feat(cli): redesign model fallback with native cross-fallback and OpenAI separation

- Add OpenAI/ChatGPT as separate subscription option (--openai flag)
- Implement native tier cross-fallback (Claude → OpenAI → Gemini)
- Change fallback order: Native → OpenCode Zen → GitHub Copilot → Z.ai
- Add explore agent special logic: max20 → haiku, else → grok-code
- Add critical warning when Claude is not configured
- Add tests for ChatGPT-only and explore agent cases

src/cli/config-manager.test.ts

@@ -201,11 +201,12 @@ describe("config-manager ANTIGRAVITY_PROVIDER_CONFIG", () => {
 })
 
 describe("generateOmoConfig - model fallback system", () => {
-  test("generates native models when Claude available", () => {
-    // #given user has Claude subscription
+  test("generates native sonnet models when Claude standard subscription", () => {
+    // #given user has Claude standard subscription (not max20)
     const config: InstallConfig = {
       hasClaude: true,
       isMax20: false,
+      hasOpenAI: false,
       hasGemini: false,
       hasCopilot: false,
       hasOpencodeZen: false,
@@ -215,17 +216,37 @@ describe("generateOmoConfig - model fallback system", () => {
     // #when generating config
     const result = generateOmoConfig(config)
 
-    // #then should use native anthropic models
+    // #then should use native anthropic sonnet (cost-efficient for standard plan)
     expect(result.$schema).toBe("https://raw.githubusercontent.com/code-yeongyu/oh-my-opencode/master/assets/oh-my-opencode.schema.json")
     expect(result.agents).toBeDefined()
+    expect((result.agents as Record<string, { model: string }>).Sisyphus.model).toBe("anthropic/claude-sonnet-4-5")
+  })
+
+  test("generates native opus models when Claude max20 subscription", () => {
+    // #given user has Claude max20 subscription
+    const config: InstallConfig = {
+      hasClaude: true,
+      isMax20: true,
+      hasOpenAI: false,
+      hasGemini: false,
+      hasCopilot: false,
+      hasOpencodeZen: false,
+      hasZaiCodingPlan: false,
+    }
+
+    // #when generating config
+    const result = generateOmoConfig(config)
+
+    // #then should use native anthropic opus (max power for max20 plan)
     expect((result.agents as Record<string, { model: string }>).Sisyphus.model).toBe("anthropic/claude-opus-4-5")
   })
 
-  test("uses github-copilot fallback when only copilot available", () => {
-    // #given user has only copilot
+  test("uses github-copilot sonnet fallback when only copilot available", () => {
+    // #given user has only copilot (no max plan)
     const config: InstallConfig = {
       hasClaude: false,
       isMax20: false,
+      hasOpenAI: false,
       hasGemini: false,
       hasCopilot: true,
       hasOpencodeZen: false,
@@ -235,8 +256,8 @@ describe("generateOmoConfig - model fallback system", () => {
     // #when generating config
     const result = generateOmoConfig(config)
 
-    // #then should use github-copilot models
-    expect((result.agents as Record<string, { model: string }>).Sisyphus.model).toBe("github-copilot/claude-opus-4.5")
+    // #then should use github-copilot sonnet models
+    expect((result.agents as Record<string, { model: string }>).Sisyphus.model).toBe("github-copilot/claude-sonnet-4.5")
   })
 
   test("uses ultimate fallback when no providers configured", () => {
@@ -244,6 +265,7 @@ describe("generateOmoConfig - model fallback system", () => {
     const config: InstallConfig = {
       hasClaude: false,
       isMax20: false,
+      hasOpenAI: false,
       hasGemini: false,
       hasCopilot: false,
       hasOpencodeZen: false,
@@ -259,10 +281,11 @@ describe("generateOmoConfig - model fallback system", () => {
   })
 
   test("uses zai-coding-plan/glm-4.7 for librarian when Z.ai available", () => {
-    // #given user has Z.ai and Claude
+    // #given user has Z.ai and Claude max20
     const config: InstallConfig = {
       hasClaude: true,
-      isMax20: false,
+      isMax20: true,
+      hasOpenAI: false,
       hasGemini: false,
       hasCopilot: false,
       hasOpencodeZen: false,
@@ -274,7 +297,68 @@ describe("generateOmoConfig - model fallback system", () => {
 
     // #then librarian should use zai-coding-plan/glm-4.7
     expect((result.agents as Record<string, { model: string }>).librarian.model).toBe("zai-coding-plan/glm-4.7")
-    // #then other agents should use native
+    // #then other agents should use native opus (max20 plan)
     expect((result.agents as Record<string, { model: string }>).Sisyphus.model).toBe("anthropic/claude-opus-4-5")
   })
+
+  test("uses native OpenAI models when only ChatGPT available", () => {
+    // #given user has only ChatGPT subscription
+    const config: InstallConfig = {
+      hasClaude: false,
+      isMax20: false,
+      hasOpenAI: true,
+      hasGemini: false,
+      hasCopilot: false,
+      hasOpencodeZen: false,
+      hasZaiCodingPlan: false,
+    }
+
+    // #when generating config
+    const result = generateOmoConfig(config)
+
+    // #then Sisyphus should use native OpenAI (fallback within native tier)
+    expect((result.agents as Record<string, { model: string }>).Sisyphus.model).toBe("openai/gpt-5.2")
+    // #then Oracle should use native OpenAI (primary for ultrabrain)
+    expect((result.agents as Record<string, { model: string }>).oracle.model).toBe("openai/gpt-5.2-codex")
+    // #then multimodal-looker should use native OpenAI (fallback within native tier)
+    expect((result.agents as Record<string, { model: string }>)["multimodal-looker"].model).toBe("openai/gpt-5.2")
+  })
+
+  test("uses haiku for explore when Claude max20", () => {
+    // #given user has Claude max20
+    const config: InstallConfig = {
+      hasClaude: true,
+      isMax20: true,
+      hasOpenAI: false,
+      hasGemini: false,
+      hasCopilot: false,
+      hasOpencodeZen: false,
+      hasZaiCodingPlan: false,
+    }
+
+    // #when generating config
+    const result = generateOmoConfig(config)
+
+    // #then explore should use haiku (max20 plan uses Claude quota)
+    expect((result.agents as Record<string, { model: string }>).explore.model).toBe("anthropic/claude-haiku-4-5")
+  })
+
+  test("uses grok-code for explore when not max20", () => {
+    // #given user has Claude but not max20
+    const config: InstallConfig = {
+      hasClaude: true,
+      isMax20: false,
+      hasOpenAI: false,
+      hasGemini: false,
+      hasCopilot: false,
+      hasOpencodeZen: false,
+      hasZaiCodingPlan: false,
+    }
+
+    // #when generating config
+    const result = generateOmoConfig(config)
+
+    // #then explore should use grok-code (preserve Claude quota)
+    expect((result.agents as Record<string, { model: string }>).explore.model).toBe("opencode/grok-code")
+  })
 })