blockifier_test_utils,blockifier: add minimal add and mul circuit entry points

[avi-starkware]

What

Two minimal circuit entry points in the Cairo1 feature test contract, next to test_circuit:

• test_add_mod: one add gate over modulus 7 (3 + 6 = 2). Writes add_mod instances and also mul_mod instances, because every circuit input is reduced modulo the modulus through a mul gate before any add gate can run.
• test_mul_mod: one mul gate over modulus 7 (3 * 6 = 4). Writes only mul_mod instances. The entry point still declares add_mod because eval_circuit takes both builtins as implicits, but with no add gates the add_mod pointer is never advanced, so its PIE instance count is 0.

They exist so proving tests can exercise each mod builtin as narrowly as the compiler allows (the stacked PR above uses them).

Fallout

The contract grew, so the two migration-gas expect! values in crates/blockifier/src/bouncer_test.rs moved (111447819 → 114653623, 241056552 → 248313469). The compiled-class-hash estimation margin test did not move.

Verification

• cargo test -p blockifier_test_utils --test feature_contracts_compatibility_test: 3 passed
• cargo test -p blockifier bouncer::test: 30 passed
• cargo test -p starknet_os compiled_class_test: 20 passed
• PIE counters measured in the stacked PR's flow tests: test_mul_mod → add_mod: 0, mul_mod: 3; test_add_mod → add_mod: 1, mul_mod: 2.

🤖 Generated with Claude Code

[reviewable-StarkWare]

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Artifacts upload workflows:

• Started at 2026-09-15T08:51:18Z
• Started at 2026-09-15T13:18:46Z
• Started at 2026-09-15T13:45:49Z
• Started at 2026-09-15T19:42:16Z

[cursor]

PR Summary

Low Risk
Test-only contract entry points and updated gas snapshot expectations; no production execution or bouncer behavior changes.

Overview
Adds two narrow Cairo1 feature-contract entry points—test_add_mod and test_mul_mod—so proving tests can hit add_mod and mul_mod with minimal circuits (modulus 7), instead of only the broader test_circuit.

test_add_mod runs a single add gate (3 + 6 ≡ 2); test_mul_mod runs a single mul gate (3 × 6 ≡ 4). Comments document that input reduction still uses mul_mod, and that eval keeps both builtins as implicits even when no add gates run.

Because the compiled test contract is larger, the CASM hash migration gas snapshots in bouncer_test.rs are bumped (Sierra 111447819 → 114653623, proving 241056552 → 248313469); no bouncer logic changes.

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[Yoni-Starkware]

@Yoni-Starkware reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: 1 of 2 files reviewed, 1 unresolved discussion (waiting on avi-starkware).

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crates/blockifier_test_utils/resources/feature_contracts/cairo1/test_contract.cairo line 1270 at r1 (raw file):

    /// used because every circuit input is reduced modulo the modulus through a mul gate.
    #[external(v0)]
    fn test_add_mod(ref self: ContractState) {

Make sure this is not duplicated