How do I write specs that get built right the first time?

You have reached the point where your words land as you meant them, and teams build the right thing without a second pass. That is not luck. It is care taken before anyone wrote a line of code, and it saves more time than any speed you could add later. The danger now is that it looks effortless, so people copy your format and miss the thing underneath. What makes your specs work is not the template. It is that you thought through the reader's questions before they asked. Keep naming that out loud so it does not get lost. Next time a spec of yours ships clean, take five minutes to write down why it worked. One sentence. Over time that becomes something you can teach, and your clarity outlives you.