feat(agent): add durable existing-agent credential transitions

backend/app/agent_auth/repository.py

@@ -32,12 +32,18 @@ class AgentAuthRepository:
             with connection.cursor(row_factory=dict_row) as cur:
                 cur.execute(
                     """
-                    SELECT agent_id,
-                           agent_secret_hash,
-                           credential_created_at,
-                           credential_revoked_at
-                    FROM minerops_site_agents
-                    WHERE agent_id = %s
+                    SELECT identity.agent_id,
+                           agent.agent_secret_hash,
+                           agent.credential_created_at,
+                           agent.credential_revoked_at,
+                           retirement.retired_at AS legacy_auth_disabled_at
+                    FROM (VALUES (%s::text)) AS identity(agent_id)
+                    LEFT JOIN minerops_site_agents AS agent
+                      ON agent.agent_id = identity.agent_id
+                    LEFT JOIN agent_legacy_auth_retirements AS retirement
+                      ON retirement.agent_id = identity.agent_id
+                    WHERE agent.agent_id IS NOT NULL
+                       OR retirement.agent_id IS NOT NULL
                     """,
                     (agent_id,),
                 )