The session artifact for a source, opening one if this run has not already.
Returns null when the source needs no access driver at all, which is the ordinary case for a public website or a local directory — not an error, and not something to warn about.
Optionalconfiguration: ResolvedSourceConfigurationForget a source's sessions, so the next call opens fresh ones.
Check that a source can be reached, without running a stage.
This exists so "can we get at it?" is answerable on its own — from an admin screen, from a health check, from someone configuring a new source — rather than only by starting a pipeline run and reading the failure out of a process run detail row.
Resolves and caches the sessions a run needs.
One instance per run. Constructing a second one is not wrong, only wasteful — it opens its own sessions rather than sharing.