fix(BA-5878): unbreak live-stat regex and tighten log/enum

PromQL parser rejects \- as an unknown escape sequence inside a
regex literal, so re.escape over-escaping broke every container
live-stat query (kernel_id UUIDs always contain hyphens). Strip the
backslash from \- after escaping so the rendered queries are
RE2-acceptable.

Also drop the unused ValueType.RATE — no producer ever emits it and
no consumer matches on it; only MAX/AVG round-trip to the legacy
stats.* labels. And include the underlying exception in the
warning emitted from MetricRepository.query_container_live_stats so
"empty results" no longer hide the real Prometheus failure mode.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: seedspirit

src/ai/backend/common/clients/prometheus/fixed_query_builder.py

@@ -71,7 +71,7 @@ class _StatsBucket:
 
 
 def _regex_union(values: Sequence[str]) -> str:
-    return "|".join(re.escape(value) for value in values)
+    return "|".join(re.escape(value).replace(r"\-", "-") for value in values)
 
 
 def _metric_name_regex(

src/ai/backend/common/clients/prometheus/types.py

@@ -10,7 +10,6 @@ class ValueType(StrEnum):
     PCT = "pct"
     MAX = "max"
     AVG = "avg"
-    RATE = "rate"
 
     @classmethod
     def from_legacy_live_stat_label(cls, value: str) -> "ValueType":
@@ -20,7 +19,7 @@ def from_legacy_live_stat_label(cls, value: str) -> "ValueType":
 
     def to_live_stat_label(self) -> str:
         match self:
-            case ValueType.MAX | ValueType.AVG | ValueType.RATE:
+            case ValueType.MAX | ValueType.AVG:
                 return f"stats.{self.value}"
             case _:
                 return self.value

src/ai/backend/manager/repositories/metric/repository.py

@@ -70,7 +70,7 @@ async def query_container_live_stats(
             return KernelLiveStatBatchResult.empty(kernel_ids)
         try:
             values_by_kernel = await self._prometheus_client.fetch_container_live_stats(kernel_ids)
-        except (PrometheusConnectionError, FailedToGetMetric):
-            log.warning("Failed to query metrics for kernel live stats, returning empty results")
+        except (PrometheusConnectionError, FailedToGetMetric) as e:
+            log.warning("Failed to query metrics for kernel live stats: {!r}", e)
             return KernelLiveStatBatchResult.empty(kernel_ids)
         return KernelLiveStatBatchResult.from_metric_values(kernel_ids, values_by_kernel)

tests/unit/manager/services/utilization_metric/test_container_metric.py

@@ -818,30 +818,30 @@ def test_stats_queries_render_legacy_labels_from_typed_value_types(self) -> None
         assert queries.max.render() == (
             "label_replace(max_over_time((sum by (container_metric_name,kernel_id,value_type)("
             "backendai_container_utilization"
-            '{kernel_id=~"12345678\\-1234\\-5678\\-1234\\-567812345678",'
+            '{kernel_id=~"12345678-1234-5678-1234-567812345678",'
             'container_metric_name=~"io_scratch_size|mem|'
             '[A-Za-z0-9][A-Za-z0-9_-]*_(mem|util|power)",'
             'value_type="current"}))[5m:]),'
             '"value_type","stats.max","value_type",".*")'
             " or "
             "label_replace(max_over_time((sum by (container_metric_name,kernel_id,value_type)(rate("
             "backendai_container_utilization"
-            '{kernel_id=~"12345678\\-1234\\-5678\\-1234\\-567812345678",'
+            '{kernel_id=~"12345678-1234-5678-1234-567812345678",'
             'container_metric_name=~"cpu_util",value_type="current"}'
             "[5m])))[5m:]),"
             '"value_type","stats.max","value_type",".*")'
         )
         assert queries.avg.render() == (
             "label_replace(avg_over_time((sum by (container_metric_name,kernel_id,value_type)("
             "backendai_container_utilization"
-            '{kernel_id=~"12345678\\-1234\\-5678\\-1234\\-567812345678",'
+            '{kernel_id=~"12345678-1234-5678-1234-567812345678",'
             'container_metric_name=~"[A-Za-z0-9][A-Za-z0-9_-]*_util",'
             'value_type="current"}))[5m:]),'
             '"value_type","stats.avg","value_type",".*")'
             " or "
             "label_replace(avg_over_time((sum by (container_metric_name,kernel_id,value_type)(rate("
             "backendai_container_utilization"
-            '{kernel_id=~"12345678\\-1234\\-5678\\-1234\\-567812345678",'
+            '{kernel_id=~"12345678-1234-5678-1234-567812345678",'
             'container_metric_name=~"cpu_util",value_type="current"}'
             "[5m])))[5m:]),"
             '"value_type","stats.avg","value_type",".*")'