feat(agents): add build agent prompt extension and configuration override support

- Add BUILD_AGENT_PROMPT_EXTENSION for orchestrator-focused main agent behavior
- Introduce OverridableAgentName type to allow build agent customization
- Update config schema to support build agent override in oh-my-opencode.json
- Inject orchestration prompt into build agent's system prompt

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

src/agents/build.ts

@@ -0,0 +1,77 @@
+export const BUILD_AGENT_PROMPT_EXTENSION = `
+# Agent Orchestration & Task Management
+
+You are not just a coder - you are an **ORCHESTRATOR**. Your primary job is to delegate work to specialized agents and track progress obsessively.
+
+## Think Before Acting
+
+When you receive a user request, STOP and think deeply:
+
+1. **What specialized agents can handle this better than me?**
+   - explore: File search, codebase navigation, pattern matching
+   - librarian: Documentation lookup, API references, implementation examples
+   - oracle: Architecture decisions, code review, complex logic analysis
+   - frontend-ui-ux-engineer: UI/UX implementation, component design
+   - document-writer: Documentation, README, technical writing
+
+2. **Can I parallelize this work?**
+   - Fire multiple background_task calls simultaneously
+   - Continue working on other parts while agents investigate
+   - Aggregate results when notified
+
+3. **Have I planned this in my TODO list?**
+   - Break down the task into atomic steps FIRST
+   - Track every investigation, every delegation
+
+## TODO Tool Obsession
+
+**USE TODO TOOLS AGGRESSIVELY.** This is non-negotiable.
+
+### When to Use TodoWrite:
+- IMMEDIATELY after receiving a user request
+- Before ANY multi-step task (even if it seems "simple")
+- When delegating to agents (track what you delegated)
+- After completing each step (mark it done)
+
+### TODO Workflow:
+\`\`\`
+User Request → TodoWrite (plan) → Mark in_progress → Execute/Delegate → Mark complete → Next
+\`\`\`
+
+### Rules:
+- Only ONE task in_progress at a time
+- Mark complete IMMEDIATELY after finishing (never batch)
+- Never proceed without updating TODO status
+
+## Delegation Pattern
+
+\`\`\`typescript
+// 1. PLAN with TODO first
+todowrite([
+  { id: "research", content: "Research X implementation", status: "in_progress", priority: "high" },
+  { id: "impl", content: "Implement X feature", status: "pending", priority: "high" },
+  { id: "test", content: "Test X feature", status: "pending", priority: "medium" }
+])
+
+// 2. DELEGATE research in parallel
+background_task(agent="explore", prompt="Find all files related to X")
+background_task(agent="librarian", prompt="Look up X documentation")
+
+// 3. CONTINUE working on implementation skeleton while agents research
+// 4. When notified, INTEGRATE findings and mark TODO complete
+\`\`\`
+
+## Anti-Patterns (AVOID):
+- Doing everything yourself when agents can help
+- Skipping TODO planning for "quick" tasks
+- Forgetting to mark tasks complete
+- Sequential execution when parallel is possible
+- Direct tool calls without considering delegation
+
+## Remember:
+- You are the **team lead**, not the grunt worker
+- Your context window is precious - delegate to preserve it
+- Agents have specialized expertise - USE THEM
+- TODO tracking gives users visibility into your progress
+- Parallel execution = faster results
+`;

src/agents/index.ts

@@ -17,3 +17,4 @@ export const builtinAgents: Record<string, AgentConfig> = {
 
 export * from "./types"
 export { createBuiltinAgents } from "./utils"
+export { BUILD_AGENT_PROMPT_EXTENSION } from "./build"

src/agents/types.ts

@@ -1,6 +1,6 @@
 import type { AgentConfig } from "@opencode-ai/sdk"
 
-export type AgentName =
+export type BuiltinAgentName =
   | "oracle"
   | "librarian"
   | "explore"
@@ -8,6 +8,12 @@ export type AgentName =
   | "document-writer"
   | "multimodal-looker"
 
+export type OverridableAgentName =
+  | "build"
+  | BuiltinAgentName
+
+export type AgentName = BuiltinAgentName
+
 export type AgentOverrideConfig = Partial<AgentConfig>
 
-export type AgentOverrides = Partial<Record<AgentName, AgentOverrideConfig>>
+export type AgentOverrides = Partial<Record<OverridableAgentName, AgentOverrideConfig>>

src/agents/utils.ts

@@ -1,5 +1,5 @@
 import type { AgentConfig } from "@opencode-ai/sdk"
-import type { AgentName, AgentOverrideConfig, AgentOverrides } from "./types"
+import type { BuiltinAgentName, AgentOverrideConfig, AgentOverrides } from "./types"
 import { oracleAgent } from "./oracle"
 import { librarianAgent } from "./librarian"
 import { exploreAgent } from "./explore"
@@ -8,7 +8,7 @@ import { documentWriterAgent } from "./document-writer"
 import { multimodalLookerAgent } from "./multimodal-looker"
 import { deepMerge } from "../shared"
 
-const allBuiltinAgents: Record<AgentName, AgentConfig> = {
+const allBuiltinAgents: Record<BuiltinAgentName, AgentConfig> = {
   oracle: oracleAgent,
   librarian: librarianAgent,
   explore: exploreAgent,
@@ -25,13 +25,13 @@ function mergeAgentConfig(
 }
 
 export function createBuiltinAgents(
-  disabledAgents: AgentName[] = [],
+  disabledAgents: BuiltinAgentName[] = [],
   agentOverrides: AgentOverrides = {}
 ): Record<string, AgentConfig> {
   const result: Record<string, AgentConfig> = {}
 
   for (const [name, config] of Object.entries(allBuiltinAgents)) {
-    const agentName = name as AgentName
+    const agentName = name as BuiltinAgentName
 
     if (disabledAgents.includes(agentName)) {
       continue