fix(core): root re-export deprecated chat/ai type aliases

Upstream packages/chat/src/index.ts:8-27 re-exports toAiMessages plus eight
deprecated AI type aliases (AiAssistantMessage, AiFilePart, AiImagePart,
AiMessage, AiMessagePart, AiTextPart, AiUserMessage, ToAiMessagesOptions)
from the package root for backwards compatibility, each marked @deprecated
pointing at the chat/ai subpath.

Ours re-exported only to_ai_messages, so chat_sdk.AiMessage et al. did not
resolve. Add the eight deprecated root re-exports from chat_sdk.ai (the
canonical home) to match upstream's deprecated-alias surface, and pin the
behavior with a root re-export test.

No new optional-dep cost: chat_sdk.ai is already imported at the root for
to_ai_messages, and the aliased types are plain TypedDict/dataclass/Union
with no ai/zod peer-dep imports.

Author: patrick-chinchill

src/chat_sdk/__init__.py

@@ -1,6 +1,22 @@
 """Python port of Vercel Chat SDK."""
 
-from chat_sdk.ai import to_ai_messages
+# Re-exported from `chat_sdk.ai` for backwards compatibility.
+#
+# Prefer importing these from `chat_sdk.ai` in new code — that subpackage is the
+# home for every AI SDK helper (`to_ai_messages`, `create_chat_tools`, etc.).
+# The AI type aliases below are deprecated at the root and mirror upstream's
+# `packages/chat/src/index.ts` deprecated re-export surface (@deprecated → chat/ai).
+from chat_sdk.ai import (
+    AiAssistantMessage,
+    AiFilePart,
+    AiImagePart,
+    AiMessage,
+    AiMessagePart,
+    AiTextPart,
+    AiUserMessage,
+    ToAiMessagesOptions,
+    to_ai_messages,
+)
 from chat_sdk.cards import (
     Actions,
     ActionsElement,
@@ -235,6 +251,15 @@
     "post_postable_object",
     # AI
     "to_ai_messages",
+    # AI type aliases — deprecated at the root; canonical home is chat_sdk.ai.
+    "AiAssistantMessage",
+    "AiFilePart",
+    "AiImagePart",
+    "AiMessage",
+    "AiMessagePart",
+    "AiTextPart",
+    "AiUserMessage",
+    "ToAiMessagesOptions",
     # Standalone reviver for workflow-safe deserialization
     "reviver",
     # Card builders (PascalCase primary — matches source TS SDK)

tests/test_root_reexports.py

@@ -0,0 +1,51 @@
+"""Root package re-export surface.
+
+Upstream (`packages/chat/src/index.ts`) re-exports `toAiMessages` plus eight
+deprecated AI type aliases from the package root for backwards compatibility,
+each marked `@deprecated` and pointing at the canonical `chat/ai` subpath.
+
+These tests pin the Python equivalent: `chat_sdk.AiMessage` (and friends)
+resolve at the root and are identical objects to their canonical
+`chat_sdk.ai` home, while `chat_sdk.ai` remains the preferred import.
+"""
+
+from __future__ import annotations
+
+import chat_sdk
+import chat_sdk.ai as chat_sdk_ai
+
+# The exact set of deprecated AI type aliases re-exported from the root,
+# mirroring upstream index.ts:8-27.
+_DEPRECATED_AI_TYPE_ALIASES = (
+    "AiAssistantMessage",
+    "AiFilePart",
+    "AiImagePart",
+    "AiMessage",
+    "AiMessagePart",
+    "AiTextPart",
+    "AiUserMessage",
+    "ToAiMessagesOptions",
+)
+
+
+def test_deprecated_ai_type_aliases_resolve_at_root() -> None:
+    for name in _DEPRECATED_AI_TYPE_ALIASES:
+        assert hasattr(chat_sdk, name), f"chat_sdk.{name} should resolve at the root"
+
+
+def test_root_ai_aliases_are_the_canonical_objects() -> None:
+    # The root re-export must be the same object as the canonical chat_sdk.ai
+    # home — not a fresh shadow type — so isinstance / identity checks agree.
+    for name in _DEPRECATED_AI_TYPE_ALIASES:
+        assert getattr(chat_sdk, name) is getattr(chat_sdk_ai, name)
+
+
+def test_deprecated_ai_type_aliases_in_dunder_all() -> None:
+    for name in _DEPRECATED_AI_TYPE_ALIASES:
+        assert name in chat_sdk.__all__, f"{name} missing from chat_sdk.__all__"
+
+
+def test_to_ai_messages_still_re_exported_at_root() -> None:
+    # The helper that the aliases accompany stays available and canonical.
+    assert chat_sdk.to_ai_messages is chat_sdk_ai.to_ai_messages
+    assert "to_ai_messages" in chat_sdk.__all__