Add M31ToU32 AIR component with full prove+verify

[alon-f]

Summary

• Add the auto-generated M31ToU32 gate AIR component (circuit_eval, framework eval, witness trace)
• Add preprocessed column generation for M31ToU32 (input_addr, output_addr, multiplicity)
• Pad m31_to_u32 gates in finalize_context (same pattern as eq, qm31_ops, blake)
• Register component in ComponentList, CircuitComponents, all_circuit_components, trace pipeline
• Full prove+verify integration test

Test plan

• test_prove_and_stark_verify_m31_to_u32_context — creates 32 m31_to_u32 gates, proves, STARK-verifies
• test_evaluation_result — auto-generated constraint accumulator unit test
• All existing tests pass (cargo test -r — 191 tests, 0 failures, 0 warnings)

🤖 Generated with Claude Code

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Note

Medium Risk
Adds a new AIR component and corresponding witness/preprocessed-trace plumbing, changing proof composition and trace layout. Also increases INTERACTION_POW_BITS, which affects PoW verification parameters and could break compatibility if configs aren’t updated everywhere.

Overview
Adds a new m_31_to_u_32 AIR component end-to-end (constraint eval + framework component + witness generation) to prove conversion of an M31 wire into packed u32 limbs, including required RangeCheck_16/Gate lookups.

Integrates the component through circuit preprocessing and proving: generates new preprocessed columns (m31_to_u32_input_addr, m31_to_u32_output_addr, m31_to_u32_multiplicity), pads m31_to_u32 gates during finalize_context, registers the component in component lists/prover pipelines/statement all_circuit_components, and adds a full prove+verify test plus updated expected preprocessed roots/sample eval constants.

Separately updates INTERACTION_POW_BITS from 8 to 20 and refreshes the privacy recursion consts hash.

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Stale privacy preprocessed root not updated

Medium Severity

PRIVACY_RECURSION_CIRCUIT_PREPROCESSED_ROOT was not updated even though finalize_context now calls pad_m31_to_u32, which adds N_LANES M31ToU32 padding gates to any circuit that previously had none (including the privacy recursion circuit). This adds three new preprocessed columns to the circuit's trace, changing its preprocessed Merkle root. The analogous FIBONACCI_CIRCUIT_PREPROCESSED_ROOT was correctly updated in this PR. PRIVACY_RECURSION_CIRCUIT_CONSTS_HASH appears to have been recomputed using the stale root, making both constants internally consistent but semantically incorrect. Any production code using PRIVACY_RECURSION_CIRCUIT_PREPROCESSED_ROOT to verify actual privacy recursion proofs against the expected circuit would fail or accept proofs against the wrong circuit.

Additional Locations (1)

• crates/circuit_prover/src/prover_test.rs#L279-L281