Merge fix-empty-slot-drop: reorder drop lands in empty slots and beyond the extent (trailing row)

src/bank_panel.cpp

@@ -1411,7 +1411,13 @@ void drawCardDropTarget(LICE_IBitmap* bmp, const RECT& region, bool isBanks, Reg
 
     const RECT grid = regionGridRect(region, isBanks);
     const RegionDisplay disp = regionDisplay(region, isBanks, reg);
-    for (const SlotCellRect& r : disp.slotRects) {
+    // Use the drop rects (includes the trailing row past maxSlot) so a beyond-extent
+    // target slot gets a visible highlight cue, not silence.
+    const int gridW = grid.right - grid.left;
+    const int maxSlot = disp.bank ? disp.bank->slots.maxSlot() : -1;
+    std::vector<SlotCellRect> dropRects = computeSlotRectsForDrop(maxSlot, gridW, kGrid);
+    for (SlotCellRect& r : dropRects) { r.x += grid.left; r.y += grid.top; }
+    for (const SlotCellRect& r : dropRects) {
         if (r.slot != g_panel.dragTargetSlot) continue;
         if (r.y >= grid.bottom) return;  // below the viewport (no scroll)
         const LICE_pixel hot = toLice(roleColor(Role::AccentHot));
@@ -2738,11 +2744,21 @@ void classifyCardDrag(int x, int y) {
     if (!destBank.empty() && destBank == g_panel.dragSourceBankId) {
         // Same-bank grid: a reorder/replace target. Resolve the slot the pointer sits over
         // in the SOURCE bank's own region display + whether it is occupied.
+        // Uses computeSlotRectsForDrop (one trailing row past maxSlot) so a drop beyond
+        // the last occupied card resolves to a valid trailing slot, not a -1 miss.
         mods.region = DropRegion::SameBankGrid;
         const bool isBanks = g_panel.dragSourceRegion == Region::Banks;
         const RECT region = isBanks ? banksRegionRect(w, h) : poolRegionRect(w, h);
         const RegionDisplay disp = regionDisplay(region, isBanks, g_panel.dragSourceRegion);
-        const int slot = hitTestSlot(x, y, disp.slotRects);
+        const RECT grid = regionGridRect(region, isBanks);
+        const int gridW = grid.right - grid.left;
+        const std::vector<SlotCellRect> dropRects =
+            computeSlotRectsForDrop(disp.bank ? disp.bank->slots.maxSlot() : -1,
+                                    gridW, kGrid);
+        // Translate the drop rects to client space (matching regionDisplay's translation).
+        std::vector<SlotCellRect> dropRectsClient = dropRects;
+        for (SlotCellRect& r : dropRectsClient) { r.x += grid.left; r.y += grid.top; }
+        const int slot = hitTestSlot(x, y, dropRectsClient);
         mods.targetSlot   = slot;
         mods.slotOccupied = slot >= 0 && !disp.idAtSlot(slot).empty();
         g_panel.dragTargetSlot = slot;

src/card_drag.cpp

@@ -73,6 +73,16 @@ std::vector<SlotCellRect> computeSlotRects(int maxSlot, int panelWidth,
     return rects;
 }
 
+std::vector<SlotCellRect> computeSlotRectsForDrop(int maxSlot, int panelWidth,
+                                                   const GridSpec& spec) {
+    const int cols = columnsForWidth(panelWidth, spec);
+    // One trailing row of slots past the last occupied slot — the drop-target extension.
+    // When maxSlot < 0 (empty bank) the trailing row begins at slot 0.
+    const int firstTrailing = maxSlot + 1;
+    const int newMax = firstTrailing + cols - 1;  // fills one full trailing row
+    return computeSlotRects(newMax, panelWidth, spec);
+}
+
 int hitTestSlot(int px, int py, const std::vector<SlotCellRect>& rects) {
     for (const SlotCellRect& r : rects) {
         // Half-open bounds so adjacent rects never both claim a pixel.

src/card_drag.h

@@ -128,6 +128,16 @@ struct SlotCellRect {
 std::vector<SlotCellRect> computeSlotRects(int maxSlot, int panelWidth,
                                            const GridSpec& spec);
 
+// Like computeSlotRects but extends one full trailing row of slots beyond maxSlot so a
+// drop pointer past the last occupied card still resolves to a valid target slot. The
+// trailing slots (maxSlot+1 .. maxSlot+cols) are empty — a drop on any of them calls
+// reorderSample with that slot index, which places the card there directly (no shift,
+// because the slot is empty). Used ONLY for drop hit-testing; the draw path uses
+// computeSlotRects (no trailing ghost row in the visual).
+// When maxSlot < 0 the trailing row starts at slot 0 (same as a fresh bank with no cards).
+std::vector<SlotCellRect> computeSlotRectsForDrop(int maxSlot, int panelWidth,
+                                                   const GridSpec& spec);
+
 // Hit-tests a point against slot rects (half-open bounds, matching hitTestCell). Returns
 // the SLOT index (rect.slot) of the first rect containing the point, or -1 on a miss (gap,
 // margin, below the last row). NOTE the return is the slot index, NOT the vector index —

tests/test_bank_book.cpp

@@ -995,6 +995,26 @@ static void testReorderSampleSameSlotIsNoOp() {
     CHECK(book.serialize() == jsonBefore);
 }
 
+// Reorder to a slot BEYOND the current maxSlot — the trailing-drop case. The model
+// places the card at the exact target slot (no shift, slot is empty), leaving the card's
+// old slot empty. This is the pure-layer gate for the DAW beyond-extent drop repro.
+static void testReorderSampleBeyondMaxSlot() {
+    BankBook book;
+    CHECK(book.pool().index.add(sampleWith("a")) == AddResult::Added);
+    CHECK(book.pool().index.add(sampleWith("b")) == AddResult::Added);
+    book.reconcileSlots();  // a@0, b@1 -> maxSlot = 1
+    CHECK(book.pool().slots.maxSlot() == 1);
+
+    // Drag "b" to slot 5 (well beyond maxSlot=1). Should succeed: slot 5 is empty,
+    // no insert-shift needed, b just takes slot 5.
+    CHECK(book.reorderSample("id-b", kPoolBankId, 5));
+    CHECK(book.pool().slots.slotOf("id-b") == 5);
+    CHECK(book.pool().slots.slotOf("id-a") == 0);  // a untouched
+    // maxSlot is now 5; slot 1 is empty (gap).
+    CHECK(book.pool().slots.maxSlot() == 5);
+    CHECK(book.pool().slots.idAt(1).empty());  // b's old slot is now a gap
+}
+
 // --- BankBook L7: Alt-replace mutator ----------------------------------------
 
 static void testReplaceSampleTakesSlotAndRemovesOccupant() {
@@ -1113,6 +1133,7 @@ int main() {
     testOrderedSampleIdsReconcilesLazily();
     testReorderSampleRejectsUnknown();
     testReorderSampleSameSlotIsNoOp();
+    testReorderSampleBeyondMaxSlot();
     testReplaceSampleTakesSlotAndRemovesOccupant();
     testReplaceSampleNonDestructiveFileStays();
     testReplaceSampleRejectionsNoMutation();

tests/test_card_drag.cpp

@@ -176,6 +176,66 @@ static void testHitTestSlotMiss() {
     CHECK(hitTestSlot(115, 15, r) == -1);   // inter-cell gap between slot 0 (ends x=110) and slot 1 (starts x=120)
 }
 
+// --- computeSlotRectsForDrop — beyond-extent trailing row ---------------------
+// Spec: kSpec, 340px wide, 3 cols. maxSlot=2 -> render rects for 0..2.
+// Drop rects extend one trailing row: slots 0..2 (existing) + 3..5 (trailing).
+
+static void testDropRectsExtendOneTrailingRow() {
+    // computeSlotRects(2, ...) gives 3 rects (0..2). Drop rects should give 6 (0..5).
+    const std::vector<SlotCellRect> render = computeSlotRects(2, 340, kSpec);
+    const std::vector<SlotCellRect> drop   = computeSlotRectsForDrop(2, 340, kSpec);
+    CHECK(render.size() == 3);
+    CHECK(drop.size() == 6);
+    // First three match (existing slots preserved).
+    for (std::size_t i = 0; i < 3; ++i) {
+        CHECK(drop[i].slot == render[i].slot);
+        CHECK(drop[i].x == render[i].x && drop[i].y == render[i].y);
+    }
+    // Slot 3 starts the trailing row: row 1, col 0. y = gap + 1*(40+10) = 60.
+    CHECK(drop[3].slot == 3);
+    CHECK(drop[3].x == 10 && drop[3].y == 60);
+}
+
+static void testDropRectsEmptyBankHasTrailingRow() {
+    // maxSlot=-1 (no occupied slots): drop rects start at slot 0 (one trailing row).
+    const std::vector<SlotCellRect> drop = computeSlotRectsForDrop(-1, 340, kSpec);
+    CHECK(drop.size() == 3);   // 3 cols = one trailing row
+    CHECK(drop[0].slot == 0);
+    CHECK(drop[1].slot == 1);
+    CHECK(drop[2].slot == 2);
+}
+
+static void testBeyondExtentResolvesToTrailingSlot() {
+    // A pointer placed in the trailing row (below the last occupied card row) resolves
+    // to a valid slot via the drop rects, but returns -1 via the render rects — this is
+    // the exact gap the fix closes.
+    const std::vector<SlotCellRect> render = computeSlotRects(2, 340, kSpec);
+    const std::vector<SlotCellRect> drop   = computeSlotRectsForDrop(2, 340, kSpec);
+    // Slot 3 rect: row 1, col 0. A point at (15, 65) is inside it (y=60..99, x=10..109).
+    CHECK(hitTestSlot(15, 65, render) == -1);   // render rects: miss — bug confirmed
+    CHECK(hitTestSlot(15, 65, drop)   ==  3);   // drop rects: hits trailing slot 3 — fix
+}
+
+static void testGapPixelStillMissesInDropRects() {
+    // Inter-cell pixel gaps should still be misses even in the drop rects.
+    const std::vector<SlotCellRect> drop = computeSlotRectsForDrop(4, 340, kSpec);
+    // x=115 is in the gap between slot 0 (x=10..109) and slot 1 (x=120..219).
+    CHECK(hitTestSlot(115, 15, drop) == -1);
+    // Top-left margin (before any cell) is still a miss.
+    CHECK(hitTestSlot(0, 0, drop) == -1);
+}
+
+static void testEmptySlotWithinExtentHitsViaRenderRects() {
+    // Slot 1 is empty (gap), slot 0 and slot 2 are "occupied" (just position — the
+    // render rects cover ALL slots 0..maxSlot including empties). A pointer at slot 1's
+    // cell center returns slot 1 from both render AND drop rects.
+    const std::vector<SlotCellRect> render = computeSlotRects(2, 340, kSpec);
+    const std::vector<SlotCellRect> drop   = computeSlotRectsForDrop(2, 340, kSpec);
+    // Slot 1: x = gap + 1*(100+10) = 120, y = gap = 10. Center: (170, 30).
+    CHECK(hitTestSlot(170, 30, render) == 1);  // works via render rects (existing)
+    CHECK(hitTestSlot(170, 30, drop)   == 1);  // also works via drop rects
+}
+
 int main() {
     testNoDragIsNone();
     testEmptyPayloadIsNone();
@@ -194,6 +254,11 @@ int main() {
     testSlotRectsDenseMatchesGrid();
     testHitTestSlotReturnsSlotIndex();
     testHitTestSlotMiss();
+    testDropRectsExtendOneTrailingRow();
+    testDropRectsEmptyBankHasTrailingRow();
+    testBeyondExtentResolvesToTrailingSlot();
+    testGapPixelStillMissesInDropRects();
+    testEmptySlotWithinExtentHitsViaRenderRects();
 
     if (g_fail == 0) std::printf("card_drag: all tests passed\n");
     else std::printf("card_drag: %d CHECK(s) FAILED\n", g_fail);