[Core] Add get_session_name() to RuntimeContext

[marwan116]

Description

Currently, there's no public API to retrieve the Ray session name. Users need to use private APIs like ray._private.worker.global_worker.node.session_name or query the dashboard REST API. This makes it difficult to filter Prometheus metrics by cluster when multiple clusters run the same application name, since Ray metrics use the SessionName label (which contains the session_name value).

Checks

• I've run scripts/format.sh to lint the code
• I've included any doc changes needed
• I've added tests for my changes
• I've updated the changelog (if needed)

[gemini-code-assist]

Code Review

This pull request introduces a new public API, get_session_name(), to the RuntimeContext. This is a valuable addition, as it provides a standardized way to access the Ray session name, which is particularly useful for monitoring and filtering Prometheus metrics across different clusters. The implementation is clean, and the accompanying tests are well-written, covering both driver and remote task contexts. My only suggestion is a minor documentation improvement to enhance clarity.

[edoakes]

this should raise an exception type rather than be an assertion

assertions are typically used for invariant checking (they should only fail if an unexpected internal system state occurred)

Suggested change

	assert (
	ray.is_initialized()
	), "Session name is not available because Ray has not been initialized."
	if not ray.is_initialized():
	raise RuntimeError("Session name is not available because Ray has not been initialized.")

[marwan116]

Makes sense - FWIW I copied this assertion from the already implemented get_worker_id and get_node_id

[marwan116]

I know it is technically out of scope for this PR but I will add a commit fixing the get_worker_id, get_node_id and get_job_id methods to raise exceptions instead of relying on asserts.

[marwan116]

Please review the last two commits to resolve 🙏

[edoakes]

Thanks @marwan116