starknet_os_flow_tests,starknet_os,starknet_transaction_prover: test the single proof against the verifier

[einat-starkware]

Part 7 (last) of the single-proof verification stack. Extracts the Cairo digest entry-point runner (starknet_os::test_utils::proof_fact_fold_runner) and the verifier-task fixtures (starknet_transaction_prover::verifier_task::test_utils) into shared test utilities, and adds the combined tests:

• test_cairo_processed_proof_digest_matches_circuit_verifier_output: the Cairo0 processed-proof output digest over the fixture's proof facts, packed the way the OS output packs it, satisfies the real circuit verifier's output comparison.
• test_os_emitted_output_feeds_verifier_task_comparison: a full OS run over one transaction carrying valid proof facts emits exactly the expected packed digest and count, and feeding the OS's emitted values into the verifier-task comparison cleanly rejects a verifier run over different proof facts as a digest mismatch. (A fully-matching OS-in-the-loop path needs a proof generated over OS-valid proof facts — the fixture carries the proving side's test-task hash, which the OS rejects.)

Stack: #15090 ← #15091 ← #15092 ← #15064 ← #15086 ← #15088 ← this PR.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XmPJM3Wph4QLmFmhcxVsh4

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PR Summary

Low Risk
Test-only refactors and new integration coverage; no production verifier or OS execution path changes.

Overview
Refactors proof-fact verification test helpers into shared modules and adds end-to-end flow tests that tie Cairo digest logic, OS output, and the real circuit verifier together.

Shared utilities: Cairo0 entry-point helpers move from proof_fact_fold_test.rs into starknet_os::test_utils::proof_fact_fold_runner. Verifier gzip fixtures and run_one_leaf_verifier_task() move into starknet_transaction_prover::verifier_task::test_utils, gated by a new testing feature (optional flate2). starknet_os’s testing feature now pulls in apollo_starknet_os_program/test_programs; flow tests enable starknet_transaction_prover/testing.

New integration tests in proof_fact_verifier_test.rs:

• test_cairo_processed_proof_digest_matches_circuit_verifier_output: Rust/Cairo processed-proof digest from fixture proof facts, packed like OS output, passes verify_circuit_verifier_task_output against a real one-leaf verifier run.
• test_os_emitted_output_feeds_verifier_task_comparison: Full OS run with one proof-facts transaction checks n_proof_facts_transactions and packed processed_proof_output_* against expected digests; feeding those OS values into verifier comparison against the different fixture proof correctly yields VerificationDigestMismatch (documenting that a full match needs OS-aligned proof facts, not the proving-side fixture hash alone).

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