refactor(chat): Add command suggestions for common single-word inputs (#953)

Improve user experience by detecting when users type common commands like
exit, quit, or help without the leading slash prefix. Instead of
making unnecessary LLM calls, provide helpful suggestions to use the
proper command format (e.g., '/quit', '/help').

🤖 Assisted by [Amazon Q Developer](https://aws.amazon.com/q/developer)

Author: kkashilk

crates/q_cli/src/cli/chat/command.rs

@@ -126,9 +126,32 @@ Adding relevant files to your context helps Amazon Q provide more accurate and h
 }
 
 impl Command {
+    // Check if input is a common single-word command that should use slash prefix
+    fn check_common_command(input: &str) -> Option<String> {
+        let input_lower = input.trim().to_lowercase();
+        match input_lower.as_str() {
+            "exit" | "quit" | "q" | "exit()" => {
+                Some("Did you mean to use the command '/quit' to exit? Type '/quit' to exit.".to_string())
+            },
+            "clear" | "cls" => Some(
+                "Did you mean to use the command '/clear' to clear the conversation? Type '/clear' to clear."
+                    .to_string(),
+            ),
+            "help" | "?" => Some(
+                "Did you mean to use the command '/help' for help? Type '/help' to see available commands.".to_string(),
+            ),
+            _ => None,
+        }
+    }
+
     pub fn parse(input: &str) -> Result<Self, String> {
         let input = input.trim();
 
+        // Check for common single-word commands without slash prefix
+        if let Some(suggestion) = Self::check_common_command(input) {
+            return Err(suggestion);
+        }
+
         if let Some(command) = input.strip_prefix("/") {
             let parts: Vec<&str> = command.split_whitespace().collect();
 
@@ -426,4 +449,44 @@ mod tests {
             assert_eq!(&Command::parse(input).unwrap(), parsed, "{}", input);
         }
     }
+
+    #[test]
+    fn test_common_command_suggestions() {
+        let test_cases = vec![
+            (
+                "exit",
+                "Did you mean to use the command '/quit' to exit? Type '/quit' to exit.",
+            ),
+            (
+                "quit",
+                "Did you mean to use the command '/quit' to exit? Type '/quit' to exit.",
+            ),
+            (
+                "q",
+                "Did you mean to use the command '/quit' to exit? Type '/quit' to exit.",
+            ),
+            (
+                "clear",
+                "Did you mean to use the command '/clear' to clear the conversation? Type '/clear' to clear.",
+            ),
+            (
+                "cls",
+                "Did you mean to use the command '/clear' to clear the conversation? Type '/clear' to clear.",
+            ),
+            (
+                "help",
+                "Did you mean to use the command '/help' for help? Type '/help' to see available commands.",
+            ),
+            (
+                "?",
+                "Did you mean to use the command '/help' for help? Type '/help' to see available commands.",
+            ),
+        ];
+
+        for (input, expected_message) in test_cases {
+            let result = Command::parse(input);
+            assert!(result.is_err(), "Expected error for input: {}", input);
+            assert_eq!(result.unwrap_err(), expected_message);
+        }
+    }
 }