A component's hooks (from useState, useEffect, etc.) are stored as a plain list attached to its fiber. Every render walks that list from the start, in the SAME call order the hooks were declared in -- which is exactly why hook calls can never be conditional: the mapping from "the 3rd use_state() call in this render" to "hook slot #2 in the list" only holds if every render walks the cursor starting from 0.

Right now, a component's state resets or scrambles on its SECOND render onward -- the first render always looks correct, which is what makes this bug sneaky.

Your task: find the bug in ComponentInstance.start_render() and fix it. use_state()'s cursor-advancing logic is already correct -- don't change it.

Example that currently fails

instance = ComponentInstance()

instance.start_render()
_, count_index = instance.use_state(0)
instance.set_state(count_index, 5)   # simulate calling the setter

instance.start_render()
count_value, count_index_2 = instance.use_state(0)
count_value       # should be 5 (the persisted update)
count_index_2     # should be 0 (same slot as before)
# currently: start_render() only resets _cursor when self.hooks is EMPTY
# -- true for the very first render, false for every render after, so
# the cursor keeps climbing instead of restarting at 0, and use_state
# ends up reading/creating the WRONG slot on every render after the first.

Real-world grounding

• React's hooks dispatcher and the hook linked list attached to each fiber: packages/react-reconciler/src/ReactFiberHooks.js -- see renderWithHooks, which resets workInProgressHook/the hook cursor to the start of the list at the BEGINNING of every render, not just the first one.

Real React's hook list is an actual linked list (each hook has a next pointer) rather than an indexed array, and additionally re-validates hook COUNT between renders in development mode (the "Rendered more hooks than during the previous render" warning) -- this exercise implements the cursor-reset mechanism whose absence is what that warning is guarding against.