## Summary
`deleteUserWebpushSubscription` in `coderd/webpush.go` had incorrect
error handling that masked database errors as 404 responses.
## Bug
`GetWebpushSubscriptionsByUserID` is a `:many` query — it returns `([],
nil)` when no rows match, never `sql.ErrNoRows`. The previous `if/else
if` chain:
```go
if existing, err := api.Database.GetWebpushSubscriptionsByUserID(ctx, user.ID); err != nil && errors.Is(err, sql.ErrNoRows) {
// dead code — :many queries never return sql.ErrNoRows
} else if idx := slices.IndexFunc(existing, ...); idx == -1 {
// real DB errors fall through here, existing is nil, idx is -1 → 404
}
```
Any real database error (connection failure, timeout, authorization
error) fell through to the `else if` branch where `slices.IndexFunc(nil,
...)` returns `-1`, returning 404 "subscription not found" instead of
500.
## Fix
Split into two separate checks so database errors properly return 500:
```go
existing, err := api.Database.GetWebpushSubscriptionsByUserID(ctx, user.ID)
if err != nil {
// 500
}
if idx := slices.IndexFunc(existing, ...); idx == -1 {
// 404
}
```
## Testing
Added `TestDeleteWebpushSubscription/database_error_returns_500` which
wraps the DB store to inject an error into
`GetWebpushSubscriptionsByUserID` and asserts the handler returns 500
(not 404).
* Adds `codersdk.ExperimentWebPush` (`web-push`)
* Adds a `coderd/webpush` package that allows sending native push
notifications via `github.com/SherClockHolmes/webpush-go`
* Adds database tables to store push notification subscriptions.
* Adds an API endpoint that allows users to subscribe/unsubscribe, and
send a test notification (404 without experiment, excluded from API docs)
* Adds server CLI command to regenerate VAPID keys (note: regenerating
the VAPID keypair requires deleting all existing subscriptions)
---------
Co-authored-by: Kyle Carberry <kyle@carberry.com>
Cian Johnston