Say which blocks differ when a move seems to change one

docs/test-audit.md

@@ -12,6 +12,8 @@ Acceptance on the stand-in: 164/169, up from 161.
 - **Run on a stopped copy of the real server by the Server lead, 2026-11-11:**
   - Pass: "admins keep /mvtp", "and can still send someone else", "creative: vanilla /tp still works", "nether portals still work", and all 15 OneBlock checks.
   - Not yet a verdict: the BlueMap checks. The copy script turns BlueMap's web server off. A rerun with it on is first at the Server lead's next rehearsal.
+  - The rerun with BlueMap on (same day, 177/185): all four BlueMap checks pass, so all five setup checks pass on the real copy.
+  - Open: "a move changes no block" found 7 of 67,840 blocks different there. It finds 0 on the stand-in. Waystation's code sets no world block on a move (only display entities), and the test itself cuts a platform into real terrain just before, which lets water, leaves and loose blocks settle. That's the likely cause, not a proven one. The check now names the blocks that differ, and reports how much the chunk changes by itself in the 5 seconds before the move, so the next run on a copy settles it.
   - The copy's other failures come from that server's own settings, not from Waystation or the checks. Its tribute chests and gate prices aren't set up the way the suite's are, and the test-only hook plugin isn't on it. The crash test needs the chest, so it fails with it.
 
 ## 2026-11-11: other versions (K349)

test/acceptance.mjs

@@ -52,6 +52,16 @@ function hashArea(b, cx, cz, y0, y1, chunks = 0) {
 // Grass and dirt flip by themselves between boots, with no plugin installed: measured, so ignored here.
 const NATURAL = new Set([8, 9, 10])
 const hashDiff = (a, b) => { let d = 0; for (let i = 0; i < a.length; i++) if (a[i] !== b[i] && a[i] !== -1 && b[i] !== -1 && !(NATURAL.has(a[i]) && NATURAL.has(b[i]))) d++; return d }
+/** Which blocks differ between two hashArea snapshots of one chunk column, as "x y z: from -> to", for a failure's detail. */
+function hashDiffDetail(b, a1, a2, cx, cz, y0, y1, max = 8) {
+  const out = []; let i = 0
+  for (let x = cx << 4; x < (cx + 1) << 4; x++) for (let z = cz << 4; z < (cz + 1) << 4; z++) for (let y = y0; y <= y1; y++, i++) {
+    const p = a1[i], q = a2[i]
+    if (p === q || p === -1 || q === -1 || (NATURAL.has(p) && NATURAL.has(q))) continue
+    if (out.length < max) out.push(`${x} ${y} ${z}: ${b.registry.blocksByStateId[p]?.name ?? p} -> ${b.registry.blocksByStateId[q]?.name ?? q}`)
+  }
+  return out.join('; ')
+}
 const reliable = async (cmd, ms = 500) => s.ask(cmd, ms)
 
 // ---------- Phase 0: baseline with no plugin ----------
@@ -388,7 +398,12 @@ console.log('\n# Paying in hearts')
 await setMove({ rest: 300 })
 await heal(a); await bedAt(a, goodAt)
 await s.ask(`execute in meadow run tp carl ${goodAt.x} ${goodAt.y} ${goodAt.z}`, 2000)
+// Real terrain changes by itself (water, leaves, falling blocks), more so right after flat() cut into it. Two looks
+// before the move show how much, so a difference after the move can be told from the world's own.
+const hEarlier = hashArea(carl2, good[0], good[1], -64, 200)
+await sleep(5000)
 const h1 = hashArea(carl2, good[0], good[1], -64, 200)
+if (hashDiff(hEarlier, h1)) console.log(`  the chunk changes by itself: ${hashDiff(hEarlier, h1)} blocks in 5 s before the move (${hashDiffDetail(carl2, hEarlier, h1, good[0], good[1], -64, 200)})`)
 win = await clickChest(a); clearChat(a); clearChat(carl2)
 const hpBefore = await realHealth(a)
 check('with health to spare, the chest offers hearts', !!win && menuItems(win).length === 1 && menuItems(win)[0].name === 'redstone')
@@ -398,7 +413,7 @@ const hpAfter = await realHealth(a)
 check('exactly 6 hearts taken', Math.abs(hpBefore - 12 - hpAfter) < 0.01, `${hpBefore} -> ${hpAfter}`)
 await s.ask(`execute in meadow run tp carl ${goodAt.x} ${goodAt.y} ${goodAt.z}`, 2000)
 const h2 = hashArea(carl2, good[0], good[1], -64, 200)
-check('a move changes no block', hashDiff(h1, h2) === 0, `${hashDiff(h1, h2)} differ of ${h1.length}`)
+check('a move changes no block', hashDiff(h1, h2) === 0, `${hashDiff(h1, h2)} differ of ${h1.length}: ${hashDiffDetail(carl2, h1, h2, good[0], good[1], -64, 200)}`)
 check('others in the world are told it moved, not where', carl2.chat_log.some(m => /has moved. Nobody is saying where/.test(m)))
 const movedA = await rdNow()
 check('it moved to the bed\'s chunk', movedA.x >> 4 === good[0] && movedA.z >> 4 === good[1])