diff --git a/packages/uipath-core/pyproject.toml b/packages/uipath-core/pyproject.toml
index 959122a11..147726394 100644
--- a/packages/uipath-core/pyproject.toml
+++ b/packages/uipath-core/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "uipath-core"
-version = "0.5.15"
+version = "0.5.16"
 description = "UiPath Core abstractions"
 readme = { file = "README.md", content-type = "text/markdown" }
 requires-python = ">=3.11"
diff --git a/packages/uipath-core/src/uipath/core/chat/content.py b/packages/uipath-core/src/uipath/core/chat/content.py
index cc6300490..4ae8b169c 100644
--- a/packages/uipath-core/src/uipath/core/chat/content.py
+++ b/packages/uipath-core/src/uipath/core/chat/content.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import uuid
 from typing import Any, Sequence
 
 from pydantic import BaseModel, ConfigDict, Field
@@ -95,7 +96,7 @@ class UiPathConversationContentPartData(BaseModel):
 
     mime_type: str = Field(..., alias="mimeType")
     data: InlineOrExternal
-    citations: Sequence[UiPathConversationCitationData]
+    citations: Sequence[UiPathConversationCitationData] = Field(default_factory=list)
     is_transcript: bool | None = Field(None, alias="isTranscript")
     is_incomplete: bool | None = Field(None, alias="isIncomplete")
     name: str | None = None
@@ -106,11 +107,13 @@ class UiPathConversationContentPartData(BaseModel):
 class UiPathConversationContentPart(UiPathConversationContentPartData):
     """Represents a single part of message content."""
 
-    content_part_id: str = Field(..., alias="contentPartId")
-    created_at: str = Field(..., alias="createdAt")
-    updated_at: str = Field(..., alias="updatedAt")
+    content_part_id: str = Field(
+        default_factory=lambda: str(uuid.uuid4()), alias="contentPartId"
+    )
+    created_at: str | None = Field(None, alias="createdAt")
+    updated_at: str | None = Field(None, alias="updatedAt")
 
     # Override to use full type
-    citations: Sequence[UiPathConversationCitation]
+    citations: Sequence[UiPathConversationCitation] = Field(default_factory=list)
 
     model_config = ConfigDict(validate_by_name=True, validate_by_alias=True)
diff --git a/packages/uipath-core/src/uipath/core/chat/message.py b/packages/uipath-core/src/uipath/core/chat/message.py
index 9d6aa248d..37aa2bd76 100644
--- a/packages/uipath-core/src/uipath/core/chat/message.py
+++ b/packages/uipath-core/src/uipath/core/chat/message.py
@@ -1,5 +1,6 @@
 """Message-level events."""
 
+import uuid
 from typing import Any, Sequence
 
 from pydantic import BaseModel, ConfigDict, Field
@@ -61,7 +62,9 @@ class UiPathConversationMessageData(BaseModel):
     content_parts: Sequence[UiPathConversationContentPartData] = Field(
         ..., alias="contentParts"
     )
-    tool_calls: Sequence[UiPathConversationToolCallData] = Field(..., alias="toolCalls")
+    tool_calls: Sequence[UiPathConversationToolCallData] = Field(
+        default_factory=list, alias="toolCalls"
+    )
 
     model_config = ConfigDict(validate_by_name=True, validate_by_alias=True)
 
@@ -69,15 +72,19 @@ class UiPathConversationMessageData(BaseModel):
 class UiPathConversationMessage(UiPathConversationMessageData):
     """Represents a single message within an exchange."""
 
-    message_id: str = Field(..., alias="messageId")
-    created_at: str = Field(..., alias="createdAt")
-    updated_at: str = Field(..., alias="updatedAt")
+    message_id: str = Field(
+        default_factory=lambda: str(uuid.uuid4()), alias="messageId"
+    )
+    created_at: str | None = Field(None, alias="createdAt")
+    updated_at: str | None = Field(None, alias="updatedAt")
     span_id: str | None = Field(None, alias="spanId")
 
     # Overrides to use full types
     content_parts: Sequence[UiPathConversationContentPart] = Field(
         ..., alias="contentParts"
     )
-    tool_calls: Sequence[UiPathConversationToolCall] = Field(..., alias="toolCalls")
+    tool_calls: Sequence[UiPathConversationToolCall] = Field(
+        default_factory=list, alias="toolCalls"
+    )
 
     model_config = ConfigDict(validate_by_name=True, validate_by_alias=True)
diff --git a/packages/uipath-core/tests/chat/__init__.py b/packages/uipath-core/tests/chat/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/packages/uipath-core/tests/chat/test_message.py b/packages/uipath-core/tests/chat/test_message.py
new file mode 100644
index 000000000..113d34a66
--- /dev/null
+++ b/packages/uipath-core/tests/chat/test_message.py
@@ -0,0 +1,59 @@
+"""Tests for `UiPathConversationMessage` input validation.
+
+Conversational Agent Service contract treats `role` + `contentParts` as
+the load-bearing fields for an inbound user message. `messageId` and
+`contentPartId` are GUIDs that identify entities in the conversation
+hierarchy; when omitted on input, the model fills them with fresh
+UUIDs (matching what `uipath dev` does server-side). `createdAt`,
+`updatedAt`, `spanId`, and `toolCalls` are server-allocated and absent
+from client input.
+
+These tests pin that behavior so `--input-file` payloads from
+`uip codedagent run` validate against the model without requiring
+callers to hand-generate UUIDs.
+"""
+
+from __future__ import annotations
+
+from uipath.core.chat import UiPathConversationMessage
+
+
+def test_minimal_user_message_validates_and_fills_ids() -> None:
+    msg = UiPathConversationMessage.model_validate(
+        {
+            "role": "user",
+            "contentParts": [
+                {
+                    "mimeType": "text/plain",
+                    "data": {"inline": "hello world"},
+                }
+            ],
+        }
+    )
+    assert msg.role == "user"
+    assert msg.tool_calls == []
+    assert msg.created_at is None
+    assert msg.updated_at is None
+    assert msg.message_id  # auto-generated UUID
+    assert msg.content_parts[0].content_part_id  # auto-generated UUID
+    assert msg.content_parts[0].citations == []
+
+
+def test_explicit_ids_are_preserved() -> None:
+    msg = UiPathConversationMessage.model_validate(
+        {
+            "messageId": "00000000-0000-0000-0000-000000000001",
+            "role": "user",
+            "contentParts": [
+                {
+                    "contentPartId": "00000000-0000-0000-0000-000000000002",
+                    "mimeType": "text/plain",
+                    "data": {"inline": "hello world"},
+                }
+            ],
+        }
+    )
+    assert msg.message_id == "00000000-0000-0000-0000-000000000001"
+    assert (
+        msg.content_parts[0].content_part_id == "00000000-0000-0000-0000-000000000002"
+    )
diff --git a/packages/uipath-core/uv.lock b/packages/uipath-core/uv.lock
index ab6e6aa14..9b043599c 100644
--- a/packages/uipath-core/uv.lock
+++ b/packages/uipath-core/uv.lock
@@ -3,7 +3,7 @@ revision = 3
 requires-python = ">=3.11"
 
 [options]
-exclude-newer = "0001-01-01T00:00:00Z" # This has no effect and is included for backwards compatibility when using relative exclude-newer values.
+exclude-newer = "2026-05-20T15:11:06.1716446Z"
 exclude-newer-span = "P2D"
 
 [[package]]
@@ -1011,7 +1011,7 @@ wheels = [
 
 [[package]]
 name = "uipath-core"
-version = "0.5.15"
+version = "0.5.16"
 source = { editable = "." }
 dependencies = [
     { name = "opentelemetry-instrumentation" },
diff --git a/packages/uipath-platform/uv.lock b/packages/uipath-platform/uv.lock
index 53728076b..c3b60638d 100644
--- a/packages/uipath-platform/uv.lock
+++ b/packages/uipath-platform/uv.lock
@@ -3,7 +3,7 @@ revision = 3
 requires-python = ">=3.11"
 
 [options]
-exclude-newer = "0001-01-01T00:00:00Z" # This has no effect and is included for backwards compatibility when using relative exclude-newer values.
+exclude-newer = "2026-05-20T15:43:10.4544027Z"
 exclude-newer-span = "P2D"
 
 [options.exclude-newer-package]
@@ -1063,7 +1063,7 @@ wheels = [
 
 [[package]]
 name = "uipath-core"
-version = "0.5.15"
+version = "0.5.16"
 source = { editable = "../uipath-core" }
 dependencies = [
     { name = "opentelemetry-instrumentation" },
diff --git a/packages/uipath/uv.lock b/packages/uipath/uv.lock
index d29f9a146..449f50872 100644
--- a/packages/uipath/uv.lock
+++ b/packages/uipath/uv.lock
@@ -3,7 +3,7 @@ revision = 3
 requires-python = ">=3.11"
 
 [options]
-exclude-newer = "0001-01-01T00:00:00Z" # This has no effect and is included for backwards compatibility when using relative exclude-newer values.
+exclude-newer = "2026-05-20T15:14:33.9075119Z"
 exclude-newer-span = "P2D"
 
 [options.exclude-newer-package]
@@ -2659,7 +2659,7 @@ dev = [
 
 [[package]]
 name = "uipath-core"
-version = "0.5.15"
+version = "0.5.16"
 source = { editable = "../uipath-core" }
 dependencies = [
     { name = "opentelemetry-instrumentation" },