fix(tui/utils): corrected state restoration for TTY and environment variables

- Corrected TTY property restoration to properly delete injected properties instead of redefining them as truthy values.
- Updated environment restoration to modify process.env keys individually to prevent breaking environment object reference bindings.
- Prevented pollution of TTY-gated code and environment variable state across test suites.

packages/tui/test/process-terminal-render-harness.ts

@@ -132,7 +132,12 @@ export function createProcessTerminalRenderHarness(
 			setTerminalHeadless(previousHeadless);
 			for (const spy of spies) spy.mockRestore();
 			for (const [target, key, descriptor] of PRISTINE) {
+				// A piped test run has no own `isTTY`/`columns`/`rows` descriptor, so
+				// the captured pristine value is `undefined`. Deleting the forced
+				// property restores that absent state — skipping it would leak
+				// `isTTY = true` and poison TTY-gated code (e.g. mermaid color auto-detect).
 				if (descriptor) Object.defineProperty(target, key, descriptor);
+				else Reflect.deleteProperty(target, key);
 			}
 		},
 	};

packages/utils/test/logger-error-serialization.test.ts

@@ -12,18 +12,25 @@ import { logger } from "@oh-my-pi/pi-utils";
  */
 
 let tempDir: string;
-let restoredEnv: NodeJS.ProcessEnv;
+let prevAgentDir: string | undefined;
 
 beforeAll(() => {
 	tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-logger-error-"));
-	restoredEnv = { ...process.env };
 	// `getLogsDir()` honors OMP_AGENT_DIR / HOME for its base; pin to our tmp.
+	// Restore only this key on teardown — reassigning `process.env` wholesale
+	// would replace the live binding with a plain object, diverging it from
+	// `Bun.env` and poisoning every env-reading test that runs afterwards.
+	prevAgentDir = process.env.OMP_AGENT_DIR;
 	process.env.OMP_AGENT_DIR = tempDir;
 	logger.setTransports({ file: tempDir, console: false });
 });
 
 afterAll(() => {
-	process.env = restoredEnv;
+	if (prevAgentDir === undefined) {
+		delete process.env.OMP_AGENT_DIR;
+	} else {
+		process.env.OMP_AGENT_DIR = prevAgentDir;
+	}
 	logger.setTransports({ file: false, console: false });
 	fs.rmSync(tempDir, { force: true, recursive: true });
 });