The Role of Fiber in React Rendering (Part 2)...

In Part 1, we opened up React's Fiber engine and looked at the basics: what a Fiber node is, how the linked list tree is wired with child/sibling/return pointers, how the two-phase walk (beginWork down, completeWork up) processes every component, and how reconciliation diffs old Fibers against new elements. Now we go deeper. This part covers the systems that make Fiber actually powerful: double buffering, effect flags, priority lanes, where your hooks live, and the three sub-phases of the commit