refactor(docker): container CPU and memory live in the one metric store (#5752)

#5752 "Container CPU and memory history lives in the one metric store;
docker_metrics and docker_metrics_hourly are retired". Container cpu_pct and
mem_pct already went to plugin_metrics for alerting; now mem_usage_bytes does
too, and every snapshot in an ingest (backlog included) is recorded at its
own time. The container history chart, Busiest Containers, a service's
history and the MCP container tools read plugin_metrics under resource
"<host>/<container>", rolled up and pruned by the shared metric retention.

docker_012_drop_metrics drops both tables. Their history is not copied
(lesson #5221 "A data migration's cost is set by the live table"); the
store already holds 7 days of container CPU and memory %. Docker retention
now prunes only lifecycle events, and Settings -> Thresholds has one
"Metric retention" card for every source.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

plugins/docker/migrations/env.py

@@ -15,7 +15,7 @@ sys.path.insert(0, str(Path(__file__).parent.parent.parent.parent))
 
 from steward.models.base import Base
 import steward.models  # noqa: F401
-from plugins.docker.models import DockerContainer, DockerMetric  # noqa: F401
+from plugins.docker.models import DockerContainer  # noqa: F401
 
 config = context.config
 if config.config_file_name is not None:

plugins/docker/migrations/versions/docker_012_drop_metrics.py

@@ -0,0 +1,56 @@
+"""Container CPU and memory move to the one metric store
+
+Drops docker_metrics and docker_metrics_hourly (#5752). Container cpu_pct,
+mem_pct and mem_usage_bytes are recorded into plugin_metrics as source
+"docker", resource "<host>/<container>", and roll up with every other metric.
+CPU and memory % were already recorded there for alerting, so their history
+stays; memory in bytes starts fresh.
+
+Revision ID: docker_012_drop_metrics
+Revises: docker_011_host_status
+Create Date: 2026-10-14
+"""
+from typing import Sequence, Union
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "docker_012_drop_metrics"
+down_revision: Union[str, None] = "docker_011_host_status"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.execute("DROP TABLE IF EXISTS docker_metrics_hourly")
+    op.execute("DROP TABLE IF EXISTS docker_metrics")
+
+
+def downgrade() -> None:
+    op.create_table(
+        "docker_metrics",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column("host_id", sa.String(36), sa.ForeignKey("hosts.id", ondelete="CASCADE"),
+                  nullable=False, index=True),
+        sa.Column("container_name", sa.String(255), nullable=False, index=True),
+        sa.Column("scraped_at", sa.DateTime(timezone=True), nullable=False, index=True),
+        sa.Column("cpu_pct", sa.Float, nullable=False),
+        sa.Column("mem_pct", sa.Float, nullable=False),
+        sa.Column("mem_usage_bytes", sa.BigInteger, nullable=False),
+    )
+    op.create_index("ix_docker_metrics_host_container_time", "docker_metrics",
+                    ["host_id", "container_name", "scraped_at"])
+    op.create_table(
+        "docker_metrics_hourly",
+        sa.Column("id", sa.String(36), primary_key=True),
+        sa.Column("host_id", sa.String(36), sa.ForeignKey("hosts.id", ondelete="CASCADE"),
+                  nullable=False),
+        sa.Column("container_name", sa.String(255), nullable=False),
+        sa.Column("bucket", sa.DateTime(timezone=True), nullable=False),
+        sa.Column("cpu_pct", sa.Float, nullable=False),
+        sa.Column("mem_pct", sa.Float, nullable=False),
+        sa.Column("mem_usage_bytes", sa.BigInteger, nullable=False),
+        sa.Column("sample_count", sa.Integer, nullable=False),
+        sa.UniqueConstraint("host_id", "container_name", "bucket",
+                            name="uq_docker_metrics_hourly_bucket"),
+    )
+    op.create_index("ix_docker_metrics_hourly_bucket", "docker_metrics_hourly", ["bucket"])