feat(chat): inject referenced-chat context into the new-chat agent input

Thread mentioned_thread_ids from the route through the orchestrator into
input-state assembly, resolve them for the requesting user, and append
the rendered referenced-chat block to the agent's query context.

surfsense_backend/app/routes/new_chat_routes.py

@@ -1800,6 +1800,7 @@ async def handle_new_chat(
                 mentioned_connector_ids=request.mentioned_connector_ids,
                 mentioned_connectors=mentioned_connectors_payload,
                 mentioned_documents=mentioned_documents_payload,
+                mentioned_thread_ids=request.mentioned_thread_ids,
                 needs_history_bootstrap=thread.needs_history_bootstrap,
                 thread_visibility=thread.visibility,
                 current_user_display_name=user.display_name or "A team member",
@@ -2296,6 +2297,7 @@ async def regenerate_response(
                     mentioned_connector_ids=request.mentioned_connector_ids,
                     mentioned_connectors=mentioned_connectors_payload,
                     mentioned_documents=mentioned_documents_payload,
+                    mentioned_thread_ids=request.mentioned_thread_ids,
                     checkpoint_id=target_checkpoint_id,
                     needs_history_bootstrap=thread.needs_history_bootstrap,
                     thread_visibility=thread.visibility,

surfsense_backend/app/tasks/chat/streaming/flows/new_chat/input_state.py

@@ -33,6 +33,10 @@ from app.agents.chat.runtime.mention_resolver import (
     resolve_mentions,
     substitute_in_text,
 )
+from app.agents.chat.runtime.referenced_chat_context import (
+    render_referenced_chats_block,
+    resolve_referenced_chats,
+)
 from app.db import (
     ChatVisibility,
     NewChatThread,
@@ -67,6 +71,8 @@ async def build_new_chat_input_state(
     mentioned_folder_ids: list[int] | None,
     mentioned_connectors: list[dict[str, Any]] | None,
     mentioned_documents: list[dict[str, Any]] | None,
+    mentioned_thread_ids: list[int] | None,
+    requesting_user_id: str | None,
     needs_history_bootstrap: bool,
     thread_visibility: ChatVisibility,
     current_user_display_name: str | None,
@@ -112,10 +118,22 @@ async def build_new_chat_input_state(
         mentioned_documents=mentioned_documents,
     )
 
+    # Referenced-chat context is path-independent, so resolve it in every
+    # filesystem mode (unlike the doc/folder mention substitution above).
+    referenced_chats = await resolve_referenced_chats(
+        session,
+        search_space_id=search_space_id,
+        requesting_user_id=requesting_user_id,
+        current_chat_id=chat_id,
+        mentioned_thread_ids=mentioned_thread_ids,
+    )
+    referenced_chat_context = render_referenced_chats_block(referenced_chats)
+
     final_query = _render_query_with_context(
         agent_user_query=agent_user_query,
         mentioned_connectors=mentioned_connectors,
         recent_reports=recent_reports,
+        referenced_chat_context=referenced_chat_context,
     )
 
     if thread_visibility == ChatVisibility.SEARCH_SPACE and current_user_display_name:
@@ -203,10 +221,13 @@ def _render_query_with_context(
     agent_user_query: str,
     mentioned_connectors: list[dict[str, Any]] | None,
     recent_reports: list[Report],
+    referenced_chat_context: str | None = None,
 ) -> str:
-    """Prepend the ``<mentioned_connectors>`` then ``<report_context>`` blocks.
+    """Prepend ``<mentioned_connectors>``, ``<report_context>``, then
+    ``<referenced_chat_context>`` blocks.
 
-    Order is load-bearing for legacy parity.
+    Order of connectors then reports is load-bearing for legacy parity;
+    referenced chats are appended last as read-only background.
     """
     context_parts: list[str] = []
 
@@ -233,6 +254,9 @@ def _render_query_with_context(
             "</report_context>"
         )
 
+    if referenced_chat_context:
+        context_parts.append(referenced_chat_context)
+
     if context_parts:
         context = "\n\n".join(context_parts)
         return f"{context}\n\n<user_query>{agent_user_query}</user_query>"

surfsense_backend/app/tasks/chat/streaming/flows/new_chat/orchestrator.py

@@ -129,6 +129,7 @@ async def stream_new_chat(
     mentioned_connector_ids: list[int] | None = None,
     mentioned_connectors: list[dict[str, Any]] | None = None,
     mentioned_documents: list[dict[str, Any]] | None = None,
+    mentioned_thread_ids: list[int] | None = None,
     checkpoint_id: str | None = None,
     needs_history_bootstrap: bool = False,
     thread_visibility: ChatVisibility | None = None,
@@ -433,6 +434,8 @@ async def stream_new_chat(
             mentioned_folder_ids=mentioned_folder_ids,
             mentioned_connectors=mentioned_connectors,
             mentioned_documents=mentioned_documents,
+            mentioned_thread_ids=mentioned_thread_ids,
+            requesting_user_id=user_id,
             needs_history_bootstrap=needs_history_bootstrap,
             thread_visibility=visibility,
             current_user_display_name=current_user_display_name,