[autoCAT6]

Rationale for this change

Writing an AES_GCM_CTR_V1 file with a plaintext footer currently records AES_GCM_V1 in the footer metadata. Readers then select GCM for the CTR data pages and fail to read them. This also reproduces with arrow-go v18.8.0.

Related to #566 and apache/arrow#54884.

What changes are included in this PR?

Serialize the configured file algorithm directly, preserving its AAD settings. Footer signing is unchanged.

Add a generated-file regression for both algorithms, encrypted and plaintext footers, and stored or externally supplied AAD prefixes. It checks serialized metadata and round-trip values, plus rejection of a corrupted plaintext-footer signature.

Are these changes tested?

The regression fails on the original code in all three CTR/plaintext cases and passes with the fix.

• All 18 Parquet packages pass with -race -tags assert. The focused regression also passes with assert,noasm.
• Files from this commit read correctly with arrow-go v18.8.0, the C++ reader from GH-51669: [C++][Parquet] Preserve cipher in plaintext footer metadata arrow#54884, and parquet-java 1.18.1, including all column values.
• Vet and lint pass for the changed packages. Apache RAT passes. Broader vet/lint checks report only the existing BitRun benchmark warning and three schema QF1001 suggestions, also reproduced on the unchanged base.

Are there any user-facing changes?

New CTR files with plaintext footers declare the correct cipher and can be read back. No API changes.

AI was used for the implementation, tests and PR description.

[zeroshade]

Thanks — a clean fix. Writing encryptProps.Algorithm() directly matches the encrypted-footer path (GetFileCryptoMetaData), and dropping the special-casing of AadPrefix is safe because the properties only carry a prefix when it's stored in the file. The test covers both ciphers across encrypted/plaintext footers and stored/external AAD, and the three CTR plaintext cases fail without the fix. The signature check confirms footer signing still uses GCM.

Minor, non-blocking: this repo prefers folding new tests into an existing test file where one fits, and using memory.NewCheckedAllocator in reader tests.

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[autoCAT6]

Moved the regression into file_reader_test.go and added a checked allocator to each case, with an assertion that all reader allocations are released after cleanup.

go test -race -tags assert ./parquet/... passes. The focused assert,noasm regression, vet and lint for the affected packages, and RAT also pass.