No per-frame allocations in the 'doesn't connect' marks (t87)

docs/PROJECT_MAP.md

@@ -288,10 +288,10 @@ Pipes, pumps and outlets: each joined line holds one liquid as a count, not as g
 Per-tick machine work: steam engines, fans, belts, filters, screw conveyors (machinesTick).
 - functions: engineIntake, fanBlow, machinesTick
 
-### src/sim/joins.js (125 lines)
+### src/sim/joins.js (134 lines)
 Travel-directed transport ends. Precomputed probes; world/plan queries allocate nothing. End indices stay geometric: left/right, or up/down for vertical screws.
 - functions: pieceEnds, joinCandidate, endJoin, pieceJoins, endAt, joinIsDrop, joinSnap, nearMiss
-- variables: JOIN_ENDS, NO_PIECE
+- variables: JOIN_ENDS, NO_PIECE, NEAR_MISS_VIEW
 
 ### src/sim/conveyors.js (213 lines)
 How belts, filters and screw conveyors move what is on or in them. What rests on a belt or filter rides along: the whole stack standing on the carrying surface steps one cell toward d together (belts run front of the line first, so the way ahead is clear). If a powder grain is blocked, the load above it stands still and the belt slips underneath. A filter's own material drops through it instead, unless it is already full.

docs/agent-log.md

@@ -4,6 +4,17 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-29: t87 reuse the near-miss view (Codex)
+
+- Reused one scratch view, its entry array and get/has methods in src/sim/joins.js;
+  replaced the two-row temporary array with a numeric loop. Connection rules unchanged.
+- Files: src/sim/joins.js, docs/PROJECT_MAP.md, tasks/t87* and this log. Map regenerated.
+- All 41 headless suites pass; every suite's before/after output matches excluding timings
+  (/tmp/t87-determinism.diff empty). Pixel test/play.py passes with no console errors.
+  Frozen shots/t87-{before,after}.png match exactly; inspected the after image and red marks.
+- test/t_smooth.py fails elbow/collar and ghost-preview image checks on both original and
+  refactored code, with no page errors; left those existing failures outside t87's scope.
+
 ## 2026-10-29: t83 remove old-save conversions (Codex)
 
 - Removed only spring, solid-pipe, single-material-filter and foreground-tree conversions

src/sim/joins.js

@@ -108,16 +108,25 @@ function joinSnap(code, v, cells) {
 // A drop join counts as connected. The moved block is tried through a small override view of
 // `planned`, so ghost maps are never copied.
 const NO_PIECE = [0, 0];
+// Synchronous join queries never retain this scratch view or call nearMiss recursively.
+const NEAR_MISS_VIEW = {
+  source: -1, moved: -1, planned: null, entry: [0, 0],
+  get(k) {
+    return k === this.source ? NO_PIECE : k === this.moved ? this.entry : this.planned ? this.planned.get(k) : undefined;
+  },
+  has(k) { return this.get(k) !== undefined; }
+};
 function nearMiss(bx, by, end, planned = null) {
   const b = by * BW + bx, p = planned && planned.get(b), code = p ? p[0] : blockP[b], v = p ? p[1] : blockV[b];
   const own = pieceEnds(code, v);
   if (!own[end] || endJoin(bx, by, end, planned) >= 0) return 0;
-  const entry = [code, v];
-  for (const dy of [-1, 1]) {
+  const view = NEAR_MISS_VIEW;
+  view.source = b; view.planned = planned;
+  view.entry[0] = code; view.entry[1] = v;
+  for (let dy = -1; dy <= 1; dy += 2) {
     const y = by + dy, nb = y * BW + bx;
     if (y < 0 || y >= BH || blockP[nb] || (planned && planned.get(nb))) continue;
-    const view = { get: k => k === b ? NO_PIECE : k === nb ? entry : planned ? planned.get(k) : undefined };
-    view.has = k => view.get(k) !== undefined;
+    view.moved = nb;
     const j = endJoin(bx, y, end, view);
     if (j >= 0 && !joinIsDrop(bx, y, end, j, view) && (own[end].diagonal || endAt(j >> 1, j & 1, view).diagonal)) return dy;
   }