## What
Follow-up to #731 (per-budget email notifications). Two changes:
1. **Enable budget email notifications by default.** They shipped opt-in
with every toggle defaulting to `false`, so no one received them. They
are now on by default.
2. **Coalesce budget alerts into one email per transaction.** A single
transaction that crossed a budget's limit could send two emails for the
same budget (the "new transaction" notice *and* the over/close-limit
alert). Now at most one email is sent per budget per assignment.
## Enable by default
- `user_settings.budget_notify_on_*` column defaults flipped to `true`,
and **all existing `user_settings` and `budgets` rows are backfilled to
`true`** so current users and budgets start notifying — not just new
ones.
- `BudgetController::store` and
`NotificationPreferenceController::index` fall back to `true` when a
user has no settings row yet.
- `UserSettingFactory` reflects the new default.
- The `budgets` columns keep their own `false` DB default on purpose:
new budgets are seeded from the user's `user_settings` defaults at
creation, so only the one-off backfill is needed there.
## Coalescing
`BudgetNotificationService::processPeriod` now sends **at most one email
per budget per transaction assignment**, picking the most severe
applicable event with priority **over-limit > close-to-limit >
new-transaction**, and passes the triggering transaction through to
whichever fires. So a transaction that pushes a budget over its limit
produces a single over-limit email that still names the transaction and
shows how far over the budget is.
Preserved from #731: the atomic per-period `close_to_limit_notified` /
`over_limit_notified` claim (one email per crossing, safe under
concurrent workers), the reset-and-re-notify path when spending drops
back below the threshold, and the no-emails-on-historical-backfill
guarantee. Coalescing is **per budget** — a transaction matching two
different budgets still sends one email to each.
## Trade-offs (deliberate)
- **`notify_on_new_transaction` is on by default**, which means one
email per transaction assigned to any budget (no batching yet — flagged
in #731). A catch-all budget matches every expense, so this can be
high-volume; the whole-user-base backfill also produces a send spike on
first sync after deploy. Batching the new-transaction type into a daily
digest (mirroring the bank-sync digest) is the natural follow-up if
volume proves noisy.
- The migration backfill is intentionally unconditional and one-way for
data: `down()` restores the column defaults but not the backfilled row
values.
## Every email links to the settings page
Each budget email already carries a "Manage notifications in
notification settings" link (`route('notifications.index')`) so users
can turn any of them off. A render-test assertion now locks this in.
## Tests
- Coalescing: a single limit-crossing transaction sends exactly one
over-limit email that references the triggering transaction.
- On-by-default: a new budget created without custom preferences enables
all three types.
- All existing #731 sending/preference tests still pass (dedup,
re-notify after drop, no-limit budgets, historical backfill sends
nothing, enabling while already over).
QA (backend): rendered the coalesced over-limit email and confirmed it
names the transaction, shows "Over by", and links to the settings page;
verified the migration backfill flips pre-existing `false` rows to
`true` against a real DB.
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