Re-add markdown streaming (#2029)

Wait for newlines, then render markdown on a line by line basis. Word wrap it for the current terminal size and then spit it out line by line into the UI. Also adds tests and fixes some UI regressions.

codex-rs/tui/src/render/line_utils.rs

@@ -0,0 +1,45 @@
+use ratatui::text::Line;
+use ratatui::text::Span;
+
+/// Clone a borrowed ratatui `Line` into an owned `'static` line.
+pub fn line_to_static(line: &Line<'_>) -> Line<'static> {
+    Line {
+        style: line.style,
+        alignment: line.alignment,
+        spans: line
+            .spans
+            .iter()
+            .map(|s| Span {
+                style: s.style,
+                content: std::borrow::Cow::Owned(s.content.to_string()),
+            })
+            .collect(),
+    }
+}
+
+/// Append owned copies of borrowed lines to `out`.
+pub fn push_owned_lines<'a>(src: &[Line<'a>], out: &mut Vec<Line<'static>>) {
+    for l in src {
+        out.push(line_to_static(l));
+    }
+}
+
+/// Consider a line blank if it has no spans or only spans whose contents are
+/// empty or consist solely of spaces (no tabs/newlines).
+pub fn is_blank_line_spaces_only(line: &Line<'_>) -> bool {
+    if line.spans.is_empty() {
+        return true;
+    }
+    line.spans
+        .iter()
+        .all(|s| s.content.is_empty() || s.content.chars().all(|c| c == ' '))
+}
+
+/// Consider a line blank if its spans are empty or all span contents are
+/// whitespace when trimmed.
+pub fn is_blank_line_trim(line: &Line<'_>) -> bool {
+    if line.spans.is_empty() {
+        return true;
+    }
+    line.spans.iter().all(|s| s.content.trim().is_empty())
+}

codex-rs/tui/src/render/markdown_utils.rs

@@ -0,0 +1,72 @@
+/// Returns true if the provided text contains an unclosed fenced code block
+/// (opened by ``` or ~~~, closed by a matching fence on its own line).
+pub fn is_inside_unclosed_fence(s: &str) -> bool {
+    let mut open = false;
+    for line in s.lines() {
+        let t = line.trim_start();
+        if t.starts_with("```") || t.starts_with("~~~") {
+            if !open {
+                open = true;
+            } else {
+                // closing fence on same pattern toggles off
+                open = false;
+            }
+        }
+    }
+    open
+}
+
+/// Remove fenced code blocks that contain no content (whitespace-only) to avoid
+/// streaming empty code blocks like ```lang\n``` or ```\n```.
+pub fn strip_empty_fenced_code_blocks(s: &str) -> String {
+    // Only remove complete fenced blocks that contain no non-whitespace content.
+    // Leave all other content unchanged to avoid affecting partial streams.
+    let lines: Vec<&str> = s.lines().collect();
+    let mut out = String::with_capacity(s.len());
+    let mut i = 0usize;
+    while i < lines.len() {
+        let line = lines[i];
+        let trimmed_start = line.trim_start();
+        let fence_token = if trimmed_start.starts_with("```") {
+            "```"
+        } else if trimmed_start.starts_with("~~~") {
+            "~~~"
+        } else {
+            ""
+        };
+        if !fence_token.is_empty() {
+            // Find a matching closing fence on its own line.
+            let mut j = i + 1;
+            let mut has_content = false;
+            let mut found_close = false;
+            while j < lines.len() {
+                let l = lines[j];
+                if l.trim() == fence_token {
+                    found_close = true;
+                    break;
+                }
+                if !l.trim().is_empty() {
+                    has_content = true;
+                }
+                j += 1;
+            }
+            if found_close && !has_content {
+                // Drop i..=j and insert at most a single blank separator line.
+                if !out.ends_with('\n') {
+                    out.push('\n');
+                }
+                i = j + 1;
+                continue;
+            }
+            // Not an empty fenced block; emit as-is.
+            out.push_str(line);
+            out.push('\n');
+            i += 1;
+        } else {
+            out.push_str(line);
+            out.push('\n');
+            i += 1;
+        }
+    }
+    out
+}

codex-rs/tui/src/render/mod.rs

@@ -0,0 +1,2 @@
+pub mod line_utils;
+pub mod markdown_utils;