fix: reject non-interactive tui

CHANGELOG.md

@@ -79,6 +79,10 @@ versions (0.x) may contain breaking changes; they are always listed under a
 
 ### Fixed
 
+- **`oxide tui` now rejects non-interactive stdin/stdout before terminal setup.**
+  It prints a clear hint to use `oxide sql` or `oxide explain` for scripted output
+  and exits with usage code 2 instead of leaking a raw ENXIO-style terminal error.
+
 - **The dashboard's Describe panel no longer prints a truncated percentile as
   if it were the value.** `approx_percentile_cont` renders full precision, and
   the panel's six-character columns were clipped from the right, so the 2M-row

crates/oxidelake-runtime/src/bin/oxide.rs

@@ -157,6 +157,10 @@ async fn main() -> anyhow::Result<()> {
             tables,
             target,
         } => {
+            if !oxidelake_tui::is_interactive_terminal() {
+                eprintln!("{}", oxidelake_tui::NON_INTERACTIVE_TERMINAL_MESSAGE);
+                std::process::exit(2);
+            }
             let model = match &query {
                 Some(sql) => {
                     let session = session(None, target, &tables).await?;

crates/oxidelake-runtime/tests/cli.rs

@@ -24,6 +24,15 @@ fn oxide() -> Command {
     Command::cargo_bin("oxide").unwrap()
 }
 
+#[test]
+fn tui_rejects_non_interactive_terminal() {
+    oxide()
+        .arg("tui")
+        .assert()
+        .code(2)
+        .stderr("oxide tui needs an interactive terminal; use oxide sql or oxide explain for non-interactive output\n");
+}
+
 fn gen_data(dir: &Path, rows: u64) {
     let assert = oxide()
         .args([

crates/oxidelake-tui/src/app.rs

@@ -1,6 +1,6 @@
 //! The real-terminal event loop (crossterm) with DEC 2026 synchronized updates.
 
-use std::io::{self, Write};
+use std::io::{self, IsTerminal, Write};
 use std::time::Duration;
 
 use crossterm::event::{self, Event, KeyCode, KeyEvent, KeyEventKind, KeyModifiers};
@@ -12,6 +12,14 @@ use crate::model::DashboardModel;
 use crate::render::render;
 use crate::state::{AppState, KeyInput, Transition};
 
+/// Message shown when the dashboard is started without an interactive terminal.
+pub const NON_INTERACTIVE_TERMINAL_MESSAGE: &str = "oxide tui needs an interactive terminal; use oxide sql or oxide explain for non-interactive output";
+
+/// Whether both input and output are attached to an interactive terminal.
+pub fn is_interactive_terminal() -> bool {
+    io::stdin().is_terminal() && io::stdout().is_terminal()
+}
+
 /// Maps a crossterm key event onto the dashboard's input alphabet. Key
 /// releases (reported by some terminals) are ignored.
 pub fn key_input_from_crossterm(key: &KeyEvent) -> Option<KeyInput> {
@@ -52,6 +60,12 @@ pub fn run_terminal(
     tick: Option<Duration>,
     mut refresh: impl FnMut(&mut DashboardModel),
 ) -> io::Result<()> {
+    if !is_interactive_terminal() {
+        return Err(io::Error::new(
+            io::ErrorKind::NotConnected,
+            NON_INTERACTIVE_TERMINAL_MESSAGE,
+        ));
+    }
     let mut terminal = ratatui::try_init()?;
     let mut state = AppState::new(model.plan().len());
     let result = (|| -> io::Result<()> {

crates/oxidelake-tui/src/lib.rs

@@ -20,7 +20,10 @@ pub mod model;
 pub mod render;
 pub mod state;
 
-pub use app::{draw_frame, key_input_from_crossterm, run_terminal};
+pub use app::{
+    NON_INTERACTIVE_TERMINAL_MESSAGE, draw_frame, is_interactive_terminal,
+    key_input_from_crossterm, run_terminal,
+};
 pub use model::{ColumnProfile, DashboardModel, demo_model};
 pub use render::render;
 pub use state::{AppState, KeyInput, Panel, Transition};