fix: use xdg-open on linux

tool.gpt

@@ -1,5 +1,5 @@
 context: github.com/gptscript-ai/context/os
-tools: service, port, open-file-nix, open-nix, open-file-windows, open-windows
+tools: service, port, open-file-nix, open-nix, open-file-windows, open-windows, open-file-mac, open-mac
 params: file: (optional) A reference to a tool file. Can refer to either a local or remote file.
 
 Never run steps in parallel.
@@ -8,11 +8,14 @@ Perform the following steps in the order they appear:
 1. Run the service
 2. Get the port for the running service
 3. If no {file} was provided AND the local operating system is windows, use the open-windows tool then skip the remaining steps
+3. If no {file} was provided AND the local operating system is Darwin, use the open-mac tool then skip the remaining steps
 4. If no {file} was provided use the open-nix tool then skip the remaining steps
 5. If the operating system is windows, use the open-file-windows tool then skip the remaining steps
+5. If the operating system is Darwin, use the open-file-mac tool then skip the remaining steps
 6. Use the open-file-nix tool
 
 ---
+
 name: service
 
 #!sys.daemon /usr/bin/env npm run --prefix ${GPTSCRIPT_TOOL_DIR} dev
@@ -33,7 +36,7 @@ arg: file: The file to open
 
 #!/usr/bin/env sh
 
-open http://localhost:${PORT}/run?file=${FILE}
+xdg-open http://localhost:${PORT}/run?file=${FILE}
 
 ---
 
@@ -42,7 +45,7 @@ arg: port: The port the service is listening on
 
 #!/usr/bin/env sh
 
-open http://localhost:${PORT}
+xdg-open http://localhost:${PORT}
 
 ---
 
@@ -62,3 +65,23 @@ arg: port: The port the service is listening on
 #!/usr/bin/env powershell.exe
 
 start http://localhost:$env:PORT
+
+---
+
+name: open-file-mac
+arg: port: The port the service is listening on
+arg: file: The file to open
+
+#!/usr/bin/env sh
+
+open http://localhost:${PORT}/run?file=${FILE}
+
+---
+
+name: open-mac
+arg: port: The port the service is listening on
+
+#!/usr/bin/env sh
+
+open http://localhost:${PORT}
+