R9 Web Push, then the honest version: VAPID key, push subscriptions, encrypted pushes, 4.5.0 advertised

The server's VAPID key (PushKeys, made on first need, in Mongo) is the instance API's vapid.public_key and every app's
vapid_key. /api/v1/push/subscription (POST, GET, PUT, DELETE) keeps one subscription per access token, so per persona;
every notification kept (never a filtered one) is queued as a SendPush job for the subscriptions whose alert and policy
admit it, and sent through the `push` client (the safe handler, https only) encrypted as RFC 8291 aes128gcm or the
aesgcm draft with an ES256 VAPID JWT. 404/410 delete the subscription, 429/5xx/timeouts retry, other answers drop the
push. Subscriptions end with their tokens (revocation, sessions ended, suspension, deletion, a restore); backups hold
neither keys nor subscriptions. The walk of every Mastodon 4.3-4.5 client route (docs/MASTODON-API.md) added
conversations/:id/unread, domain_blocks/preview, v2 notifications clear and PUT policy, /oauth/userinfo and stubs, so both
instance APIs now say 4.5.0 (compatible; PrivaPub <release>). The pasture gets a push sink (pushsink.test) and
scenarios/push.sh in batch A.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WpVCoDeM1qUTRp4fXQdfof

PrivaPub/Models/Social/ConversationState.cs

@@ -10,6 +10,7 @@ namespace PrivaPub.Models.Social
 		public string ConversationId { get; set; }
 		public string LastReadPostId { get; set; }
 		public string HiddenUpTo { get; set; }
+		public bool MarkedUnread { get; set; }//Mastodon's POST /api/v1/conversations/:id/unread, until it is read again (R9)
 		public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
 	}
 }

PrivaPub/Models/Social/PushSubscription.cs

@@ -0,0 +1,34 @@
+using MongoDB.Entities;
+
+namespace PrivaPub.Models.Social
+{
+	// A Web Push subscription (completion program R9). One per Mastodon access token, as on Mastodon (a new one made with the
+	// same token replaces it), and so one persona's, the token's subject: never its login's, so nothing pairs sibling
+	// personas. It holds the token it was made with, which the encrypted payload carries back to the client as Mastodon's
+	// does (`access_token`), so it goes the moment the token does: revoked (/oauth/revoke, its login's sessions ended), its
+	// persona suspended, moved or deleted, a restore. Never in a backup (ServerBackup.Excluded).
+	public class PushSubscription : Entity
+	{
+		public string AvatarId { get; set; }
+		public string TokenId { get; set; }//the OpenIddict token's id; unique
+		public string AccessToken { get; set; }//the bearer token as the client sent it when it subscribed
+		public string Endpoint { get; set; }//the push service's URL for this client
+		public string P256dh { get; set; }//the client's ECDH public key: an uncompressed P-256 point, base64url as it sent it
+		public string Auth { get; set; }//its 16-byte authentication secret, base64url as it sent it
+		public bool Standard { get; set; }//RFC 8291 aes128gcm and RFC 8292 `vapid` when true (Mastodon 4.4), else the aesgcm draft
+		public List<string> Alerts { get; set; } = new();//the alerts turned on, by Mastodon's names (WebPush.Alerts)
+		public PushPolicy Policy { get; set; } = PushPolicy.All;
+		public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+		public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
+	}
+
+	// whose notifications are pushed (Mastodon's data[policy]): everyone's, the accounts the persona follows, the accounts
+	// that follow it, nobody's
+	public enum PushPolicy
+	{
+		All,
+		Followed,
+		Follower,
+		None
+	}
+}