During the עשרת ימי תשובה we make insertions into the שמונה עשרה, each of which contains the word לחיים, meaning "for life."
What is the source for insisting on pronouncing it "zachrenu l'chayim," "uch'sov l'chayim," etc. (with a schwa) instead of "lachayim" (with a patach) in each case?