fix(kiro): map GPT-5.6 reasoning effort fields

Route GPT-5.6 reasoning effort through Kiro's native reasoning.effort field instead of the legacy Claude output_config.effort path. GPT-5.6 models now emit reasoning.effort for low/medium/high/xhigh, with max mapped to the xhigh wire value.

Preserve the Responses API reasoning.effort through the OpenAI intermediate by copying it to reasoning_effort before the field is dropped. Skip legacy thinking_mode prompt tags when a supported native GPT effort is emitted, while keeping the legacy fallback for unsupported values (auto/minimal/ultra) and explicit disable semantics (none/off/disabled). Claude adaptive effort continues to use thinking plus output_config.effort.

tests/unit/openai-to-kiro.test.js

@@ -316,42 +316,100 @@ describe("openaiToKiroRequest", () => {
       });
     });
 
-    it("maps GPT-5.6 reasoning.effort high to Kiro CLI reasoning fields", () => {
+    it.each([
+      ["high", "gpt-5.6-sol"],
+      ["medium", "kiro/gpt-5.6-terra"],
+      ["low", "gpt-5.6-luna"],
+    ])("maps GPT-5.6 reasoning.effort %s without legacy prompt tags", (effort, model) => {
       const body = {
-        reasoning: { effort: "high" },
-        messages: [{ role: "user", content: "Think deeply" }]
+        reasoning: { effort },
+        messages: [{ role: "user", content: "Use the requested effort" }]
+      };
+
+      const result = openaiToKiroRequest(model, body, true, {});
+
+      expect(result.additionalModelRequestFields).toEqual({
+        reasoning: { effort },
+      });
+      expect(systemPromptOf(result)).not.toContain("<thinking_mode>");
+      expect(systemPromptOf(result)).not.toContain("<max_thinking_length>");
+      expect(contentOf(result)).not.toContain("<thinking_mode>");
+      expect(contentOf(result)).not.toContain("<max_thinking_length>");
+    });
+
+    it.each([
+      ["xhigh", "gpt-5.6-terra", "xhigh"],
+      ["max", "gpt-5.6-sol", "xhigh"],
+    ])("preserves GPT-5.6 effort %s as supported wire effort %s", (effort, model, wireEffort) => {
+      const body = {
+        reasoning: { effort },
+        messages: [{ role: "user", content: "Use extended effort" }]
+      };
+
+      const result = openaiToKiroRequest(model, body, true, {});
+
+      expect(result.additionalModelRequestFields).toEqual({
+        reasoning: { effort: wireEffort },
+      });
+      expect(systemPromptOf(result)).not.toContain("<thinking_mode>");
+      expect(systemPromptOf(result)).not.toContain("<max_thinking_length>");
+    });
+
+    it("omits GPT-5.6 effort fields and legacy prompt tags when effort is absent", () => {
+      const body = {
+        messages: [{ role: "user", content: "No explicit reasoning effort" }]
       };
 
       const result = openaiToKiroRequest("gpt-5.6-sol", body, true, {});
 
-      expect(systemPromptOf(result)).toContain("<max_thinking_length>24576</max_thinking_length>");
-      expect(result.additionalModelRequestFields).toEqual({
-        reasoning: { effort: "high" },
-      });
+      expect(result.additionalModelRequestFields).toBeUndefined();
+      expect(systemPromptOf(result)).not.toContain("<thinking_mode>");
+      expect(systemPromptOf(result)).not.toContain("<max_thinking_length>");
     });
 
-    it("maps prefixed GPT-5.6 reasoning_effort medium to Kiro CLI reasoning fields", () => {
+    it.each(["auto", "minimal", "ultra"])(
+      "keeps the legacy thinking fallback for unsupported GPT-5.6 effort %s",
+      (effort) => {
+        const body = {
+          reasoning: { effort },
+          messages: [{ role: "user", content: "Use legacy thinking" }]
+        };
+
+        const result = openaiToKiroRequest("gpt-5.6-luna", body, true, {});
+
+        expect(result.additionalModelRequestFields).toBeUndefined();
+        expect(systemPromptOf(result)).toContain("<thinking_mode>enabled</thinking_mode>");
+        expect(systemPromptOf(result)).toContain("<max_thinking_length>");
+      }
+    );
+
+    it.each(["none", "off", "disabled"])(
+      "keeps GPT-5.6 reasoning intentionally disabled for effort %s",
+      (effort) => {
+        const body = {
+          reasoning: { effort },
+          messages: [{ role: "user", content: "Do not reason" }]
+        };
+
+        const result = openaiToKiroRequest("gpt-5.6-luna", body, true, {});
+
+        expect(result.additionalModelRequestFields).toBeUndefined();
+        expect(systemPromptOf(result)).not.toContain("<thinking_mode>");
+        expect(systemPromptOf(result)).not.toContain("<max_thinking_length>");
+      }
+    );
+
+    it("keeps the thinking-alias fallback when GPT effort is blank", () => {
       const body = {
-        reasoning_effort: "medium",
-        messages: [{ role: "user", content: "Think normally" }]
+        reasoning: { effort: "" },
+        messages: [{ role: "user", content: "Use the thinking alias" }]
       };
 
-      const result = openaiToKiroRequest("kiro/gpt-5.6-terra", body, true, {});
-
-      expect(result.additionalModelRequestFields).toEqual({
-        reasoning: { effort: "medium" },
-      });
-    });
-
-    it("does not forward unsupported GPT-5.6 effort values", () => {
-      const body = {
-        reasoning: { effort: "ultra" },
-        messages: [{ role: "user", content: "Unknown effort" }]
-      };
-
-      const result = openaiToKiroRequest("gpt-5.6-luna", body, true, {});
+      const result = openaiToKiroRequest("gpt-5.6-sol-thinking", body, true, {});
 
       expect(result.additionalModelRequestFields).toBeUndefined();
+      expect(systemPromptOf(result)).toContain("<thinking_mode>enabled</thinking_mode>");
+      expect(systemPromptOf(result)).toContain("<max_thinking_length>");
     });
 
     it("does not send additionalModelRequestFields for legacy Kiro model ids", () => {