documents: presses read back through quotes, code, HTML and front matter

Each drawn character finds its written one, skipping only white
space, escapes and quote marks, so a press lands on the character
itself. Code, front matter and link definitions read back line for
line. An HTML block keeps each text run's source byte, and an alert
keeps its text past the marker; alert() now takes the source.

A secondary press refuses a target its write-back changed, and its
focus no longer opens an empty document. Run's element stack moves to
tree/stack.rs and the HTML-block reader to tree/html_block.rs.

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

src/documents/document/point.rs

@@ -6,6 +6,7 @@ use markdown::mdast;
 use super::{DocumentEvent, MarkdownDocument, edit::Landing, edit::moved};
 use crate::documents::{
     render::{OnPoint, Place, Pointed},
+    tree::lines_at,
     tree::{alert, is_toc},
 };
 
@@ -35,7 +36,7 @@ impl TargetBlock {
             mdast::Node::Paragraph(_) if is_toc(node, source) => Self::Toc,
             mdast::Node::Paragraph(_) => Self::Paragraph,
             mdast::Node::Heading(heading) => Self::Heading(heading.depth),
-            mdast::Node::Blockquote(quote) if alert(quote).is_some() => Self::Alert,
+            mdast::Node::Blockquote(quote) if alert(quote, source).is_some() => Self::Alert,
             mdast::Node::Blockquote(_) => Self::Quote,
             mdast::Node::List(_) => Self::List,
             mdast::Node::Code(_) => Self::Code,
@@ -73,6 +74,10 @@ impl MarkdownDocument {
             // The drawing counts from its block's start.
             let at = match &pointed.place {
                 Place::Text(inline, drawn) => inline.source_at(&parsed.text[start..], *drawn),
+                // Unreadable lines land at their start.
+                Place::Lines { text, from, at } => {
+                    Some(lines_at(&parsed.text[start..], *from, text, *at).unwrap_or(*from))
+                }
                 Place::At(at) => Some(*at),
                 Place::Block => None,
             }
@@ -104,6 +109,7 @@ impl MarkdownDocument {
             block => block.flatten(),
         };
         let kind = block.map(|block| block.kind);
+        let pressed = block.map(|block| self.parsed.text[block.range.clone()].to_string());
         let at = at.or(block.map(|block| block.range.start));
         let written = self.commit(cx);
         if written.is_some() {
@@ -119,8 +125,17 @@ impl MarkdownDocument {
                 None => return log::warn!("markdown document: the pressed text was written over"),
             },
         };
+        // A write-back may change the pressed block.
+        let now = (self.parsed.blocks.iter())
+            .find(|block| block.range.start <= at && at <= block.range.end)
+            .map(|block| self.parsed.text[block.range.clone()].to_string());
+        if written.is_some() && pressed.is_some() && now != pressed {
+            return log::warn!("markdown document: the write-back changed the pressed block");
+        }
         self.editor
             .update(cx, |editor, cx| editor.select(std::iter::once(at..at), cx));
+        // Its focus opens no empty block.
+        self.pointing = !self.focus.is_focused(window);
         window.focus(&self.focus, cx);
         log::info!("markdown document: a secondary press puts the caret at byte {at}");
         cx.emit(DocumentEvent::Pointed(DocumentTarget {