"""Computes a linear warmup schedule value based on the current step.

This function calculates a linearly increasing value from `start_value` to `end_value` over the course of `warmup_steps`. If the current `step` exceeds `warmup_steps`, the function returns `end_value`.

Args:
    step (int): The current step number. Must be non-negative.
    warmup_steps (int): The number of steps over which the warmup occurs. Must be non-negative.
    start_value (float): The initial value at step 0. Must be non-negative.
    end_value (float): The target value after warmup_steps. Must be positive and greater than or equal to start_value.

Returns:
    float: The computed value based on the linear warmup schedule.

Raises:
    ValueError: If any of the following conditions are met:
        - `warmup_steps` is negative.
        - `step` is negative.
        - `start_value` is negative.
        - `end_value` is non-positive.
        - `start_value` is greater than `end_value`.
"""