fix: skip /init when AGENTS.md already exists (#5242)

This change aborts /init if an AGENTS.md already exists to avoid plainly
overwriting it.

<img width="581" height="24" alt="Screenshot 2025-10-15 at 9 43 07 PM"
src="https://github.com/user-attachments/assets/f8be51f7-dcb1-4f90-8062-18d4e852300a"
/>

codex-rs/tui/src/chatwidget.rs

@@ -7,6 +7,7 @@ use codex_core::config::Config;
 use codex_core::config_types::Notifications;
 use codex_core::git_info::current_branch_name;
 use codex_core::git_info::local_git_branches;
+use codex_core::project_doc::DEFAULT_PROJECT_DOC_FILENAME;
 use codex_core::protocol::AgentMessageDeltaEvent;
 use codex_core::protocol::AgentMessageEvent;
 use codex_core::protocol::AgentReasoningDeltaEvent;
@@ -1130,6 +1131,14 @@ impl ChatWidget {
                 self.app_event_tx.send(AppEvent::NewSession);
             }
             SlashCommand::Init => {
+                let init_target = self.config.cwd.join(DEFAULT_PROJECT_DOC_FILENAME);
+                if init_target.exists() {
+                    let message = format!(
+                        "{DEFAULT_PROJECT_DOC_FILENAME} already exists here. Skipping /init to avoid overwriting it."
+                    );
+                    self.add_info_message(message, None);
+                    return;
+                }
                 const INIT_PROMPT: &str = include_str!("../prompt_for_init_command.md");
                 self.submit_text_message(INIT_PROMPT.to_string());
             }

codex-rs/tui/src/chatwidget/tests.rs

@@ -49,6 +49,7 @@ use std::io::BufRead;
 use std::io::BufReader;
 use std::path::PathBuf;
 use tempfile::NamedTempFile;
+use tempfile::tempdir;
 use tokio::sync::mpsc::error::TryRecvError;
 use tokio::sync::mpsc::unbounded_channel;
 
@@ -769,6 +770,38 @@ fn review_popup_custom_prompt_action_sends_event() {
     assert!(found, "expected OpenReviewCustomPrompt event to be sent");
 }
 
+#[test]
+fn slash_init_skips_when_project_doc_exists() {
+    let (mut chat, mut rx, mut op_rx) = make_chatwidget_manual();
+    let tempdir = tempdir().unwrap();
+    let existing_path = tempdir.path().join(DEFAULT_PROJECT_DOC_FILENAME);
+    std::fs::write(&existing_path, "existing instructions").unwrap();
+    chat.config.cwd = tempdir.path().to_path_buf();
+
+    chat.dispatch_command(SlashCommand::Init);
+
+    match op_rx.try_recv() {
+        Err(TryRecvError::Empty) => {}
+        other => panic!("expected no Codex op to be sent, got {other:?}"),
+    }
+
+    let cells = drain_insert_history(&mut rx);
+    assert_eq!(cells.len(), 1, "expected one info message");
+    let rendered = lines_to_single_string(&cells[0]);
+    assert!(
+        rendered.contains(DEFAULT_PROJECT_DOC_FILENAME),
+        "info message should mention the existing file: {rendered:?}"
+    );
+    assert!(
+        rendered.contains("Skipping /init"),
+        "info message should explain why /init was skipped: {rendered:?}"
+    );
+    assert_eq!(
+        std::fs::read_to_string(existing_path).unwrap(),
+        "existing instructions"
+    );
+}
+
 /// The commit picker shows only commit subjects (no timestamps).
 #[test]
 fn review_commit_picker_shows_subjects_without_timestamps() {