1. I have an improvement idea (architecture, code organization, dependency handling, code checkers, etc.).

2. I propose it to the tech lead (he's not actually a lead, but works at the company the longest and is most knowledgeable and has most influence on decision making).

3. He doesn't accept it. I ran-out-of-arguments/cannot convince him.

4. A few weeks, even months, pass.

5. He proposes the idea as his own.

6. The manager accepts it.

I kinda furious at the moment because it happened again today. I think it's just weird to go to my manager and say it was my idea in the first place. Why he should believe me?

Any ideas how to handle it?