test: fix flaky sentinel_status_slash by asserting the fault on the checkpoint slot

[AztecBot]

Summary

Root-cause fix for the sentinel_status_slash.parallel.test.ts flake (added in #23286) instead of skipping it. The two malicious-proposer tests now discover the slot at which the fault is actually recorded rather than asserting it on the pre-warped block-proposer slot.

(This PR previously carried a .test_patterns.yml skip on next; per maintainer request the skip is dropped and the PR now carries the fix on merge-train/spartan, where the test lives.)

Root cause

The failing merge-train run (test log http://ci.aztec-labs.com/83589a3b1ce4a8b7) shows every honest observer recording the target proposer as checkpoint-missed at the warped slot (15), with zero checkpoint-invalid / checkpoint-unvalidated / checkpoint-valid for it anywhere — the malicious node didn't even self-record checkpoint-valid for that slot.

checkpoint-missed means block proposals were seen for the slot, but no checkpoint-proposal re-execution outcome was recorded for it (sentinel.ts getSlotActivity). The re-execution outcome that drives checkpoint-invalid / checkpoint-unvalidated is keyed by proposal.slotNumber — the slot at which a node closes a checkpoint (proposal_handler.ts:887). A proposer self-records checkpoint-valid only when it actually builds a checkpoint proposal.

warpToSlotBeforeTargetProposer warps to the target's block-proposer slot and the test then asserts the fault at exactly that slot. But a proposer emits a checkpoint proposal only when its slot closes a checkpoint, and that does not reliably coincide with the warped block-proposer slot. When the warped slot is mid-checkpoint, no outcome is ever keyed to it → checkpoint-missed. Whether the proposer slot lines up with a checkpoint close shifts with pipelining/wall-clock timing, so it flakes (it fails on every retry, so the e2e-p2p-epoch-flakes group does not absorb it).

Fix

Stop pinning the pre-warped slot. New helper findObservedStatusSlot polls an observer for the slot at which it records the expected fault status (checkpoint-unvalidated / checkpoint-invalid); the test then requires every honest observer to agree at that slot and the malicious node to self-record checkpoint-valid for the same slot. The warp is kept purely to cut wall-clock by advancing near the proposer region.

This stays faithful to what the test verifies: it still fails (times out) if the malicious proposal is never detected, so it does not mask a genuine propagation/detection bug — it only removes the brittle assumption that the fault lands on one specific pre-chosen slot.

Verification

• Type/usage review only: findObservedStatusSlot reuses the same getValidatorsStats() → history shape and retryUntil pattern as the existing helpers; SlotNumber / ValidatorStatusInSlot / retryUntil are already imported.
• Not run locally: this is an intermittent e2e p2p flake; a single local run would not establish flake-freedom and a full build + repeated e2e grind is impractical to do reliably in-session. CI on this draft exercises the test; a rerun grind is the real confirmation bar.

Related

• Replaces the skip approach (the prior content of this PR and the now-closed test: skip flaky sentinel_status_slash on merge-train/spartan #23443).
• Adjacent to palla/fix-sentinel-inactivity-want-to-slash (changes the sentinel inactivity computation), which is independent of this test-timing fix.

[AztecBot]

Flakey Tests

🤖 says: This CI run detected 1 tests that failed, but were tolerated due to a .test_patterns.yml entry.

\033FLAKED\033 (8;;http://ci.aztec-labs.com/19510dc24c8b4691�19510dc24c8b46918;;�): yarn-project/kv-store/scripts/run_test.sh src/sqlite-opfs/internal/ordered-binary-browser.test.ts (2s) (code: 0)