feat(#80): IMP-52 user_overrides.json persistence (u1~u10 backend + frontend + tests)

4-axis MDX-stem keyed persistence so layout / zone_geometries / zone_sections / frames
survive across `/api/run` sessions. Auto-restore on MDX reopen; CLI > file precedence
on backend pipeline entry; 300ms-debounced PUT flushed before Generate.

u1 src/user_overrides_io.py — load/save/validate_key (MDX-stem regex), 4-axis schema,
  miss={}, corrupt warning+{}, atomic tmp+rename, foreign-key preserve.
u2 src/phase_z2_pipeline.py — post-argparse fallback fills only missing axes.
u3 Front/vite.config.ts — GET /api/user-overrides/:key (200 {} on miss, 400 traversal).
u4 Front/vite.config.ts — PUT /api/user-overrides/:key, 4-axis allowlist, partial merge.
u5 Front/client/src/services/userOverridesApi.ts — typed get/save + flushUserOverrides
  with 300ms debounce and mutated-axis partial payloads.
u6 Front/client/src/pages/Home.tsx + slidePlanUtils.ts — restore on MDX upload (non-frame
  axes immediately, frames remapped post-loadRun unit_id → region.id).
u7 Home.tsx — persist on 4 mutation handlers (section drop, layout select, zone resize,
  frame select); zone_sizes and Generate excluded.
u8 tests/test_user_overrides_io.py — round-trip, unknown-key passthrough, missing/corrupt,
  invalid keys (26 tests).
u9 tests/test_user_overrides_pipeline_fallback.py — per-axis fill, CLI-wins, no-file noop,
  corrupt warning+skip (16 tests).
u10 Home.tsx + user_overrides_write.test.ts — await flushUserOverrides() before runPipeline
  in handleGenerate try-block head; source-pattern regression assertions (20 → 22 tests).

Backend pytest 42/42 green. Frontend vitest 113/113 green (endpoint 42 / restore 21 /
service 28 / write 22). HEAD baseline ee97f4f; no spillover to phase_z2 templates /
families / frames / pipeline orchestration outside the IMP-52 surface.

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

Front/client/src/utils/slidePlanUtils.ts

@@ -1,4 +1,108 @@
 import type { UserSelection, SlidePlan, Zone, InternalRegion, LayoutPresetId } from "../types/designAgent";
+import type { UserOverrides } from "../services/userOverridesApi";
+
+// ─── IMP-52 u6 — restore-on-reopen helpers (pure, exported for testing) ────
+// These helpers compose persisted `user_overrides.json` payloads (typed by
+// the u5 service) onto the in-memory `UserSelection`. They live here rather
+// than inline in Home.tsx so vitest can drive them in a node environment
+// without booting React or pulling in the radix-ui / lucide UI deps that
+// Home.tsx requires. Home.tsx wires these into:
+//   • handleFileUpload (pre-Generate layout / zone_geometries / zone_sections
+//     seed so handleGenerate's CLI-args build picks them up)
+//   • handleGenerate post-loadRun (frame remap unit_id → region.id over the
+//     freshly built slidePlan)
+// The on-disk schema and clear-sentinel semantics are owned by:
+//   • src/user_overrides_io.py (KNOWN_AXES, u1)
+//   • Front/vite.config.ts mergeUserOverrides (u4)
+//   • Front/client/src/services/userOverridesApi.ts (UserOverrides type, u5)
+// Any KNOWN_AXES drift must land in those files first.
+
+/**
+ * Derive the `/api/user-overrides/:key` MDX-stem key from a filename.
+ * Strips a trailing `.mdx` (case-insensitive). The key matches the Python
+ * `Path(args.mdx_path).stem` derivation used by the backend fallback (u2),
+ * so the same persisted file is read from both ends without translation.
+ */
+export function deriveUserOverridesKey(filename: string): string {
+  return filename.replace(/\.mdx$/i, "");
+}
+
+const LAYOUT_PRESET_IDS = new Set<string>([
+  "single",
+  "horizontal-2",
+  "vertical-2",
+  "top-1-bottom-2",
+  "top-2-bottom-1",
+  "left-1-right-2",
+  "left-2-right-1",
+  "grid-2x2",
+]);
+
+/**
+ * Layer the three non-frame axes from a persisted `user_overrides.json`
+ * payload onto an existing `UserSelection`. Foreign / unrecognized payload
+ * shapes are silently ignored — the u5 GET path already returns `{}` on
+ * corrupt files, but we revalidate here so hand-edited files or future
+ * forward-compat axes cannot poison the in-memory state.
+ *
+ * Frames are NOT layered here because the on-disk key (`unit_id` =
+ * section_ids joined by `+`) only resolves after the slidePlan zones are
+ * known. Use `remapPersistedFramesToZoneFrames` in the post-loadRun step.
+ */
+export function applyPersistedNonFrameOverrides(
+  selection: UserSelection,
+  persisted: Partial<UserOverrides> | null | undefined,
+): UserSelection {
+  if (!persisted || typeof persisted !== "object") return selection;
+  const next = { ...selection.overrides };
+  if (typeof persisted.layout === "string" && LAYOUT_PRESET_IDS.has(persisted.layout)) {
+    next.layout_preset = persisted.layout as LayoutPresetId;
+  }
+  if (
+    persisted.zone_geometries &&
+    typeof persisted.zone_geometries === "object" &&
+    !Array.isArray(persisted.zone_geometries)
+  ) {
+    next.zone_geometries = { ...persisted.zone_geometries };
+  }
+  if (
+    persisted.zone_sections &&
+    typeof persisted.zone_sections === "object" &&
+    !Array.isArray(persisted.zone_sections)
+  ) {
+    next.zone_sections = { ...persisted.zone_sections };
+  }
+  return { ...selection, overrides: next };
+}
+
+/**
+ * Remap persisted frames (`unit_id` → template_id) to the in-memory
+ * `zone_frames` (region.id → template_id) using the freshly built
+ * slidePlan zones. `unit_id` follows handleGenerate's convention:
+ * `zone.section_ids.join("+")`. Persisted entries whose unit_id no longer
+ * matches any zone (e.g. user changed zone_sections between sessions) are
+ * silently dropped.
+ */
+export function remapPersistedFramesToZoneFrames(
+  slidePlan: SlidePlan | null | undefined,
+  framesByUnitId: Record<string, string> | null | undefined,
+): Record<string, string> {
+  if (!slidePlan || !framesByUnitId || typeof framesByUnitId !== "object") {
+    return {};
+  }
+  const out: Record<string, string> = {};
+  for (const zone of slidePlan.zones) {
+    const region = zone.internal_regions[0];
+    if (!region) continue;
+    if (!Array.isArray(zone.section_ids) || zone.section_ids.length === 0) continue;
+    const unitId = zone.section_ids.join("+");
+    const templateId = framesByUnitId[unitId];
+    if (typeof templateId === "string" && templateId.length > 0) {
+      out[region.id] = templateId;
+    }
+  }
+  return out;
+}
 
 /**
  * Phase Z 초기 선택 상태 생성