Per review: expose run-to-run continuity as a boolean `continuity` flag on
cronjob create/update instead of asking users to know the reserved
context_from='self' value. The flag translates to the 'self' entry in
context_from internally (create: appends/omits; update: adds or removes
'self' while preserving other upstream refs). Schema documents the flag and
steers context_from back to job-id chaining only. Docs updated; 7 new tests.
Teknium
2e7a46cc27