fix(models): update Gemini 3 to 3.1 Pro and add Kimi to writing category fallback

Closes #2065

Closes #1968

src/agents/types.test.ts

@@ -47,8 +47,8 @@ describe("isGptModel", () => {
   });
 
   test("gemini models are not gpt", () => {
-    expect(isGptModel("google/gemini-3-pro")).toBe(false);
-    expect(isGptModel("litellm/gemini-3-pro")).toBe(false);
+    expect(isGptModel("google/gemini-3.1-pro")).toBe(false);
+    expect(isGptModel("litellm/gemini-3.1-pro")).toBe(false);
   });
 
   test("opencode provider is not gpt", () => {
@@ -58,29 +58,29 @@ describe("isGptModel", () => {
 
 describe("isGeminiModel", () => {
   test("#given google provider models #then returns true", () => {
-    expect(isGeminiModel("google/gemini-3-pro")).toBe(true);
+    expect(isGeminiModel("google/gemini-3.1-pro")).toBe(true);
     expect(isGeminiModel("google/gemini-3-flash")).toBe(true);
     expect(isGeminiModel("google/gemini-2.5-pro")).toBe(true);
   });
 
   test("#given google-vertex provider models #then returns true", () => {
-    expect(isGeminiModel("google-vertex/gemini-3-pro")).toBe(true);
+    expect(isGeminiModel("google-vertex/gemini-3.1-pro")).toBe(true);
     expect(isGeminiModel("google-vertex/gemini-3-flash")).toBe(true);
   });
 
   test("#given github copilot gemini models #then returns true", () => {
-    expect(isGeminiModel("github-copilot/gemini-3-pro")).toBe(true);
+    expect(isGeminiModel("github-copilot/gemini-3.1-pro")).toBe(true);
     expect(isGeminiModel("github-copilot/gemini-3-flash")).toBe(true);
   });
 
   test("#given litellm proxied gemini models #then returns true", () => {
-    expect(isGeminiModel("litellm/gemini-3-pro")).toBe(true);
+    expect(isGeminiModel("litellm/gemini-3.1-pro")).toBe(true);
     expect(isGeminiModel("litellm/gemini-3-flash")).toBe(true);
     expect(isGeminiModel("litellm/gemini-2.5-pro")).toBe(true);
   });
 
   test("#given other proxied gemini models #then returns true", () => {
-    expect(isGeminiModel("custom-provider/gemini-3-pro")).toBe(true);
+    expect(isGeminiModel("custom-provider/gemini-3.1-pro")).toBe(true);
     expect(isGeminiModel("ollama/gemini-3-flash")).toBe(true);
   });
 

src/agents/utils.test.ts

@@ -988,7 +988,7 @@ describe("buildAgent with category and skills", () => {
     const agent = buildAgent(source["test-agent"], TEST_MODEL)
 
     // #then - category's built-in model is applied
-    expect(agent.model).toBe("google/gemini-3-pro")
+    expect(agent.model).toBe("google/gemini-3.1-pro")
   })
 
   test("agent with category and existing model keeps existing model", () => {