fix: detect GPT models behind proxy providers (litellm, ollama) in isGptModel

isGptModel only matched openai/ and github-copilot/gpt- prefixes, causing
models like litellm/gpt-5.2 to fall into the Claude code path. This
injected Claude-specific thinking config, which the opencode runtime
translated into a reasoningSummary API parameter — rejected by OpenAI.

Extract model name after provider prefix and match against GPT model
name patterns (gpt-*, o1, o3, o4).

Closes #1788

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/agents/types.test.ts

@@ -0,0 +1,49 @@
+import { describe, test, expect } from "bun:test";
+import { isGptModel } from "./types";
+
+describe("isGptModel", () => {
+  test("standard openai provider models", () => {
+    expect(isGptModel("openai/gpt-5.2")).toBe(true);
+    expect(isGptModel("openai/gpt-4o")).toBe(true);
+    expect(isGptModel("openai/o1")).toBe(true);
+    expect(isGptModel("openai/o3-mini")).toBe(true);
+  });
+
+  test("github copilot gpt models", () => {
+    expect(isGptModel("github-copilot/gpt-5.2")).toBe(true);
+    expect(isGptModel("github-copilot/gpt-4o")).toBe(true);
+  });
+
+  test("litellm proxied gpt models", () => {
+    expect(isGptModel("litellm/gpt-5.2")).toBe(true);
+    expect(isGptModel("litellm/gpt-4o")).toBe(true);
+    expect(isGptModel("litellm/o1")).toBe(true);
+    expect(isGptModel("litellm/o3-mini")).toBe(true);
+    expect(isGptModel("litellm/o4-mini")).toBe(true);
+  });
+
+  test("other proxied gpt models", () => {
+    expect(isGptModel("ollama/gpt-4o")).toBe(true);
+    expect(isGptModel("custom-provider/gpt-5.2")).toBe(true);
+  });
+
+  test("gpt4 prefix without hyphen (legacy naming)", () => {
+    expect(isGptModel("litellm/gpt4o")).toBe(true);
+    expect(isGptModel("ollama/gpt4")).toBe(true);
+  });
+
+  test("claude models are not gpt", () => {
+    expect(isGptModel("anthropic/claude-opus-4-6")).toBe(false);
+    expect(isGptModel("anthropic/claude-sonnet-4-5")).toBe(false);
+    expect(isGptModel("litellm/anthropic.claude-opus-4-5")).toBe(false);
+  });
+
+  test("gemini models are not gpt", () => {
+    expect(isGptModel("google/gemini-3-pro")).toBe(false);
+    expect(isGptModel("litellm/gemini-3-pro")).toBe(false);
+  });
+
+  test("opencode provider is not gpt", () => {
+    expect(isGptModel("opencode/claude-opus-4-6")).toBe(false);
+  });
+});

src/agents/types.ts

@@ -66,8 +66,18 @@ export interface AgentPromptMetadata {
   keyTrigger?: string
 }
 
+function extractModelName(model: string): string {
+  return model.includes("/") ? model.split("/").pop() ?? model : model
+}
+
+const GPT_MODEL_PREFIXES = ["gpt-", "gpt4", "o1", "o3", "o4"]
+
 export function isGptModel(model: string): boolean {
-  return model.startsWith("openai/") || model.startsWith("github-copilot/gpt-")
+  if (model.startsWith("openai/") || model.startsWith("github-copilot/gpt-"))
+    return true
+
+  const modelName = extractModelName(model).toLowerCase()
+  return GPT_MODEL_PREFIXES.some((prefix) => modelName.startsWith(prefix))
 }
 
 export type BuiltinAgentName =