fix(s3-followup): enforce V5 rule 4 + mark H3/H4/H5/V5/V6 done

serialization.hpp: `found_dofvector` was set but never checked after
the parse loop, leaving rule 4 of the strict-subset (§doc line 285)
unenforced.  Add the missing post-loop throw so a ConformalResult XML
that omits the <DOFVector> element is rejected with a clear error
instead of silently returning an empty x.  Update the docstring to
remove the misleading "silently returns" note.

finding-orchestration.md: mark H3/H4/H5/V5/V6 ✅ and record the S3
session as complete.  Implementation landed in commit 135bcf0 (P1
merge bd613a6); PR #45 code commits were redundant — the only net-new
change in this follow-up is the V5 enforcement fix + tracker update.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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