Operator context moved to first-class system turns, leaving _reminders written
by nothing and read by nothing. Nulling it (the prior 060 step) left a writable
dead column — a foot-gun inviting accidental reuse. Drop it outright and remove
every reference in one shot so there is no half-alive state:
- migration 060: replace the wholesale null with batch_alter_table drop_column
(per migration 027); downgrade re-adds the empty column to match the 059
schema (the envelope un-wrap stays irreversible).
- _schema.py: remove the column.
- _sqlite / _postgresql: drop the reminders save param, the INSERT/bulk values,
and both SELECT columns.
- reconstruct_messages: the row tuple is now 8/9-tuple (event_id shifts from
index 9 to 8); _utils + the _row test helper updated.
- _protocol / memory save_message: drop the reminders param + docstrings.
- tests: replace the reminders-roundtrip tests with a _source-only file and a
060 drop-column assertion; remove the obsolete legacy-reminders wire test.
No production caller passed reminders=, and the SELECT no longer reads the
column, so an un-migrated DB simply ignores any residual values.
Patrick Buckley