Merge pull request '#261: keep line number gutter visible during horizontal scroll' (#265) from fix-261 into dev

internal/web/static/app.css

@@ -299,8 +299,14 @@ html[data-wrap] .float { overflow-x: hidden; }
 .code-head .dot { width: 8px; height: 8px; border-radius: 50%; background: var(--accent); }
 .code {
   font-family: var(--font-mono); font-size: var(--code-fs); line-height: var(--code-lh);
-  padding: 14px 0; display: flex; overflow-x: auto;
+  padding: 14px 0; display: flex; overflow-x: hidden;
 }
+/* #261: horizontal scroll must live on the codebody, not the .code flex
+   container — a container-level scroll takes the gutter with it when the
+   user scrolls long lines. The gutter sits OUTSIDE the scroll container and
+   stays visible; the codebody shrinks to the remaining space and scrolls
+   (min-width: 0 lets it shrink below its content width inside the flex row). */
+.code .codebody { flex: 1 1 auto; min-width: 0; overflow-x: auto; }
 /* #167: the gutter must not drive the flex layout — its content width
    (row count × number width) shrinks the code column, which re-wraps lines,
    which grows the gutter: a feedback loop. Pin the gutter with a fixed
@@ -310,7 +316,7 @@ html[data-wrap] .float { overflow-x: hidden; }
 .code .gutter { flex-shrink: 0; }
 /* gutter/code share line metrics; the editor gutter keeps its own padding (#50) */
 .code .gutter { padding-top: 0; padding-bottom: 0; }
-.codebody { padding: 0 18px; white-space: pre; }
+.codebody { padding: 0 18px; white-space: pre; overflow-x: auto; }
 /* #167: each logical line is its own block so offsetTop identifies its first visual row */
 .codeline { display: block; }
 /* #167 rev: gutter number spans must stack one per visual row (wrap on) */