fix(tui): preserve code block indentation in selection

Render code indentation spaces as selectable cells so copied fenced code keeps its leading whitespace.

ui-tui/src/components/markdown.tsx

@@ -114,6 +114,25 @@ const renderTable = (k: number, rows: string[][], t: Theme) => {
   )
 }
 
+const codeText = (text: string, color: string | undefined, key: number | string, t: Theme) => (
+  <Text color={color ?? (text.trim() ? undefined : t.color.dim)} key={key}>
+    {text}
+  </Text>
+)
+
+const plainCodeLine = (text: string, t: Theme) => {
+  const indent = text.match(/^\s+/)?.[0] ?? ''
+
+  return indent ? (
+    <>
+      {codeText(indent, undefined, 'indent', t)}
+      {text.slice(indent.length)}
+    </>
+  ) : (
+    text
+  )
+}
+
 function MdInline({ t, text }: { t: Theme; text: string }) {
   const parts: ReactNode[] = []
 
@@ -316,19 +335,7 @@ function MdImpl({ compact, t, text }: MdProps) {
 
             {block.map((l, j) => {
               if (highlighted) {
-                return (
-                  <Text key={j}>
-                    {highlightLine(l, lang, t).map(([color, text], kk) =>
-                      color ? (
-                        <Text color={color} key={kk}>
-                          {text}
-                        </Text>
-                      ) : (
-                        <Text key={kk}>{text}</Text>
-                      )
-                    )}
-                  </Text>
-                )
+                return <Text key={j}>{highlightLine(l, lang, t).map(([color, text], kk) => codeText(text, color, kk, t))}</Text>
               }
 
               const add = isDiff && l.startsWith('+')
@@ -342,7 +349,7 @@ function MdImpl({ compact, t, text }: MdProps) {
                   dimColor={isDiff && !add && !del && !hunk && l.startsWith(' ')}
                   key={j}
                 >
-                  {l}
+                  {plainCodeLine(l, t)}
                 </Text>
               )
             })}