P3179R9 Parallel Range Algorithms

WG21-P3179R9 Parallel Range Algorithms
WG21-P3709R2 Reconsider Parallel ranges::rotate_copy And ranges::reverse_copy
WG21-P3923R0 Additional NB Comment Resolutions For Kona 2025 (section 2.6)
LWG-4297 Missing permutable constraint for iterator overloads in Parallel Range Algorithms
LWG-4431 Parallel std::ranges::destroy should allow exceptions
LWG-4441 ranges::rotate do not handle sized-but-not-sized-sentinel ranges correctly
LWG-4492 std::generate and std::ranges::generate wording is unclear for parallel algorithms
LWG-4544 Parallel overload of ranges::set_difference should return in_in_out_result
LWG-4548 Parallel ranges::set_intersection should not do unnecessary work

Wording clarifications:
LWG-4463 Change wording to 'model' from 'subsumes' in [algorithms.parallel.user]
LWG-4464 [alg.merge] Wording tweaks
LWG-4465 [alg.partitions] Clarify Returns: element

INCREASED feature-test macro:

#define __cpp_lib_parallel_algorithm 202506L

Note: We are not yet accepting PRs for C++26 features.

Start by reading WG21-P3179R9 and the listed follow-up papers and LWG issues to understand the requested C++26 parallel range algorithms. The issue provides no source files or tests, and explicitly says PRs are not yet being accepted, so there is no newcomer-ready implementation path or stated verification procedure.