feat: add File.tryRead, File.tryWrite, File.tryDelete returning Result

Add safe variants of File operations that return Result<T, String> instead
of crashing with RuntimeError. This prevents server crashes when a file
is missing or unwritable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/interpreter.rs

@@ -3991,6 +3991,72 @@ impl Interpreter {
                 }
             }
 
+            // ===== File Effect (safe Result-returning variants) =====
+            ("File", "tryRead") => {
+                let path = match request.args.first() {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.tryRead requires a string path".to_string(),
+                        span: None,
+                    }),
+                };
+                match std::fs::read_to_string(&path) {
+                    Ok(content) => Ok(Value::Constructor {
+                        name: "Ok".to_string(),
+                        fields: vec![Value::String(content)],
+                    }),
+                    Err(e) => Ok(Value::Constructor {
+                        name: "Err".to_string(),
+                        fields: vec![Value::String(format!("Failed to read file '{}': {}", path, e))],
+                    }),
+                }
+            }
+            ("File", "tryWrite") => {
+                let path = match request.args.first() {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.tryWrite requires a string path".to_string(),
+                        span: None,
+                    }),
+                };
+                let content = match request.args.get(1) {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.tryWrite requires string content".to_string(),
+                        span: None,
+                    }),
+                };
+                match std::fs::write(&path, &content) {
+                    Ok(()) => Ok(Value::Constructor {
+                        name: "Ok".to_string(),
+                        fields: vec![Value::Unit],
+                    }),
+                    Err(e) => Ok(Value::Constructor {
+                        name: "Err".to_string(),
+                        fields: vec![Value::String(format!("Failed to write file '{}': {}", path, e))],
+                    }),
+                }
+            }
+            ("File", "tryDelete") => {
+                let path = match request.args.first() {
+                    Some(Value::String(s)) => s.clone(),
+                    _ => return Err(RuntimeError {
+                        message: "File.tryDelete requires a string path".to_string(),
+                        span: None,
+                    }),
+                };
+                match std::fs::remove_file(&path) {
+                    Ok(()) => Ok(Value::Constructor {
+                        name: "Ok".to_string(),
+                        fields: vec![Value::Unit],
+                    }),
+                    Err(e) => Ok(Value::Constructor {
+                        name: "Err".to_string(),
+                        fields: vec![Value::String(format!("Failed to delete file '{}': {}", path, e))],
+                    }),
+                }
+            }
+
             // ===== Process Effect =====
             ("Process", "exec") => {
                 use std::process::Command;