bugfix

internal/acp/queries/session_usage.sql

@@ -0,0 +1,9 @@
+-- name: InsertSessionUsage :one
+-- 写一条 per-turn 用量账目。source_event_id 非空时按唯一索引去重（同一事件
+-- 重复 Observe 不会重复入账）；返回受影响行数判定是否实际插入。
+INSERT INTO acp_session_usage (
+  session_id, user_id, project_id, agent_kind_id, model_id,
+  prompt_tokens, completion_tokens, thinking_tokens, cost_usd, source_event_id
+) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
+ON CONFLICT (source_event_id) WHERE source_event_id IS NOT NULL DO NOTHING
+RETURNING id;