Is there anywhere in a run object I can store launcher-specific data? Specifically a task ID to use later for termination.

Lots of launchers use tags for this, e.g. https://sourcegraph.com/github.com/dagster-io/dagster/-/blob/python_modules/dagster/dagster/core/launcher/default_run_launcher.py#L77:24

👍

One tricky thing is there might be a race condition (that we should fix) if the tag is set after execution has already started, that's why the launcher is careful to set the tag before execution actually starts

I see you reworked the launcher code last month wheee