Fix the persistent flakiness in `test_incremental_repair_race_window_promotes_unrepaired_data` (SCYLLADB-1478, reopened).
After restarting servers[1], the topology coordinator can initiate a **residual re-repair** when it sees tablets stuck in the `repair` stage. This re-repair flushes memtables on all replicas and marks post-repair data as repaired, contaminating the test state and masking the compaction-merge bug the test is designed to detect. The assertion then fails on the *next* retry because the previous attempt's re-repair left behind repaired sstables containing post-repair keys.
1. **Propagating `current_key` through the exception** — correctly advanced the key counter on retry, but the contaminated tablet metadata from the prior re-repair (repaired sstables with post-repair keys) was still present, causing assertion failures on the next attempt.
2. **DROP TABLE + CREATE TABLE between retries** — the tablet metadata (sstables_repaired_at, repair stage) is tied to the tablet identity, and recreating the table in the same keyspace still showed residual state issues.
Instead of trying to clean up contaminated state, each retry creates a **completely fresh keyspace** (unique name via `create_new_test_keyspace`). This gives entirely new tablets with no residual repair metadata from prior attempts. Combined with broader detection of coordinator changes and residual re-repairs, the test reliably retries before any contamination can cause false failures.
The detection is now comprehensive:
- **Broadened coordinator check**: any coordinator change (`new_coord != coord`), not just migration to servers[1]
- **Re-repair detection** at three points: post-restart, during the compaction poll, and after injection release — grep for `"Initiating tablet repair host="` in the coordinator log
1. **`test: extract _setup_table_for_race_window helper`** — pure code-movement refactor that extracts keyspace+table+data+repair1+data+flush into a reusable helper. Easily verifiable as a no-op behavioral change.
2. **`test: fix race window test flakiness from residual re-repair`** — the actual fix: broadened detection logic + re-repair grep at 3 points + fresh-keyspace retry on exception.
Passed 1000 consecutive runs with the fix applied. Without the fix, about 2% flakiness was observed in debug mode.
Fixes: SCYLLADB-1478
So far, we haven't observed flakiness of this test on branches, so not backporting yet. Will backport if seen.
Closesscylladb/scylladb#29721
* github.com:scylladb/scylladb:
test: fix race window test flakiness from residual re-repair
test: extract _setup_table_for_race_window helper for race window test
d33bb6ea00