feat: add GEMINI_CLI environment variable to spawned shell commands (#4791)

docs/cli/commands.md

@@ -282,3 +282,5 @@ The `!` prefix lets you interact with your system's shell directly from within G
       - When exited, the UI reverts to its standard appearance and normal Gemini CLI behavior resumes.
 
 - **Caution for all `!` usage:** Commands you execute in shell mode have the same permissions and impact as if you ran them directly in your terminal.
+
+- **Environment Variable:** When a command is executed via `!` or in shell mode, the `GEMINI_CLI=1` environment variable is set in the subprocess's environment. This allows scripts or tools to detect if they are being run from within the Gemini CLI.

docs/tools/shell.md

@@ -60,6 +60,10 @@ run_shell_command(command="npm run dev &", description="Start development server
 - **Error handling:** Check the `Stderr`, `Error`, and `Exit Code` fields to determine if a command executed successfully.
 - **Background processes:** When a command is run in the background with `&`, the tool will return immediately and the process will continue to run in the background. The `Background PIDs` field will contain the process ID of the background process.
 
+## Environment Variables
+
+When `run_shell_command` executes a command, it sets the `GEMINI_CLI=1` environment variable in the subprocess's environment. This allows scripts or tools to detect if they are being run from within the Gemini CLI.
+
 ## Command Restrictions
 
 You can restrict the commands that can be executed by the `run_shell_command` tool by using the `coreTools` and `excludeTools` settings in your configuration file.