You are given an ordered list of 2D points `[(x1, y1), (x2, y2), ..., (xn, yn)]`. Connecting each consecutive pair of points forms a piecewise linear function. Given a target value `target_x`, return the corresponding `y` value on the function at that x-coordinate. Assume: - The points are ordered by increasing `x`. - The function is defined by straight-line interpolation between consecutive points. - `target_x` may coincide with an existing point or fall between two adjacent points. Clarify how you would handle edge cases such as: - `target_x` outside the covered x-range - duplicate x-values - invalid input with fewer than 2 points Example: - Points: `[(1, 2), (3, 6), (5, 4)]` - `target_x = 2` - Output: `4`, because the point lies on the line segment between `(1, 2)` and `(3, 6)`.