fix· Sandboxes
A CLI warning no longer makes a task refuse a readable ticket
A warning printed by the Linear or GitHub CLI in the sandbox no longer makes a task decide it can't read your ticket.
Our sandboxes mix a command's warnings into its output, so a stray CLI notice could break the check that the agent can read the ticket, and the task stopped as if the ticket were unreadable. The same notice could also end up in the default-branch name we look up when a clone doesn't record one. Both lookups now ignore warnings; a command that actually fails is still treated as a failure.
#1507