test: verify_db_legacy intermittently races txindex synchronization

[thepastaclaw]

Failure

evo_dip3_activation_tests/verify_db_legacy intermittently fails in CI at src/test/evo_deterministicmns_tests.cpp:102:

fatal error: in "evo_dip3_activation_tests/verify_db_legacy": critical check txFrom has failed

Latest occurrence: https://github.com/dashpay/dash/actions/runs/29099324049/job/86389057100

This occurred in the linux64_sqlite-build / Build source job for #7424. That PR changes only src/chainlock/handler.cpp, src/chainlock/handler.h, and src/test/llmq_chainlock_tests.cpp; it does not touch the failing deterministic-masternode test.

Root cause

FuncVerifyDB mines a non-coinbase collateral transaction, then a later signing path looks it up through GetTransaction/g_txindex. The txindex background thread is asynchronous, so the lookup can race indexing and return no transaction.

Open PR #7266 already contains the focused fix: wait for txindex synchronization before querying the mined non-coinbase transaction. It also cites an earlier occurrence in run 23958304920.

Reproduction / evidence

The failure is intermittent. On the #7424 branch build, the focused command passed 10 consecutive runs:

src/test/test_dash --run_test=evo_dip3_activation_tests/verify_db_legacy --catch_system_errors=no --log_level=test_suite

CI hit the race once with random seed ddfad7b3915a91009dd907bd1a76abcfe8e3ad8703752f0ed29110aa6c26201f.

Proposed resolution

Rebase/refresh and merge #7266 (or an equivalent txindex synchronization fix).

[thepastaclaw]

Additional reconciliation for the same occurrence: https://github.com/dashpay/dash/actions/runs/29099324049/job/86389057100 failed after the SQLite build succeeded, in evo_dip3_activation_tests/verify_db_legacy when GetTransaction returned no txFrom. Confirmed #7424 changes only src/chainlock/handler.cpp, src/chainlock/handler.h, and src/test/llmq_chainlock_tests.cpp. No new findings or PR-branch changes; #7266 remains the focused txindex-synchronization fix.