perf: sync protocol and core hardening updates

deploy/migrations/0062_private_message_idempotency.up.sql

@@ -0,0 +1,25 @@
+ALTER TABLE private_messages
+    ADD COLUMN request_fingerprint bytea NOT NULL DEFAULT '\x',
+    ADD COLUMN recipient_delivered boolean NOT NULL DEFAULT false;
+
+-- 旧行没有保存原始请求指纹，保留空 fingerprint，使后续重放显式返回
+-- RANDOM_ID_DUPLICATE，禁止从可能已编辑的消息投影猜测/修复原请求。
+-- recipient_delivered 可由同一私聊事实表精确回填，用于区分「被 block 后本就
+-- 不投递」与「声明已投递但 recipient box 丢失」两种状态。
+UPDATE private_messages AS p
+SET recipient_delivered = true
+WHERE p.sender_user_id <> p.recipient_user_id
+  AND EXISTS (
+    SELECT 1
+    FROM message_boxes AS b
+    WHERE b.private_message_id = p.id
+      AND b.owner_user_id = p.recipient_user_id
+  );
+
+-- Keep these defaults after the expand step.  A pre-0062 process does not name
+-- either column in INSERT, so dropping them while that process can still serve
+-- traffic turns an otherwise compatible rolling deployment into a NOT NULL
+-- failure.  The empty fingerprint is an explicit "unknown legacy receipt"
+-- sentinel: the new replay path rejects it as RANDOM_ID_DUPLICATE before it can
+-- interpret recipient_delivered.  It must never be reconstructed from mutable
+-- message_boxes.