dashboard / erock/vaxis / fix(vxfw/list): check if index is out of bounds #95 rss

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diff --git a/vxfw/surface_test.go b/vxfw/surface_test.go
new file mode 100644
index 0000000..6400880
--- /dev/null
+++ b/vxfw/surface_test.go
@@ -0,0 +1,37 @@
+package vxfw_test
+
+import (
+	"testing"
+
+	"git.sr.ht/~rockorager/vaxis"
+	"git.sr.ht/~rockorager/vaxis/vxfw"
+)
+
+func TestWriteCellBoundsCheck(t *testing.T) {
+	// Create a surface where Size claims more cells than Buffer actually has.
+	// This simulates the bug where Size and Buffer get out of sync.
+	s := vxfw.Surface{
+		Size: vxfw.Size{
+			Width:  100,
+			Height: 100,
+		},
+		Buffer: make([]vaxis.Cell, 50), // Only 50 cells, but Size claims 10000
+	}
+
+	cell := vaxis.Cell{
+		Character: vaxis.Character{
+			Grapheme: "x",
+			Width:    1,
+		},
+	}
+
+	// This should not panic even though the index would be out of bounds
+	// if we only checked against Size.
+	s.WriteCell(99, 99, cell) // Would calculate index 9999, but Buffer only has 50 cells
+
+	// Also test that valid writes still work
+	s.WriteCell(0, 0, cell)
+	if s.Buffer[0].Character.Grapheme != "x" {
+		t.Errorf("expected cell at (0,0) to be written, got %q", s.Buffer[0].Character.Grapheme)
+	}
+}

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diff --git a/vxfw/vxfw.go b/vxfw/vxfw.go
index 9f1ae13..5ac9252 100644
--- a/vxfw/vxfw.go
+++ b/vxfw/vxfw.go
@@ -155,6 +155,9 @@ func (s *Surface) WriteCell(col uint16, row uint16, cell vaxis.Cell) {
 		return
 	}
 	i := (row * s.Size.Width) + col
+	if int(i) >= len(s.Buffer) {
+		return
+	}
 	s.Buffer[i] = cell
 }