fix(tui): prevented test env from suppressing interactive launch

Scoped test-runtime detection to explicit runner markers and Bun test entrypoints, so application NODE_ENV/BUN_ENV values no longer make ProcessTerminal headless.

Added subprocess regression coverage and propagated the private marker to test children.

Fixes #7261

scripts/ci-test-ts.ts

@@ -467,9 +467,9 @@ async function runTestCommand(testCommand: TestCommand): Promise<void> {
 	}
 }
 
-// Child env shared by every spawned test process: the parent env with all CI
-// credential / cloud-config variables scrubbed (see SCRUBBED_ENV_* above) and
-// GITHUB_ACTIONS cleared so suites resolve only against their own fixtures.
+// Child env shared by every spawned test process: the parent env with the
+// private test-runtime marker set, all CI credential / cloud-config variables
+// scrubbed (see SCRUBBED_ENV_* above), and GITHUB_ACTIONS cleared.
 //
 // GC knobs (both needed — they gate different JSC mechanisms):
 // - `BUN_JSC_useConcurrentGC=0` stops the collector from marking concurrently
@@ -493,6 +493,7 @@ function buildChildEnv(): Record<string, string | undefined> {
 	const env: Record<string, string | undefined> = {
 		...Bun.env,
 		GITHUB_ACTIONS: "",
+		PI_TEST_RUNTIME: "1",
 		BUN_JSC_useConcurrentGC: "0",
 		BUN_JSC_numberOfGCMarkers: "1",
 	};