Merge bitcoin/bitcoin#29735: AcceptMultipleTransactions: Fix workspace not being set as client_maxfeerate failure

4ba1d0b55339c3ea90e2bcd64662a06f0f90dd46 fuzz: Add coverage for client_maxfeerate (Greg Sanders)
91d7d8f22a1c528db14fa743c66cd861ea00e84b AcceptMultipleTransactions: Fix workspace client_maxfeerate (Greg Sanders)
f3aa5bd5eb6d1088f98a4dc7daaab0e17a7d5529 fill_mempool: assertions and docsctring update (Greg Sanders)
a3da63e8febe475f2250f6432bca237d31fa9107 Move fill_mempool to util function (Greg Sanders)
73b68bd8b4f9447e30091c7f8c3dc91a086bd93b fill_mempool: remove subtest-specific comment (Greg Sanders)

Pull request description:

  Bug causes an `Assume()` failure due to the expectation that the individual result should be invalid when done over `submitpackage` via rpc.

  Bug introduced by https://github.com/bitcoin/bitcoin/pull/28950 , and I discovered it rebasing https://github.com/bitcoin/bitcoin/pull/28984 since it's easier to hit in that test scenario.

  Tests in place were only checking `AcceptSingleTransaction`-level checks due to package evaluation only triggering when minfee is too high for the parent transaction.

  Added test along with fix, moving the fill_mempool utility into a common area for re-use.

ACKs for top commit:
  glozow:
    reACK 4ba1d0b55339c3ea90e2bcd64662a06f0f90dd46
  theStack:
    ACK 4ba1d0b55339c3ea90e2bcd64662a06f0f90dd46
  ismaelsadeeq:
    re-ACK https://github.com/bitcoin/bitcoin/commit/4ba1d0b55339c3ea90e2bcd64662a06f0f90dd46  via [diff](https://github.com/bitcoin/bitcoin/compare/4fe7d150eb3c85a6597d8fc910fe1490358197ad..4ba1d0b55339c3ea90e2bcd64662a06f0f90dd46)

Tree-SHA512: 3729bdf7f25d04e232f173ccee04ddbb2afdaafa3d04292a01cecf58fb11b3b2bc133e8490277f1a67622b62d17929c242dc980f9bb647896beea4332ee35306

2 files changed, 10 insertions, 2 deletions

diff --git a/src/test/fuzz/package_eval.cpp b/src/test/fuzz/package_eval.cpp
index c801c2e325..c201118bce 100644
--- a/src/test/fuzz/package_eval.cpp
+++ b/src/test/fuzz/package_eval.cpp
@@ -276,8 +276,14 @@ FUZZ_TARGET(tx_package_eval, .init = initialize_tx_pool)
         // (the package is a test accept and ATMP is a submission).
         auto single_submit = txs.size() == 1 && fuzzed_data_provider.ConsumeBool();
 
+        // Exercise client_maxfeerate logic
+        std::optional<CFeeRate> client_maxfeerate{};
+        if (fuzzed_data_provider.ConsumeBool()) {
+            client_maxfeerate = CFeeRate(fuzzed_data_provider.ConsumeIntegralInRange<CAmount>(-1, 50 * COIN), 100);
+        }
+
         const auto result_package = WITH_LOCK(::cs_main,
-                                    return ProcessNewPackage(chainstate, tx_pool, txs, /*test_accept=*/single_submit, /*client_maxfeerate=*/{}));
+                                    return ProcessNewPackage(chainstate, tx_pool, txs, /*test_accept=*/single_submit, client_maxfeerate));
 
         // Always set bypass_limits to false because it is not supported in ProcessNewPackage and
         // can be a source of divergence.
diff --git a/src/validation.cpp b/src/validation.cpp
index 8a78f2106d..048c97529a 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1366,7 +1366,9 @@ PackageMempoolAcceptResult MemPoolAccept::AcceptMultipleTransactions(const std::
         // Individual modified feerate exceeded caller-defined max; abort
         // N.B. this doesn't take into account CPFPs. Chunk-aware validation may be more robust.
         if (args.m_client_maxfeerate && CFeeRate(ws.m_modified_fees, ws.m_vsize) > args.m_client_maxfeerate.value()) {
-            package_state.Invalid(PackageValidationResult::PCKG_TX, "max feerate exceeded");
+            // Need to set failure here both individually and at package level
+            ws.m_state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "max feerate exceeded", "");
+            package_state.Invalid(PackageValidationResult::PCKG_TX, "transaction failed");
             // Exit early to avoid doing pointless work. Update the failed tx result; the rest are unfinished.
             results.emplace(ws.m_ptx->GetWitnessHash(), MempoolAcceptResult::Failure(ws.m_state));
             return PackageMempoolAcceptResult(package_state, std::move(results));