refactor(BA-6004): split validate_query_template into DTO validators module

- Extract validate_query_template into common/dto/manager/v2/prometheus_query_preset/validators.py,
  making it self-contained (no longer constructs MetricPreset).
- Move preset.py (LabelMatcher, LabelOperator, MetricPreset) into
  manager/clients/prometheus/, completing the common->manager move.
- Remove the now-empty common/clients/prometheus/ package.

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

Author: seedspirit

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

@@ -10,11 +10,13 @@
 from pydantic import Field, field_validator
 
 from ai.backend.common.api_handlers import SENTINEL, BaseRequestModel, Sentinel
-from ai.backend.common.clients.prometheus.preset import validate_query_template
 from ai.backend.common.dto.clients.prometheus.defs import PROMETHEUS_DURATION_PATTERN
 from ai.backend.common.dto.clients.prometheus.request import QueryTimeRange
 from ai.backend.common.dto.manager.defs import DEFAULT_PAGE_LIMIT, MAX_PAGE_LIMIT
 from ai.backend.common.dto.manager.query import StringFilter
+from ai.backend.common.dto.manager.v2.prometheus_query_preset.validators import (
+    validate_query_template,
+)
 
 from .types import QueryDefinitionOrder
 

src/ai/backend/common/dto/manager/prometheus_query_preset/request.py

@@ -11,11 +11,11 @@
 from pydantic import Field, field_validator
 
 from ai.backend.common.api_handlers import SENTINEL, BaseRequestModel, Sentinel
-from ai.backend.common.clients.prometheus.preset import validate_query_template
 from ai.backend.common.dto.clients.prometheus.defs import PROMETHEUS_DURATION_PATTERN
 from ai.backend.common.dto.manager.query import StringFilter, UUIDFilter
 
 from .types import OrderDirection, QueryDefinitionOrderField
+from .validators import validate_query_template
 
 __all__ = (
     # Options inputs

src/ai/backend/common/dto/manager/v2/prometheus_query_preset/request.py

@@ -0,0 +1,50 @@
+"""Request DTO validators for prometheus_query_preset templates."""
+
+from __future__ import annotations
+
+import re
+
+from ai.backend.common.exception import InvalidMetricPresetTemplate
+
+__all__ = ("validate_query_template",)
+
+_PLACEHOLDER_NAMES = frozenset({"labels", "window", "group_by"})
+_BRACE_BLOCK_RE = re.compile(r"\{([^{}]*)\}")
+_UNSUPPORTED_TEMPLATE_VAR_RE = re.compile(r"\$\{[^}]+\}|\$[A-Za-z_][A-Za-z0-9_]*")
+
+
+def _escape_non_placeholders(template: str) -> str:
+    def repl(match: re.Match[str]) -> str:
+        name = match.group(1)
+        start, end = match.span()
+        text = match.string
+        already_wrapped = (
+            start > 0 and text[start - 1] == "{" and end < len(text) and text[end] == "}"
+        )
+        if name not in _PLACEHOLDER_NAMES:
+            return match.group(0) if already_wrapped else "{{" + name + "}}"
+        if name != "labels":
+            return match.group(0)
+        return match.group(0) if already_wrapped else "{{" + match.group(0) + "}}"
+
+    return _BRACE_BLOCK_RE.sub(repl, template)
+
+
+def validate_query_template(template: str) -> str:
+    """Reject empty templates, foreign variables, or malformed braces."""
+    if not template.strip():
+        raise InvalidMetricPresetTemplate("Template must not be empty.")
+    unsupported_vars = _UNSUPPORTED_TEMPLATE_VAR_RE.findall(template)
+    if unsupported_vars:
+        placeholders = ", ".join(f"{{{name}}}" for name in sorted(_PLACEHOLDER_NAMES))
+        raise InvalidMetricPresetTemplate(
+            f"Unsupported template variables: {unsupported_vars}. "
+            f"Use placeholders {placeholders} or literal PromQL values."
+        )
+    try:
+        _escape_non_placeholders(template).format(labels="", window="", group_by="")
+    except (ValueError, KeyError, IndexError) as e:
+        raise InvalidMetricPresetTemplate(
+            f"Failed to render PromQL template ({type(e).__name__}: {e}): {template!r}"
+        ) from e
+    return template

src/ai/backend/common/dto/manager/v2/prometheus_query_preset/validators.py

@@ -4,14 +4,18 @@
     ContainerMetricQueryBuilder,
     LabelValuesQuery,
 )
+from .preset import LabelMatcher, LabelOperator, MetricPreset
 from .querier import ContainerMetricQuerier, MetricQuerier
 from .types import MetricValue, ValueType
 
 __all__ = [
     "ContainerLiveStatQueryBuilder",
     "ContainerMetricQueryBuilder",
     "ContainerMetricQuerier",
+    "LabelMatcher",
+    "LabelOperator",
     "LabelValuesQuery",
+    "MetricPreset",
     "MetricQuerier",
     "MetricValue",
     "PrometheusClient",

src/ai/backend/manager/clients/prometheus/__init__.py

@@ -8,7 +8,6 @@
     ClientKey,
     ClientPool,
 )
-from ai.backend.common.clients.prometheus.preset import LabelMatcher, MetricPreset
 from ai.backend.common.dto.clients.prometheus.request import QueryTimeRange
 from ai.backend.common.dto.clients.prometheus.response import (
     LabelValueResponse,
@@ -30,6 +29,7 @@
     KernelLiveStatBatchResult,
     MetricResultValue,
 )
+from ai.backend.manager.clients.prometheus.preset import LabelMatcher, MetricPreset
 
 DEFAULT_TIMEOUT_SECONDS: float = 30.0
 

src/ai/backend/manager/clients/prometheus/client.py

@@ -3,7 +3,6 @@
 from dataclasses import dataclass
 from typing import Final
 
-from ai.backend.common.clients.prometheus.preset import LabelMatcher, MetricPreset
 from ai.backend.common.metrics.types import (
     CONTAINER_UTILIZATION_METRIC_LABEL_NAME,
     CONTAINER_UTILIZATION_METRIC_NAME,
@@ -16,6 +15,7 @@
     ContainerMetricOptionalLabel,
     MetricType,
 )
+from ai.backend.manager.clients.prometheus.preset import LabelMatcher, MetricPreset
 from ai.backend.manager.clients.prometheus.querier import ContainerMetricQuerier
 from ai.backend.manager.clients.prometheus.types import ValueType
 

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

@@ -7,13 +7,13 @@
 from typing import Final, Self
 from uuid import UUID
 
-from ai.backend.common.clients.prometheus.preset import MetricPreset
 from ai.backend.common.dto.clients.prometheus.response import (
     MetricResponseInfo,
     PrometheusResponse,
 )
 from ai.backend.common.exception import InvalidAPIParameters
 from ai.backend.common.types import KernelId
+from ai.backend.manager.clients.prometheus.preset import MetricPreset
 from ai.backend.manager.clients.prometheus.types import MetricValue, ValueType
 
 __all__ = [

src/ai/backend/manager/clients/prometheus/metric_types.py

@@ -8,26 +8,6 @@
 
 _PLACEHOLDER_NAMES = frozenset({"labels", "window", "group_by"})
 _BRACE_BLOCK_RE = re.compile(r"\{([^{}]*)\}")
-# `$ident` / `${ident}` — foreign templating syntax (Grafana, shell, etc.)
-# that Backend.AI does not substitute and is almost always unintended in PromQL.
-_UNSUPPORTED_TEMPLATE_VAR_RE = re.compile(r"\$\{[^}]+\}|\$[A-Za-z_][A-Za-z0-9_]*")
-
-
-def validate_query_template(template: str) -> str:
-    """Reject empty templates, foreign variables, or malformed braces.
-
-    Returns the dry-run rendered template (useful for inspection in tests).
-    """
-    if not template.strip():
-        raise InvalidMetricPresetTemplate("Template must not be empty.")
-    unsupported_vars = _UNSUPPORTED_TEMPLATE_VAR_RE.findall(template)
-    if unsupported_vars:
-        placeholders = ", ".join(f"{{{name}}}" for name in sorted(_PLACEHOLDER_NAMES))
-        raise InvalidMetricPresetTemplate(
-            f"Unsupported template variables: {unsupported_vars}. "
-            f"Use placeholders {placeholders} or literal PromQL values."
-        )
-    return MetricPreset(template=template).render()
 
 
 def _escape_non_placeholders(template: str) -> str:

…kend/common/clients/prometheus/preset.py …end/manager/clients/prometheus/preset.pysrc/ai/backend/common/clients/prometheus/preset.py renamed to src/ai/backend/manager/clients/prometheus/preset.py src/ai/backend/common/clients/prometheus/preset.py renamed to src/ai/backend/manager/clients/prometheus/preset.py

@@ -3,7 +3,7 @@
 from dataclasses import dataclass
 from uuid import UUID
 
-from ai.backend.common.clients.prometheus.preset import LabelMatcher
+from ai.backend.manager.clients.prometheus.preset import LabelMatcher
 from ai.backend.manager.clients.prometheus.types import ValueType