fix(session-ui): stop shell text showing through the copy button (#59901)

Co-authored-by: Brendonovich <14191578+Brendonovich@users.noreply.github.com>

Author: opencode-agent[bot]

packages/session-ui/src/components/message-part.css

@@ -778,9 +778,27 @@
       margin: 4px;
     }
 
+    /* The ghost button is transparent, so paint the section's background behind it. It fades out to the left, top
+       and bottom so text at its edges softens instead of being cut, and runs to the card edge on the right. It is
+       solid only across the button's height and never takes pointer events, so there is no gutter and the lines
+       below keep the full width. The top stops at the section edge, so it never covers the border above the output. */
+    [data-slot="bash-copy"]::before {
+      content: "";
+      position: absolute;
+      z-index: -1;
+      inset: -4px -4px -8px -24px;
+      background: var(--bash-section-background);
+      mask-image:
+        linear-gradient(to right, transparent, #000 24px),
+        linear-gradient(transparent, #000 8px, #000 calc(100% - 8px), transparent);
+      mask-composite: intersect;
+      pointer-events: none;
+    }
+
     [data-slot="bash-result"] {
+      --bash-section-background: var(--v2-background-bg-layer-01);
       border-block-start: 0.5px solid var(--v2-border-border-base);
-      background: var(--v2-background-bg-layer-01);
+      background: var(--bash-section-background);
       color: var(--v2-text-text-muted);
     }
 
@@ -790,6 +808,7 @@
     }
 
     [data-slot="bash-command"] {
+      --bash-section-background: var(--v2-background-bg-base);
       color: var(--v2-text-text-base);
     }
   }