diff --git a/opencode_bridge/routes.py b/opencode_bridge/routes.py
index 0aa8b78..067c7e8 100644
--- a/opencode_bridge/routes.py
+++ b/opencode_bridge/routes.py
@@ -14,20 +14,14 @@ from .session_manager import SessionManager
 log = logging.getLogger("opencode_bridge.routes")
 
 
-MODE_SYSTEM_PROMPTS = {
-    "optimize": (
-        "你是一个代码优化专家。请基于用户提供的代码上下文，"
-        "返回只包含优化后代码的回复，不要任何解释或 markdown 围栏。"
-    ),
-    "fix": (
-        "你是一个 Python 排错专家。用户给出了一段产生错误的代码和 traceback，"
-        "请返回只包含修复后代码的回复，不要任何解释或 markdown 围栏。"
-    ),
-    "edit": (
-        "你是一个代码编辑助手。基于用户的指令修改给定代码，"
-        "返回只包含修改后完整代码的回复，不要任何解释或 markdown 围栏。"
-    ),
-}
+# Unified system prompt — the LLM (OpenCode) itself judges whether the user's
+# natural-language instruction is an optimize / fix / edit request, based on
+# the code context and the optional <traceback> in the parts below.
+UNIFIED_SYSTEM_PROMPT = (
+    "你是一个代码编辑助手。基于提供的代码上下文（以及 traceback，如果有），"
+    "按照用户的指令修改代码。返回只包含修改后完整代码的回复，"
+    "不要任何解释或 markdown 围栏。"
+)
 
 
 def make_client(handler: APIHandler) -> OpenCodeClient:
@@ -52,12 +46,13 @@ def get_session_manager(handler: APIHandler) -> SessionManager:
     return sm
 
 
-def _build_request_body(mode: str, prompt: str, context: dict) -> dict:
+def _build_request_body(prompt: str, context: dict) -> dict:
     """Build full request body for OpenCode POST /session/:id/message.
 
-    Returns dict with 'parts' (list) and 'system' (str) keys.
+    Returns dict with 'parts' (list) and 'system' (str) keys. No mode concept:
+    the LLM interprets the user's natural-language instruction, with the code
+    context and the optional traceback in front of it.
     """
-    system = MODE_SYSTEM_PROMPTS[mode]
     parts: list[dict] = []
 
     if context.get("previousCode"):
@@ -85,10 +80,10 @@ def _build_request_body(mode: str, prompt: str, context: dict) -> dict:
         ),
     })
 
-    if mode == "edit" and prompt:
+    if prompt:
         parts.append({"type": "text", "text": "<instruction>\n%s\n</instruction>" % prompt})
 
-    return {"parts": parts, "system": system}
+    return {"parts": parts, "system": UNIFIED_SYSTEM_PROMPT}
 
 
 def _strip_code_fence(s: str) -> str:
@@ -157,7 +152,6 @@ class EditHandler(APIHandler):
     async def post(self):
         try:
             body = json.loads(self.request.body)
-            mode = body["mode"]
             prompt = body.get("prompt", "")
             context = body["context"]
             provider_id = body.get("providerId") or None
@@ -177,7 +171,7 @@ class EditHandler(APIHandler):
         sm = get_session_manager(self)
         try:
             sid = await sm.get_or_create(notebook_path)
-            request_body = _build_request_body(mode, prompt, context)
+            request_body = _build_request_body(prompt, context)
             result = await client.send_message_sync(
                 sid,
                 request_body["parts"],
@@ -195,7 +189,6 @@ class EditHandler(APIHandler):
 
             self.finish(json.dumps({
                 "ok": True,
-                "mode": mode,
                 "finalSource": final_source,
                 "sessionId": sid,
                 "notebookPath": notebook_path,
diff --git a/opencode_bridge/tests/test_routes.py b/opencode_bridge/tests/test_routes.py
index e93d6dc..32b9b39 100644
--- a/opencode_bridge/tests/test_routes.py
+++ b/opencode_bridge/tests/test_routes.py
@@ -115,7 +115,6 @@ async def test_edit_handler(monkeypatch, jp_fetch):
     )
 
     body = json.dumps({
-        "mode": "edit",
         "prompt": "Add type hints",
         "context": {
             "notebookPath": "test.ipynb",