fix(auxiliary): keep ZAI Coding Plan routing

agent/auxiliary_client.py

@@ -1271,13 +1271,20 @@ def _to_openai_base_url(base_url: str) -> str:
     Anthropic-**only** custom gateways (path ends in ``/anthropic`` but has no
     sibling ``/v1``) must keep their path; rewriting them to ``/v1`` yields 404
     on compression/vision/title_generation (#83642).
+
+    ZAI exposes its general API and Coding Plan on separate endpoints.  Its
+    Anthropic-compatible Coding Plan endpoint maps to ``/api/coding/paas/v4``
+    on the OpenAI wire, not the general ``/api/paas/v4`` endpoint.  Rewriting
+    to the general endpoint changes the billing pool and can return a false
+    insufficient-balance error for a valid Coding Plan key.
     """
     url = str(base_url or "").strip().rstrip("/")
     if url.endswith("/anthropic"):
-        # ZAI (open.bigmodel.cn) uses /api/anthropic for Anthropic wire
-        # but /api/paas/v4 for OpenAI wire — the generic /v1 rewrite is wrong.
-        if "open.bigmodel.cn" in url or "bigmodel" in url:
-            rewritten = url[: -len("/anthropic")] + "/paas/v4"
+        # ZAI uses /api/anthropic for the Coding Plan's Anthropic wire.  The
+        # matching OpenAI-wire endpoint is /api/coding/paas/v4; /api/paas/v4
+        # is the independently billed general API.
+        if "open.bigmodel.cn" in url or "bigmodel" in url or "api.z.ai" in url:
+            rewritten = url[: -len("/anthropic")] + "/coding/paas/v4"
             logger.debug("Auxiliary client: rewrote ZAI base URL %s → %s", url, rewritten)
             return rewritten
         if _is_dual_surface_anthropic_host(url):

tests/agent/test_minimax_auxiliary_url.py

@@ -1,7 +1,9 @@
-"""Tests for MiniMax auxiliary client URL normalization.
+"""Tests for Anthropic-to-OpenAI auxiliary URL normalization.
 
 MiniMax and MiniMax-CN set inference_base_url to the /anthropic path.
-The auxiliary client uses the OpenAI SDK, which needs /v1 instead.
+The auxiliary client uses the OpenAI SDK, which needs /v1 instead. ZAI's
+Anthropic endpoint belongs to Coding Plan, whose OpenAI-compatible peer is the
+separately billed /api/coding/paas/v4 endpoint.
 """
 
 import sys
@@ -37,5 +39,17 @@ class TestToOpenaiBaseUrl:
         url = "https://minimax.io.evil.example.com/anthropic"
         assert _to_openai_base_url(url) == url
 
+    def test_zai_anthropic_routes_to_coding_plan_openai_endpoint(self):
+        assert (
+            _to_openai_base_url("https://api.z.ai/api/anthropic")
+            == "https://api.z.ai/api/coding/paas/v4"
+        )
+
+    def test_bigmodel_anthropic_routes_to_coding_plan_openai_endpoint(self):
+        assert (
+            _to_openai_base_url("https://open.bigmodel.cn/api/anthropic")
+            == "https://open.bigmodel.cn/api/coding/paas/v4"
+        )
+
     def test_none(self):
         assert _to_openai_base_url(None) == ""