perf: sync protocol and core hardening updates

deploy/migrations/0069_dispatch_outbox_user_heads.up.sql

@@ -0,0 +1,80 @@
+-- Claim 只需要查看每个用户当前未完成 head。把 head 持久化后，领取复杂度由
+-- “扫描全部 outbox 积压并 DISTINCT ON”降为“扫描有积压的用户 lane”。
+-- 迁移期间阻止并发写，保证 backfill 与随后安装的触发器之间没有缺口。
+LOCK TABLE dispatch_outbox IN SHARE ROW EXCLUSIVE MODE;
+
+CREATE TABLE dispatch_outbox_user_heads (
+    target_user_id bigint PRIMARY KEY,
+    head_id bigint NOT NULL,
+    head_pts integer NOT NULL CHECK (head_pts >= 0),
+    logical_shard smallint GENERATED ALWAYS AS (
+        mod(target_user_id, 256::bigint)::smallint
+    ) STORED,
+    CHECK (logical_shard >= 0 AND logical_shard < 256)
+);
+
+CREATE INDEX dispatch_outbox_user_heads_shard_idx
+    ON dispatch_outbox_user_heads (logical_shard, target_user_id);
+
+INSERT INTO dispatch_outbox_user_heads (target_user_id, head_id, head_pts)
+SELECT DISTINCT ON (target_user_id)
+    target_user_id,
+    id,
+    pts
+FROM dispatch_outbox
+ORDER BY target_user_id ASC, pts ASC, id ASC;
+
+CREATE FUNCTION dispatch_outbox_maintain_user_head()
+RETURNS trigger
+LANGUAGE plpgsql
+AS $$
+DECLARE
+    removed_head bigint;
+BEGIN
+    IF TG_OP = 'INSERT' THEN
+        INSERT INTO dispatch_outbox_user_heads (target_user_id, head_id, head_pts)
+        VALUES (NEW.target_user_id, NEW.id, NEW.pts)
+        ON CONFLICT (target_user_id) DO UPDATE
+        SET head_id = EXCLUDED.head_id,
+            head_pts = EXCLUDED.head_pts
+        WHERE (EXCLUDED.head_pts, EXCLUDED.head_id) <
+              (dispatch_outbox_user_heads.head_pts, dispatch_outbox_user_heads.head_id);
+        RETURN NULL;
+    END IF;
+
+    -- 删除非 head 不需要重算。删除 head 时用 (target_user_id, pts, id)
+    -- 索引找下一条；failed head 同样会一直阻塞，直到被显式删除。
+    DELETE FROM dispatch_outbox_user_heads
+    WHERE target_user_id = OLD.target_user_id
+      AND head_id = OLD.id
+    RETURNING head_id INTO removed_head;
+
+    IF removed_head IS NOT NULL THEN
+        INSERT INTO dispatch_outbox_user_heads (target_user_id, head_id, head_pts)
+        SELECT target_user_id, id, pts
+        FROM dispatch_outbox
+        WHERE target_user_id = OLD.target_user_id
+        ORDER BY pts ASC, id ASC
+        LIMIT 1
+        ON CONFLICT (target_user_id) DO UPDATE
+        SET head_id = EXCLUDED.head_id,
+            head_pts = EXCLUDED.head_pts
+        WHERE (EXCLUDED.head_pts, EXCLUDED.head_id) <
+              (dispatch_outbox_user_heads.head_pts, dispatch_outbox_user_heads.head_id);
+    END IF;
+    RETURN NULL;
+END;
+$$;
+
+CREATE TRIGGER dispatch_outbox_insert_user_head
+AFTER INSERT ON dispatch_outbox
+FOR EACH ROW
+EXECUTE FUNCTION dispatch_outbox_maintain_user_head();
+
+CREATE TRIGGER dispatch_outbox_delete_user_head
+AFTER DELETE ON dispatch_outbox
+FOR EACH ROW
+EXECUTE FUNCTION dispatch_outbox_maintain_user_head();
+
+-- Claim 已不再读取表达式 shard 索引；移除它避免每次 enqueue 的重复写放大。
+DROP INDEX IF EXISTS dispatch_outbox_logical_shard_head_idx;