test_retry_descriptor_detects_truncation intermittent failure

  stdout ───

    running 1 test
    bin: "/home/runner/work/coreutils/coreutils/target/debug/coreutils"
    run: /home/runner/work/coreutils/coreutils/target/debug/coreutils tail -s.1 --max-unchanged-stats=1 --follow=descriptor --retry watchme ---disable-inotify
    touch: /tmp/.tmpTaz8ea/watchme
    write(truncate): /tmp/.tmpTaz8ea/watchme
    write(truncate): /tmp/.tmpTaz8ea/watchme
    test test_tail::test_retry_descriptor_detects_truncation ... FAILED

    failures:

    ---- test_tail::test_retry_descriptor_detects_truncation stdout ----
    ---- test_tail::test_retry_descriptor_detects_truncation stderr ----


    failures:
        test_tail::test_retry_descriptor_detects_truncation

    test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 5812 filtered out; finished in 1.15s
    
  stderr ───

    thread 'main' (58361) panicked at tests/by-util/test_tail.rs:1472:14:
    assertion failed: `(left == right)`

    Diff < left / right > :
     tail: warning: --retry only effective for the initial open
     tail: cannot open 'watchme' for reading: No such file or directory
     tail: 'watchme' has appeared;  following new file
    >tail: watchme: file truncated
     


    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: test run failed
Error: Process completed with exit code 100.

https://github.com/uutils/coreutils/actions/runs/33324689551/job/99292635561?pr=14252

Start with tests/by-util/test_tail.rs around line 1472 and reproduce test_tail::test_retry_descriptor_detects_truncation using the failing tail command from the log. Compare the expected and intermittent stderr output, then trace the retry and truncation behavior. Done means the test no longer fails intermittently while preserving the expected diagnostics.