Implement two-pointer unique-pair sum search

Given a nondecreasing integer array nums and an integer target, return all unique value pairs [a, b] with a <= b such that a + b == target. Use the two-pointer technique to achieve O(n) time and O( 1) extra space beyond the output, and ensure duplicates in nums do not produce duplicate pairs. Additionally: a) Describe how you would return indices instead of values and any implications for stability. b) Explain how you would adapt the method if nums arrives as a stream that cannot be fully stored in memory. c) Analyze time and space complexity.