Welcome! There are other useful pages on the 6502 wiki: I recommend you also check the index
here.
Note first - I think you know this, but to emphasise - that the 6502 doesn't jump to FFFC or any other vector: it jumps through the vector, which is to say it picks up the new PC value from the vector.
The action of each instruction in the 6502 is driven mostly from the so-called Decode ROM or Decode PLA and then the so-called Random Logic which is physically between the Decode and the Datapath. That includes interrupts and reset, which are all handled as variations of the BRK opcode.
When the interrupt, BRK, or reset gets to the cycles where the vector is fetched, there are just a few transistors which modify a default value of FFFF, pulling down one or more of the low bits to construct the right value.
You can watch the reset sequence with a visual6502 URL like
this. You'll notice the three bits which control the three LSBs of the vector are called pipeVectorA2, pipeVectorA1, pipeVectorA0
Perhaps see Michael Steil's page:
Internals of BRK/IRQ/NMI/RESET on a MOS 6502