[Engine] avoid hanging on PleReader initialization failures

[j-luwierski]

Problem and result

On current upstream main, PleReader::open() still hangs during cleanup if read-buffer allocation fails or if a reader is reopened with a table range beyond EOF. The failed open() never returns its existing error. After this change, it closes cleanly and a later valid open/read succeeds.

Related discussion

Retested the report in #3045, which was closed during the 0.2.0-beta tracker reset. The original PR #3046 was also closed in that reset.

Approach

Publish the in-flight slot count only after the buffers and free-slot list are ready, and reset the count when closing. Add Linux CPU-only lifecycle coverage for normal reads, failed reopen, and injected allocation failure in caller-thread and I/O-worker modes. The allocation failure uses link-time posix_memalign wrapping and does not add production fault-injection behavior.

Validation

Linux x86_64, GCC 14.2.0, CUDA 13.4.92, NVIDIA RTX 4070 Ti SUPER; base revision e88ee39d1d6be6e3364183af3b39b62a7ed6f211, candidate revision 9f4b65fc.

Passed:

• CPU: cmake -S . -B build/ple-reader-beta -DSTRATA_BUILD_TESTS=ON -DSTRATA_WERROR=ON; cmake --build build/ple-reader-beta --target ple_reader_lifecycle_test direct_file_async_test -j2; and ctest --test-dir build/ple-reader-beta --output-on-failure -R '^(ple_reader_(reads|reopen|alloc)_(caller|threaded)|direct_file_async_test)$': targets built and all 7 tests passed.
• CUDA: cmake -S . -B build/ple-reader-cuda -DSTRATA_BUILD_TESTS=ON -DSTRATA_WERROR=OFF -DSTRATA_ENABLE_CUDA=ON -DCMAKE_CUDA_COMPILER=/usr/local/cuda-13.4/bin/nvcc; cmake --build build/ple-reader-cuda --target strata ple_reader_lifecycle_test direct_file_async_test -j2: all targets built.
• CUDA CTest: ctest --test-dir build/ple-reader-cuda --output-on-failure -R '^(ple_reader_(reads|reopen|alloc)_(caller|threaded)|direct_file_async_test)$': all 7 tests passed.
• Reproduced on unchanged base revision e88ee39d: both read controls passed; reopen and injected alloc cases timed out after 2 seconds in caller and threaded modes (4 hangs).
• git diff --check origin/main...HEAD: passed.

Failed:

• With STRATA_WERROR=ON, the CUDA build command cmake --build build/ple-reader-cuda --target strata ple_reader_lifecycle_test direct_file_async_test -j2 stopped on -Werror=misleading-indentation in unchanged src/core/layer.cpp. The CUDA build passed with WERROR disabled; warnings are outside this change.

Not run:

• HIP and SYCL builds: hipcc, dpcpp and icpx are unavailable.
• Windows runtime checks and real model inference.

Limits

The reproduction uses a synthetic file and real DirectFile I/O on Linux; it verifies initialization and recovery behavior, not a production memory-pressure incident or model inference.