pan start auto-plan: work agent never starts after planning finalizes #4554

Seen 2026-10-10 on mind-your-now (polyrepo). pan start MIN-1046 (and 6 others) printed "Auto-planning session started … The work agent will start automatically after planning finalizes." Planning finished (pan show state planned, planning-min-* sessions idle), but no work agent spawned; pan show --health reported agent terminal session is not running. A second manual pan start <id> spawned the work agent from the existing plan. Possibly related to #4553 (workspace setup aborted on the first attempt, then resumed). Reported from MYN conversation 20261010-9403.