feat(config): add custom_agents overrides and strict agent validation

src/config/schema.test.ts

@@ -530,6 +530,79 @@ describe("Sisyphus-Junior agent override", () => {
       expect(result.data.agents?.momus?.category).toBe("quick")
     }
   })
+
+  test("schema accepts custom_agents override keys", () => {
+    // given
+    const config = {
+      custom_agents: {
+        translator: {
+          model: "google/gemini-3-flash-preview",
+          temperature: 0,
+        },
+      },
+    }
+
+    // when
+    const result = OhMyOpenCodeConfigSchema.safeParse(config)
+
+    // then
+    expect(result.success).toBe(true)
+    if (result.success) {
+      expect(result.data.custom_agents?.translator?.model).toBe("google/gemini-3-flash-preview")
+      expect(result.data.custom_agents?.translator?.temperature).toBe(0)
+    }
+  })
+
+  test("schema rejects unknown keys under agents", () => {
+    // given
+    const config = {
+      agents: {
+        sisyphuss: {
+          model: "openai/gpt-5.3-codex",
+        },
+      },
+    }
+
+    // when
+    const result = OhMyOpenCodeConfigSchema.safeParse(config)
+
+    // then
+    expect(result.success).toBe(false)
+  })
+
+  test("schema rejects built-in agent names under custom_agents", () => {
+    // given
+    const config = {
+      custom_agents: {
+        sisyphus: {
+          model: "openai/gpt-5.3-codex",
+        },
+      },
+    }
+
+    // when
+    const result = OhMyOpenCodeConfigSchema.safeParse(config)
+
+    // then
+    expect(result.success).toBe(false)
+  })
+
+  test("schema rejects built-in agent names under custom_agents case-insensitively", () => {
+    // given
+    const config = {
+      custom_agents: {
+        Sisyphus: {
+          model: "openai/gpt-5.3-codex",
+        },
+      },
+    }
+
+    // when
+    const result = OhMyOpenCodeConfigSchema.safeParse(config)
+
+    // then
+    expect(result.success).toBe(false)
+  })
 })
 
 describe("BrowserAutomationProviderSchema", () => {