[Auto] Add Mistral regex patch regression test (cluster-45081-3): merged 1 of 2 PRs

[evalstate]

Cluster: cluster-45081-3

Merged:

• Fix AttributeError in _patch_mistral_regex when fix_mistral_regex=True  huggingface/transformers#45317: Canonical PR; merged cleanly locally and adds a regression test for fix_mistral_regex=True. Source fix was already present on current origin/main.

Skipped:

• fix AttributeError in _patch_mistral_regex huggingface/transformers#45086: Superseded by PR Fix AttributeError in _patch_mistral_regex when fix_mistral_regex=True  huggingface/transformers#45317/current main; attempted merge was clean but produced no content changes.

Failed:

• None

Notes:

• Issue _patch_mistral_regex crashes with AttributeError: 'tokenizers.Tokenizer' object has no attribute 'backend_tokenizer' when loading Mistral tokenizer with fix_mistral_regex=True huggingface/transformers#45081 is still open.
• Final local diff vs origin/main is the added regression test in tests/models/auto/test_tokenization_auto.py.
• Repo was left with no merge in progress.
• Untracked runtime/session artifacts were left untouched.

Validation:

• Attempted: pytest tests/models/auto/test_tokenization_auto.py::AutoTokenizerTest::test_auto_tokenizer_mistral_patching_applies_pretokenizer -q
• Result: did not run because local environment is missing safetensors (ModuleNotFoundError: No module named 'safetensors').

Next steps:

• Install missing test dependency safetensors before rerunning the targeted pytest command.
• Rerun pytest tests/models/auto/test_tokenization_auto.py::AutoTokenizerTest::test_auto_tokenizer_mistral_patching_applies_pretokenizer -q.

[evalstate]

Trace for this mergeability run: https://huggingface.co/datasets/evalstate/transformers-merge-experiments/blob/main/2604241115-1bP959__dev__codex.jsonl