diff --git a/src/landppt/services/slide/slide_edit_agent_service.py b/src/landppt/services/slide/slide_edit_agent_service.py
index 383dd2f..e05a653 100644
--- a/src/landppt/services/slide/slide_edit_agent_service.py
+++ b/src/landppt/services/slide/slide_edit_agent_service.py
@@ -15,6 +15,10 @@ from pydantic import BaseModel
 
 AgentEditMode = Literal["slide", "element"]
 
+_MAX_CONVERSATION_HISTORY_MESSAGES = 10
+_MAX_CONVERSATION_HISTORY_TOTAL_CHARS = 6000
+_MAX_CONVERSATION_HISTORY_MESSAGE_CHARS = 1200
+
 
 class SlideEditAgentRequest(BaseModel):
     projectId: str
@@ -1008,6 +1012,7 @@ class SlideEditAgentService:
             "selected_element_id": request.selectedElementId,
             "selected_element_html": request.selectedElementHtml,
             "user_request": request.userRequest,
+            "conversation_history": self._conversation_history_context(request),
             "current_html": runner.current_html,
             "vision": self._vision_context(request),
             "available_tools": self._tool_schemas(runner),
@@ -1016,10 +1021,59 @@ class SlideEditAgentService:
         }
         return (
             "Use a ReAct loop to edit this PPT slide. Choose exactly one action. "
-            "Use final when the draft is ready. Return strict JSON only.\n\n"
+            "Use conversation_history for continuity, but execute the latest "
+            "user_request. Use final when the draft is ready. Return strict JSON only.\n\n"
             + json.dumps(context, ensure_ascii=False, indent=2)
         )
 
+    def _conversation_history_context(
+        self, request: SlideEditAgentRequest
+    ) -> List[Dict[str, str]]:
+        cleaned: List[Dict[str, str]] = []
+        total_chars = 0
+
+        for item in reversed(request.chatHistory or []):
+            if len(cleaned) >= _MAX_CONVERSATION_HISTORY_MESSAGES:
+                break
+            if not isinstance(item, dict):
+                continue
+
+            role = str(item.get("role") or "").strip().lower()
+            if role not in {"user", "assistant"}:
+                continue
+
+            content = str(item.get("content") or "").strip()
+            if not content:
+                continue
+
+            remaining_chars = _MAX_CONVERSATION_HISTORY_TOTAL_CHARS - total_chars
+            if remaining_chars <= 0:
+                break
+
+            max_chars = min(
+                remaining_chars,
+                _MAX_CONVERSATION_HISTORY_MESSAGE_CHARS,
+            )
+            content = self._truncate_history_content(content, max_chars)
+            if not content:
+                continue
+
+            cleaned.append({"role": role, "content": content})
+            total_chars += len(content)
+
+        cleaned.reverse()
+        return cleaned
+
+    @staticmethod
+    def _truncate_history_content(content: str, max_chars: int) -> str:
+        if max_chars <= 0:
+            return ""
+        if len(content) <= max_chars:
+            return content
+        if max_chars <= 3:
+            return content[:max_chars]
+        return content[: max_chars - 3].rstrip() + "..."
+
     def _vision_context(self, request: SlideEditAgentRequest) -> Dict[str, Any]:
         attachments: List[Dict[str, Any]] = []
         if request.slideScreenshot:
diff --git a/tests/test_slide_edit_agent_service.py b/tests/test_slide_edit_agent_service.py
index e32243c..5085326 100644
--- a/tests/test_slide_edit_agent_service.py
+++ b/tests/test_slide_edit_agent_service.py
@@ -381,6 +381,53 @@ def test_tool_runner_build_proposal_strips_agent_ids():
     assert proposal.validation.valid is True
 
 
+def _agent_prompt_context(service: SlideEditAgentService, request: SlideEditAgentRequest):
+    runner = SlideEditToolRunner(SlideEditAgentContext.from_request(request))
+    prompt = service._build_prompt(request, runner, scratchpad=[], max_iterations=6)
+    return json.loads(prompt.split("\n\n", 1)[1])
+
+
+def test_slide_edit_agent_prompt_includes_sanitized_conversation_history():
+    service = SlideEditAgentService()
+    request = _tool_request(
+        chatHistory=[
+            {"role": "system", "content": "Do not include this."},
+            {"role": "user", "content": "Make the heading shorter first."},
+            {"role": "assistant", "content": "I shortened the heading."},
+            {"role": "tool", "content": "Internal tool output."},
+            {"role": "assistant", "content": "   "},
+        ]
+    )
+
+    context = _agent_prompt_context(service, request)
+
+    assert context["conversation_history"] == [
+        {"role": "user", "content": "Make the heading shorter first."},
+        {"role": "assistant", "content": "I shortened the heading."},
+    ]
+    assert context["user_request"] == "Make the title shorter"
+
+
+def test_slide_edit_agent_prompt_limits_conversation_history_to_recent_messages():
+    service = SlideEditAgentService()
+    history = [
+        {"role": "user", "content": f"message {index}"}
+        for index in range(14)
+    ]
+    history.append({"role": "assistant", "content": "x" * 1500})
+    request = _tool_request(chatHistory=history)
+
+    context = _agent_prompt_context(service, request)
+    conversation_history = context["conversation_history"]
+
+    assert len(conversation_history) == 10
+    assert conversation_history[0] == {"role": "user", "content": "message 5"}
+    assert conversation_history[-2] == {"role": "user", "content": "message 13"}
+    assert conversation_history[-1]["role"] == "assistant"
+    assert conversation_history[-1]["content"].endswith("...")
+    assert len(conversation_history[-1]["content"]) <= 1200
+
+
 class _FakePPTService:
     def __init__(self, responses):
         self.responses = list(responses)