update jlibghostty

The persistent black bars in the partial-repaint path were clearRect leaving
the run's fractional edge pixels transparent, which showed the near-black pane
background as a seam against the adjacent un-repainted line. Confirmed with the
debugRepaint toggle: filling the span opaque removed the bars entirely.

Fill the repaint run with PANE_BACKGROUND (the default cell background) instead
of clearing to transparent; per-cell backgrounds paint over it as before. Safe
because the per-column path never runs while kitty graphics are present (those
force a full render), so no below-text image needs a transparent row canvas.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -14,3 +14,4 @@ build
 build
 .gradle
 bin
+.worktrees

flake.lock

@@ -70,11 +70,11 @@
         "nixpkgs": "nixpkgs"
       },
       "locked": {
-        "lastModified": 1780256181,
+        "lastModified": 1780258814,
-        "narHash": "sha256-/saXdnYMbAMfP7u6USSqtNkBIgqZhU+CPr3F8tUQhHU=",
+        "narHash": "sha256-8rxL7xaZ/loYg3zdt0w5+hfNyHFVknDZN360NzrtCsQ=",
         "ref": "refs/heads/main",
-        "rev": "db5ee5d20daf8855de3a3b2fa9349eced70946f0",
+        "rev": "6a3d5aa0b0b1f738c958e2a2f0249574c07d9c4d",
-        "revCount": 21,
+        "revCount": 23,
         "type": "git",
         "url": "https://gitea.gregorlohaus.com/gregor/jlibghostty.git"
       },

src/main/java/com/gregor/jprototerm/TerminalPaneNode.java

@@ -50,6 +50,13 @@ final class TerminalPaneNode extends Region {
             Boolean.getBoolean("jprototerm.fullRowRepaint")
                     || "1".equals(System.getenv("JPROTOTERM_FULL_ROW_REPAINT"));
 
+    // Debug toggle: paint each repaint run's cleared span red instead of clearing it to
+    // transparent. If the black bars turn red, they are spans repaintColumns clears but never
+    // refills; if they stay black, those pixels are never touched by repaintColumns at all.
+    private static final boolean DEBUG_REPAINT =
+            Boolean.getBoolean("jprototerm.debugRepaint")
+                    || "1".equals(System.getenv("JPROTOTERM_DEBUG_REPAINT"));
+
     private static final Color DEFAULT_FOREGROUND = Color.rgb(225, 229, 235);
     private static final Color SELECTED_BACKGROUND = Color.rgb(52, 92, 140);
     private static final Color PANE_BACKGROUND = Color.rgb(9, 10, 12);
@@ -839,7 +846,15 @@ final class TerminalPaneNode extends Region {
             double x = TerminalMetrics.PADDING + startColumn * cellWidth;
             double width = (endColumn - startColumn + 1) * cellWidth;
 
-            gc.clearRect(x, 0.0, width, canvas.getHeight());
+            // Opaque base fill rather than clearRect: a transparent clear leaves the run's
+            // fractional edge pixels transparent, which show the near-black pane background
+            // as a thin seam bar against the adjacent (un-repainted) line. Filling opaque
+            // removes every transparent pixel; per-cell backgrounds then paint on top, and
+            // default-background cells correctly show PANE_BACKGROUND. Safe because the
+            // per-column path never runs while kitty graphics (which need a transparent row
+            // canvas for below-text images) are present.
+            gc.setFill(DEBUG_REPAINT ? Color.RED : PANE_BACKGROUND);
+            gc.fillRect(x, 0.0, width, canvas.getHeight());
             if (startColumn == 0) {
                 gc.setFill(rowEdgeBackground(row, true));
                 gc.fillRect(0.0, 0.0, TerminalMetrics.PADDING, canvas.getHeight());