reverse/start answers upgrade_url: null when no plan can be bought right
now. The CLI treated that like a missing field and built its own plans
link, so a Free account under gate "block" was sent to a page where it
can't buy. Now null means no link anywhere: the JSON prints
upgrade_url: null and subscribe_command: null (billing subscribe would
open that same plans page), the refusal says a plan can't be purchased
right now instead of naming the subscribe command, and the skill runs
nothing and passes on no link. Only an absent field (an older server)
falls back to the plans page; a string is used as is.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
