The Armistice Agreement of 1949 defines the status of Israel as of that time. It took place after the end of the Palestine Mandate, after UN Resolution 181, after Israel declared itself to be a state, and after the 1948 war.
The armistice was called by UN resolution. There was no surrender. No country lost any land in that war.
All of the internationally recognized borders mentioned were between Lebanon and Palestine, Syria and Palestine, Jordan and Palestine, and Egypt and Palestine. No borders were mentioned for Israel.
The "green line" (that was specifically stated to NOT be national or political borders) defined areas of occupation. It did not change Palestine's internationally recognized borders.
The cease fire was between "Israeli forces" and the forces of the other countries. "Israel" was not mentioned.
Article I in all the agreements started with: "With a view to promoting the return of permanent peace in Palestine..."
The Avalon Project : Lebanese-Israeli General Armistice Agreement, March 23, 1949
The Avalon Project : Israeli-Syrian General Armistice Agreement, July 20, 1949
The Avalon Project : Jordanian-Israeli General Armistice Agreement, April 3, 1949
The Avalon Project : Egyptian-Israeli General Armistice Agreement, February 24, 1949