gh-47798: Add a `subprocess.run_pipeline()` API#142080

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gpshead wants to merge 12 commits intopython:mainfrom

gpshead:claude/subprocess-pipe-chaining-01R27VPueru4RfRXYDsV5TmW

Commits on Nov 29, 2025

Add subprocess.run_pipeline() for command pipe chaining

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Add documentation for subprocess.run_pipeline()

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Refactor run_pipeline() to use multiplexed I/O

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Add deadlock prevention tests for run_pipeline()

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Simplify _communicate_streams() to only accept file objects

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Improve test_pipeline_large_data_with_stderr to use large stderr

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Remove obsolete XXX comment about non-blocking I/O

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Refactor POSIX communicate I/O into shared _communicate_io_posix()

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Fix _communicate_streams_windows to avoid blocking with large input

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Fix memoryview and closed stdin handling in _communicate_streams_posix

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Factor out _flush_stdin() and _make_input_view() helpers

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Support universal_newlines and use _translate_newlines in run_pipeline

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