diff --git a/surfsense_backend/app/tasks/chat/llm_history_normalizer.py b/surfsense_backend/app/tasks/chat/llm_history_normalizer.py
new file mode 100644
index 000000000..e3470d06b
--- /dev/null
+++ b/surfsense_backend/app/tasks/chat/llm_history_normalizer.py
@@ -0,0 +1,89 @@
+"""Convert persisted chat content into provider-safe LangChain history.
+
+Assistant UI parts are a UI/storage shape, not an LLM prompt shape. This module
+extracts only model-safe content before prior turns are replayed to a provider.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+_USER_CONTENT_TYPES = {"text", "image", "image_url"}
+
+
+def _text_from_block(block: dict[str, Any]) -> str:
+    value = block.get("text") or block.get("content") or ""
+    return value if isinstance(value, str) else ""
+
+
+def assistant_content_to_llm_text(content: Any) -> str:
+    """Return visible assistant text, dropping reasoning/UI/provider blocks."""
+    if isinstance(content, str):
+        return content
+    if isinstance(content, dict):
+        return _text_from_block(content)
+    if not isinstance(content, list):
+        return ""
+
+    text_chunks: list[str] = []
+    for block in content:
+        if isinstance(block, str):
+            if block:
+                text_chunks.append(block)
+            continue
+        if not isinstance(block, dict):
+            continue
+        if block.get("type") == "text":
+            text = _text_from_block(block)
+            if text:
+                text_chunks.append(text)
+    return "\n".join(text_chunks)
+
+
+def user_content_to_llm_content(
+    content: Any,
+    *,
+    allow_images: bool = True,
+) -> str | list[dict[str, Any]]:
+    """Return provider-safe user text/image content for LangChain."""
+    if isinstance(content, str):
+        return content
+    if isinstance(content, dict):
+        return _text_from_block(content)
+    if not isinstance(content, list):
+        return ""
+
+    parts: list[dict[str, Any]] = []
+    text_chunks: list[str] = []
+    for block in content:
+        if isinstance(block, str):
+            if block:
+                text_chunks.append(block)
+            continue
+        if not isinstance(block, dict):
+            continue
+        block_type = block.get("type")
+        if block_type not in _USER_CONTENT_TYPES:
+            continue
+        if block_type == "text":
+            text = _text_from_block(block)
+            if text:
+                parts.append({"type": "text", "text": text})
+                text_chunks.append(text)
+        elif allow_images and block_type == "image":
+            image = block.get("image")
+            if isinstance(image, str) and image.startswith("data:"):
+                parts.append({"type": "image_url", "image_url": {"url": image}})
+        elif allow_images and block_type == "image_url":
+            image_url = block.get("image_url")
+            if isinstance(image_url, dict):
+                url = image_url.get("url")
+                if isinstance(url, str) and url.startswith("data:"):
+                    parts.append({"type": "image_url", "image_url": {"url": url}})
+            elif isinstance(image_url, str) and image_url.startswith("data:"):
+                parts.append({"type": "image_url", "image_url": {"url": image_url}})
+
+    if allow_images and any(part.get("type") == "image_url" for part in parts):
+        return parts
+    return "\n".join(text_chunks)
+
diff --git a/surfsense_backend/app/tasks/chat/message_parts_normalizer.py b/surfsense_backend/app/tasks/chat/message_parts_normalizer.py
new file mode 100644
index 000000000..953282e9f
--- /dev/null
+++ b/surfsense_backend/app/tasks/chat/message_parts_normalizer.py
@@ -0,0 +1,86 @@
+"""Normalize final LangChain assistant messages into assistant-ui parts.
+
+Live streaming remains the primary source for rich, incremental UI state.
+This module is only used after the graph has finished so refresh persistence
+does not depend on provider-specific streaming chunk shapes.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Iterable
+from typing import Any
+
+from langchain_core.messages import AIMessage
+
+
+def _text_from_content(content: Any) -> str:
+    if isinstance(content, str):
+        return content
+    if not isinstance(content, list):
+        return ""
+
+    text_parts: list[str] = []
+    for block in content:
+        if not isinstance(block, dict):
+            continue
+        if block.get("type") != "text":
+            continue
+        value = block.get("text") or block.get("content") or ""
+        if isinstance(value, str) and value:
+            text_parts.append(value)
+    return "".join(text_parts)
+
+
+def normalize_ai_message_to_parts(message: AIMessage | Any | None) -> list[dict[str, Any]]:
+    """Return user-visible assistant-ui parts for a final AI message.
+
+    We intentionally do not backfill provider ``thinking`` /
+    ``reasoning_content`` blocks here. If reasoning streamed live, the
+    ``AssistantContentBuilder`` already captured it. If it only exists in the
+    final model payload, persisting it retroactively could expose content the
+    UI never showed during the turn.
+    """
+    if message is None:
+        return []
+
+    text = _text_from_content(getattr(message, "content", None)).strip()
+    if not text:
+        return []
+    return [{"type": "text", "text": text}]
+
+
+def last_ai_message(messages: Iterable[Any] | None) -> AIMessage | Any | None:
+    if messages is None:
+        return None
+    for message in reversed(list(messages)):
+        if isinstance(message, AIMessage):
+            return message
+        if getattr(message, "type", None) == "ai":
+            return message
+    return None
+
+
+def final_assistant_parts_from_messages(messages: Iterable[Any] | None) -> list[dict[str, Any]]:
+    return normalize_ai_message_to_parts(last_ai_message(messages))
+
+
+def has_non_empty_text_part(parts: Iterable[dict[str, Any]]) -> bool:
+    return any(
+        part.get("type") == "text"
+        and isinstance(part.get("text"), str)
+        and bool(part.get("text", "").strip())
+        for part in parts
+    )
+
+
+def merge_streamed_and_final_parts(
+    streamed_parts: list[dict[str, Any]],
+    final_parts: list[dict[str, Any]],
+) -> list[dict[str, Any]]:
+    """Use final-state text only when streaming captured no answer text."""
+    if has_non_empty_text_part(streamed_parts):
+        return streamed_parts
+    if not has_non_empty_text_part(final_parts):
+        return streamed_parts
+    return [*streamed_parts, *final_parts]
+
diff --git a/surfsense_backend/app/tasks/chat/streaming/agent/event_loop.py b/surfsense_backend/app/tasks/chat/streaming/agent/event_loop.py
index d96144bcd..fb7548818 100644
--- a/surfsense_backend/app/tasks/chat/streaming/agent/event_loop.py
+++ b/surfsense_backend/app/tasks/chat/streaming/agent/event_loop.py
@@ -25,6 +25,9 @@ from app.tasks.chat.streaming.graph_stream.event_stream import stream_output
 from app.tasks.chat.streaming.helpers.interrupt_inspector import (
     all_interrupt_values,
 )
+from app.tasks.chat.message_parts_normalizer import (
+    final_assistant_parts_from_messages,
+)
 from app.tasks.chat.streaming.shared.stream_result import StreamResult
 from app.tasks.chat.streaming.shared.utils import safe_float
 from app.utils.perf import get_perf_logger
@@ -75,6 +78,9 @@ async def stream_agent_events(
 
     state = await agent.aget_state(config)
     state_values = getattr(state, "values", {}) or {}
+    result.final_message_parts = final_assistant_parts_from_messages(
+        state_values.get("messages")
+    )
 
     # Safety net: if astream_events was cancelled before
     # KnowledgeBasePersistenceMiddleware.aafter_agent ran, any staged work
diff --git a/surfsense_backend/app/tasks/chat/streaming/flows/shared/assistant_finalize.py b/surfsense_backend/app/tasks/chat/streaming/flows/shared/assistant_finalize.py
index be1f102f3..3f767c60b 100644
--- a/surfsense_backend/app/tasks/chat/streaming/flows/shared/assistant_finalize.py
+++ b/surfsense_backend/app/tasks/chat/streaming/flows/shared/assistant_finalize.py
@@ -53,6 +53,7 @@ async def finalize_assistant_message(
     ):
         return
 
+    from app.tasks.chat.message_parts_normalizer import merge_streamed_and_final_parts
     from app.tasks.chat.persistence import finalize_assistant_turn
 
     builder_stats: dict[str, int] | None = None
@@ -74,6 +75,10 @@ async def finalize_assistant_message(
                 "text": stream_result.accumulated_text or "",
             }
         ]
+    content_payload = merge_streamed_and_final_parts(
+        content_payload,
+        stream_result.final_message_parts,
+    )
 
     if builder_stats is not None:
         _perf_log.info(
diff --git a/surfsense_backend/app/tasks/chat/streaming/shared/stream_result.py b/surfsense_backend/app/tasks/chat/streaming/shared/stream_result.py
index a940e8a9f..5e164070a 100644
--- a/surfsense_backend/app/tasks/chat/streaming/shared/stream_result.py
+++ b/surfsense_backend/app/tasks/chat/streaming/shared/stream_result.py
@@ -35,3 +35,7 @@ class StreamResult:
     # (``StreamResult`` is logged in some error branches) from dumping a
     # potentially-large parts list.
     content_builder: Any | None = field(default=None, repr=False)
+    # User-visible assistant message parts derived from the final LangGraph
+    # state. Used after streaming completes as a provider-agnostic persistence
+    # backfill when no text chunks reached the live stream.
+    final_message_parts: list[dict[str, Any]] = field(default_factory=list)
diff --git a/surfsense_backend/app/utils/content_utils.py b/surfsense_backend/app/utils/content_utils.py
index 05a4610c7..aae936888 100644
--- a/surfsense_backend/app/utils/content_utils.py
+++ b/surfsense_backend/app/utils/content_utils.py
@@ -18,6 +18,11 @@ from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload
 
+from app.tasks.chat.llm_history_normalizer import (
+    assistant_content_to_llm_text,
+    user_content_to_llm_content,
+)
+
 if TYPE_CHECKING:
     from app.db import ChatVisibility
 
@@ -95,17 +100,28 @@ async def bootstrap_history_from_db(
     langchain_messages: list[HumanMessage | AIMessage] = []
 
     for msg in db_messages:
-        text_content = extract_text_content(msg.content)
-        if not text_content:
-            continue
         if msg.role == "user":
+            user_content = user_content_to_llm_content(
+                msg.content,
+                allow_images=False,
+            )
+            if not user_content:
+                continue
             if is_shared:
                 author_name = (
                     msg.author.display_name if msg.author else None
                 ) or "A team member"
-                text_content = f"**[{author_name}]:** {text_content}"
-            langchain_messages.append(HumanMessage(content=text_content))
+                if isinstance(user_content, str):
+                    user_content = f"**[{author_name}]:** {user_content}"
+                elif user_content and user_content[0].get("type") == "text":
+                    user_content[0] = {
+                        **user_content[0],
+                        "text": f"**[{author_name}]:** {user_content[0].get('text', '')}",
+                    }
+            langchain_messages.append(HumanMessage(content=user_content))
         elif msg.role == "assistant":
-            langchain_messages.append(AIMessage(content=text_content))
+            assistant_text = assistant_content_to_llm_text(msg.content)
+            if assistant_text:
+                langchain_messages.append(AIMessage(content=assistant_text))
 
     return langchain_messages
diff --git a/surfsense_backend/tests/unit/agents/chat/runtime/test_llm_config_sanitizer.py b/surfsense_backend/tests/unit/agents/chat/runtime/test_llm_config_sanitizer.py
new file mode 100644
index 000000000..00d38b4b1
--- /dev/null
+++ b/surfsense_backend/tests/unit/agents/chat/runtime/test_llm_config_sanitizer.py
@@ -0,0 +1,40 @@
+"""Regression tests for model-boundary message sanitization."""
+
+from __future__ import annotations
+
+import pytest
+from langchain_core.messages import AIMessage
+
+from app.agents.chat.runtime.llm_config import _sanitize_messages
+
+pytestmark = pytest.mark.unit
+
+
+def test_sanitize_messages_strips_provider_specific_thinking_blocks() -> None:
+    original = AIMessage(
+        content=[
+            {"type": "thinking", "thinking": "private reasoning"},
+            {"type": "text", "text": "visible answer"},
+        ]
+    )
+
+    sanitized = _sanitize_messages([original])
+
+    assert sanitized[0].content == "visible answer"
+    assert original.content == [
+        {"type": "thinking", "thinking": "private reasoning"},
+        {"type": "text", "text": "visible answer"},
+    ]
+
+
+def test_sanitize_messages_sets_tool_only_ai_content_to_none() -> None:
+    message = AIMessage(
+        content="",
+        tool_calls=[{"name": "search", "args": {"q": "x"}, "id": "call_1"}],
+    )
+
+    sanitized = _sanitize_messages([message])
+
+    assert sanitized[0].content is None
+    assert message.content == ""
+
diff --git a/surfsense_backend/tests/unit/tasks/chat/test_llm_history_normalizer.py b/surfsense_backend/tests/unit/tasks/chat/test_llm_history_normalizer.py
new file mode 100644
index 000000000..14bb030cd
--- /dev/null
+++ b/surfsense_backend/tests/unit/tasks/chat/test_llm_history_normalizer.py
@@ -0,0 +1,62 @@
+"""Unit tests for provider-safe LLM history normalization."""
+
+from __future__ import annotations
+
+import pytest
+
+from app.tasks.chat.llm_history_normalizer import (
+    assistant_content_to_llm_text,
+    user_content_to_llm_content,
+)
+
+pytestmark = pytest.mark.unit
+
+
+def test_assistant_ui_parts_drop_thinking_steps_for_llm_history() -> None:
+    content = [
+        {"type": "data-thinking-steps", "data": [{"id": "thinking-1"}]},
+        {"type": "text", "text": "visible answer"},
+    ]
+
+    assert assistant_content_to_llm_text(content) == "visible answer"
+
+
+def test_provider_thinking_blocks_are_not_replayed_to_llm() -> None:
+    content = [
+        {"type": "thinking", "thinking": "private reasoning"},
+        {"type": "text", "text": "final answer"},
+    ]
+
+    assert assistant_content_to_llm_text(content) == "final answer"
+
+
+def test_unknown_assistant_blocks_are_dropped() -> None:
+    content = [
+        {"type": "redacted_thinking", "data": "hidden"},
+        {"type": "tool_use", "name": "search"},
+        {"type": "text", "text": "kept"},
+    ]
+
+    assert assistant_content_to_llm_text(content) == "kept"
+
+
+def test_user_images_convert_to_openai_compatible_image_url_blocks() -> None:
+    content = [
+        {"type": "text", "text": "look"},
+        {"type": "image", "image": "data:image/png;base64,abc"},
+    ]
+
+    assert user_content_to_llm_content(content, allow_images=True) == [
+        {"type": "text", "text": "look"},
+        {"type": "image_url", "image_url": {"url": "data:image/png;base64,abc"}},
+    ]
+
+
+def test_user_images_can_be_dropped_for_text_only_history() -> None:
+    content = [
+        {"type": "text", "text": "look"},
+        {"type": "image", "image": "data:image/png;base64,abc"},
+    ]
+
+    assert user_content_to_llm_content(content, allow_images=False) == "look"
+
diff --git a/surfsense_backend/tests/unit/tasks/chat/test_message_parts_normalizer.py b/surfsense_backend/tests/unit/tasks/chat/test_message_parts_normalizer.py
new file mode 100644
index 000000000..173d03ed5
--- /dev/null
+++ b/surfsense_backend/tests/unit/tasks/chat/test_message_parts_normalizer.py
@@ -0,0 +1,68 @@
+"""Unit tests for final assistant message part normalization."""
+
+from __future__ import annotations
+
+import pytest
+from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
+
+from app.tasks.chat.message_parts_normalizer import (
+    final_assistant_parts_from_messages,
+    merge_streamed_and_final_parts,
+    normalize_ai_message_to_parts,
+)
+
+pytestmark = pytest.mark.unit
+
+
+def test_string_ai_message_content_becomes_text_part() -> None:
+    assert normalize_ai_message_to_parts(AIMessage(content="hello")) == [
+        {"type": "text", "text": "hello"}
+    ]
+
+
+def test_deepseek_thinking_plus_text_blocks_backfill_only_text() -> None:
+    message = AIMessage(
+        content=[
+            {"type": "thinking", "thinking": "hidden reasoning"},
+            {"type": "text", "text": "Yo bro! What's up?"},
+        ],
+        additional_kwargs={"reasoning_content": "hidden reasoning"},
+    )
+
+    assert normalize_ai_message_to_parts(message) == [
+        {"type": "text", "text": "Yo bro! What's up?"}
+    ]
+
+
+def test_final_parts_use_last_ai_message_and_skip_trailing_tool_messages() -> None:
+    messages = [
+        HumanMessage(content="ask"),
+        AIMessage(content="draft"),
+        ToolMessage(content="tool output", tool_call_id="tc-1"),
+        AIMessage(content=[{"type": "text", "text": "final answer"}]),
+        ToolMessage(content="trailing tool noise", tool_call_id="tc-2"),
+    ]
+
+    assert final_assistant_parts_from_messages(messages) == [
+        {"type": "text", "text": "final answer"}
+    ]
+
+
+def test_merge_adds_final_text_when_stream_only_has_thinking_steps() -> None:
+    streamed = [
+        {
+            "type": "data-thinking-steps",
+            "data": [{"id": "thinking-1", "status": "completed"}],
+        }
+    ]
+    final = [{"type": "text", "text": "visible answer"}]
+
+    assert merge_streamed_and_final_parts(streamed, final) == [*streamed, *final]
+
+
+def test_merge_does_not_duplicate_when_stream_already_has_text() -> None:
+    streamed = [{"type": "text", "text": "streamed answer"}]
+    final = [{"type": "text", "text": "final answer"}]
+
+    assert merge_streamed_and_final_parts(streamed, final) == streamed
+