A timestamp’s local wall-clock fields. History views render times the way
an operator reads a clock, so they need the local date as well as the
local time: a span that crosses midnight has to widen from HH:MM to a
dated form, and only the calendar day can tell them that.
Breaks a millisecond timestamp into local wall-clock fields. Uses the same
localtime_r path as local_minute so scheduling and rendering agree on
what “local” means, including across DST.
Finds the next real instant whose local wall clock matches minute.
Starting at the next whole minute makes the current minute mean its next
occurrence, while scanning real instants handles DST transitions.
Reads an RFC3339 timestamp back to milliseconds since the epoch — the
inverse of format_timestamp, for renderings that hold only the
envelope’s string form and need to do arithmetic on it.