* fix(events): read a non-filename run ID as an unknown run on JSONL
The run-scoped routes (events, messages, workspace-changes) pass the URL's
run_id straight to the event store. With run_events.backend: jsonl, an ID
that cannot be a filename (run.1, a%20b, %2e%2e) raised ValueError and
surfaced as a 500, while the memory and database stores return an empty
result.
JSONL reads and deletes now treat such an ID as an unknown run through one
helper, _existing_run_file(), which returns before building any path.
Writes still reject it.
* docs(changelog): reference #6070 for the JSONL run ID fix
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
777961f84e