[MarkCole]

Is the tech lead actually proposing it as his idea? As in "Last night I had this idea x, we should do that". Or is he saying to the manager "We should implement x now because..." but leaving out who had the idea?

If it's the latter, he may be doing it unintentionally. I've known devs that don't have the best social skills, and they maybe don't realise that people would like to have credit for their ideas. It may just be that they mulled it over for some time and came to the conclusion it was a good idea. They may have even forgot who gave them the original idea. It may then be a good idea to talk with them and ask why they didn't give you credit.

Moving forward, my suggestion would be to have an email with others copied in. At most places I've worked we've had a developers@ / team.xy@ email. Maybe an email to that address with the idea, and asking for everyones feedback?