Displacement Engine

The technological methods to travel from one shard to another are referred to collectively as displacement engines. The name is taken from the original Displacement Engine that was simultaneously invented on Shards 1, 2, and 3. Shard 3's Displacement Engine, now a museum, is a massive complex containing multiple power plants, control stations, and cooling grids surrounding the central "gate" generator.
Dimensional gates were the standard methods to travel the shards for first and second-generation agents. While the technology became smaller, power requirements and the need for complex calculations necessitated dedicated facilities and staff. Though some, like Benton McKay 17's "Caramel Drive", were designed to be mobile... if occupying the bay of a capital starship can be considered mobile.
Additionally, the early technology only worked for a slim few. While many could survive stepping between shards, most suffered severely with conditions akin to rapid onset dementia and radiation poisoning. Thus, agent qualification was often at the mercy of compatibility, with "agent families" breeding accusations of exclusivity and nepotism.
All of that changed with the discovery of Shard 99. Two sentient species were found within this shard, both spread across multiple planets, galaxies apart, despite neither of them having reached the communication age. While the tribal race of humanoids told stories of "dancing across worlds", it was the small vulpine quadrupeds that held the secret. These cinderfoxes could naturally step across shards. Thought to be a defense mechanism against their larger aggressors, the foxes used the ability more like Shard 17's "Shard Surfing" to travel great distances, and few had mastered the ability to jaunt dimensions.
The cinderfoxes of Shard 99 were quickly inducted into the Agency (the humanoids would join later) and worked with experienced agents to hone their natural interdimensional abilities. However, they made poor agents themselves. Talkative to a fault and prone to instinctual cowardice, few foxes managed to fit the Agency's high aspirations. But they could chaperone almost anyone across dimensions. Once paired with an Agent, the two could shard step without equipment and with minimal risk of side effects.
The discovery of Shard 99 and its cinderfoxes democratized interdimensional travel, leading to a golden age of exploration and discovery. But the Agency saw a path mirroring that of the first shards; conquest and ruin. As the illegal trade of foxes grew, the Agency sought to regain control. Thus began the Cronicle project.
The current evolution of interdimensional travel technology is the Chronicle; a small circular clam-shell device the size of a pocket watch. It is essentially a personal displacement engine, calibrated to one individual. The vast majority of agents utilize chronicles; the devices are strictly controlled by the Agency. Shard 99 is now a preserve, protected by the Agency to safeguard the dimension's denizens and the Agency's power. Cinderfoxes may still join the Agency's ranks as scribes and observers, but few act as partners to agents.