mempool cache fixes (CON-324)

[pompon0]

• made mempool cache all executed txs, not just the ones already in mempool
• made mempool cache txs which failed nonce/priority check
• made priorityReservoir include txs which are pending when insterted, but become ready later

[cursor]

PR Summary

Medium Risk
Changes admission deduplication and priority-hint sampling in the mempool path, which can alter which txs are accepted or dropped under load.

Overview
Tightens mempool LRU cache and priority sampling so behavior matches the intended “seen tx” semantics.

Cache: Failed insert paths (duplicate, stale nonce, same-nonce rejection) now cache.Push the hash so CheckTx won’t keep re-admitting rejected txs. On block Update, every hash in TxResults is cached up front, including txs that never sat in byHash, so executed work is remembered even when the tx wasn’t in the pool.

Priority reservoir: priorityReservoir.Add moves out of Insert and runs only when a tx actually becomes ready—on nonce-chain promotion, non-EVM insert, or higher-priority same-nonce replacement—so pending EVM txs that later unlock still feed the drop-priority hint sampler.

^{Reviewed by Cursor Bugbot for commit 946c405. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jun 4, 2026, 8:11 AM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.27%. Comparing base (1a1b8cd) to head (946c405).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3547      +/-   ##
==========================================
- Coverage   59.12%   58.27%   -0.86%     
==========================================
  Files        2218     2144      -74     
  Lines      183132   174564    -8568     
==========================================
- Hits       108285   101721    -6564     
+ Misses      65082    63781    -1301     
+ Partials     9765     9062     -703     

Flag	Coverage Δ
sei-chain-pr	73.67% <100.00%> (?)
sei-db	70.41% <ø> (ø)
sei-db-state-db	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sei-tendermint/internal/mempool/tx.go	92.95% <100.00%> (+0.09%)	⬆️

... and 74 files with indirect coverage changes

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