Avoid mutating global STDOUT & STDERR (#1837)

[MitchLewis930]

PR_051

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Note

Low Risk
Behavior change is limited to how Puma::Events handles IO objects (dup + sync), with test-only adjustments elsewhere; low risk unless callers relied on Events.stdout being the exact same Ruby object as STDOUT/STDERR.

Overview
Puma Events now duplicates the passed stdout/stderr IO objects on initialization before setting sync, preventing Puma from mutating the global STDOUT/STDERR state.

Tests are updated to reflect the new semantics (stdio no longer equals the global constants, but points at the same underlying file descriptor) and add coverage that Events.stdio forces sync true without changing STDOUT.sync; TCPLogger tests are adjusted to ensure subprocess IO capture still observes logger output.

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Cursor Bugbot has reviewed your changes and found 2 potential issues.

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Test does not restore STDOUT.sync global state

Low Severity

The new test_stdio_respects_sync test sets STDOUT.sync = false but never restores it to its original value. Other tests in this file use ensure blocks to restore global state after modification (e.g., ENV["PUMA_DEBUG"]). This missing cleanup causes test pollution and could lead to flaky behavior in other tests that depend on STDOUT.sync being in its default state.

 

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Test compares inspect strings that have different formats

Medium Severity

The test_stdio test compares STDOUT.inspect with events.stdout.inspect, but events.stdout is a dup of $stdout. In Ruby, STDOUT.inspect typically returns #<IO:<STDOUT>> while STDOUT.dup.inspect returns #<IO:fd 1> - different string formats that won't be equal. The test's approach of comparing inspect strings is unreliable for verifying the same file handle; comparing fileno values would be more robust.