Was the foundation stone an open portal by design, or did Berem open it?

Question

In the Dragons of The Spring Dawning, it is revealed that Berem the Everman has found the Foundation Stone shortly after the Cataclysm. Takhisis used it as a portal to enter Krynn, but she could only enter as a shadow, not fully (as she did in the Age of Dreams and was forced to leave through Huma's sacrifice). In the end, Berem closed it, reuniting with his sister.

Did Takhisis create an open portal during/right after the Cataclysm, or did Berem inadvertently open it by removing the Green Gemstone?

Answer 1

There appears to be a contradition:

According to Dragons of Spring Dawning Book 3 Chapter 4 Everman's Story, Berem opened it by prying loose the Green Gemstone

Takhisis: (in Berem's story)

“ ‘Long ago was I banished from this world, and only through a piece of the world may I enter again. The jeweled column was—for me—a locked door, keeping me prisoner. You have freed me, mortal, and therefore I give you what you seek—the green gemstone is yours!’

Berem:

“There is terrible, mocking laughter. I feel a great pain in my chest. Looking down, I see the green gemstone embedded in my flesh, even as you see it now.

But in the Prologue to The Dragons Of The Hourglass Mage, Takhisis was already using the Stone as a portal, until blocked by Jasla's death:

Takhisis, Queen of Darkness, was still imprisoned in the Abyss. All the exits were guarded. If she tried to break free, the other gods would know and they would stop her. Still, she never quit seeking a way back into the world, and one day, in her restless roaming, she came upon a great prize. Takhisis discovered the Foundation Stone. The other gods did not know it still existed. She realized that she could use the stone to return to the world.

...

Takhisis, cloaked in darkness, slipped into the world through the gate left open by the Foundation Stone. She woke her evil dragons and ordered them to steal the eggs of the good dragons, who slumbered in their lairs. She prepared to prosecute her war with all her might and power. Then she discovered one day that her way into the world through the Foundation Stone had been blocked.

A man named Berem and his sister, Jasla, were walking together when they came upon the Foundation Stone.

^{... (story of Berem's downfall skipped, as not relevant)}

Takhisis had been witness to this tragedy and had reveled in Berem’s downfall … until she tried to cross the Foundation Stone. She found her entrance barred by a chain forged of love. Jasla’s spirit blocked her way. Now only the Dark Queen’s shadow could be cast over Krynn. Her power over man was reduced; she would have to rely on mortals to prosecute her war.

Answer 2

I think that this is less than a contradiction than you think. The Foundation Stone is a corrupted Temple of Paladine that, after the Cataclysm, found its way into the Abyss while still being on Krynn. This is how Takhisis is able to use it to enter Krynn.

However, nearly the same moment she discovered it in the Abyss, Berem and Jasla discovered it on Krynn. Berem recognized it as a temple of the gods. Thus he sought to remove the green gem, since the gods wouldn't need it anymore. Jasla tries to stop him from doing this, and Berem kills her. Takhisis tries to come through, but Jasla has blocked her path. The only way for Takhisis to go through now is for the green gem to be put back in its place.

There's an analogy that Berem uses about the whole thing, how he feels like he's trying to push on a door that'll never close, or something to that effect. So, Berem didn't open the portal. He effectively blocked it by pulling out the green gem AND killing his sister. Now for Takhisis to enter, the gem must be put back, effectively killing Berem and freeing Jasla's spirit.