apollo_starknet_os_program,starknet_os: cite the circuit hashes' source and add todos

[einat-starkware]

Part of the single-proof verification stack. Comments only, no code changes.

• Records where the circuit hash constants come from: the leaf verifier (trace log size 20) and multiverifier entries of the proving repo's canonical_small registry, crates/stwo_run_and_prove_recursive_tree/test_data/circuit_registry.json at the pinned proving rev (2b495a36).
• TODO: import the circuit hashes from the proving repo's registry once it is exposed from a crate, instead of copying them. The registry isn't vendored here: a static copy would only cross-check the constants against a second copy, and couldn't catch upstream changes.
• TODO (Rust and Cairo): accept the leaf verifiers of all the registry's trace sizes, not only one (production covers 25–29). The multiverifier outputs each verified leaf's circuit hash unchecked, so the OS must check it against the registry's list of leaf verifier hashes, selecting it by a range-checked index, since an unchecked index reads cells the prover chooses. For now the OS accepts a single leaf verifier (canonical_small, trace log size 20).

Stack: #15092 ← this PR ← #15164 ← #15161 ← #15166 ← #15167 ← #15168 ← #15169 ← #15163 ← #15064 ← #15162

🤖 Generated with Claude Code

https://claude.ai/code/session_015X6kWZhBXFeNyPwSuKTohy

[cursor]

PR Summary

Low Risk
Comment-only changes with no runtime or verification logic modified.

Overview
Documentation-only update for proof-fact folding circuit hash constants in Rust (proof_fact_fold.rs) and Cairo (proof_fact_fold.cairo).

Rust now documents that LEAF_VERIFIER_CIRCUIT_HASH and MULTIVERIFIER_CIRCUIT_HASH match the proving repo’s canonical_small registry (circuit_registry.json at rev 2b495a36), aligned with the Cairo OS program. New TODOs call out importing hashes from the proving crate instead of duplicating them, switching from test canonical_small values to production registry when available, and verifying leaf verifier circuit hashes for every registry trace size (not only log size 20)—with range-checked indexing because multiverifier exposes leaf hashes unchecked.

Cairo gets a matching TODO on get_leaf_verifier_circuit_hash() about supporting all registry leaf verifiers via a range-checked index.

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[reviewable-StarkWare]

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