feat: add idle timeout and parent process death detection

Prevents orphaned bbs-md processes when SSH sessions disconnect
uncleanly. Adds two mechanisms:

- Parent death check: polls getppid() each loop iteration and exits
  when the parent (sshd) dies, detecting session orphaning immediately.
- Idle timeout: configurable idle_timeout_minutes in bbs.toml (default
  0 = disabled) exits after no keyboard/mouse input for the duration.

Cargo.lock

@@ -223,6 +223,7 @@ dependencies = [
  "ansi-to-tui",
  "clap",
  "image",
+ "libc",
  "notify",
  "pulldown-cmark",
  "ratatui 0.30.0",

Cargo.toml

@@ -18,3 +18,4 @@ walkdir = "2.5"
 ureq = "2.12"
 ratatui-image = { version = "10.0", default-features = false }
 image = "0.25"
+libc = "0.2"

src/app.rs

@@ -161,6 +161,10 @@ pub enum ShutdownReason {
     UserQuit,
     /// A SIGHUP or SIGTERM was received.
     Signal,
+    /// No user input for the configured idle timeout duration.
+    IdleTimeout,
+    /// Parent process (sshd) died — SSH session is gone.
+    ParentDied,
 }
 
 // ── HistoryEntry ──────────────────────────────────────────────────────────────
@@ -277,6 +281,13 @@ pub struct App {
     image_records: Vec<crate::renderer::ImageRecord>,
     /// Cache of loaded images keyed by source string.
     image_cache: HashMap<String, ImageCacheEntry>,
+
+    // ── Session lifecycle ──────────────────────────────────────────────────
+    /// Timestamp of the last keyboard or mouse input from the user.
+    last_input_at: Instant,
+    /// PID of the parent process at startup (typically sshd).
+    /// If getppid() changes, the parent died and the session is orphaned.
+    initial_ppid: u32,
 }
 
 impl App {
@@ -352,6 +363,8 @@ impl App {
             picker,
             image_records,
             image_cache: HashMap::new(),
+            last_input_at: Instant::now(),
+            initial_ppid: unsafe { libc::getppid() } as u32,
         }
     }
 
@@ -399,9 +412,11 @@ impl App {
             if event::poll(Duration::from_millis(250))? {
                 match event::read()? {
                     Event::Key(key) => {
+                        self.last_input_at = Instant::now();
                         self.handle_key(key);
                     }
                     Event::Mouse(mouse) => {
+                        self.last_input_at = Instant::now();
                         self.handle_mouse(mouse);
                     }
                     Event::Resize(w, _h) => {
@@ -411,6 +426,20 @@ impl App {
                 }
             }
 
+            // 3.1 Check idle timeout (0 = disabled)
+            if self.config.idle_timeout_minutes > 0 {
+                let timeout = Duration::from_secs(self.config.idle_timeout_minutes * 60);
+                if self.last_input_at.elapsed() >= timeout {
+                    return Ok(ShutdownReason::IdleTimeout);
+                }
+            }
+
+            // 3.2 Check if parent process (sshd) died — session is orphaned
+            let current_ppid = unsafe { libc::getppid() } as u32;
+            if current_ppid != self.initial_ppid {
+                return Ok(ShutdownReason::ParentDied);
+            }
+
             // 3a. Check for filesystem events (non-blocking)
             if let Some(ref mut watcher) = self.file_watcher {
                 loop {

src/config.rs

@@ -30,6 +30,12 @@ pub struct Config {
     /// terminals where protocol detection fails or produces garbled output.
     #[serde(default)]
     pub force_halfblocks: bool,
+
+    /// Idle session timeout in minutes. When no keyboard or mouse input is
+    /// received for this duration, the session exits automatically.
+    /// Set to 0 to disable (default).
+    #[serde(default)]
+    pub idle_timeout_minutes: u64,
 }
 
 fn default_vault_path() -> PathBuf {
@@ -58,6 +64,7 @@ impl Default for Config {
             max_remote_document_size: default_max_remote_document_size(),
             max_remote_image_size: default_max_remote_image_size(),
             force_halfblocks: false,
+            idle_timeout_minutes: 0,
         }
     }
 }

src/main.rs

@@ -175,6 +175,14 @@ fn main() {
             // SIGHUP or SIGTERM — SSH disconnect or graceful OS shutdown.
             // Exit silently: there may be nobody on the other end to see a message.
         }
+        Ok(app::ShutdownReason::IdleTimeout) => {
+            // Idle timeout — user may still be watching, show a brief message.
+            println!("\r\nSession timed out due to inactivity.\r");
+        }
+        Ok(app::ShutdownReason::ParentDied) => {
+            // Parent process (sshd) died — SSH session is gone.
+            // Exit silently: there is nobody on the other end.
+        }
         Err(e) => {
             // I/O error from the event loop
             if e.kind() == std::io::ErrorKind::BrokenPipe {