feat: enhance error handling in OAuth URL building and client creation; improve tool argument sanitization

src/tool/fs/edit.rs

@@ -56,6 +56,9 @@ impl Tool for Edit {
         if reason.trim().is_empty() {
             anyhow::bail!("reason must be a non-empty string");
         }
+        if old.is_empty() {
+            anyhow::bail!("'old' must be a non-empty string; use 'write' to replace entire file contents");
+        }
         let check_matches = check_graduated_checks(&rel, &new_str, &ctx.graduated_checks);
         let replace_all = args.get("replace_all").and_then(|v| v.as_bool()).unwrap_or(false);
         let path: PathBuf = resolve_path(&ctx.workspaces, &rel)?;