test(stm): consolidate the recursive circuit MockProver tests

[hjeljeli32]

Content

This PR consolidates the MockProver tests in circuits::halo2_ivc and replaces every negative case's verify().is_err() with an exact failure signature. Consolidating test functions saves nothing, since MockProver::run re-synthesizes on every call, so only removing invocations helps. The tests were also weaker than their names: six were found to reject even with their tampering removed, because the cheap stimulus pairs empty proof slots with a trivial accumulator, which balances only at genesis where the gating scales both accumulator contributions to the group identity.

Measured locally at -j 4 on the ci-tests-snark profile: the slow tier goes from 403.2 s to 277.9 s aggregated and 107.0 s to 76.5 s wall, 22 tests becoming 15 and 20 MockProver invocations becoming 14. Net of −6.5 s drift on untouched tests, −118.7 s is attributable; about 65 s of the saving went on four deliberately added invocations. Fast tier unchanged at 541 passing. Per-item numbers are in #3464.

Changes

• Failure-signature helper (tests/common/failure_signature.rs): a runner generic over Circuit<NativeField> asserting that the failing rows on the public-statement instance column are exactly the expected set and that every failure is a permutation failure. Unit-tested on a minimal two-instance-column circuit.
• Public-input layout (tests/common/public_input_layout.rs): named row accessors for the global, state and accumulator sections, so no test carries a row literal, guarded by section-length and serialization-order tests.
• Satisfiable non-genesis fixtures (tests/common/helpers.rs, tests/transitions/positive.rs): same-epoch and next-epoch stimuli built from the committed step assets, so nothing is proved at test time, plus two untampered acceptance cases; the first in-circuit positive coverage of non-genesis steps.
• Consolidated binding cases (tests/transitions/negative/): thirteen single-field cases become three, one per transition context. Coverage widens at no cost, the step counter and the two genesis verification-key rows having been untested.
• Preimage encoding cases (tests/encoding/negative.rs): the three byte-range cases now assert the message row plus the decoded field their window feeds, flipping one byte rather than filling a range. A new case isolates the message equality.
• Accumulator case (tests/in_circuit/accumulator.rs): an untampered canary on a clone, then the whole accumulator section asserted rather than one element. Keeps its freshly proved certificate, the only unseen proof the circuit verifies.
• Row-dependent mutation delta: mutations add row + 1, since two tampered cells in one permutation class stay equal under a shared delta and left one accumulator row unreported.
• Deletions: in_circuit/state_transition.rs in full and public_inputs.rs's slow module: six cases, three vacuous and three duplicating the genesis case. Both weak rejection helpers are gone.
• Genesis-only stimulus made explicit: the trivial-accumulator builders are renamed to say genesis and assert the step counter is zero, their generic names having invited the non-genesis use.
• Not covered, unchanged from main: the chain-link constraints have no negative coverage, which the deleted cases did not provide either, and an exact row set does not prove each row carries the field named for it. Both are recorded for follow-up.

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • All check jobs of the CI have succeeded
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested
• Documentation
  • No new TODOs introduced

Issue(s)

Closes #3464

[github-actions]

Test Results

     5 files  ± 0     209 suites  ±0   1h 49m 11s ⏱️ + 49m 41s
 3 465 tests +69   3 465 ✅ +69  0 💤 ±0  0 ❌ ±0 
11 328 runs  +78  11 328 ✅ +78  0 💤 ±0  0 ❌ ±0 

Results for commit 9f019ec. ± Comparison against base commit 6ca6181.

♻️ This comment has been updated with latest results.

[Copilot]

Pull request overview

Consolidates recursive-circuit MockProver tests while strengthening rejection assertions with exact failure signatures.

Changes:

• Adds public-input layout and failure-signature helpers.
• Introduces satisfiable non-genesis fixtures and positive checks.
• Consolidates negative transition, encoding, and accumulator cases.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
transitions/positive.rs	Adds non-genesis acceptance tests.
transitions/negative/same_epoch.rs	Consolidates same-epoch binding checks.
transitions/negative/next_epoch.rs	Consolidates next-epoch binding checks.
transitions/negative/genesis.rs	Consolidates genesis public-input checks.
transitions/mod.rs	Clarifies transition-test scope.
in_circuit/state_transition.rs	Removes redundant negative tests.
in_circuit/public_inputs.rs	Removes migrated MockProver checks.
in_circuit/mod.rs	Updates test organization documentation.
in_circuit/accumulator.rs	Checks the complete accumulator signature.
golden/positive.rs	Uses explicit genesis fixtures.
encoding/negative.rs	Adds exact preimage failure signatures.
common/public_input_layout.rs	Defines named public-input rows.
common/mod.rs	Exposes new test helpers.
common/helpers.rs	Adds asset-backed step fixtures.
common/generators/mod.rs	Removes unused generator exports.
common/failure_signature.rs	Adds exact MockProver failure classification.

Suppressed comments (1)

mithril-stm/src/circuits/halo2_ivc/tests/common/public_input_layout.rs:58

• These crate-visible enum variants are missing doc comments. Document each variant so the public row-layout API remains self-describing.

pub(crate) enum StateField {

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[damrobi]

LGTM 👍
Just one small nitpick and the Copilot comments that seem relevant

[jpraynaud]

LGTM 👍