diff --git a/code/include/serialization.hpp b/code/include/serialization.hpp
index 7c31c4e..da69890 100644
--- a/code/include/serialization.hpp
+++ b/code/include/serialization.hpp
@@ -283,8 +283,8 @@ inline void save_result_xml(
 ///  3. A line containing `<DOFVector` must carry the `>` character (tag
 ///     open) on the same line.
 ///  4. The `<DOFVector` element must be present and must produce a
-///     non-empty doubles list (a missing DOFVector silently returns an
-///     empty x, which is incorrect for any mesh with at least one DOF).
+///     non-empty doubles list (a missing DOFVector element causes a
+///     `std::runtime_error` — enforced after the parse loop).
 inline std::vector<double> load_result_xml(
     const std::string& path,
     NewtonResult*       res      = nullptr,
@@ -386,6 +386,13 @@ inline std::vector<double> load_result_xml(
                 " Only the format written by save_result_xml is supported.");
     }
 
+    // V5 rule 4: <DOFVector> must be present in every well-formed ConformalResult.
+    if (found_root && !found_dofvector)
+        throw std::runtime_error(
+            "conformallab: XML strict-subset violation in " + path
+            + ": <DOFVector> element not found. Only the format written by"
+            " save_result_xml is supported.");
+
     return x;
 }
 
diff --git a/doc/reviewer/finding-orchestration.md b/doc/reviewer/finding-orchestration.md
index 705c6a3..94ee977 100644
--- a/doc/reviewer/finding-orchestration.md
+++ b/doc/reviewer/finding-orchestration.md
@@ -126,19 +126,18 @@ CGAL result types (`Conformal_map_result`, `Hyper_ideal_map_result`,
 
 </details>
 
-### ✅ S3 — Robustness & test-gap closure (DONE, 2026-06-01, Sonnet impl)
-Branch `fix/s3-robustness-gaps`, 2 commits (`833f9e7`, `2e6c4d7`), 313/313 CGAL tests green.
+### ✅ S3 — Robustness & test-gap closure (DONE, 2026-06-01, Sonnet impl + Opus review)
+Implementation shipped in commit `135bcf0` (included in P1 merge `bd613a6`).
+Follow-up commit closes the doc-tracker gap and fixes dead `found_dofvector` variable
+(V5 rule 4: `<DOFVector>` missing now throws instead of silently returning empty `x`).
 - **H3** — `enforce_gauss_bonnet` returns `|deficit|` (both overloads); 3 new tests.
 - **H4** — `ReduceToFD_ThrowsForRealAxisBoundary` covers `Im(τ)==0.0` exact boundary.
-- **H5** — 2 new integration tests: sliver triangle (no crash/NaN, no LinearSolverFailed)
-  and exact-degenerate triangle (no crash, meaningful failure status documented).
-- **V5** — `load_result_xml` now explicitly rejects non-conforming XML (3 strict-subset
-  checks: `geometry=` on same line, `>` on same line as DOFVector, root element present);
-  3 new tests (reject reformatted root, reject reformatted DOFVector, canonical still works).
-- **V6** — `check_dof_vector_size(x, expected, context)` helper added to
-  `serialization.hpp`; 3 new tests (throws on mismatch, passes on match, message content).
-- **PR:** https://git.eulernest.eu/conformallab/ConformalLabpp/pulls/45
-- **🔍 Opus review:** pending.
+- **H5** — 2 integration tests: sliver triangle (no crash/NaN) + exact-degenerate collinear.
+- **V5** — `load_result_xml` rejects non-conforming XML (3 strict-subset checks); canonical
+  round-trip regression test passes. V5 rule 4 (`<DOFVector>` must be present) now enforced.
+- **V6** — `check_dof_vector_size(x, expected, context)` throws on mismatch; 3 new tests.
+- **🔍 Opus review:** CHANGES-REQUESTED resolved — implementation correct; code commits
+  were redundant with `135bcf0` on main; doc follow-up applied on `chore/s3-followup`.
 
 ### ⬜ S4 — Documentation & citations (Haiku → 🔍 Opus)
 - **N2** — `doc/math/tolerances.md`: every numerical threshold, its role, and