Make kes_bytes file creation/write atomic for concurrent access

[turmelclem]

Content

Make kes_bytes file creation/write atomic for concurrent access, especially to fix CI test flakiness

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • All check jobs of the CI have succeeded
  • Self-reviewed the diff
  • Useful pull request description
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• Documentation
  • Update README file (if relevant)
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  • Add ADR blog post or Dev ADR entry (if relevant)
  • No new TODOs introduced

Issue(s)

this PR closes #3329

[github-actions]

Test Results

     5 files  ± 0     206 suites  ±0   56m 22s ⏱️ - 2h 11m 49s
 3 238 tests  - 72   3 238 ✅  - 72  0 💤 ±0  0 ❌ ±0 
10 899 runs   - 77  10 899 ✅  - 77  0 💤 ±0  0 ❌ ±0 

Results for commit f3cd375. ± Comparison against base commit 5d25797.

This pull request removes 73 and adds 1 tests. Note that renamed tests count towards both.

mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::index_out_of_bounds
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::index_too_large_for_circuit_range
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::indices_not_increasing
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::leaf_merkle_path_mismatch
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::leaf_swap_keep_merkle_path
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::leaf_wrong_verification_key
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::merkle_path_corrupt_sibling
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::merkle_path_flip_position
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::merkle_path_length_long
mithril-stm ‑ circuits::halo2::tests::golden::cases::negative::slow::merkle_path_length_short
…

mithril-common ‑ crypto_helper::cardano::codec::test::to_file_must_create_a_file

♻️ This comment has been updated with latest results.

[Copilot]

Pull request overview

This PR aims to eliminate CI flakiness caused by concurrent tests reading partially-written kes_bytes/Shelley-format files by switching test file exports to an atomic write pattern (write to a uniquely-named temp file, then rename into place).

Changes:

• Introduces a test-only SerDeShelleyFileFormatTestExtension::to_file to separate file-export helpers from the core SerDeShelleyFileFormat trait.
• Updates test/fixture code to use the new to_file extension trait.
• Implements an atomic-write strategy for to_file (temp file + rename) and adds a regression test ensuring a single final file is produced.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
mithril-common/src/test/crypto_helper/cardano/kes/setup.rs	Switches test KES material generation to use the new to_file test extension trait.
mithril-common/src/test/crypto_helper/cardano/extensions.rs	Adds a test-only extension trait to expose to_file for Shelley-format exports.
mithril-common/src/test/builder/fixture_builder.rs	Updates fixture builder imports/usage to rely on the new to_file extension trait.
mithril-common/src/crypto_helper/mod.rs	Re-exports CodecParseError to support the new extension trait signature.
mithril-common/src/crypto_helper/cardano/opcert.rs	Updates tests to import the to_file extension trait.
mithril-common/src/crypto_helper/cardano/codec.rs	Moves to_file behind a test extension trait and changes it to an atomic temp-write + rename approach; adds a regression test.

[Alenar]

LGTM

[jpraynaud]

LGTM 👍