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>

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]] = {}