diff --git a/haiku_rag_slim/haiku/rag/agents/chat/agent.py b/haiku_rag_slim/haiku/rag/agents/chat/agent.py
index af67a6d7..149bd049 100644
--- a/haiku_rag_slim/haiku/rag/agents/chat/agent.py
+++ b/haiku_rag_slim/haiku/rag/agents/chat/agent.py
@@ -92,6 +92,7 @@ def prepare_chat_context(
 def create_chat_agent(
     config: AppConfig,
     features: list[str] | None = None,
+    preamble: str | None = None,
 ) -> Agent[ChatDeps, str]:
     """Create the chat agent with composed toolsets.
 
@@ -100,6 +101,9 @@ def create_chat_agent(
         features: List of features to enable. Defaults to DEFAULT_FEATURES
             (search, documents, qa). Available features: "search",
             "documents", "qa", "analysis".
+        preamble: Optional custom identity/rules section for the system prompt.
+            When provided, replaces the default identity prompt. Tool guidance,
+            feature rules, and closing are still appended by the builder.
 
     Returns:
         The configured chat agent.
@@ -133,7 +137,7 @@ def create_chat_agent(
         model,
         deps_type=ChatDeps,
         output_type=str,
-        instructions=build_chat_prompt(features),
+        instructions=build_chat_prompt(features, preamble=preamble),
         toolsets=toolsets,
         retries=3,
     )
diff --git a/haiku_rag_slim/haiku/rag/agents/chat/prompts.py b/haiku_rag_slim/haiku/rag/agents/chat/prompts.py
index a39349b3..f86d9f3e 100644
--- a/haiku_rag_slim/haiku/rag/agents/chat/prompts.py
+++ b/haiku_rag_slim/haiku/rag/agents/chat/prompts.py
@@ -26,7 +26,10 @@ _PROMPT_QA_CLOSING = (
 )
 
 
-def build_chat_prompt(features: list[str]) -> str:
+def build_chat_prompt(
+    features: list[str],
+    preamble: str | None = None,
+) -> str:
     """Build a chat system prompt from the given feature list.
 
     Each feature adds its relevant tool guidance to the prompt.
@@ -34,11 +37,14 @@ def build_chat_prompt(features: list[str]) -> str:
 
     Args:
         features: List of feature names (e.g., ["search", "documents", "qa"]).
+        preamble: Optional custom identity/rules section. When provided,
+            replaces the default identity prompt. Tool guidance, feature
+            rules, and closing are still appended.
 
     Returns:
         The composed system prompt string.
     """
-    parts = [_PROMPT_BASE]
+    parts = [preamble if preamble is not None else _PROMPT_BASE]
 
     # Add feature-specific critical rules
     if "qa" in features:
diff --git a/haiku_rag_slim/haiku/rag/agents/chat/state.py b/haiku_rag_slim/haiku/rag/agents/chat/state.py
index f3619fb2..ef985cb0 100644
--- a/haiku_rag_slim/haiku/rag/agents/chat/state.py
+++ b/haiku_rag_slim/haiku/rag/agents/chat/state.py
@@ -16,6 +16,7 @@ class ChatSessionState(BaseModel):
 
     initial_context: str | None = None
     citations: list[Citation] = []
+    citations_history: list[list[Citation]] = []
     qa_history: list["QAHistoryEntry"] = []
     session_context: SessionContext | None = None
     document_filter: list[str] = []
diff --git a/tests/agents/chat/test_features.py b/tests/agents/chat/test_features.py
index 21c89134..a438cd7e 100644
--- a/tests/agents/chat/test_features.py
+++ b/tests/agents/chat/test_features.py
@@ -155,3 +155,35 @@ def test_build_chat_prompt_includes_analysis():
     assert "analyze" in prompt
     assert "search" in prompt
     assert "ask" in prompt
+
+
+def test_build_chat_prompt_with_preamble():
+    """Custom preamble replaces the default identity section."""
+    custom = "You are a custom assistant."
+    prompt = build_chat_prompt(DEFAULT_FEATURES, preamble=custom)
+
+    assert prompt.startswith(custom)
+    # Tool guidance should still be appended
+    assert "search" in prompt
+    assert "ask" in prompt
+    # Default identity should NOT be present
+    assert "haiku.rag" not in prompt
+
+
+def test_build_chat_prompt_without_preamble_uses_default():
+    """Without preamble, the default identity section is used."""
+    prompt = build_chat_prompt(DEFAULT_FEATURES)
+
+    assert "haiku.rag" in prompt
+
+
+def test_create_chat_agent_with_preamble():
+    """create_chat_agent passes preamble through to build_chat_prompt."""
+    custom = "You are a domain expert."
+    agent = create_chat_agent(Config, preamble=custom)
+
+    assert agent is not None
+    # _instructions is the internal list of instruction strings/callables
+    assert any(
+        custom in instr for instr in agent._instructions if isinstance(instr, str)
+    )
diff --git a/tests/agents/chat/test_state.py b/tests/agents/chat/test_state.py
index 34c50651..19220c87 100644
--- a/tests/agents/chat/test_state.py
+++ b/tests/agents/chat/test_state.py
@@ -1,4 +1,5 @@
 from haiku.rag.agents.chat.state import ChatSessionState
+from haiku.rag.agents.research.models import Citation
 from haiku.rag.tools.session import SessionContext, SessionState
 
 
@@ -113,3 +114,28 @@ def test_chat_session_state_model_dump_json_serializes_datetime():
     # datetime should be serialized as ISO string, not datetime object
     assert isinstance(snapshot["session_context"]["last_updated"], str)
     assert snapshot["session_context"]["last_updated"] == "2025-01-27T12:00:00"
+
+
+def test_chat_session_state_citations_history_default():
+    """citations_history defaults to empty list."""
+    state = ChatSessionState()
+    assert state.citations_history == []
+
+
+def test_chat_session_state_citations_history_roundtrip():
+    """citations_history serializes and deserializes correctly."""
+    citation = Citation(
+        index=1,
+        document_id="d1",
+        chunk_id="c1",
+        document_uri="test://doc",
+        document_title="Doc",
+        page_numbers=[],
+        headings=None,
+        content="content",
+    )
+    state = ChatSessionState(citations_history=[[citation]])
+    data = state.model_dump(mode="json")
+    restored = ChatSessionState.model_validate(data)
+    assert len(restored.citations_history) == 1
+    assert restored.citations_history[0][0].chunk_id == "c1"