feat(tui): Set TURBO_IS_TUI environment variable when using TUI.

crates/turborepo-lib/src/task_graph/visitor.rs

@@ -912,6 +912,12 @@ impl ExecContext {
         cmd.envs(self.execution_env.iter());
         // Always last to make sure it overwrites any user configured env var.
         cmd.env("TURBO_HASH", &self.task_hash);
+
+        // Allow downstream tools to detect if the task is being ran with TUI
+        if self.experimental_ui {
+            cmd.env("TURBO_IS_TUI", "true");
+        }
+
         // enable task access tracing
 
         // set the trace file env var - frameworks that support this can use it to

docs/repo-docs/reference/system-environment-variables.mdx

@@ -39,6 +39,7 @@ System environment variables are always overridden by flag values provided direc
 
 Turborepo will make the following environment variables available within your tasks while they are executing:
 
-| Variable     | Description                             |
-| ------------ | --------------------------------------- |
-| `TURBO_HASH` | The hash of the currently running task. |
+| Variable       | Description                                                                                  |
+| -------------- | -------------------------------------------------------------------------------------------- |
+| `TURBO_HASH`   | The hash of the currently running task.                                                      |
+| `TURBO_IS_TUI` | When using the [TUI](/repo/docs/reference/configuration#ui), this variable is set to `true`. |