feat(notifications): the inbox store, one writer, coalescing and retention (#5338)

M489 step 1. The event bus is fire-and-forget, so a client that isn't
connected never hears that a request completed or that tracks went missing.
user_notifications is the durable record; the bus only nudges.

- Migration 0073: user_notifications (kind CHECK-gated, payload jsonb,
  read_at, coalesce_key, emailed_at) and user_notification_prefs (per user,
  per kind: inbox, phone, email). A missing pref row means the kind's
  defaults, so nothing is seeded.
- internal/notifications.Notifier is the only writer. It resolves recipients
  (admin kinds reach admins only, and never the excepted user), honours the
  inbox pref (phone and email ride on it), writes, and publishes a
  contentless notification.created nudge per recipient.
- Burst-prone admin kinds coalesce into one unread row: tracks_missing and
  scan_failed add up their counts, duplicates_found and playback_errors take
  the latest total. Once read, the next event is a new row.
- Retention: read rows go after 90 days, anything after a year, on the
  library_changes compactor's daily shape.

Tests: unit (channel rules, kind table) and integration (recipients, nudge,
coalescing both ways, prefs, owner-scoped idempotent mark-read, every kind
against both schema CHECKs, retention cut-offs).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/dbq/models.go

@@ -831,6 +831,26 @@ type UserNormalizationPref struct {
 	UpdatedAt  pgtype.Timestamptz
 }
 
+type UserNotification struct {
+	ID          pgtype.UUID
+	UserID      pgtype.UUID
+	Kind        string
+	Payload     []byte
+	CreatedAt   pgtype.Timestamptz
+	ReadAt      pgtype.Timestamptz
+	CoalesceKey *string
+	EmailedAt   pgtype.Timestamptz
+}
+
+type UserNotificationPref struct {
+	UserID    pgtype.UUID
+	Kind      string
+	Inbox     bool
+	Phone     bool
+	Email     bool
+	UpdatedAt pgtype.Timestamptz
+}
+
 type YouMightLikeAlbum struct {
 	UserID  pgtype.UUID
 	AlbumID pgtype.UUID

internal/db/dbq/notifications.sql.go

@@ -0,0 +1,346 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: notifications.sql
+
+package dbq
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+const countUnreadNotifications = `-- name: CountUnreadNotifications :one
+SELECT count(*) FROM user_notifications
+ WHERE user_id = $1 AND read_at IS NULL
+`
+
+func (q *Queries) CountUnreadNotifications(ctx context.Context, userID pgtype.UUID) (int64, error) {
+	row := q.db.QueryRow(ctx, countUnreadNotifications, userID)
+	var count int64
+	err := row.Scan(&count)
+	return count, err
+}
+
+const insertNotification = `-- name: InsertNotification :one
+
+INSERT INTO user_notifications (user_id, kind, payload)
+VALUES ($1, $2, $3)
+RETURNING id
+`
+
+type InsertNotificationParams struct {
+	UserID  pgtype.UUID
+	Kind    string
+	Payload []byte
+}
+
+// M489 notifications inbox (#726). Rows are written only through
+// internal/notifications.Notifier, which decides recipients and honours each
+// recipient's inbox preference before it reaches these.
+func (q *Queries) InsertNotification(ctx context.Context, arg InsertNotificationParams) (pgtype.UUID, error) {
+	row := q.db.QueryRow(ctx, insertNotification, arg.UserID, arg.Kind, arg.Payload)
+	var id pgtype.UUID
+	err := row.Scan(&id)
+	return id, err
+}
+
+const listAdminUserIDs = `-- name: ListAdminUserIDs :many
+SELECT id FROM users WHERE is_admin = true ORDER BY created_at, id
+`
+
+func (q *Queries) ListAdminUserIDs(ctx context.Context) ([]pgtype.UUID, error) {
+	rows, err := q.db.Query(ctx, listAdminUserIDs)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []pgtype.UUID
+	for rows.Next() {
+		var id pgtype.UUID
+		if err := rows.Scan(&id); err != nil {
+			return nil, err
+		}
+		items = append(items, id)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const listNotificationPrefsForKind = `-- name: ListNotificationPrefsForKind :many
+SELECT user_id, inbox, phone, email
+  FROM user_notification_prefs
+ WHERE kind = $1 AND user_id = ANY($2::uuid[])
+`
+
+type ListNotificationPrefsForKindParams struct {
+	Kind    string
+	UserIds []pgtype.UUID
+}
+
+type ListNotificationPrefsForKindRow struct {
+	UserID pgtype.UUID
+	Inbox  bool
+	Phone  bool
+	Email  bool
+}
+
+// The stored prefs of one kind for a set of recipients. A recipient with no
+// row has the kind's defaults.
+func (q *Queries) ListNotificationPrefsForKind(ctx context.Context, arg ListNotificationPrefsForKindParams) ([]ListNotificationPrefsForKindRow, error) {
+	rows, err := q.db.Query(ctx, listNotificationPrefsForKind, arg.Kind, arg.UserIds)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListNotificationPrefsForKindRow
+	for rows.Next() {
+		var i ListNotificationPrefsForKindRow
+		if err := rows.Scan(
+			&i.UserID,
+			&i.Inbox,
+			&i.Phone,
+			&i.Email,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const listNotificationPrefsForUser = `-- name: ListNotificationPrefsForUser :many
+SELECT kind, inbox, phone, email
+  FROM user_notification_prefs
+ WHERE user_id = $1
+`
+
+type ListNotificationPrefsForUserRow struct {
+	Kind  string
+	Inbox bool
+	Phone bool
+	Email bool
+}
+
+func (q *Queries) ListNotificationPrefsForUser(ctx context.Context, userID pgtype.UUID) ([]ListNotificationPrefsForUserRow, error) {
+	rows, err := q.db.Query(ctx, listNotificationPrefsForUser, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListNotificationPrefsForUserRow
+	for rows.Next() {
+		var i ListNotificationPrefsForUserRow
+		if err := rows.Scan(
+			&i.Kind,
+			&i.Inbox,
+			&i.Phone,
+			&i.Email,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const listNotifications = `-- name: ListNotifications :many
+SELECT id, kind, payload, created_at, read_at
+  FROM user_notifications
+ WHERE user_id = $1
+   AND ($2::timestamptz IS NULL
+        OR (created_at, id) < ($2::timestamptz, $3::uuid))
+ ORDER BY created_at DESC, id DESC
+ LIMIT $4
+`
+
+type ListNotificationsParams struct {
+	UserID          pgtype.UUID
+	BeforeCreatedAt pgtype.Timestamptz
+	BeforeID        pgtype.UUID
+	PageLimit       int32
+}
+
+type ListNotificationsRow struct {
+	ID        pgtype.UUID
+	Kind      string
+	Payload   []byte
+	CreatedAt pgtype.Timestamptz
+	ReadAt    pgtype.Timestamptz
+}
+
+// Newest first, keyset-paged on (created_at, id). Pass both cursor halves
+// from the last row of the previous page, or neither for the first page.
+func (q *Queries) ListNotifications(ctx context.Context, arg ListNotificationsParams) ([]ListNotificationsRow, error) {
+	rows, err := q.db.Query(ctx, listNotifications,
+		arg.UserID,
+		arg.BeforeCreatedAt,
+		arg.BeforeID,
+		arg.PageLimit,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []ListNotificationsRow
+	for rows.Next() {
+		var i ListNotificationsRow
+		if err := rows.Scan(
+			&i.ID,
+			&i.Kind,
+			&i.Payload,
+			&i.CreatedAt,
+			&i.ReadAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const markAllNotificationsRead = `-- name: MarkAllNotificationsRead :execrows
+UPDATE user_notifications
+   SET read_at = now()
+ WHERE user_id = $1 AND read_at IS NULL
+`
+
+func (q *Queries) MarkAllNotificationsRead(ctx context.Context, userID pgtype.UUID) (int64, error) {
+	result, err := q.db.Exec(ctx, markAllNotificationsRead, userID)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected(), nil
+}
+
+const markNotificationRead = `-- name: MarkNotificationRead :execrows
+UPDATE user_notifications
+   SET read_at = COALESCE(read_at, now())
+ WHERE id = $1 AND user_id = $2
+`
+
+type MarkNotificationReadParams struct {
+	ID     pgtype.UUID
+	UserID pgtype.UUID
+}
+
+// Scoped to the owner: another user's id matches no row. Marking an already
+// read row keeps its original read_at and still matches, so a repeat is not
+// mistaken for "not yours".
+func (q *Queries) MarkNotificationRead(ctx context.Context, arg MarkNotificationReadParams) (int64, error) {
+	result, err := q.db.Exec(ctx, markNotificationRead, arg.ID, arg.UserID)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected(), nil
+}
+
+const trimNotifications = `-- name: TrimNotifications :execrows
+DELETE FROM user_notifications
+ WHERE (read_at IS NOT NULL AND read_at < $1)
+    OR created_at < $2
+`
+
+type TrimNotificationsParams struct {
+	ReadCutoff pgtype.Timestamptz
+	AnyCutoff  pgtype.Timestamptz
+}
+
+// Retention: read rows go after read_cutoff, and anything at all after
+// any_cutoff, so an inbox nobody opens doesn't grow without bound either.
+func (q *Queries) TrimNotifications(ctx context.Context, arg TrimNotificationsParams) (int64, error) {
+	result, err := q.db.Exec(ctx, trimNotifications, arg.ReadCutoff, arg.AnyCutoff)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected(), nil
+}
+
+const upsertCoalescedNotification = `-- name: UpsertCoalescedNotification :one
+INSERT INTO user_notifications (user_id, kind, payload, coalesce_key)
+VALUES ($1, $2, $3, $4)
+ON CONFLICT (user_id, coalesce_key) WHERE read_at IS NULL AND coalesce_key IS NOT NULL
+DO UPDATE SET
+    payload = CASE
+        WHEN $5::boolean THEN
+            EXCLUDED.payload || jsonb_build_object('count',
+                COALESCE((user_notifications.payload->>'count')::bigint, 0)
+              + COALESCE((EXCLUDED.payload->>'count')::bigint, 0))
+        ELSE EXCLUDED.payload
+    END,
+    created_at = now(),
+    emailed_at = NULL
+RETURNING id
+`
+
+type UpsertCoalescedNotificationParams struct {
+	UserID      pgtype.UUID
+	Kind        string
+	Payload     []byte
+	CoalesceKey *string
+	SumCount    bool
+}
+
+// One unread row per (user, coalesce_key). A new event while that row is
+// unread updates it in place and moves it back to the top of the inbox.
+//
+// sum_count: the payload's `count` adds to the unread row's count rather than
+// replacing it. For kinds whose event is "N more happened" (tracks marked
+// missing). Kinds whose event states the whole current total (pending
+// duplicate groups) pass false and the payload simply replaces.
+//
+// emailed_at is cleared so the newer state goes out in the next batch; an
+// emailed-but-unread row that keeps growing is news the user hasn't seen.
+func (q *Queries) UpsertCoalescedNotification(ctx context.Context, arg UpsertCoalescedNotificationParams) (pgtype.UUID, error) {
+	row := q.db.QueryRow(ctx, upsertCoalescedNotification,
+		arg.UserID,
+		arg.Kind,
+		arg.Payload,
+		arg.CoalesceKey,
+		arg.SumCount,
+	)
+	var id pgtype.UUID
+	err := row.Scan(&id)
+	return id, err
+}
+
+const upsertNotificationPref = `-- name: UpsertNotificationPref :exec
+INSERT INTO user_notification_prefs (user_id, kind, inbox, phone, email)
+VALUES ($1, $2, $3, $4, $5)
+ON CONFLICT (user_id, kind) DO UPDATE SET
+    inbox      = EXCLUDED.inbox,
+    phone      = EXCLUDED.phone,
+    email      = EXCLUDED.email,
+    updated_at = now()
+`
+
+type UpsertNotificationPrefParams struct {
+	UserID pgtype.UUID
+	Kind   string
+	Inbox  bool
+	Phone  bool
+	Email  bool
+}
+
+func (q *Queries) UpsertNotificationPref(ctx context.Context, arg UpsertNotificationPrefParams) error {
+	_, err := q.db.Exec(ctx, upsertNotificationPref,
+		arg.UserID,
+		arg.Kind,
+		arg.Inbox,
+		arg.Phone,
+		arg.Email,
+	)
+	return err
+}

internal/db/migrations/0073_user_notifications.down.sql

@@ -0,0 +1,2 @@
+DROP TABLE IF EXISTS user_notification_prefs;
+DROP TABLE IF EXISTS user_notifications;

internal/db/migrations/0073_user_notifications.up.sql

@@ -0,0 +1,74 @@
+-- M489: a persistent, per-user notifications inbox (#726).
+--
+-- The event bus is fire-and-forget: a client that is not connected when a
+-- request completes, or when the scanner marks tracks missing, never hears of
+-- it. A row here is the durable record; the bus only nudges open clients to
+-- come and read it.
+--
+-- `kind` is CHECK-gated (rule 36). A new kind adds its value here, in the
+-- same migration as the code that produces it. The list is mirrored in
+-- internal/notifications/kinds.go, and both CHECKs below must agree with it.
+
+CREATE TABLE user_notifications (
+    id            uuid        PRIMARY KEY DEFAULT gen_random_uuid(),
+    user_id       uuid        NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    kind          text        NOT NULL CHECK (kind IN (
+                      'request_approved',
+                      'request_rejected',
+                      'request_completed',
+                      'request_pending',
+                      'quarantine_flagged',
+                      'scan_failed',
+                      'tracks_missing',
+                      'duplicates_found',
+                      'playback_errors'
+                  )),
+    payload       jsonb       NOT NULL DEFAULT '{}'::jsonb,
+    created_at    timestamptz NOT NULL DEFAULT now(),
+    read_at       timestamptz,
+    -- Burst-prone kinds share one key per user. While a row with that key is
+    -- unread, a new event updates it in place rather than adding another, so
+    -- fourteen missing tracks are one notification with a count.
+    coalesce_key  text,
+    -- Stamped once the row has gone out in an email (or been judged not to
+    -- need one), so the digest never sends the same item twice.
+    emailed_at    timestamptz
+);
+
+-- The inbox list, newest first.
+CREATE INDEX user_notifications_user_created_idx
+    ON user_notifications (user_id, created_at DESC);
+
+-- The unread badge, and the digest's selection of unread rows.
+CREATE INDEX user_notifications_unread_idx
+    ON user_notifications (user_id, created_at DESC)
+    WHERE read_at IS NULL;
+
+-- At most one unread row per coalesce key per user. The upsert in
+-- notifications.sql targets this index.
+CREATE UNIQUE INDEX user_notifications_coalesce_idx
+    ON user_notifications (user_id, coalesce_key)
+    WHERE read_at IS NULL AND coalesce_key IS NOT NULL;
+
+-- Per user, per kind: which channels a kind reaches. A missing row means the
+-- kind's defaults (internal/notifications/kinds.go), so nothing is seeded and
+-- a new kind needs no backfill.
+CREATE TABLE user_notification_prefs (
+    user_id     uuid        NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    kind        text        NOT NULL CHECK (kind IN (
+                    'request_approved',
+                    'request_rejected',
+                    'request_completed',
+                    'request_pending',
+                    'quarantine_flagged',
+                    'scan_failed',
+                    'tracks_missing',
+                    'duplicates_found',
+                    'playback_errors'
+                )),
+    inbox       boolean     NOT NULL,
+    phone       boolean     NOT NULL,
+    email       boolean     NOT NULL,
+    updated_at  timestamptz NOT NULL DEFAULT now(),
+    PRIMARY KEY (user_id, kind)
+);

internal/db/queries/notifications.sql

@@ -0,0 +1,93 @@
+-- M489 notifications inbox (#726). Rows are written only through
+-- internal/notifications.Notifier, which decides recipients and honours each
+-- recipient's inbox preference before it reaches these.
+
+-- name: InsertNotification :one
+INSERT INTO user_notifications (user_id, kind, payload)
+VALUES (sqlc.arg(user_id), sqlc.arg(kind), sqlc.arg(payload))
+RETURNING id;
+
+-- name: UpsertCoalescedNotification :one
+-- One unread row per (user, coalesce_key). A new event while that row is
+-- unread updates it in place and moves it back to the top of the inbox.
+--
+-- sum_count: the payload's `count` adds to the unread row's count rather than
+-- replacing it. For kinds whose event is "N more happened" (tracks marked
+-- missing). Kinds whose event states the whole current total (pending
+-- duplicate groups) pass false and the payload simply replaces.
+--
+-- emailed_at is cleared so the newer state goes out in the next batch; an
+-- emailed-but-unread row that keeps growing is news the user hasn't seen.
+INSERT INTO user_notifications (user_id, kind, payload, coalesce_key)
+VALUES (sqlc.arg(user_id), sqlc.arg(kind), sqlc.arg(payload), sqlc.arg(coalesce_key))
+ON CONFLICT (user_id, coalesce_key) WHERE read_at IS NULL AND coalesce_key IS NOT NULL
+DO UPDATE SET
+    payload = CASE
+        WHEN sqlc.arg(sum_count)::boolean THEN
+            EXCLUDED.payload || jsonb_build_object('count',
+                COALESCE((user_notifications.payload->>'count')::bigint, 0)
+              + COALESCE((EXCLUDED.payload->>'count')::bigint, 0))
+        ELSE EXCLUDED.payload
+    END,
+    created_at = now(),
+    emailed_at = NULL
+RETURNING id;
+
+-- name: ListNotifications :many
+-- Newest first, keyset-paged on (created_at, id). Pass both cursor halves
+-- from the last row of the previous page, or neither for the first page.
+SELECT id, kind, payload, created_at, read_at
+  FROM user_notifications
+ WHERE user_id = sqlc.arg(user_id)
+   AND (sqlc.narg(before_created_at)::timestamptz IS NULL
+        OR (created_at, id) < (sqlc.narg(before_created_at)::timestamptz, sqlc.narg(before_id)::uuid))
+ ORDER BY created_at DESC, id DESC
+ LIMIT sqlc.arg(page_limit);
+
+-- name: CountUnreadNotifications :one
+SELECT count(*) FROM user_notifications
+ WHERE user_id = $1 AND read_at IS NULL;
+
+-- name: MarkNotificationRead :execrows
+-- Scoped to the owner: another user's id matches no row. Marking an already
+-- read row keeps its original read_at and still matches, so a repeat is not
+-- mistaken for "not yours".
+UPDATE user_notifications
+   SET read_at = COALESCE(read_at, now())
+ WHERE id = sqlc.arg(id) AND user_id = sqlc.arg(user_id);
+
+-- name: MarkAllNotificationsRead :execrows
+UPDATE user_notifications
+   SET read_at = now()
+ WHERE user_id = $1 AND read_at IS NULL;
+
+-- name: TrimNotifications :execrows
+-- Retention: read rows go after read_cutoff, and anything at all after
+-- any_cutoff, so an inbox nobody opens doesn't grow without bound either.
+DELETE FROM user_notifications
+ WHERE (read_at IS NOT NULL AND read_at < sqlc.arg(read_cutoff))
+    OR created_at < sqlc.arg(any_cutoff);
+
+-- name: ListAdminUserIDs :many
+SELECT id FROM users WHERE is_admin = true ORDER BY created_at, id;
+
+-- name: ListNotificationPrefsForUser :many
+SELECT kind, inbox, phone, email
+  FROM user_notification_prefs
+ WHERE user_id = $1;
+
+-- name: ListNotificationPrefsForKind :many
+-- The stored prefs of one kind for a set of recipients. A recipient with no
+-- row has the kind's defaults.
+SELECT user_id, inbox, phone, email
+  FROM user_notification_prefs
+ WHERE kind = sqlc.arg(kind) AND user_id = ANY(sqlc.arg(user_ids)::uuid[]);
+
+-- name: UpsertNotificationPref :exec
+INSERT INTO user_notification_prefs (user_id, kind, inbox, phone, email)
+VALUES (sqlc.arg(user_id), sqlc.arg(kind), sqlc.arg(inbox), sqlc.arg(phone), sqlc.arg(email))
+ON CONFLICT (user_id, kind) DO UPDATE SET
+    inbox      = EXCLUDED.inbox,
+    phone      = EXCLUDED.phone,
+    email      = EXCLUDED.email,
+    updated_at = now();