Fix/tui windows multiline paste (#2544)

Introduce a minimal paste-burst heuristic in the chat composer so Enter
is treated as a newline during paste-like bursts (plain chars arriving
in very short intervals), avoiding premature submit after the first line
on Windows consoles that lack bracketed paste.

- Detect tight sequences of plain Char events; open a short window where
Enter inserts a newline instead of submitting.
- Extend the window on newline to handle blank lines in pasted content.
- No behavior change for terminals that already emit Event::Paste; no
OS/env toggles added.

codex-rs/tui/src/bottom_pane/chat_composer.rs

@@ -34,6 +34,13 @@ use std::cell::RefCell;
 use std::collections::HashMap;
 use std::path::Path;
 use std::path::PathBuf;
+use std::time::Duration;
+use std::time::Instant;
+
+// Heuristic thresholds for detecting paste-like input bursts.
+const PASTE_BURST_MIN_CHARS: u16 = 3;
+const PASTE_BURST_CHAR_INTERVAL: Duration = Duration::from_millis(8);
+const PASTE_ENTER_SUPPRESS_WINDOW: Duration = Duration::from_millis(120);
 
 /// If the pasted content exceeds this number of characters, replace it with a
 /// placeholder in the UI.
@@ -82,6 +89,13 @@ pub(crate) struct ChatComposer {
     has_focus: bool,
     attached_images: Vec<AttachedImage>,
     placeholder_text: String,
+    // Heuristic state to detect non-bracketed paste bursts.
+    last_plain_char_time: Option<Instant>,
+    consecutive_plain_char_burst: u16,
+    paste_burst_until: Option<Instant>,
+    // Buffer to accumulate characters during a detected non-bracketed paste burst.
+    paste_burst_buffer: String,
+    in_paste_burst_mode: bool,
 }
 
 /// Popup state – at most one can be visible at any time.
@@ -115,6 +129,11 @@ impl ChatComposer {
             has_focus: has_input_focus,
             attached_images: Vec::new(),
             placeholder_text,
+            last_plain_char_time: None,
+            consecutive_plain_char_burst: 0,
+            paste_burst_until: None,
+            paste_burst_buffer: String::new(),
+            in_paste_burst_mode: false,
         }
     }
 
@@ -202,6 +221,10 @@ impl ChatComposer {
         } else {
             self.textarea.insert_str(&pasted);
         }
+        // Explicit paste events should not trigger Enter suppression.
+        self.last_plain_char_time = None;
+        self.consecutive_plain_char_burst = 0;
+        self.paste_burst_until = None;
         self.sync_command_popup();
         self.sync_file_search_popup();
         true
@@ -614,6 +637,60 @@ impl ChatComposer {
                 modifiers: KeyModifiers::NONE,
                 ..
             } => {
+                // If we're in a paste-like burst capture, treat Enter as part of the burst
+                // and accumulate it rather than submitting or inserting immediately.
+                // Do not treat Enter as paste inside a slash-command context.
+                let in_slash_context = matches!(self.active_popup, ActivePopup::Command(_))
+                    || self
+                        .textarea
+                        .text()
+                        .lines()
+                        .next()
+                        .unwrap_or("")
+                        .starts_with('/');
+                if (self.in_paste_burst_mode || !self.paste_burst_buffer.is_empty())
+                    && !in_slash_context
+                {
+                    self.paste_burst_buffer.push('\n');
+                    let now = Instant::now();
+                    // Keep the window alive so subsequent lines are captured too.
+                    self.paste_burst_until = Some(now + PASTE_ENTER_SUPPRESS_WINDOW);
+                    return (InputResult::None, true);
+                }
+                // If we have pending placeholder pastes, submit immediately to expand them.
+                if !self.pending_pastes.is_empty() {
+                    let mut text = self.textarea.text().to_string();
+                    self.textarea.set_text("");
+                    for (placeholder, actual) in &self.pending_pastes {
+                        if text.contains(placeholder) {
+                            text = text.replace(placeholder, actual);
+                        }
+                    }
+                    self.pending_pastes.clear();
+                    if text.is_empty() {
+                        return (InputResult::None, true);
+                    }
+                    self.history.record_local_submission(&text);
+                    return (InputResult::Submitted(text), true);
+                }
+
+                // During a paste-like burst, treat Enter as a newline instead of submit.
+                let now = Instant::now();
+                let tight_after_char = self
+                    .last_plain_char_time
+                    .is_some_and(|t| now.duration_since(t) <= PASTE_BURST_CHAR_INTERVAL);
+                let recent_after_char = self
+                    .last_plain_char_time
+                    .is_some_and(|t| now.duration_since(t) <= PASTE_ENTER_SUPPRESS_WINDOW);
+                let burst_by_count =
+                    recent_after_char && self.consecutive_plain_char_burst >= PASTE_BURST_MIN_CHARS;
+                let in_burst_window = self.paste_burst_until.is_some_and(|until| now <= until);
+
+                if tight_after_char || burst_by_count || in_burst_window {
+                    self.textarea.insert_str("\n");
+                    self.paste_burst_until = Some(now + PASTE_ENTER_SUPPRESS_WINDOW);
+                    return (InputResult::None, true);
+                }
                 let mut text = self.textarea.text().to_string();
                 self.textarea.set_text("");
 
@@ -645,6 +722,94 @@ impl ChatComposer {
 
     /// Handle generic Input events that modify the textarea content.
     fn handle_input_basic(&mut self, input: KeyEvent) -> (InputResult, bool) {
+        // If we have a buffered non-bracketed paste burst and enough time has
+        // elapsed since the last char, flush it before handling a new input.
+        let now = Instant::now();
+        let timed_out = self
+            .last_plain_char_time
+            .is_some_and(|t| now.duration_since(t) > PASTE_BURST_CHAR_INTERVAL);
+        if timed_out && (!self.paste_burst_buffer.is_empty() || self.in_paste_burst_mode) {
+            let pasted = std::mem::take(&mut self.paste_burst_buffer);
+            self.in_paste_burst_mode = false;
+            // Reuse normal paste path (handles large-paste placeholders).
+            self.handle_paste(pasted);
+        }
+
+        // If we're capturing a burst and receive Enter, accumulate it instead of inserting.
+        if matches!(input.code, KeyCode::Enter)
+            && (self.in_paste_burst_mode || !self.paste_burst_buffer.is_empty())
+        {
+            self.paste_burst_buffer.push('\n');
+            self.paste_burst_until = Some(now + PASTE_ENTER_SUPPRESS_WINDOW);
+            return (InputResult::None, true);
+        }
+
+        // Intercept plain Char inputs to optionally accumulate into a burst buffer.
+        if let KeyEvent {
+            code: KeyCode::Char(ch),
+            modifiers,
+            ..
+        } = input
+        {
+            let has_ctrl_or_alt =
+                modifiers.contains(KeyModifiers::CONTROL) || modifiers.contains(KeyModifiers::ALT);
+            if !has_ctrl_or_alt {
+                // Update burst heuristics.
+                match self.last_plain_char_time {
+                    Some(prev) if now.duration_since(prev) <= PASTE_BURST_CHAR_INTERVAL => {
+                        self.consecutive_plain_char_burst =
+                            self.consecutive_plain_char_burst.saturating_add(1);
+                    }
+                    _ => {
+                        self.consecutive_plain_char_burst = 1;
+                    }
+                }
+                self.last_plain_char_time = Some(now);
+
+                // If we're already buffering, capture the char into the buffer.
+                if self.in_paste_burst_mode {
+                    self.paste_burst_buffer.push(ch);
+                    // Keep the window alive while we receive the burst.
+                    self.paste_burst_until = Some(now + PASTE_ENTER_SUPPRESS_WINDOW);
+                    return (InputResult::None, true);
+                } else if self.consecutive_plain_char_burst >= PASTE_BURST_MIN_CHARS {
+                    // Do not start burst buffering while typing a slash command (first line starts with '/').
+                    let first_line = self.textarea.text().lines().next().unwrap_or("");
+                    if first_line.starts_with('/') {
+                        // Keep heuristics but do not buffer.
+                        self.paste_burst_until = Some(now + PASTE_ENTER_SUPPRESS_WINDOW);
+                        // Insert normally.
+                        self.textarea.input(input);
+                        let text_after = self.textarea.text();
+                        self.pending_pastes
+                            .retain(|(placeholder, _)| text_after.contains(placeholder));
+                        return (InputResult::None, true);
+                    }
+                    // Begin buffering from this character onward.
+                    self.paste_burst_buffer.push(ch);
+                    self.in_paste_burst_mode = true;
+                    // Keep the window alive to continue capturing.
+                    self.paste_burst_until = Some(now + PASTE_ENTER_SUPPRESS_WINDOW);
+                    return (InputResult::None, true);
+                }
+
+                // Not buffering: insert normally and continue.
+                self.textarea.input(input);
+                let text_after = self.textarea.text();
+                self.pending_pastes
+                    .retain(|(placeholder, _)| text_after.contains(placeholder));
+                return (InputResult::None, true);
+            } else {
+                // Modified char ends any burst: flush buffered content before applying.
+                if !self.paste_burst_buffer.is_empty() || self.in_paste_burst_mode {
+                    let pasted = std::mem::take(&mut self.paste_burst_buffer);
+                    self.in_paste_burst_mode = false;
+                    self.handle_paste(pasted);
+                }
+            }
+        }
+
+        // For non-char inputs (or after flushing), handle normally.
         // Special handling for backspace on placeholders
         if let KeyEvent {
             code: KeyCode::Backspace,
@@ -659,6 +824,37 @@ impl ChatComposer {
         self.textarea.input(input);
         let text_after = self.textarea.text();
 
+        // Update paste-burst heuristic for plain Char (no Ctrl/Alt) events.
+        let crossterm::event::KeyEvent {
+            code, modifiers, ..
+        } = input;
+        match code {
+            KeyCode::Char(_) => {
+                let has_ctrl_or_alt = modifiers.contains(KeyModifiers::CONTROL)
+                    || modifiers.contains(KeyModifiers::ALT);
+                if has_ctrl_or_alt {
+                    // Modified char: clear burst window.
+                    self.consecutive_plain_char_burst = 0;
+                    self.last_plain_char_time = None;
+                    self.paste_burst_until = None;
+                    self.in_paste_burst_mode = false;
+                    self.paste_burst_buffer.clear();
+                }
+                // Plain chars handled above.
+            }
+            KeyCode::Enter => {
+                // Keep burst window alive (supports blank lines in paste).
+            }
+            _ => {
+                // Other keys: clear burst window and any buffer (after flushing earlier).
+                self.consecutive_plain_char_burst = 0;
+                self.last_plain_char_time = None;
+                self.paste_burst_until = None;
+                self.in_paste_burst_mode = false;
+                // Do not clear paste_burst_buffer here; it should have been flushed above.
+            }
+        }
+
         // Check if any placeholders were removed and remove their corresponding pending pastes
         self.pending_pastes
             .retain(|(placeholder, _)| text_after.contains(placeholder));