how can I get sed to quit after the first matching address range?

You can do this with a loop in GNU sed:

sed -n '/trigger/{p; :loop n; p; /trigger/q; b loop}'

Explanation:

1. When you see the first /trigger/, start a block of commands
2. p — print the line
3. :loop — set a label named loop
4. n — get the next line
5. p — print the line
6. /trigger/q — if the line matches /trigger/ then exit sed
7. b — jump to loop