Re-derive the floor-size test fixtures from the constants and move the ceiling to sample_bands.h

tests/test_sample_bands.cpp

@@ -5,8 +5,10 @@
 // three-band vertical inventory (chrome over waveform over decks, no overlap, no
 // inversion) asserted as pure geometry with no paint call; the waveform band's two-lane
 // floor and the bands-clip-rather-than-squeeze rule on a short window; the deck band's
-// bottom anchor and its exact requested height; and the lane split (mono = one full-band
-// lane, stereo = two lanes with the seam gap between them).
+// bottom anchor and its exact requested height; the same stack/anchor/degrade properties
+// re-anchored AT the allocator's own kEditorMinWidth/kEditorMinHeight floor rather than only
+// below it; and the lane split (mono = one full-band lane, stereo = two lanes with the seam
+// gap between them).
 
 #include "../src/core/instrument/ui/sample_bands.h"
 
@@ -104,6 +106,56 @@ static void testDegenerateWindowYieldsNoInvertedRects() {
     CHECK(tiny.decks.right() >= tiny.decks.x);
 }
 
+// --- the allocator at its own floor (kEditorMinWidth x kEditorMinHeight) -------
+
+// The allocator's own client-area floor is a fact IT owns (kEditorMinWidth/kEditorMinHeight
+// above); the fixtures above validate the general shape entirely below that floor (840x620,
+// 840x160). These anchor the same properties AT the floor itself, so a floor move that broke
+// the stack there would have nothing else in this file to catch it.
+
+static void testBandsStackWithoutOverlapAtTheEditorFloor() {
+    const SampleBands b = computeSampleBands(kEditorMinWidth, kEditorMinHeight, 120);
+    CHECK(b.chrome.y == 0);
+    CHECK(b.chrome.width == kEditorMinWidth);
+    CHECK(b.chrome.height == kTitleHeight + kChromeRowHeight);
+    CHECK(b.waveform.y >= b.chrome.bottom());
+    CHECK(b.decks.y >= b.waveform.bottom());
+    CHECK(b.waveform.x == kPad && b.waveform.right() == kEditorMinWidth - kPad);
+    CHECK(b.decks.x == kPad && b.decks.right() == kEditorMinWidth - kPad);
+}
+
+static void testDeckBandIsBottomAnchoredAtTheEditorFloor() {
+    constexpr int deckH = 120;
+    const SampleBands b = computeSampleBands(kEditorMinWidth, kEditorMinHeight, deckH);
+    CHECK(b.decks.height == deckH);
+    CHECK(b.decks.bottom() == kEditorMinHeight - kPad);
+}
+
+// At a representative two-row deck height (216px — the ceiling test_deck_groups.cpp bounds
+// the wrapped deck to), the waveform gets exactly what the floor's own height leaves it: an
+// equality, not a bound, so a floor-height change that quietly ate into the waveform's slack
+// would fail here rather than only widen/narrow a `>=`.
+static void testWaveformGetsExactlyTheFloorsRemainingHeightAtATwoRowDeck() {
+    constexpr int twoRowDeckH = 216;
+    const SampleBands b = computeSampleBands(kEditorMinWidth, kEditorMinHeight, twoRowDeckH);
+    const int expected = kEditorMinHeight - kPad - twoRowDeckH - 2 * kBandGap -
+                          (kTitleHeight + kChromeRowHeight);
+    CHECK(b.waveform.height == expected);
+    CHECK(b.waveform.height == 358);
+    CHECK(b.waveform.height >= kWaveformMinHeight);
+}
+
+// The floor is not immune to the degrade path: a deck grown too tall for the floor's OWN
+// height still hits the floor-wins rule instead of squeezing the waveform below its usable
+// minimum — the sub-floor fixtures above cover the general rule; this is the same rule
+// exercised at the allocator's own minimum width.
+static void testAnOversizedDeckAtTheFloorStillDegradesGracefully() {
+    const SampleBands b = computeSampleBands(kEditorMinWidth, kEditorMinHeight, 500);
+    CHECK(b.waveform.height == kWaveformMinHeight);
+    CHECK(b.decks.y >= b.waveform.bottom());
+    CHECK(b.decks.bottom() > kEditorMinHeight);  // clipped below the floor's own window
+}
+
 // --- the waveform band's lanes ------------------------------------------------
 
 static void testMonoUsesOneFullBandLane() {
@@ -149,6 +201,10 @@ int main() {
     testWaveformNeverShrinksBelowTheTwoLaneFloor();
     testTwoLaneFloorHoldsTwoUsableLanes();
     testDegenerateWindowYieldsNoInvertedRects();
+    testBandsStackWithoutOverlapAtTheEditorFloor();
+    testDeckBandIsBottomAnchoredAtTheEditorFloor();
+    testWaveformGetsExactlyTheFloorsRemainingHeightAtATwoRowDeck();
+    testAnOversizedDeckAtTheFloorStillDegradesGracefully();
     testMonoUsesOneFullBandLane();
     testStereoSplitsIntoTwoLanesWithTheSeamGap();
     testStereoOddRemainderGoesToTheUpperLane();