diff --git a/packages/provider-bridge-acp/src/bridge/bridge.test.ts b/packages/provider-bridge-acp/src/bridge/bridge.test.ts
index bf3a7ff86..a1e4868ae 100644
--- a/packages/provider-bridge-acp/src/bridge/bridge.test.ts
+++ b/packages/provider-bridge-acp/src/bridge/bridge.test.ts
@@ -1271,21 +1271,26 @@ describe("acp bridge", () => {
     expect(agentMessageTexts()).toContain("selected-model:fake/strong");
   });
 
-  it("falls back to session/set_model when the model config option errors", async () => {
-    const { providerThreadId } = await startThread({
-      envVars: {
-        FAKE_ACP_MODEL_CONFIG: "1",
-        FAKE_ACP_SET_CONFIG_MODEL_ERROR: "1",
-      },
-      model: "fake/strong",
-    });
-
-    sendTurnRequest("turn/start", providerThreadId, {
-      input: [{ type: "text", text: "echo-selected-model", mentions: [] }],
-    });
-    await waitForTurnCompleted();
+  it("preserves model config errors without using session/set_model", async () => {
+    const requestLog = join(workspaceDir, "model-config-error-requests.jsonl");
+    let startError: Error | undefined;
+    try {
+      await startThread({
+        envVars: {
+          FAKE_ACP_MODEL_CONFIG: "1",
+          FAKE_ACP_REQUEST_LOG: requestLog,
+          FAKE_ACP_SET_CONFIG_MODEL_ERROR: "1",
+        },
+        model: "fake/strong",
+      });
+    } catch (error) {
+      startError = error instanceof Error ? error : new Error(String(error));
+    }
 
-    expect(agentMessageTexts()).toContain("selected-model:fake/strong");
+    expect.soft(startError?.message ?? "").toContain("model config probe failed");
+    expect(
+      loggedAcpRequests(requestLog).map((request) => request.method),
+    ).not.toContain("session/set_model");
   });
 
   it("selects ACP-native models from session models state", async () => {