feat(agents): add category and skills support to buildAgent

Extend buildAgent() to support:
- category: inherit model/temperature from DEFAULT_CATEGORIES
- skills: prepend resolved skill content to agent prompt

Includes comprehensive test coverage for new functionality.

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/agents/utils.test.ts

@@ -1,5 +1,6 @@
 import { describe, test, expect } from "bun:test"
 import { createBuiltinAgents } from "./utils"
+import type { AgentConfig } from "@opencode-ai/sdk"
 
 describe("createBuiltinAgents with model overrides", () => {
   test("Sisyphus with default model has thinking config", () => {
@@ -85,3 +86,182 @@ describe("createBuiltinAgents with model overrides", () => {
     expect(agents.Sisyphus.temperature).toBe(0.5)
   })
 })
+
+describe("buildAgent with category and skills", () => {
+  const { buildAgent } = require("./utils")
+
+  test("agent with category inherits category settings", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          category: "visual-engineering",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.model).toBe("google/gemini-3-pro-preview")
+    expect(agent.temperature).toBe(0.7)
+  })
+
+  test("agent with category and existing model keeps existing model", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          category: "visual-engineering",
+          model: "custom/model",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.model).toBe("custom/model")
+    expect(agent.temperature).toBe(0.7)
+  })
+
+  test("agent with skills has content prepended to prompt", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          skills: ["frontend-ui-ux"],
+          prompt: "Original prompt content",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.prompt).toContain("Role: Designer-Turned-Developer")
+    expect(agent.prompt).toContain("Original prompt content")
+    expect(agent.prompt).toMatch(/Designer-Turned-Developer[\s\S]*Original prompt content/s)
+  })
+
+  test("agent with multiple skills has all content prepended", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          skills: ["frontend-ui-ux"],
+          prompt: "Agent prompt",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.prompt).toContain("Role: Designer-Turned-Developer")
+    expect(agent.prompt).toContain("Agent prompt")
+  })
+
+  test("agent without category or skills works as before", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          model: "custom/model",
+          temperature: 0.5,
+          prompt: "Base prompt",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.model).toBe("custom/model")
+    expect(agent.temperature).toBe(0.5)
+    expect(agent.prompt).toBe("Base prompt")
+  })
+
+  test("agent with category and skills applies both", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          category: "high-iq",
+          skills: ["frontend-ui-ux"],
+          prompt: "Task description",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.model).toBe("openai/gpt-5.2")
+    expect(agent.temperature).toBe(0.1)
+    expect(agent.prompt).toContain("Role: Designer-Turned-Developer")
+    expect(agent.prompt).toContain("Task description")
+  })
+
+  test("agent with non-existent category has no effect", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          category: "non-existent",
+          prompt: "Base prompt",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.model).toBeUndefined()
+    expect(agent.prompt).toBe("Base prompt")
+  })
+
+  test("agent with non-existent skills only prepends found ones", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          skills: ["frontend-ui-ux", "non-existent-skill"],
+          prompt: "Base prompt",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.prompt).toContain("Role: Designer-Turned-Developer")
+    expect(agent.prompt).toContain("Base prompt")
+  })
+
+  test("agent with empty skills array keeps original prompt", () => {
+    // #given
+    const source = {
+      "test-agent": () =>
+        ({
+          description: "Test agent",
+          skills: [],
+          prompt: "Base prompt",
+        }) as AgentConfig,
+    }
+
+    // #when
+    const agent = buildAgent(source["test-agent"])
+
+    // #then
+    expect(agent.prompt).toBe("Base prompt")
+  })
+})