migration.backfill_can_fail: Computed backfill can fail

Computed backfill can fail.

Area 5, Data; not declinable; the next step is usually the agent's.

A title can be empty or longer than five characters, so its length can break Rank's min or max, and nothing says what such a record's rank would be:

example

migration {    Todo.rank: {        backfill: Rank(text.length(Todo.title))    }}

text

error: The backfill for `Todo.rank` can fail --> database/migrations/20261020T1401_add_rank/changes.jadpo:3:19  |3 |         backfill: Rank(text.length(Todo.title))  |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can break `Rank`'s `min` and `max`  reason: A backfill gives every `Todo` record already stored a value, and a record whose value failed would have none, so nothing in a backfill may fail.  next: Work the value out with operations that can't fail, such as `integer.min` and `integer.max` to keep a number in its range (agent)  rule: migration.backfill_can_fail  help: https://jadpo.dev/docs/errors/migration.backfill_can_failcheck failed: 1 error, 4 files

Kept in its range with integer.min and integer.max, the construction can't fail, and the backfill runs.