Documents: open cells keep presses; finds open their cell

A press inside the open cell stays with its field. Find opens the
cell holding a match. A closing backslash no longer escapes the
next pipe. A right press after typed pipes reads the right byte.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/documents/document/mod.rs

@@ -246,7 +246,7 @@ impl MarkdownDocument {
         let written = match open.append {
             true if typed.is_empty() => String::new(),
             true => format!("{}{typed}", joint(text)),
-            false if open.cell.is_some() => cells::guarded(typed),
+            false if open.cell.is_some() => cells::kept(typed),
             false => typed.to_string(),
         };
         [&text[..open.range.start], &written, &text[open.range.end..]].concat()