feat: record the observability fields end to end through telemetry

src/polygateway/telemetry/postgres.py

@@ -6,7 +6,7 @@
 ① 结构性失败(建池/建表)→ warning 一次后永久降级(池置 None 短路);
 ② 运行时单条写失败 → 逐条 warning 丢弃,不降级不重试(连接抖动由
 asyncpg 池自恢复;避免浸泡开头一次抖动导致后续全程失遥测)。
-构造不连库(lazy),18 列 schema 与 SQLite 版同名同序。
+构造不连库(lazy),20 列 schema 与 SQLite 版同名同序。
 """
 
 from __future__ import annotations
@@ -39,10 +39,18 @@ CREATE TABLE IF NOT EXISTS llm_calls (
     cache_hit          BOOLEAN NOT NULL DEFAULT FALSE,
     error              TEXT,
     cost               DOUBLE PRECISION,
-    created_at         TIMESTAMPTZ NOT NULL DEFAULT now()
+    created_at         TIMESTAMPTZ NOT NULL DEFAULT now(),
+    cached_prompt_tokens INTEGER,
+    model_reported       TEXT
 );
 """
 
+# 新列排在 created_at 之后: 与旧表 ALTER 追加的位置一致(见 sqlite.py 同款注释)
+_BACKFILL = (
+    "ALTER TABLE llm_calls ADD COLUMN IF NOT EXISTS cached_prompt_tokens INTEGER",
+    "ALTER TABLE llm_calls ADD COLUMN IF NOT EXISTS model_reported TEXT",
+)
+
 _COLUMNS = (
     "call_id",
     "parent_call_id",
@@ -62,6 +70,8 @@ _COLUMNS = (
     "cache_hit",
     "error",
     "cost",
+    "cached_prompt_tokens",
+    "model_reported",
 )
 
 _INSERT = (
@@ -104,6 +114,9 @@ class PostgresRecorder:
                     self._pool = await asyncpg.create_pool(self._dsn, timeout=10)
                 async with self._pool.acquire() as conn:
                     await conn.execute(_DDL)
+                    for statement in _BACKFILL:
+                        # 已存在的旧表补新列(issue #3);ADD COLUMN IF NOT EXISTS 原生幂等
+                        await conn.execute(statement)
                 self._schema_ready = True
                 return self._pool
             except asyncio.CancelledError: