Slim fixture: mic-mistral3-slim

A 8.6M-parameter fixture for the mistral3 MIC, covering mistralai/Mistral-Small-3.1-24B-Instruct-2503. It is a test artifact, not a usable model, tagged test-artifact to keep it out of candidate-model search.

• Fixture key 2b7376f25a44. It covers every checkpoint whose processor files are byte-identical and whose config matches after shrinking.
• Same architecture, smaller config: Mistral3ForConditionalGeneration, shrunk by the generic rule in sweep.py (vision num_hidden_layers 2, text num_hidden_layers 2).
• Processor files copied byte for byte from mistralai/Mistral-Small-3.1-24B-Instruct-2503: SYSTEM_PROMPT.txt, chat_template.json, generation_config.json, params.json, preprocessor_config.json, processor_config.json, special_tokens_map.json, tekken.json, tokenizer.json, tokenizer_config.json.
• Random weights (seed 17). They passed the input-sensitivity gate: every perturbation of the contract's inputs moved the logits by at least 0.001 (weakest: input_ids:reverse, 1.75), so no training was needed.
• Same tensor names as the real checkpoint. The real checkpoint has every parameter, and so does the fixture.
• Saved in bfloat16, the dtype mistralai/Mistral-Small-3.1-24B-Instruct-2503 loads in by default.
• Finite in float32, bfloat16, and float16 (forward, loss, gradients).

Built by build_fixtures.py; build.json records the pinned sources, gate results, and file hashes. The source repository commits only README.md and build.json; rebuild the other files with python example/build_fixtures.py --fixture mic-mistral3-slim.