feat(adapters): add nested trajectory support for AgentStack (#1273)

Ref: #1081

Signed-off-by: Lukáš Janeček <xjacka@gmail.com>

Author: xjacka

python/beeai_framework/adapters/a2a/agents/_utils.py

@@ -1,12 +1,18 @@
 # Copyright 2025 © BeeAI a Series of LF Projects, LLC
 # SPDX-License-Identifier: Apache-2.0
+from typing import Any
+from uuid import uuid4
+
 from beeai_framework.backend.message import (
     AnyMessage,
     AssistantMessage,
     CustomMessageContent,
+    Message,
     MessageTextContent,
+    Role,
     UserMessage,
 )
+from beeai_framework.logger import Logger
 from beeai_framework.utils.strings import to_json
 
 try:
@@ -16,6 +22,8 @@
         "Optional module [a2a] not found.\nRun 'pip install \"beeai-framework[a2a]\"' to install."
     ) from e
 
+logger = Logger(__name__)
+
 
 def convert_a2a_to_framework_message(input: a2a_types.Message | a2a_types.Artifact) -> AnyMessage:
     msg = (
@@ -47,3 +55,49 @@ def convert_a2a_to_framework_message(input: a2a_types.Message | a2a_types.Artifa
                 )
             )
     return msg
+
+
+def convert_to_a2a_message(
+    input: str | list[AnyMessage] | AnyMessage | a2a_types.Message,
+    *,
+    context_id: str | None = None,
+    task_id: str | None = None,
+    reference_task_ids: list[str] | None = None,
+    metadata: dict[str, Any] | None = None,
+) -> a2a_types.Message:
+    if isinstance(input, list) and input and isinstance(input[-1], Message):
+        if len(input) == 0:
+            raise ValueError("Input cannot be empty")
+        elif len(input) > 1:
+            logger.warn("Input contains more than one message, only the last one will be used.")
+        return convert_to_a2a_message(
+            input[-1], context_id=context_id, task_id=task_id, reference_task_ids=reference_task_ids, metadata=metadata
+        )
+    elif isinstance(input, str):
+        return a2a_types.Message(
+            role=a2a_types.Role.user,
+            parts=[a2a_types.Part(root=a2a_types.TextPart(text=input))],
+            message_id=uuid4().hex,
+            context_id=context_id,
+            task_id=task_id,
+            reference_task_ids=reference_task_ids,
+            metadata=metadata,
+        )
+    elif isinstance(input, Message):
+        return a2a_types.Message(
+            role=a2a_types.Role.agent if input.role == Role.ASSISTANT else a2a_types.Role.user,
+            parts=[a2a_types.Part(root=a2a_types.TextPart(text=input.text))],
+            message_id=uuid4().hex,
+            context_id=context_id,
+            task_id=task_id,
+            reference_task_ids=reference_task_ids,
+            metadata=(metadata or {}) | input.meta or None,
+        )
+    elif isinstance(input, a2a_types.Message):
+        input.metadata = (input.metadata or {}) | (metadata or {})
+        input.context_id = context_id or input.context_id
+        input.task_id = task_id or input.task_id
+        input.reference_task_ids = reference_task_ids or input.reference_task_ids
+        return input
+    else:
+        raise ValueError("Unsupported message type. Can not convert to a2a message.")

python/beeai_framework/adapters/a2a/agents/agent.py

@@ -4,7 +4,6 @@
 import ssl
 from collections.abc import Callable, Mapping, Sequence
 from typing import Any, Literal, Unpack
-from uuid import uuid4
 
 import httpx
 import httpx._types as httpx_types
@@ -15,7 +14,7 @@
 from httpx._urls import URL, QueryParams  # noqa: F401
 from pydantic import BaseModel, ConfigDict
 
-from beeai_framework.adapters.a2a.agents._utils import convert_a2a_to_framework_message
+from beeai_framework.adapters.a2a.agents._utils import convert_a2a_to_framework_message, convert_to_a2a_message
 from beeai_framework.adapters.a2a.agents.events import (
     A2AAgentErrorEvent,
     A2AAgentUpdateEvent,
@@ -42,7 +41,6 @@
     AnyMessage,
     AssistantMessage,
     Message,
-    Role,
 )
 from beeai_framework.context import RunContext
 from beeai_framework.emitter import Emitter
@@ -353,34 +351,15 @@ def convert_to_a2a_message(
         context_id: str | None = None,
         metadata: dict[str, Any] | None = None,
     ) -> a2a_types.Message:
-        if isinstance(input, str):
-            return a2a_types.Message(
-                role=a2a_types.Role.user,
-                parts=[a2a_types.Part(root=a2a_types.TextPart(text=input))],
-                message_id=uuid4().hex,
-                context_id=context_id or self._context_id,
-                task_id=self._task_id if not context_id else None,
-                reference_task_ids=self._reference_task_ids if not context_id else None,
-                metadata=metadata,
-            )
-        elif isinstance(input, Message):
-            return a2a_types.Message(
-                role=a2a_types.Role.agent if input.role == Role.ASSISTANT else a2a_types.Role.user,
-                parts=[a2a_types.Part(root=a2a_types.TextPart(text=input.text))],
-                message_id=uuid4().hex,
-                context_id=context_id or self._context_id,
-                task_id=self._task_id if not context_id else None,
-                reference_task_ids=self._reference_task_ids if not context_id else None,
-                metadata=(metadata or {}) | input.meta or None,
-            )
-        elif isinstance(input, list) and input and isinstance(input[-1], Message):
-            return self.convert_to_a2a_message(input[-1], context_id=context_id, metadata=metadata)
-        elif isinstance(input, a2a_types.Message):
-            input.metadata = (input.metadata or {}) | (metadata or {})
-            input.context_id = context_id or input.context_id or self._context_id
-            return input
-        else:
-            raise ValueError("Unsupported input type")
+        return convert_to_a2a_message(
+            input,
+            metadata=metadata,
+            context_id=context_id
+            or (input.context_id if isinstance(input, a2a_types.Message) else None)
+            or self._context_id,
+            task_id=self._task_id if not context_id else None,
+            reference_task_ids=self._reference_task_ids if not context_id else None,
+        )
 
 
 def _convert_to_framework_message(