fix(tui): respect environment terminal dimensions

closes #4004

packages/tui/test/terminal.test.ts

@@ -0,0 +1,45 @@
+import assert from "node:assert";
+import { describe, it } from "node:test";
+import { ProcessTerminal } from "../src/terminal.js";
+
+describe("ProcessTerminal dimensions", () => {
+	it("falls back to COLUMNS and LINES before default dimensions", () => {
+		const previousColumnsDescriptor = Object.getOwnPropertyDescriptor(process.stdout, "columns");
+		const previousRowsDescriptor = Object.getOwnPropertyDescriptor(process.stdout, "rows");
+		const previousColumns = process.env.COLUMNS;
+		const previousLines = process.env.LINES;
+
+		try {
+			Object.defineProperty(process.stdout, "columns", { value: undefined, configurable: true });
+			Object.defineProperty(process.stdout, "rows", { value: undefined, configurable: true });
+			process.env.COLUMNS = "123";
+			process.env.LINES = "45";
+
+			const terminal = new ProcessTerminal();
+
+			assert.equal(terminal.columns, 123);
+			assert.equal(terminal.rows, 45);
+		} finally {
+			if (previousColumnsDescriptor) {
+				Object.defineProperty(process.stdout, "columns", previousColumnsDescriptor);
+			} else {
+				Reflect.deleteProperty(process.stdout, "columns");
+			}
+			if (previousRowsDescriptor) {
+				Object.defineProperty(process.stdout, "rows", previousRowsDescriptor);
+			} else {
+				Reflect.deleteProperty(process.stdout, "rows");
+			}
+			if (previousColumns === undefined) {
+				delete process.env.COLUMNS;
+			} else {
+				process.env.COLUMNS = previousColumns;
+			}
+			if (previousLines === undefined) {
+				delete process.env.LINES;
+			} else {
+				process.env.LINES = previousLines;
+			}
+		}
+	});
+});