feat(hooks): implement UserPromptSubmit with chat.message hook and injectHookMessage

- Add chat.message handler to createClaudeCodeHooksHook factory
- Integrate executeUserPromptSubmitHooks() for user prompt processing
- Use injectHookMessage() for file system based message injection
- Add sessionFirstMessageProcessed tracking for title generation skip
- Register chat.message hook in plugin entry point

This completes 100% port of Claude Code hooks from opencode-cc-plugin.

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

notepad.md

@@ -795,3 +795,51 @@ All tasks execution STARTED: Thu Dec 4 16:52:57 KST 2025
 소요 시간: ~6분
 
 ---
+
+## [2025-12-09 18:16] - hook-message-injector 사용 패턴 크로스체크
+
+### DISCOVERED ISSUES
+- **CRITICAL**: UserPromptSubmit hooks가 oh-my-opencode에 완전히 누락됨
+- opencode-cc-plugin에서는 chat.message hook으로 UserPromptSubmit 처리
+- oh-my-opencode에는 chat.message hook이 구현되지 않음
+- user-prompt-submit.ts는 정의만 있고 실제 사용처 없음
+
+### IMPLEMENTATION DECISIONS
+- PostToolUse는 이미 올바르게 구현됨:
+  * opencode-cc-plugin: result.message를 tool output에 append
+  * oh-my-opencode: 동일한 방식 사용 (claude-code-hooks/index.ts:95-97)
+  * injectHookMessage() 불필요
+- UserPromptSubmit 구현 추가:
+  * chat.message hook handler 추가 (claude-code-hooks/index.ts)
+  * executeUserPromptSubmitHooks() 호출
+  * sessionFirstMessageProcessed Set으로 첫 메시지 skip (title generation)
+  * result.messages가 있으면 injectHookMessage() 호출
+  * src/index.ts에 hook 등록
+- Import 추가:
+  * executeUserPromptSubmitHooks, UserPromptSubmitContext, MessagePart from ./user-prompt-submit
+  * injectHookMessage from ../../features/hook-message-injector
+
+### PROBLEMS FOR NEXT TASKS
+- None - UserPromptSubmit 통합 완료
+
+### VERIFICATION RESULTS
+- Ran: `bunx tsc --noEmit` → exit 0, no errors
+- Ran: `bun run build` → exit 0, successful build
+- Files modified:
+  * src/hooks/claude-code-hooks/index.ts (chat.message handler 추가)
+  * src/index.ts (chat.message hook 등록)
+- Verified OpenCode Plugin API: chat.message hook 공식 지원 확인 (@opencode-ai/plugin/dist/index.d.ts:112-123)
+
+### LEARNINGS
+- OpenCode Plugin API에 chat.message hook 존재:
+  * input: sessionID, agent?, model?, messageID?
+  * output: message, parts[]
+- PostToolUse는 tool output에 직접 append (injectHookMessage 불필요)
+- UserPromptSubmit는 file system injection 사용 (injectHookMessage 필수)
+- opencode-cc-plugin 구조: src/plugin/chat-handler.ts → handleChatMessage()
+- oh-my-opencode 구조: src/hooks/claude-code-hooks/index.ts → createClaudeCodeHooksHook()
+- 첫 메시지 skip 로직: title generation을 위해 UserPromptSubmit hooks 실행 안 함
+
+소요 시간: ~8분
+
+---

src/hooks/claude-code-hooks/index.ts

@@ -10,6 +10,11 @@ import {
   type PostToolUseContext,
   type PostToolUseClient,
 } from "./post-tool-use"
+import {
+  executeUserPromptSubmitHooks,
+  type UserPromptSubmitContext,
+  type MessagePart,
+} from "./user-prompt-submit"
 import {
   executeStopHooks,
   type StopContext,
@@ -17,10 +22,99 @@ import {
 import { cacheToolInput, getToolInput } from "./tool-input-cache"
 import { getTranscriptPath } from "./transcript"
 import { log } from "../../shared"
+import { injectHookMessage } from "../../features/hook-message-injector"
 
 export function createClaudeCodeHooksHook(ctx: PluginInput) {
+  const sessionFirstMessageProcessed = new Set<string>()
 
   return {
+    "chat.message": async (
+      input: {
+        sessionID: string
+        agent?: string
+        model?: { providerID: string; modelID: string }
+        messageID?: string
+      },
+      output: {
+        message: Record<string, unknown>
+        parts: Array<{ type: string; text?: string; [key: string]: unknown }>
+      }
+    ): Promise<void> => {
+      try {
+        const claudeConfig = await loadClaudeHooksConfig()
+        const extendedConfig = await loadPluginExtendedConfig()
+
+        const textParts = output.parts.filter((p) => p.type === "text" && p.text)
+        const prompt = textParts.map((p) => p.text ?? "").join("\n")
+
+        const isFirstMessage = !sessionFirstMessageProcessed.has(input.sessionID)
+        sessionFirstMessageProcessed.add(input.sessionID)
+
+        if (isFirstMessage) {
+          log("[Claude Hooks] Skipping UserPromptSubmit on first message for title generation")
+          return
+        }
+
+        let parentSessionId: string | undefined
+        try {
+          const sessionInfo = await ctx.client.session.get({
+            path: { id: input.sessionID },
+          })
+          parentSessionId = sessionInfo.data?.parentID
+        } catch {}
+
+        const messageParts: MessagePart[] = textParts.map((p) => ({
+          type: p.type as "text",
+          text: p.text,
+        }))
+
+        const userPromptCtx: UserPromptSubmitContext = {
+          sessionId: input.sessionID,
+          parentSessionId,
+          prompt,
+          parts: messageParts,
+          cwd: ctx.directory,
+        }
+
+        const result = await executeUserPromptSubmitHooks(
+          userPromptCtx,
+          claudeConfig,
+          extendedConfig
+        )
+
+        if (result.block) {
+          throw new Error(result.reason ?? "Hook blocked the prompt")
+        }
+
+        if (result.messages.length > 0) {
+          const hookContent = result.messages.join("\n\n")
+          const message = output.message as {
+            agent?: string
+            model?: { modelID?: string; providerID?: string }
+            path?: { cwd?: string; root?: string }
+            tools?: Record<string, boolean>
+          }
+
+          const success = injectHookMessage(input.sessionID, hookContent, {
+            agent: message.agent,
+            model: message.model,
+            path: message.path ?? { cwd: ctx.directory, root: "/" },
+            tools: message.tools,
+          })
+
+          log(
+            success
+              ? "[Claude Hooks] Hook message injected via file system"
+              : "[Claude Hooks] File injection failed",
+            { sessionID: input.sessionID }
+          )
+        }
+      } catch (error) {
+        log("[Claude Hooks] chat.message error:", error)
+        throw error
+      }
+    },
+
     "tool.execute.before": async (
       input: { tool: string; sessionID: string; callID: string },
       output: { args: Record<string, unknown> }

src/index.ts

@@ -86,6 +86,10 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
   return {
     tool: builtinTools,
 
+    "chat.message": async (input, output) => {
+      await claudeCodeHooks["chat.message"]?.(input, output)
+    },
+
     config: async (config) => {
       const builtinAgents = createBuiltinAgents(
         pluginConfig.disabled_agents,