wrap markdown at render time (#4506)

This results in correctly indenting list items with long lines.

<img width="1006" height="251" alt="Screenshot 2025-09-30 at 10 00
48 AM"
src="https://github.com/user-attachments/assets/0a076cf6-ca3c-4efb-b3af-dc07617cdb6f"
/>

codex-rs/tui/src/markdown_stream.rs

@@ -8,13 +8,15 @@ use crate::markdown;
 pub(crate) struct MarkdownStreamCollector {
     buffer: String,
     committed_line_count: usize,
+    width: Option<usize>,
 }
 
 impl MarkdownStreamCollector {
-    pub fn new() -> Self {
+    pub fn new(width: Option<usize>) -> Self {
         Self {
             buffer: String::new(),
             committed_line_count: 0,
+            width,
         }
     }
 
@@ -40,7 +42,7 @@ impl MarkdownStreamCollector {
             return Vec::new();
         };
         let mut rendered: Vec<Line<'static>> = Vec::new();
-        markdown::append_markdown(&source, &mut rendered, config);
+        markdown::append_markdown(&source, self.width, &mut rendered, config);
         let mut complete_line_count = rendered.len();
         if complete_line_count > 0
             && crate::render::line_utils::is_blank_line_spaces_only(
@@ -81,7 +83,7 @@ impl MarkdownStreamCollector {
         tracing::trace!("markdown finalize (raw source):\n---\n{source}\n---");
 
         let mut rendered: Vec<Line<'static>> = Vec::new();
-        markdown::append_markdown(&source, &mut rendered, config);
+        markdown::append_markdown(&source, self.width, &mut rendered, config);
 
         let out = if self.committed_line_count >= rendered.len() {
             Vec::new()
@@ -101,7 +103,7 @@ pub(crate) fn simulate_stream_markdown_for_tests(
     finalize: bool,
     config: &Config,
 ) -> Vec<Line<'static>> {
-    let mut collector = MarkdownStreamCollector::new();
+    let mut collector = MarkdownStreamCollector::new(None);
     let mut out = Vec::new();
     for d in deltas {
         collector.push_delta(d);
@@ -136,7 +138,7 @@ mod tests {
     #[test]
     fn no_commit_until_newline() {
         let cfg = test_config();
-        let mut c = super::MarkdownStreamCollector::new();
+        let mut c = super::MarkdownStreamCollector::new(None);
         c.push_delta("Hello, world");
         let out = c.commit_complete_lines(&cfg);
         assert!(out.is_empty(), "should not commit without newline");
@@ -148,7 +150,7 @@ mod tests {
     #[test]
     fn finalize_commits_partial_line() {
         let cfg = test_config();
-        let mut c = super::MarkdownStreamCollector::new();
+        let mut c = super::MarkdownStreamCollector::new(None);
         c.push_delta("Line without newline");
         let out = c.finalize_and_drain(&cfg);
         assert_eq!(out.len(), 1);
@@ -277,7 +279,7 @@ mod tests {
 
         // Stream a paragraph line, then a heading on the next line.
         // Expect two distinct rendered lines: "Hello." and "Heading".
-        let mut c = super::MarkdownStreamCollector::new();
+        let mut c = super::MarkdownStreamCollector::new(None);
         c.push_delta("Hello.\n");
         let out1 = c.commit_complete_lines(&cfg);
         let s1: Vec<String> = out1
@@ -335,7 +337,7 @@ mod tests {
         // Paragraph without trailing newline, then a chunk that starts with the newline
         // and the heading text, then a final newline. The collector should first commit
         // only the paragraph line, and later commit the heading as its own line.
-        let mut c = super::MarkdownStreamCollector::new();
+        let mut c = super::MarkdownStreamCollector::new(None);
         c.push_delta("Sounds good!");
         // No commit yet
         assert!(c.commit_complete_lines(&cfg).is_empty());
@@ -380,7 +382,7 @@ mod tests {
 
         // Sanity check raw markdown rendering for a simple line does not produce spurious extras.
         let mut rendered: Vec<ratatui::text::Line<'static>> = Vec::new();
-        crate::markdown::append_markdown("Hello.\n", &mut rendered, &cfg);
+        crate::markdown::append_markdown("Hello.\n", None, &mut rendered, &cfg);
         let rendered_strings: Vec<String> = rendered
             .iter()
             .map(|l| {
@@ -442,7 +444,7 @@ mod tests {
         let streamed_str = lines_to_plain_strings(&streamed);
 
         let mut rendered_all: Vec<ratatui::text::Line<'static>> = Vec::new();
-        crate::markdown::append_markdown(input, &mut rendered_all, &cfg);
+        crate::markdown::append_markdown(input, None, &mut rendered_all, &cfg);
         let rendered_all_str = lines_to_plain_strings(&rendered_all);
 
         assert_eq!(
@@ -552,7 +554,7 @@ mod tests {
 
         let full: String = deltas.iter().copied().collect();
         let mut rendered_all: Vec<ratatui::text::Line<'static>> = Vec::new();
-        crate::markdown::append_markdown(&full, &mut rendered_all, &cfg);
+        crate::markdown::append_markdown(&full, None, &mut rendered_all, &cfg);
         let rendered_all_strs = lines_to_plain_strings(&rendered_all);
 
         assert_eq!(
@@ -641,7 +643,7 @@ mod tests {
         // Compute a full render for diagnostics only.
         let full: String = deltas.iter().copied().collect();
         let mut rendered_all: Vec<ratatui::text::Line<'static>> = Vec::new();
-        crate::markdown::append_markdown(&full, &mut rendered_all, &cfg);
+        crate::markdown::append_markdown(&full, None, &mut rendered_all, &cfg);
 
         // Also assert exact expected plain strings for clarity.
         let expected = vec![
@@ -669,7 +671,7 @@ mod tests {
         let streamed_strs = lines_to_plain_strings(&streamed);
         let full: String = deltas.iter().copied().collect();
         let mut rendered: Vec<ratatui::text::Line<'static>> = Vec::new();
-        crate::markdown::append_markdown(&full, &mut rendered, &cfg);
+        crate::markdown::append_markdown(&full, None, &mut rendered, &cfg);
         let rendered_strs = lines_to_plain_strings(&rendered);
         assert_eq!(streamed_strs, rendered_strs, "full:\n---\n{full}\n---");
     }