Missing "db" folder doesn't let start the qortal core

[nbenaglia]

During bootstrapping the "db" folder is deleted and the qortal core doesn't start, showing error:

2026-01-06 21:12:54 INFO  Bootstrap:386 - Downloading full node bootstrap from http://bootstrap2.qortal.org/bootstrap-archive.7z ...
2026-01-06 21:17:56 INFO  Bootstrap:511 - Stopping repository...
2026-01-06 21:17:56 INFO  Bootstrap:511 - Deleting existing repository...
2026-01-06 21:17:56 INFO  Bootstrap:511 - Extracting bootstrap...
2026-01-06 21:18:54 ERROR HSQLDBCacheUtils:479 - No repository available
org.qortal.repository.DataException: No repository available
	at org.qortal.repository.RepositoryManager.getRepository(RepositoryManager.java:48) ~[qortal.jar:5.0.6]
	at org.qortal.repository.hsqldb.HSQLDBCacheUtils$2.run(HSQLDBCacheUtils.java:475) [qortal.jar:5.0.6]
	at java.base/java.util.TimerThread.mainLoop(Timer.java:566) [?:?]
	at java.base/java.util.TimerThread.run(Timer.java:516) [?:?]

[QuickMythril]

This log occurs because the bootstrap import temporarily closes the repository factory while the db folder is being replaced. During that window, background cache timers attempt to call RepositoryManager.getRepository() and receive “No repository available.” The error is expected during the swap, but it can look like a fatal failure and can coincide with startup issues if db is deleted before the core has fully shut down.

PR #291 addresses both aspects:

• Bootstrap flow safety: the API bootstrap now writes a one‑shot marker and restarts; on next startup the marker triggers bootstrap import before caches/timers start. This avoids deleting db while the repository is still open.
• Timer guards: cache/index/balance timers skip and log at debug when the repository factory is unavailable, eliminating “No repository available” errors during bootstrap swaps.

Once merged, bootstrapping should no longer race with shutdown, and these log errors should stop appearing.

[nbenaglia]

In Bootstrap.importFromPath(), the code:

1. Closes the repository and repository factory
2. Deletes the database directory
3. Extracts the new bootstrap
4. Creates a new repository factory

During the window between closing the old factory and creating the new one, RepositoryManager.repositoryFactory is null. However, background timer tasks in HSQLDBCacheUtils are still running:

• DB Cache Timer runs every few seconds
• Balance Recorder Timer runs every few minutes

Both timers call RepositoryManager.getRepository(), which throws "No repository available" when the factory is null.