adventure: tell a player what happened while they were away

The site could only reach somebody who was already looking at it. Push
existed and adventure used none of it, so the one communal event in the
game -- the Siege -- was invisible to anyone not sitting in Matrix, and a
player whose adventurer died found out whenever they next opened a tab.

Four opt-in categories, every one of them off until asked for: the Siege
(realm-wide, begins and ends), your expedition ending, your adventurer
wandering off, and a contract landing on you. Turning on news
notifications is not consent to be told about the game, so nothing here
enrolls anybody automatically.

No new wire. Every trigger is a dispatch already landing in
adventure_events, so this is Pete-side only and gogobee is untouched.

Two things it needed from storage. push_subscriptions now keeps the
Matrix localpart alongside the OIDC subject, because every ownership
join in the schema is keyed on the localpart and the sender runs on a
ticker with no session to read one from -- without it there is no way to
answer "whose adventurer is this". And the alerts carry their own
watermark, kept apart from the digest's: the two run on different clocks
and one column would let each consume the other's backlog.

The ownership join is re-read on every pass rather than trusted from the
subscription row, so an opt-out or a removal closes the channel at once.
It fails closed in both directions, and an unresolved owner can never
fall through to a broadcast -- a game alert naming somebody's adventurer,
delivered to the wrong phone, is a privacy leak dressed as a feature.

An existing subscription carries watermark 0, which read literally means
"has never been told anything" and would page every subscriber for the
whole history of the realm on the first tick after deploy. Those rows are
stamped to now and start from the next dispatch.

Verified against a running Pete with a real push service, real P-256
client keys and real encryption: the right person is notified, the wrong
one is not, a second pass is silent, and dropping the player from the
board takes the channel with it.

Claude-Session: https://claude.ai/code/session_012bxpQQJDjC1mTtLN3VVtBQ

internal/storage/db.go

@@ -117,6 +117,18 @@ func runMigrations(d *sql.DB) error {
 	addColumnIfMissing(d, "adventure_run_beat", "prose", "TEXT NOT NULL DEFAULT ''")
 	// Ask 7: upgrade orders carry a target tier for the 5 standard equipment slots.
 	addColumnIfMissing(d, "equip_orders", "tier", "INTEGER NOT NULL DEFAULT 0")
+	// Adventure alerts. A subscription made before they existed knows only the OIDC
+	// subject, and the adventure ownership join needs the Matrix localpart — so an
+	// existing row gets "" here and is skipped for owner-scoped alerts until the
+	// browser re-subscribes, which it does on every page load that has push on.
+	// Realm-wide alerts (the Siege) need no localpart and work immediately.
+	addColumnIfMissing(d, "push_subscriptions", "user_localpart", "TEXT NOT NULL DEFAULT ''")
+	// The adventure watermark is deliberately separate from last_notified_at: the
+	// digest and the alerts run on different clocks (6 hours vs 2 minutes), and
+	// sharing one column would let whichever ran last decide what the other had
+	// already seen. 0 on a pre-existing row is corrected to "now" on the first
+	// pass rather than replaying every dispatch Pete has ever stored.
+	addColumnIfMissing(d, "push_subscriptions", "last_adv_notified_at", "INTEGER NOT NULL DEFAULT 0")
 
 	// FTS5 virtual tables don't support IF NOT EXISTS reliably.
 	// Check sqlite_master before creating.