ReleaseProcessOverview.md: document the fixed-main-URL tarball design, add the Publish-to-main step, and add Post-Release Smoke Tests.
Closes a real gap found while rehearsing this process: Copy Up (Step 10)
happens well before the release stream exists or is packaged (Steps
17-19), so a naive design referencing the release stream's own URL in
main's install_sdp.sh would 404 for the whole window in between. Fixed by
isolating downloads/ on main (change to the main stream spec, done
separately) and adding a new Step 20 that explicitly publishes the just-
packaged tarball into main's own downloads/ -- main's fixed URL always
resolves to a real tarball (old until published, new after), exactly
mirroring Classic's single-fixed-location behavior and never exhibiting a
dead-link window.
Also added Step 22, capturing the manual post-release smoke tests
(fresh-VM install-from-scratch plus checkpoint script exercise; real
dogfooded upgrade of a live environment) that have always been done by
hand but were never written down.
Agent: Claude Code, Model: Claude Sonnet 5 (claude-sonnet-5), operating as bot_Claude_Anthropic.