feat(sisyphus-junior): add model-specific GPT prompt routing (gpt-5-4, gpt-5-3-codex, generic gpt)

Split GPT prompt into three variants with model-based routing:
- gpt-5-4.ts: GPT-5.4 optimized (expert coding agent framing, prose-first)
- gpt-5-3-codex.ts: GPT-5.3-Codex optimized (Hephaestus-style Senior Engineer)
- gpt.ts: Generic GPT fallback (Hephaestus-style, for any other GPT model)

Routing: gpt-5.4 → gpt-5-4 | gpt-5.3-codex → gpt-5-3-codex | other GPT → gpt

🤖 Generated with assistance of [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/agents/sisyphus-junior/index.test.ts

@@ -314,6 +314,30 @@ describe("createSisyphusJuniorAgentWithOverrides", () => {
       expect(result.prompt).toContain("Progress Updates")
     })
 
+    test("GPT 5.4 model uses GPT-5.4 specific prompt", () => {
+      // given
+      const override = { model: "openai/gpt-5.4" }
+
+      // when
+      const result = createSisyphusJuniorAgentWithOverrides(override)
+
+      // then
+      expect(result.prompt).toContain("expert coding agent")
+      expect(result.prompt).toContain("<tool_usage_rules>")
+    })
+
+    test("GPT 5.3 Codex model uses GPT-5.3-codex specific prompt", () => {
+      // given
+      const override = { model: "openai/gpt-5.3-codex" }
+
+      // when
+      const result = createSisyphusJuniorAgentWithOverrides(override)
+
+      // then
+      expect(result.prompt).toContain("Senior Engineer")
+      expect(result.prompt).toContain("<tool_usage_rules>")
+    })
+
     test("prompt_append is added after base prompt", () => {
       // given
       const override = { prompt_append: "CUSTOM_MARKER_FOR_TEST" }
@@ -331,7 +355,51 @@ describe("createSisyphusJuniorAgentWithOverrides", () => {
 })
 
 describe("getSisyphusJuniorPromptSource", () => {
-  test("returns 'gpt' for OpenAI models", () => {
+  test("returns 'gpt-5-4' for GPT 5.4 models", () => {
+    // given
+    const model = "openai/gpt-5.4"
+
+    // when
+    const source = getSisyphusJuniorPromptSource(model)
+
+    // then
+    expect(source).toBe("gpt-5-4")
+  })
+
+  test("returns 'gpt-5-4' for GitHub Copilot GPT 5.4", () => {
+    // given
+    const model = "github-copilot/gpt-5.4"
+
+    // when
+    const source = getSisyphusJuniorPromptSource(model)
+
+    // then
+    expect(source).toBe("gpt-5-4")
+  })
+
+  test("returns 'gpt-5-3-codex' for GPT 5.3 Codex models", () => {
+    // given
+    const model = "openai/gpt-5.3-codex"
+
+    // when
+    const source = getSisyphusJuniorPromptSource(model)
+
+    // then
+    expect(source).toBe("gpt-5-3-codex")
+  })
+
+  test("returns 'gpt-5-3-codex' for GitHub Copilot GPT 5.3 Codex", () => {
+    // given
+    const model = "github-copilot/gpt-5.3-codex"
+
+    // when
+    const source = getSisyphusJuniorPromptSource(model)
+
+    // then
+    expect(source).toBe("gpt-5-3-codex")
+  })
+
+  test("returns 'gpt' for generic GPT models", () => {
     // given
     const model = "openai/gpt-5.2"
 
@@ -342,7 +410,7 @@ describe("getSisyphusJuniorPromptSource", () => {
     expect(source).toBe("gpt")
   })
 
-  test("returns 'gpt' for GitHub Copilot GPT models", () => {
+  test("returns 'gpt' for GitHub Copilot generic GPT models", () => {
     // given
     const model = "github-copilot/gpt-4o"
 
@@ -377,7 +445,33 @@ describe("getSisyphusJuniorPromptSource", () => {
 })
 
 describe("buildSisyphusJuniorPrompt", () => {
-  test("GPT model prompt contains Hephaestus-style sections", () => {
+  test("GPT 5.4 model uses GPT-5.4 optimized prompt", () => {
+    // given
+    const model = "openai/gpt-5.4"
+
+    // when
+    const prompt = buildSisyphusJuniorPrompt(model, false)
+
+    // then
+    expect(prompt).toContain("expert coding agent")
+    expect(prompt).toContain("Scope Discipline")
+    expect(prompt).toContain("<tool_usage_rules>")
+  })
+
+  test("GPT 5.3 Codex model uses GPT-5.3-codex prompt", () => {
+    // given
+    const model = "openai/gpt-5.3-codex"
+
+    // when
+    const prompt = buildSisyphusJuniorPrompt(model, false)
+
+    // then
+    expect(prompt).toContain("Senior Engineer")
+    expect(prompt).toContain("Scope Discipline")
+    expect(prompt).toContain("<tool_usage_rules>")
+  })
+
+  test("generic GPT model uses generic GPT prompt", () => {
     // given
     const model = "openai/gpt-5.2"
 
@@ -404,9 +498,21 @@ describe("buildSisyphusJuniorPrompt", () => {
     expect(prompt).toContain("todowrite")
   })
 
-  test("useTaskSystem=true includes Task Discipline for GPT", () => {
+  test("useTaskSystem=true includes Task Discipline for GPT 5.4", () => {
     // given
-    const model = "openai/gpt-5.2"
+    const model = "openai/gpt-5.4"
+
+    // when
+    const prompt = buildSisyphusJuniorPrompt(model, true)
+
+    // then
+    expect(prompt).toContain("Task Discipline")
+    expect(prompt).toContain("task_create")
+  })
+
+  test("useTaskSystem=true includes Task Discipline for GPT 5.3 Codex", () => {
+    // given
+    const model = "openai/gpt-5.3-codex"
 
     // when
     const prompt = buildSisyphusJuniorPrompt(model, true)