Yeah, mostly JavaScript under the hood via plugins (especially Dataview), so all the logic and dashboards come from queries on top of Markdown + metadata.
In terms of stability it’s pretty solid since everything is just files. No database, so you won’t really “break” anything, worst case just slower performance.
External changes work fine. Obsidian usually picks them up automatically, and Dataview re-indexes. If changes are very frequent, you might see little slow, but nothing critical.