So in my mind, there is a leak in the Federation feeding information to Osayra about Discovery, or the Admiral this whole time was the big bad. Or there is a spy on Discovery. There is no way Osayra would have known where they were.
You don't need a leak for that part, either the on-screen explanation (which I don't think made sense or was the real one), or a tracking mechanism inside the subspace amplifier that uses Emerald Chain-technology works. However, knowing the name of the spore drive, knowing it needed a human pilot, who the pilot was and where they were to bring a mind control right to them... If they somehow got this from a scan of the ship, it's still an immense security breach and an oversight in security measures, even if no humans were involved in the disclosure, but it is also incredible enough that it's very hard to imagine how it happened without someone on the inside to feed them information.
There aren't many options:
- A Discovery crewman from the 23rd century. Individually they would be the least suspect, as they had neither the time to leave the ship and interact with anyone, nor the motivation to connect with someone from an unknown antagonist force, randomly; especially after they were willing to abandon their own time for the ship's mission. It's still the prime possibility because of the
sheer number of Discovery crewmembers (and still someone could pull a Seska), but anyone individually can be moved to the bottom of the list automatically.
- An unnamed member of the renovation crew. Also sheer number, but with much bigger chance. It's the most likely, but it would be odd choice for a story to have a spy and not somehow introduce them.
- Booker. Don't like this option. Doesn't fit with anything about his character we've seen so far. Doing 180° in his case would not be good story.
- Admiral Vance. He's the one most intimately familiar. Something feels good about Discovery proving themselves by uncovering a conspiracy on that level, it also compounds a bit of distrust I still feel towards the Federation, but it's both unrealistic for Discovery to become saviours
again and I also happen to like Vance.
- Lt. Willa. Could be. I suspected her before there was anything to suspect!
- Adira. Please NO. In hindsight some of the pieces would fit, they forced themselves on the ship, but still NO.
- The Andorian guy.
- The character played by Cronenberg. Albeit, fan theory: If that's revealed to be the answer, there would be a twist that the leak was done in the interest of the Federation, not the Emerald Chain. Somehow. It wouldn't make sense, but that's what it would be.