly replaces the file zone_sections (per-axis win); the
+    # gate's ``not overrides_section_assignments`` precondition is false.
+    assert captured["override_section_assignments"] == {"top": ["cli-section"]}
+
+
+def test_cli_section_assignment_wins_with_persisted_marker_false(
+    tmp_path, monkeypatch
+):
+    """marker=False + file zone_sections + CLI value → CLI wins; marker unread."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+    _write_marker_payload(tmp_path, False, "03")
+
+    captured: dict[str, Any] = {}
+    _exec_main_block(
+        captured,
+        [
+            "src.phase_z2_pipeline",
+            "03.mdx",
+            "--override-section-assignment",
+            "bottom=cli-section",
+        ],
+        monkeypatch,
+    )
+
+    assert captured["override_section_assignments"] == {"bottom": ["cli-section"]}
+
+
+def test_cli_section_assignment_works_without_persisted_file(
+    tmp_path, monkeypatch
+):
+    """No overrides file → CLI value flows; marker is not a CLI precondition."""
+    _redirect_overrides_root(tmp_path, monkeypatch)
+
+    captured: dict[str, Any] = {}
+    _exec_main_block(
+        captured,
+        [
+            "src.phase_z2_pipeline",
+            "03.mdx",
+            "--override-section-assignment",
+            "top=cli-only",
+        ],
+        monkeypatch,
+    )
+
+    assert captured["override_section_assignments"] == {"top": ["cli-only"]}