✨ feat: periodic update check on startup

On startup, if `update_check_interval_hours` have elapsed since the last
check, fetches the latest release tag from the Gitea API and prints a
notice when a newer version is available. Silent on network failure or
no update found.

- New `update_check` module with injected fetcher for full testability
- Cache at ~/.cache/tmuxido/update_check.json tracks timestamp + version
- `fetch_latest_tag` and `version_compare` promoted to `pub(crate)`
- 6 unit tests covering disabled, interval not elapsed, fetch triggered,
  equal versions, update available, and current-newer edge case

src/lib.rs

@@ -4,6 +4,7 @@ pub mod deps;
 pub mod self_update;
 pub mod session;
 pub mod ui;
+pub mod update_check;
 
 use anyhow::Result;
 use cache::ProjectCache;
@@ -192,6 +193,7 @@ mod tests {
             max_depth: 3,
             cache_enabled,
             cache_ttl_hours: 24,
+            update_check_interval_hours: 24,
             default_session: session::SessionConfig { windows: vec![] },
         }
     }

src/main.rs

@@ -6,6 +6,7 @@ use std::process::{Command, Stdio};
 use tmuxido::config::Config;
 use tmuxido::deps::ensure_dependencies;
 use tmuxido::self_update;
+use tmuxido::update_check;
 use tmuxido::{get_projects, launch_tmux_session, show_cache_status};
 
 #[derive(Parser, Debug)]
@@ -48,6 +49,9 @@ fn main() -> Result<()> {
     // Load config
     let config = Config::load()?;
 
+    // Periodic update check (silent on failure or no update)
+    update_check::check_and_notify(&config);
+
     // Handle cache status command
     if args.cache_status {
         show_cache_status(&config)?;

src/self_update.rs

@@ -27,7 +27,7 @@ fn detect_arch() -> Result<&'static str> {
 }
 
 /// Fetch latest release tag from Gitea API
-fn fetch_latest_tag() -> Result<String> {
+pub(crate) fn fetch_latest_tag() -> Result<String> {
     let url = format!("{}/api/v1/repos/{}/releases?limit=1&page=1", BASE_URL, REPO);
 
     let output = Command::new("curl")
@@ -166,7 +166,7 @@ pub fn self_update() -> Result<()> {
 }
 
 /// Compare two semver versions
-fn version_compare(a: &str, b: &str) -> std::cmp::Ordering {
+pub(crate) fn version_compare(a: &str, b: &str) -> std::cmp::Ordering {
     let parse = |s: &str| {
         s.split('.')
             .filter_map(|n| n.parse::<u32>().ok())

src/update_check.rs

@@ -0,0 +1,219 @@
+use anyhow::Result;
+use serde::{Deserialize, Serialize};
+use std::path::PathBuf;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use crate::config::Config;
+use crate::self_update;
+
+#[derive(Debug, Default, Serialize, Deserialize)]
+struct UpdateCheckCache {
+    last_checked: u64,
+    latest_version: String,
+}
+
+pub fn check_and_notify(config: &Config) {
+    let cache = load_cache();
+    check_and_notify_internal(
+        config.update_check_interval_hours,
+        cache,
+        &|| self_update::fetch_latest_tag(),
+        &save_cache,
+    );
+}
+
+fn check_and_notify_internal(
+    interval_hours: u64,
+    mut cache: UpdateCheckCache,
+    fetcher: &dyn Fn() -> Result<String>,
+    saver: &dyn Fn(&UpdateCheckCache),
+) -> bool {
+    if interval_hours == 0 {
+        return false;
+    }
+
+    let elapsed = elapsed_hours(cache.last_checked);
+
+    if elapsed >= interval_hours
+        && let Ok(latest) = fetcher()
+    {
+        let latest_clean = latest.trim_start_matches('v').to_string();
+        let now = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs();
+        cache.last_checked = now;
+        cache.latest_version = latest_clean;
+        saver(&cache);
+    }
+
+    let current = self_update::current_version();
+    let latest_clean = cache.latest_version.trim_start_matches('v');
+    if !latest_clean.is_empty()
+        && self_update::version_compare(latest_clean, current) == std::cmp::Ordering::Greater
+    {
+        print_update_notice(current, latest_clean);
+        return true;
+    }
+
+    false
+}
+
+fn print_update_notice(current: &str, latest: &str) {
+    let msg1 = format!("  Update available: {} \u{2192} {}  ", current, latest);
+    let msg2 = "  Run tmuxido --update to install.  ";
+    let w1 = msg1.chars().count();
+    let w2 = msg2.chars().count();
+    let width = w1.max(w2);
+    let border = "\u{2500}".repeat(width);
+    println!("\u{250c}{}\u{2510}", border);
+    println!("\u{2502}{}\u{2502}", pad_to_chars(&msg1, width));
+    println!("\u{2502}{}\u{2502}", pad_to_chars(msg2, width));
+    println!("\u{2514}{}\u{2518}", border);
+}
+
+fn pad_to_chars(s: &str, width: usize) -> String {
+    let char_count = s.chars().count();
+    if char_count >= width {
+        s.to_string()
+    } else {
+        format!("{}{}", s, " ".repeat(width - char_count))
+    }
+}
+
+fn cache_path() -> Result<PathBuf> {
+    let cache_dir = dirs::cache_dir()
+        .ok_or_else(|| anyhow::anyhow!("Could not determine cache directory"))?
+        .join("tmuxido");
+    Ok(cache_dir.join("update_check.json"))
+}
+
+fn load_cache() -> UpdateCheckCache {
+    cache_path()
+        .ok()
+        .and_then(|p| std::fs::read_to_string(p).ok())
+        .and_then(|s| serde_json::from_str(&s).ok())
+        .unwrap_or_default()
+}
+
+fn save_cache(cache: &UpdateCheckCache) {
+    if let Ok(path) = cache_path() {
+        if let Some(parent) = path.parent() {
+            let _ = std::fs::create_dir_all(parent);
+        }
+        if let Ok(json) = serde_json::to_string(cache) {
+            let _ = std::fs::write(path, json);
+        }
+    }
+}
+
+fn elapsed_hours(ts: u64) -> u64 {
+    let now = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .unwrap_or_default()
+        .as_secs();
+    now.saturating_sub(ts) / 3600
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::cell::RefCell;
+
+    fn make_cache(last_checked: u64, latest_version: &str) -> UpdateCheckCache {
+        UpdateCheckCache {
+            last_checked,
+            latest_version: latest_version.to_string(),
+        }
+    }
+
+    fn now_ts() -> u64 {
+        SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .unwrap_or_default()
+            .as_secs()
+    }
+
+    #[test]
+    fn should_not_notify_when_interval_is_zero() {
+        let cache = make_cache(0, "99.0.0");
+        let fetcher_called = RefCell::new(false);
+
+        let result = check_and_notify_internal(
+            0,
+            cache,
+            &|| {
+                *fetcher_called.borrow_mut() = true;
+                Ok("99.0.0".to_string())
+            },
+            &|_| {},
+        );
+
+        assert!(!result);
+        assert!(!fetcher_called.into_inner());
+    }
+
+    #[test]
+    fn should_not_check_when_interval_not_elapsed() {
+        let cache = make_cache(now_ts(), "");
+        let fetcher_called = RefCell::new(false);
+
+        check_and_notify_internal(
+            24,
+            cache,
+            &|| {
+                *fetcher_called.borrow_mut() = true;
+                Ok("99.0.0".to_string())
+            },
+            &|_| {},
+        );
+
+        assert!(!fetcher_called.into_inner());
+    }
+
+    #[test]
+    fn should_check_when_interval_elapsed() {
+        let cache = make_cache(0, "");
+        let fetcher_called = RefCell::new(false);
+
+        check_and_notify_internal(
+            1,
+            cache,
+            &|| {
+                *fetcher_called.borrow_mut() = true;
+                Ok(self_update::current_version().to_string())
+            },
+            &|_| {},
+        );
+
+        assert!(fetcher_called.into_inner());
+    }
+
+    #[test]
+    fn should_not_notify_when_versions_equal() {
+        let current = self_update::current_version();
+        let cache = make_cache(now_ts(), current);
+
+        let result = check_and_notify_internal(24, cache, &|| unreachable!(), &|_| {});
+
+        assert!(!result);
+    }
+
+    #[test]
+    fn should_detect_update_available() {
+        let cache = make_cache(now_ts(), "99.0.0");
+
+        let result = check_and_notify_internal(24, cache, &|| unreachable!(), &|_| {});
+
+        assert!(result);
+    }
+
+    #[test]
+    fn should_not_detect_update_when_current_is_newer() {
+        let cache = make_cache(now_ts(), "0.0.1");
+
+        let result = check_and_notify_internal(24, cache, &|| unreachable!(), &|_| {});
+
+        assert!(!result);
+    }
+}