feat: add tty meta plugin to get current terminal device

Co-authored-by: aider (openai/andrew.openrouter.qwen.qwen3-coder) <aider@aider.chat>

src/meta_plugin/system.rs

@@ -358,3 +358,45 @@ impl MetaPlugin for FullHostnameMetaPlugin {
         self.meta_name.clone()
     }
 }
+
+#[derive(Debug, Clone, Default)]
+pub struct TtyMetaPlugin {
+    meta_name: String,
+}
+
+impl TtyMetaPlugin {
+    pub fn new() -> TtyMetaPlugin {
+        TtyMetaPlugin {
+            meta_name: "tty".to_string(),
+        }
+    }
+}
+
+impl MetaPlugin for TtyMetaPlugin {
+    fn create(&self) -> Result<Box<dyn Write>> {
+        Ok(Box::new(io::sink()))
+    }
+
+    fn finalize(&mut self) -> io::Result<String> {
+        // Try to get the TTY from the TTY environment variable first
+        if let Ok(tty) = env::var("TTY") {
+            if !tty.is_empty() {
+                return Ok(tty);
+            }
+        }
+        
+        // Try to get TTY from /dev/tty (this will give us the current terminal)
+        match std::fs::read_link("/dev/tty") {
+            Ok(path) => Ok(format!("/dev/{}", path.to_string_lossy())),
+            Err(_) => Ok("not a tty".to_string()),
+        }
+    }
+
+    fn update(&mut self, _data: &[u8]) {
+        // No update needed for TTY
+    }
+
+    fn meta_name(&mut self) -> String {
+        self.meta_name.clone()
+    }
+}