Fixing flaky test

[SimonRastikian]

Fixing a flaky test.

[Description to be added]

[claude]

PR title type suggestion: This PR is missing a conventional commit type prefix. Since it's fixing source code to resolve a test flakiness issue, the type should be fix:

Suggested title: fix: resolve flaky test in running state

[claude]

Pull request overview

Fixes a flaky test (process_new_parameters_proposal__should_accept_empty_per_domain_overlay) in crates/contract/src/state/running.rs. The test was signing with state.parameters.participants()[0], but gen_valid_params_proposal keeps only a random subset of current participants (size [threshold, current_n]), so participant [0] could be absent from the proposal — causing AuthenticatedAccountId::new(proposal.participants()) inside process_new_parameters_proposal to fail with NotParticipant. The fix picks a signer present in both the current and proposed sets.

Changes:

• In the should_accept_empty_per_domain_overlay test, replace the unconditional participants()[0] signer with one selected from the proposal that is also a current participant.
• Adds a clear comment explaining the overlap-set requirement.

Reviewed changes

Per-file summary

File	Description
crates/contract/src/state/running.rs	Pick a signer in proposal ∩ current_participants so AuthenticatedAccountId::new always succeeds; previously used current_participants[0] which may not be in the random subset retained by gen_valid_params_proposal.

Findings

I verified:

• gen_valid_params_proposal keeps n_old_participants ∈ [current_k, current_n] of the existing participants, and gen_threshold_params enforces k ≥ 2, so the retained overlap is non-empty and the .expect(...) is unreachable in practice.
• The sibling tests that did not need fixing (should_reject_overlay_with_unknown_domain_id, should_apply_overlay_to_threshold_validation) hit overlay/threshold validation in process_new_parameters_proposal before the AuthenticatedAccountId::new signer check, so they are correctly unaffected by the same randomness.

No blocking issues.

Non-blocking (nits, optional):

• crates/contract/src/state/running.rs:561 — minor: iter().map(...).find(...) could be iter().find_map(|(account_id, _, _)| ...) to avoid the eager clone() on every candidate before the predicate. Not worth a re-spin on its own.

✅ Approved