fix(agents): deny apply_patch for GPT models to prevent verification hangs (#2935)

GPT models (5.3-codex, 5.4, etc.) frequently hang when using apply_patch
due to verification loops. This adds:

1. Tool restriction: apply_patch is denied for GPT variants of
   Hephaestus, Sisyphus-Junior, and Sisyphus agents
2. Prompt guidance: GPT-specific prompts now explicitly instruct using
   edit/write tools instead of apply_patch
3. Removed the 'Always use apply_patch' instruction from
   sisyphus-junior/gpt-5-4.ts that contradicted the fix

The deny is model-conditional — Claude variants retain apply_patch
access since it works reliably there.

src/agents/hephaestus/agent.test.ts

@@ -192,6 +192,8 @@ describe("createHephaestusAgent", () => {
     expect(config.prompt).toContain("You build context by examining");
     expect(config.prompt).toContain("Never chain together bash commands");
     expect(config.prompt).toContain("<tool_usage_rules>");
+    expect(config.prompt).toContain("Do not use `apply_patch`");
+    expect(config.prompt).toContain("`edit` and `write`");
   });
 
   test("GPT 5.3-codex model includes GPT-5.3 specific prompt content", () => {
@@ -205,6 +207,8 @@ describe("createHephaestusAgent", () => {
     expect(config.prompt).toContain("Senior Staff Engineer");
     expect(config.prompt).toContain("Hard Constraints");
     expect(config.prompt).toContain("<tool_usage_rules>");
+    expect(config.prompt).toContain("Do not use `apply_patch`");
+    expect(config.prompt).toContain("`edit` and `write`");
   });
 
   test("includes Hephaestus identity in prompt", () => {
@@ -219,6 +223,35 @@ describe("createHephaestusAgent", () => {
     expect(config.prompt).toContain("autonomous deep worker");
   });
 
+  test("generic GPT model includes apply_patch workaround guidance", () => {
+    // given
+    const model = "openai/gpt-4o";
+
+    // when
+    const config = createHephaestusAgent(model);
+
+    // then
+    expect(config.prompt).toContain("Do not use `apply_patch`");
+    expect(config.prompt).toContain("`edit` and `write`");
+  });
+
+  test("GPT models deny apply_patch while non-GPT models do not", () => {
+    // given
+    const gpt54Model = "openai/gpt-5.4";
+    const gptGenericModel = "openai/gpt-4o";
+    const claudeModel = "anthropic/claude-opus-4-6";
+
+    // when
+    const gpt54Config = createHephaestusAgent(gpt54Model);
+    const gptGenericConfig = createHephaestusAgent(gptGenericModel);
+    const claudeConfig = createHephaestusAgent(claudeModel);
+
+    // then
+    expect(gpt54Config.permission ?? {}).toHaveProperty("apply_patch", "deny");
+    expect(gptGenericConfig.permission ?? {}).toHaveProperty("apply_patch", "deny");
+    expect(claudeConfig.permission ?? {}).not.toHaveProperty("apply_patch");
+  });
+
   test("useTaskSystem=true produces Task Discipline prompt", () => {
     // given
     const model = "openai/gpt-5.4";