Editing a cron job with the model picker at "Default" sent provider: null
unconditionally, wiping provider-only pins (provider set, no model — the
pattern for self-hosted LLM endpoints). The combined picker cannot express
that state, so such jobs always rendered as "Default" and were silently
re-resolved to the bare global default on any save, breaking dispatch.
#4030 deliberately made clearing the picker mean "no overrides"; that
contract is preserved for explicit clears and model+provider jobs, while
provider-only pins survive saves where the picker was never touched.
- _cronProviderForClear(prevDetail, pickerTouched) decides the provider
submitted on clear: touched picker -> null; untouched + no model on the
job -> prev.provider.
- _cronModelPickerTouched is set by a change listener added when the picker
populates, and reset at openCronEdit/openCronCreate/duplicateCurrentCron.
- Tests: delegation + flag lifecycle locked in, and the helper driven
through node for provider-only / model-pinned / no-override / no-snapshot
inputs (6 passed).
Refs: #4030
