"whoever puts his trust in the LORD is kept safe" (29:25). Is that a promise that nothing will harm him?

It is a saying, and it says what it says: "The fear of man proves to be a snare, but whoever puts his trust in the LORD is kept safe" (29:25). Kept safe is sagav, and Brown-Driver-Briggs gives it, for the form used here, as "be set (securely) on high" (tap safe). The saying doesn't say what the one who trusts is kept from, or when, and these notes don't either. The book holds other sayings beside it: "for a righteous man falls seven times and rises up again" (Proverbs 24:16), and "Trust in the LORD with all your heart, and don’t lean on your own understanding" (Proverbs 3:5). The notes on Proverbs 18 look at sagav in "The LORD’s name is a strong tower: the righteous run to him, and are safe" (Proverbs 18:10). 29:25 is a saying. These notes say what it says, don't make it a guarantee that nothing hard will happen to anyone who trusts, and don't explain it away.