Clear stale hover on capture-loss and Alt-delete; derive gutter test via chromeRects

tests/test_keyboard_strip.cpp

@@ -16,9 +16,11 @@
 // unverified by this suite (see src/core/instrument/CLAUDE.md).
 
 #include "../src/core/instrument/ui/keyboard_strip.h"
-#include "../src/core/instrument/ui/sample_bands.h"  // kPad, to derive the strip width the
-                                                       // shipped default window (840x620,
+#include "../src/core/instrument/ui/sample_bands.h"   // computeSampleBands, to derive the CHROME
+                                                       // band the shipped default window (840x620,
                                                        // editor_session.cpp) hands the strip
+#include "../src/core/instrument/ui/sample_chrome.h"  // chromeRects, to derive rootStrip's width
+                                                       // the same way the shell does
 
 #include <cstdio>
 #include <string>
@@ -288,8 +290,15 @@ static void testNoteNamesFollowTheC4Convention() {
 // one pixel of resize (840->841) collapses both gutters to zero and grows every white key
 // from 10px to 11px.
 static void testGutterAtTheShippedDefaultWindowSize() {
-    constexpr int kShippedDefaultWindowW = 840;  // editor_session.cpp's ViewRect default
-    const int stripW = kShippedDefaultWindowW - 2 * kPad;  // chromeRects insets rootStrip by kPad
+    constexpr int kShippedDefaultWindowW = 840;   // editor_session.cpp's ViewRect default
+    constexpr int kShippedDefaultWindowH = 620;   // editor_session.cpp's ViewRect default
+    // Derive rootStrip's width the same way the shell does, through the real allocator +
+    // chrome layout, rather than re-deriving the inset formula — so a change to either one
+    // fails this test instead of silently moving the shipped gutter out from under it.
+    const SampleBands bands =
+        computeSampleBands(kShippedDefaultWindowW, kShippedDefaultWindowH, 0);
+    const ChromeRects chrome = chromeRects(bands.chrome, /*knobSize=*/24);
+    const int stripW = chrome.rootStrip.width;
     CHECK(stripW == 824);
 
     const StripLayout L = layoutStrip(stripW, 30);