fix(model): preserve reasoning in provider fallback resolution (#29285)

* fix(model): preserve reasoning in provider fallback resolution

* test(model): cover fallback reasoning propagation

src/agents/pi-embedded-runner/model.test.ts

@@ -200,6 +200,32 @@ describe("resolveModel", () => {
     expect(result.model?.maxTokens).toBe(32768);
   });
 
+  it("propagates reasoning from matching configured fallback model", () => {
+    const cfg = {
+      models: {
+        providers: {
+          custom: {
+            baseUrl: "http://localhost:9000",
+            models: [
+              {
+                ...makeModel("model-a"),
+                reasoning: false,
+              },
+              {
+                ...makeModel("model-b"),
+                reasoning: true,
+              },
+            ],
+          },
+        },
+      },
+    } as OpenClawConfig;
+
+    const result = resolveModel("custom", "model-b", "/tmp/agent", cfg);
+
+    expect(result.model?.reasoning).toBe(true);
+  });
+
   it("builds an openai-codex fallback for gpt-5.3-codex", () => {
     mockOpenAICodexTemplateModel();
 

src/agents/pi-embedded-runner/model.ts

@@ -103,7 +103,7 @@ export function resolveModel(
         api: providerCfg?.api ?? "openai-responses",
         provider,
         baseUrl: providerCfg?.baseUrl,
-        reasoning: false,
+        reasoning: configuredModel?.reasoning ?? false,
         input: ["text"],
         cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
         contextWindow: