Short answers, pulled from the story.
Marshal Edward Rydz-Śmigły ordered all Polish troops fighting east of the Vistula River to move toward Lwów and then to the hills along the borders with Romania and the Soviet Union. This directive aimed to organize a successful defense until winter arrived using natural lines like the Stryj and Dniester rivers.
The Red Army invaded Poland from the east on the 17th of September 1939, violating their non-aggression pact with Warsaw. This action sealed the fate of the planned defensive line before it could fully form and created a two-front war that doomed the strategy.
Approximately 120,000 Polish troops withdrew through the Romanian Bridgehead area to neutral Romania and Hungary. Most of those soldiers joined the newly-formed Polish Armed Forces in France and the United Kingdom during 1939 and 1940.
Part of the National Bank of Poland treasury consisting of 82,403 kg of gold was loaded aboard a commercial ship in the port of Constanța for transport to Western Europe. The second part of the treasury was deposited in the National Bank of Romania and returned to Poland on the 17th of September 1947.
Poland chose not to activate its formal alliance with Romania because having a safe haven offered more value than immediate war. The decision prioritized keeping the port of Constanța open for Allied merchant ships rather than risking conflict with Germany.