Editor: pin outlet, add zone labels + volume to the diagram

Three user-facing fixes:

1. Outlet was getting pushed below the tank floor by the top-down
   nudge because its ideal y is already near the bottom. Now
   outflowLevel is PINNED at its proportional y (like basinHeight
   is pinned at the rim) and a second bottom-up pass pushes
   non-pinned items upward from the outlet anchor. Result: outlet
   stays near the tank floor, dryRunLevel sits right above it, the
   rest of the stack stays readable. Two anchors, two passes.

2. Zone labels mirrored from the wiki basin-model drawio:
   - "Spare volume before spilling"  (overflowLevel ↔ maxLevel)
   - "Sewage + tank buffer"          (maxLevel      ↔ startLevel)
   - "Tank buffer"                    (startLevel    ↔ minLevel)
   - "Tank buffer"                    (minLevel      ↔ dryRunLevel)
   - "Dead volume"                    (outflowLevel  ↔ floor)
   Each sits at the midpoint of its pair of nudged thresholds and
   hides when the gap between them is too small to read (< 14 px).

3. basinVolume moved into the SVG as a pinned input above the tank
   rim (alongside basinHeight), replacing the separate form row.
   One editor, one diagram — the total volume belongs with the
   geometry.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pumpingStation.html

@@ -220,11 +220,12 @@
         const dryLvl  = (refLow != null && dryPct != null) ? refLow * (1 + dryPct / 100) : null;
         const ovfLvl  = (ovf    != null && ovfPct != null) ? ovf    * (ovfPct / 100)     : null;
 
-        // Build the right-column items. basinHeight is pinned at the
-        // tank rim; others are sorted by their proportional y and then
-        // pushed apart so every dashed line gets a minimum vertical
-        // gap for readability. The diagram is a schematic ordered
-        // list, not a strictly to-scale rendering.
+        // Right-column stack. TWO anchors: basinHeight pinned at the
+        // tank rim (top) and outflowLevel pinned at its proportional y
+        // (bottom). Everything between is nudged to maintain a minimum
+        // vertical gap via two passes — top-down from the rim, then
+        // bottom-up from the outlet — so the dashed lines keep their
+        // value-order and outlet stays near the floor where it belongs.
         const items = [
           { id: 'basinHeight',   yIdeal: DIAG.topY,                                pinned: true },
           { id: 'overflowLevel', yIdeal: yForLevel(fNum('overflowLevel'), basinH) },
@@ -232,19 +233,52 @@
           { id: 'startLevel',    yIdeal: yForLevel(fNum('startLevel'),    basinH) },
           { id: 'minLevel',      yIdeal: yForLevel(fNum('minLevel'),      basinH) },
           { id: 'dryRunLevel',   yIdeal: yForLevel(dryLvl,                basinH) },
-          { id: 'outflowLevel',  yIdeal: yForLevel(fNum('outflowLevel'),  basinH) },
+          { id: 'outflowLevel',  yIdeal: yForLevel(fNum('outflowLevel'),  basinH), pinned: true },
         ].filter(it => it.yIdeal != null);
 
         const GAP = 36;
         items.sort((a, b) => a.yIdeal - b.yIdeal);
-        let prev = -Infinity;
-        for (const it of items) {
-          if (it.pinned) { it.y = it.yIdeal; prev = it.y; continue; }
-          it.y = Math.max(it.yIdeal, prev + GAP);
-          prev = it.y;
+        for (const it of items) it.y = it.yIdeal;
+        // Pass 1: top-down — push DOWN to maintain GAP; pinned items don't move
+        for (let i = 1; i < items.length; i++) {
+          if (items[i].pinned) continue;
+          items[i].y = Math.max(items[i].y, items[i - 1].y + GAP);
+        }
+        // Pass 2: bottom-up — push UP so outflow's pin propagates up the stack
+        for (let i = items.length - 2; i >= 0; i--) {
+          if (items[i].pinned) continue;
+          items[i].y = Math.min(items[i].y, items[i + 1].y - GAP);
         }
         for (const it of items) placeItem(it.id, it.y);
 
+        // Zone labels between adjacent thresholds (italic, centered).
+        // Hidden if either bracketing threshold is missing, or the gap
+        // is too small to read (< 14 px).
+        const placeZone = (zoneId, topId, botId) => {
+          const el = document.getElementById(`ps-zone-${zoneId}`);
+          if (!el) return;
+          const top = items.find(it => it.id === topId);
+          const bot = items.find(it => it.id === botId);
+          if (!top || !bot || (bot.y - top.y) < 14) {
+            el.setAttribute('visibility', 'hidden'); return;
+          }
+          el.setAttribute('y', (top.y + bot.y) / 2 + 3);
+          el.setAttribute('visibility', 'visible');
+        };
+        placeZone('spare',   'overflowLevel', 'maxLevel');
+        placeZone('sewage',  'maxLevel',      'startLevel');
+        placeZone('buffer1', 'startLevel',    'minLevel');
+        placeZone('buffer2', 'minLevel',      'dryRunLevel');
+        // "Dead volume" sits inside the blue band between outflowLevel and the floor
+        const outflowPinned = items.find(it => it.id === 'outflowLevel');
+        const deadLbl = document.getElementById('ps-zone-dead');
+        if (deadLbl && outflowPinned && (DIAG.botY - outflowPinned.y) > 14) {
+          deadLbl.setAttribute('y', (outflowPinned.y + DIAG.botY) / 2 + 3);
+          deadLbl.setAttribute('visibility', 'visible');
+        } else if (deadLbl) {
+          deadLbl.setAttribute('visibility', 'hidden');
+        }
+
         // Inlet arrow — sole item on the left, no stacking concerns
         const inflowY = yForLevel(fNum('inflowLevel'), basinH);
         if (inflowY != null) {
@@ -385,6 +419,20 @@
     <rect x="200" y="40" width="120" height="340" fill="#F0F8FF" stroke="#333" stroke-width="1.5" />
     <!-- Dead-volume band (y + height updated dynamically below outflowLevel) -->
     <rect id="ps-deadvol" x="201" width="118" fill="#AACCE0" />
+    <!-- basinVolume — pinned above the rim -->
+    <text id="ps-label-basinVolume" x="330" y="19" fill="#333" font-weight="600">basin volume</text>
+    <foreignObject id="ps-fo-basinVolume" x="425" y="4" width="70" height="22">
+      <input xmlns="http://www.w3.org/1999/xhtml" type="number" id="node-input-basinVolume" min="0" step="0.1" />
+    </foreignObject>
+    <text id="ps-unit-basinVolume" x="500" y="19" fill="#555">m³</text>
+
+    <!-- Zone labels (mid-tank italic, positioned dynamically at midpoint between adjacent thresholds) -->
+    <text id="ps-zone-spare"   x="260" text-anchor="middle" fill="#B78200" font-size="10" font-style="italic" visibility="hidden">Spare volume before spilling</text>
+    <text id="ps-zone-sewage"  x="260" text-anchor="middle" fill="#1F4E79" font-size="10" font-style="italic" visibility="hidden">Sewage + tank buffer</text>
+    <text id="ps-zone-buffer1" x="260" text-anchor="middle" fill="#1F4E79" font-size="10" font-style="italic" visibility="hidden">Tank buffer</text>
+    <text id="ps-zone-buffer2" x="260" text-anchor="middle" fill="#1F4E79" font-size="10" font-style="italic" visibility="hidden">Tank buffer</text>
+    <text id="ps-zone-dead"    x="260" text-anchor="middle" fill="#444" font-size="10" font-style="italic" visibility="hidden">Dead volume</text>
+
 
     <!-- basinHeight — always at tank rim (y=40 in viewBox coords) -->
     <line id="ps-line-basinHeight" x1="195" y1="40" x2="325" y2="40" stroke="#333" stroke-width="1.5" />
@@ -465,11 +513,6 @@
     <text id="ps-warning" x="260" y="410" text-anchor="middle" fill="#C0392B" font-size="10" font-style="italic" visibility="hidden"></text>
   </svg>
 
-  <div class="form-row">
-    <label for="node-input-basinVolume"><i class="fa fa-cube"></i> Basin Volume (m³)</label>
-    <input type="number" id="node-input-basinVolume" min="0" step="0.1" />
-  </div>
-
   <hr>
 
   <h4>Control Strategy</h4>