feat: record sampling parameters in telemetry (port 20 to 21 fields)

Each of the three emitter entry points has a pinned meaning: only the
attempt path has an effective source, so only it merges extra_body.

src/polygateway/middleware/telemetry.py

@@ -18,6 +18,7 @@ from loguru import logger
 
 from polygateway.errors import GatewayUnavailableError, GovernanceBackendError
 from polygateway.middleware.cache import digest_messages
+from polygateway.types import canonical_sampling_json, merge_sampling
 
 if TYPE_CHECKING:
     from collections.abc import Callable
@@ -63,6 +64,10 @@ class TelemetryEmitter:
             error=error,
             cached_prompt_tokens=response.cached_prompt_tokens if response else None,
             model_reported=response.model_reported if response else None,
+            # 唯一有"生效源"的入口,故是唯一能并上 extra_body 的(设计决策 D)
+            sampling=canonical_sampling_json(
+                merge_sampling(source.extra_body, request.sampling)
+            ),
         )
 
     async def emit_cache_hit(self, *, request: ChatRequest, response: LLMResponse) -> None:
@@ -87,6 +92,9 @@ class TelemetryEmitter:
             # 统计供应商缓存命中率必须带 WHERE cache_hit = false,否则重复计数。
             cached_prompt_tokens=response.cached_prompt_tokens,
             model_reported=response.model_reported,
+            # 由最外层 TelemetryMW 调用,手上没有 source。缓存命中行无损:
+            # sampling 已进缓存 key,能命中即意味调用级参数与历史那次逐字相同
+            sampling=canonical_sampling_json(request.sampling),
         )
 
     async def emit_terminal_failure(
@@ -111,6 +119,8 @@ class TelemetryEmitter:
             error=error,
             cached_prompt_tokens=None,
             model_reported=None,
+            # 无具体源,与 model/provider/source_name 置空同一先例(设计决策 D)
+            sampling=canonical_sampling_json(request.sampling),
         )
 
     async def _record(
@@ -133,6 +143,7 @@ class TelemetryEmitter:
         error: str | None,
         cached_prompt_tokens: int | None,
         model_reported: str | None,
+        sampling: str | None,
     ) -> None:
         try:
             # 成本换算(M2 §6): 成功行按单价换算;缓存命中 0.0(未产生新调用);
@@ -172,6 +183,7 @@ class TelemetryEmitter:
                 cost=cost,
                 cached_prompt_tokens=cached_prompt_tokens,
                 model_reported=model_reported,
+                sampling=sampling,
             )
         except asyncio.CancelledError:
             raise