list what a belt is carrying, and clear it by name

The belt card's only content was a button reading "Clear stuck items", which
assumed a state the items need not be in. It now reads "Clear items", and above
it the card lists what the selected tiles hold -- one item chip per type, the
same chip the buffer sections and the HQ's block stock draw -- so a line's
contents can be read before they are removed, and can be read at all: items on a
moving belt are too small and too transient to count by eye, and items inside a
tunnel are drawn nowhere.

BeltSystem gains countItems(tiles), a query of the same kind as
forEachVisualItem: a method rather than exposed tile containers, so the per-tile
representation stays swappable. It walks the same five containers as clearTiles,
in the same order, so the list and the button cannot drift apart.

The tunnel's two ends are now told apart. Items in transit are counted on the
exit they are travelling toward, and a clear removes exactly what the panel
listed for the tile it acts on: the exit discards them, the entry leaves them
travelling. BeltSystemTest's tunnel case splits in two accordingly.

Splitters now aggregate with belts and tunnel ends. Their output filters are
per-object configuration, which an aggregate simply does not show -- a splitter
selected alone still gets them. Both cards share one BeltItemList widget, and
both derive their tiles from collectBeltTiles, so nothing is stated twice.

The mixed count summary loses the clear action it carried: a button acting on
part of a selection is worse than no button, and the tiles can be selected by
themselves.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ne3mejABZoLWKLh8fgpM3x

src/lib/sim/BeltSystem.cpp

@@ -408,14 +408,11 @@ void BeltSystem::clearTiles(const std::vector<QPoint>& tiles)
             m_tunnelEntries.find(key(tile));
         if (teIt != m_tunnelEntries.end())
         {
+            // Only what sits on the entry itself: the items already inside the tunnel
+            // are counted on its exit (REQ-UI-BELT-ITEMS) and are cleared from there, so
+            // a clear never removes more than the panel showed for the tile it acted on
+            // (REQ-BLD-TUNNEL-TRANSIT). Emptying a tunnel is done from its exit.
             teIt->second.itemSlots.clear();
-            for (TunnelLink& link : m_tunnelLinks)
-            {
-                if (link.entryTile == tile)
-                {
-                    link.items.clear();
-                }
-            }
         }
 
         const std::map<std::pair<int, int>, TunnelExitTile>::iterator txIt =
@@ -434,6 +431,83 @@ void BeltSystem::clearTiles(const std::vector<QPoint>& tiles)
     }
 }
 
+std::map<ItemType, int> BeltSystem::countItems(const std::vector<QPoint>& tiles) const
+{
+    std::map<ItemType, int> counts;
+
+    // The same five containers clearTiles walks, in the same order, so that what the
+    // panel lists and what the button removes cannot drift apart (REQ-UI-BELT-ITEMS,
+    // REQ-UI-BELT-CLEAR).
+    for (const QPoint& tile : tiles)
+    {
+        const std::map<std::pair<int, int>, BeltTile>::const_iterator bIt =
+            m_belts.find(key(tile));
+        if (bIt != m_belts.end())
+        {
+            for (const BeltItemSlot& slot : bIt->second.itemSlots)
+            {
+                counts[slot.item.type]++;
+            }
+        }
+
+        const std::map<std::pair<int, int>, SplitterTile>::const_iterator sIt =
+            m_splitters.find(key(tile));
+        if (sIt != m_splitters.end())
+        {
+            const SplitterTile& splitter = sIt->second;
+            for (const BeltItemSlot& slot : splitter.back)
+            {
+                counts[slot.item.type]++;
+            }
+            if (splitter.frontA)
+            {
+                counts[splitter.frontA->item.type]++;
+            }
+            if (splitter.frontB)
+            {
+                counts[splitter.frontB->item.type]++;
+            }
+        }
+
+        const std::map<std::pair<int, int>, TunnelEntryTile>::const_iterator teIt =
+            m_tunnelEntries.find(key(tile));
+        if (teIt != m_tunnelEntries.end())
+        {
+            for (const BeltItemSlot& slot : teIt->second.itemSlots)
+            {
+                counts[slot.item.type]++;
+            }
+        }
+
+        const std::map<std::pair<int, int>, TunnelExitTile>::const_iterator txIt =
+            m_tunnelExits.find(key(tile));
+        if (txIt != m_tunnelExits.end())
+        {
+            for (const BeltItemSlot& slot : txIt->second.itemSlots)
+            {
+                counts[slot.item.type]++;
+            }
+
+            // The tunnel's invisible cargo, counted on the end it is travelling toward.
+            // This is the only place the player can see it at all, the tunnel drawing
+            // nothing of what is inside it (REQ-BLD-TUNNEL-TRANSIT).
+            for (const TunnelLink& link : m_tunnelLinks)
+            {
+                if (link.exitTile != tile)
+                {
+                    continue;
+                }
+                for (const TunnelTransitItem& transit : link.items)
+                {
+                    counts[transit.item.type]++;
+                }
+            }
+        }
+    }
+
+    return counts;
+}
+
 // ---------------------------------------------------------------------------
 // Tick
 // ---------------------------------------------------------------------------