perf(display): cache terminal theme detection with 100ms timeout

crates/forge_display/src/code.rs

@@ -1,4 +1,5 @@
-use std::sync::Arc;
+use std::sync::{Arc, OnceLock};
+use std::time::Duration;
 
 use syntect::easy::HighlightLines;
 use syntect::highlighting::ThemeSet;
@@ -7,6 +8,12 @@ use syntect::util::as_24_bit_terminal_escaped;
 use terminal_colorsaurus::{QueryOptions, ThemeMode, theme_mode};
 use two_face::theme::EmbeddedThemeName;
 
+/// Maximum time to wait for a terminal color query response.
+const THEME_DETECT_TIMEOUT: Duration = Duration::from_millis(100);
+
+/// Process-wide cache for whether the terminal uses a dark background.
+static IS_DARK_THEME: OnceLock<bool> = OnceLock::new();
+
 /// Loads and caches syntax highlighting resources.
 #[derive(Clone)]
 pub struct SyntaxHighlighter {
@@ -25,12 +32,19 @@ impl Default for SyntaxHighlighter {
 }
 
 impl SyntaxHighlighter {
-    /// Detects whether the terminal is using a dark or light background.
+    /// Detects whether the terminal is using a dark or light background,
+    /// querying the terminal at most once per process lifetime. Subsequent
+    /// calls return the cached result. Falls back to dark mode on timeout or
+    /// if the terminal does not support color queries.
     fn is_dark_theme() -> bool {
-        match theme_mode(QueryOptions::default()) {
-            Ok(ThemeMode::Light) => false,
-            Ok(ThemeMode::Dark) | Err(_) => true,
-        }
+        *IS_DARK_THEME.get_or_init(|| {
+            let mut opts = QueryOptions::default();
+            opts.timeout = THEME_DETECT_TIMEOUT;
+            match theme_mode(opts) {
+                Ok(ThemeMode::Light) => false,
+                Ok(ThemeMode::Dark) | Err(_) => true,
+            }
+        })
     }
 
     /// Syntax-highlights `code` for the given language token (e.g. `"toml"`,

crates/forge_markdown_stream/src/utils.rs

@@ -1,5 +1,8 @@
 //! Utility functions for the markdown renderer.
 
+use std::sync::OnceLock;
+use std::time::Duration;
+
 /// Terminal theme mode (dark or light).
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum ThemeMode {
@@ -9,12 +12,24 @@ pub enum ThemeMode {
     Light,
 }
 
-/// Detects the terminal theme mode (dark or light).
+/// Maximum time to wait for a terminal color query response.
+const THEME_DETECT_TIMEOUT: Duration = Duration::from_millis(100);
+
+/// Process-wide cache for the detected terminal theme mode.
+static THEME_MODE: OnceLock<ThemeMode> = OnceLock::new();
+
+/// Detects the terminal theme mode (dark or light), querying the terminal at
+/// most once per process lifetime. Subsequent calls return the cached result.
+/// Falls back to dark mode if the terminal does not respond within the timeout.
 pub fn detect_theme_mode() -> ThemeMode {
-    use terminal_colorsaurus::{QueryOptions, ThemeMode as ColorsaurusThemeMode, theme_mode};
+    *THEME_MODE.get_or_init(|| {
+        use terminal_colorsaurus::{QueryOptions, ThemeMode as ColorsaurusThemeMode, theme_mode};
 
-    match theme_mode(QueryOptions::default()) {
-        Ok(ColorsaurusThemeMode::Light) => ThemeMode::Light,
-        Ok(ColorsaurusThemeMode::Dark) | Err(_) => ThemeMode::Dark,
-    }
+        let mut opts = QueryOptions::default();
+        opts.timeout = THEME_DETECT_TIMEOUT;
+        match theme_mode(opts) {
+            Ok(ColorsaurusThemeMode::Light) => ThemeMode::Light,
+            Ok(ColorsaurusThemeMode::Dark) | Err(_) => ThemeMode::Dark,
+        }
+    })
 }