Bring the water to a boil in a small saucepan or in a tea cup in the microwave. Remove from heat, add the tea, and let steep for 4 minutes or longer (depending on how much you want your fudge sauce to taste like tea).
Wring and remove the tea bag and pour the tea into a medium bowl. Add the chocolate, cocoa powder, and salt.
Combine the corn syrup, sugar, and heavy cream in a heavy-bottomed saucepan and stir intermittently while bringing to a boil over high heat. The moment it boils, pour it into the bowl holding the chocolate. Let sit for 1 full minute.
Slowly, slowly begin to whisk the mixture. Then continue, increasing the vigor of your whisking every 30 seconds, until the mixture is glossy and silky-smooth. This will take 2 to 4 minutes, depending on your speed and strength. You can use the sauce at this point, or store it in an airtight container in the fridge for up to 2 weeks. Do not freeze.