test(alerts): seed the agent registration with SQL, not a second model import (#5060)

Importing plugins.host_agent.models after the app loaded the plugin defines
host_agent_registrations twice (run 8310).

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

tests/integration/test_host_agent_alerts.py

@@ -1,6 +1,10 @@
 """Integration: a host-agent ingest POST evaluates alert rules on the host's
 metrics (#5060). Before, ingest wrote rows straight to plugin_metrics and no
-host_agent rule could ever fire."""
+host_agent rule could ever fire.
+
+The agent registration is seeded with plain SQL: importing the plugin's
+models again after the app loaded the plugin raises "Table already defined"
+(see test_mcp_plugin_tools)."""
 from __future__ import annotations
 
 import asyncio
@@ -23,8 +27,7 @@ def app():
 
 
 def test_ingest_fires_a_host_rule_from_a_backlog(app):
-    from sqlalchemy import select
-    from plugins.host_agent.models import HostAgentRegistration
+    from sqlalchemy import select, text
     from steward.alerts import service as alert_svc
     from steward.models.alerts import AlertEvent, AlertState, AlertStateEnum
     from steward.models.hosts import Host
@@ -41,8 +44,12 @@ def test_ingest_fires_a_host_rule_from_a_backlog(app):
                 host = Host(name=hostname, address="10.9.9.9")
                 s.add_all([user, host])
                 await s.flush()
-                s.add(HostAgentRegistration(
-                    host_id=host.id, token_hash=hashlib.sha256(token.encode()).hexdigest()))
+                await s.execute(text(
+                    "INSERT INTO host_agent_registrations "
+                    "(id, host_id, token_hash, token_created_at, created_at, updated_at) "
+                    "VALUES (:id, :host, :hash, now(), now(), now())"),
+                    {"id": str(uuid.uuid4()), "host": host.id,
+                     "hash": hashlib.sha256(token.encode()).hexdigest()})
                 s.add(PluginMetric(source_module="host_agent", resource_name=hostname,
                                    metric_name="cpu_pct", value=5.0))
                 await s.flush()