refactor: add to template agent roles

sources/agents/anthropic_base_chat.toml

@@ -3,16 +3,18 @@ schema_version = 1
 name        = "Anthropic Base Chat"
 description = "Anthropic Messages API request body (/v1/messages). Abstract — extend it and set model."
 abstract    = true
-extends     = "Chat Base"
 
 provider_instance = "Claude"
 endpoint          = "/v1/messages"
 enable_tools      = true
 tags = ["chat", "claude", "anthropic", "cloud"]
 
+system_prompt = """{{ agent_role() }}"""
+
 [body]
 max_tokens  = 8192
 temperature = 1
+stream      = true
 system   = """{% if existsIn(ctx, "system_prompt") %}{{ tojson(ctx.system_prompt) }}{% endif %}"""
 messages = """
 [ {% include "partials/anthropic_messages.jinja" %} ]