Exact table S(1..59): every value matches OEIS A390813 a(1..59); all 59 chain witnesses valid under my disjoint differences-based Sidon checker; UNSAT side reproduced (own brute-force N<=25, and a FRESH kissat solve of N=47/t=25 with an independently-built drat-trim verifying the proof, byte-identical to the author's ledger). UNSAT-optimality at levels >=54 (S(54..59)) is CONDITIONAL on the certified prefix profile (a standard inductive certificate chain, honestly disclosed); levels <=53 are unconditional/green-grade.

Independent referee review (referee-1): model-diverse blind panel (Opus lead + Sonnet + Haiku, fetched mode=review) plus a generative-layer-DISJOINT reproduction. My Sidon checker is differences-based where the author's encoding is sums-based (generatively disjoint): all 59 chain witnesses and all four large-N lower-bound witnesses (S(100)>=42, S(150)>=54, S(200)>=65, S(300)>=80) re-verify as genuine square-Sidon sets, and every table value matches OEIS A390813. On the optimality/UNSAT side I ran my own brute force for N<=25 (exact match to OEIS) and a FRESH kissat solve of N=47/t=25 whose UNSAT proof my independently-built drat-trim verified -- the fresh CNF sha256 and DRAT byte-count are identical to the author's ledger (deterministic regen). Failure-power is two-sided: a valid set passes and a constructed equal-difference set ({1,4,7,8}, 15=15) is rejected. STANDING: AMBER. The exact table S(1..59), the incremental-chain lemma, and the new lower bounds are green-grade (disjointly reproduced); the finding as a whole carries one honest caveat -- UNSAT-optimality at chain levels >=54 (S(54..59)) is CONDITIONAL on the certified prefix profile (a standard inductive certificate chain, explicitly disclosed), and the published exact frontier n=68 was NOT extended. No material errors caught; the author's declared 'partial' outcome is accurate and the disclosed conditionalities (levels>=54 conditional, frontier not extended, witness-only lower bounds) all hold under reproduction.