feat(features): add hook message injector

- Port hook-message-injector from opencode-cc-plugin (4 files)
- constants.ts: XDG-based path definitions (MESSAGE_STORAGE, PART_STORAGE)
- types.ts: MessageMeta, OriginalMessageContext, TextPart interfaces
- injector.ts: injectHookMessage() implementation with message/part storage
- index.ts: Barrel export
- Self-contained module with no import path changes needed
- Preserves XDG_DATA_HOME environment variable support
- Preserves message fallback logic for incomplete originalMessage

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

src/features/hook-message-injector/constants.ts

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+import { join } from "node:path"
+import { homedir } from "node:os"
+
+const xdgData = process.env.XDG_DATA_HOME || join(homedir(), ".local", "share")
+
+export const OPENCODE_STORAGE = join(xdgData, "opencode", "storage")
+export const MESSAGE_STORAGE = join(OPENCODE_STORAGE, "message")
+export const PART_STORAGE = join(OPENCODE_STORAGE, "part")

src/features/hook-message-injector/index.ts

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+export { injectHookMessage } from "./injector"
+export type { MessageMeta, OriginalMessageContext, TextPart } from "./types"

src/features/hook-message-injector/injector.ts

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+import { existsSync, mkdirSync, readFileSync, readdirSync, writeFileSync } from "node:fs"
+import { join } from "node:path"
+import { MESSAGE_STORAGE, PART_STORAGE } from "./constants"
+import type { MessageMeta, OriginalMessageContext, TextPart } from "./types"
+
+interface StoredMessage {
+  agent?: string
+  model?: { providerID?: string; modelID?: string }
+  tools?: Record<string, boolean>
+}
+
+function findNearestMessageWithFields(messageDir: string): StoredMessage | null {
+  try {
+    const files = readdirSync(messageDir)
+      .filter((f) => f.endsWith(".json"))
+      .sort()
+      .reverse()
+
+    for (const file of files) {
+      try {
+        const content = readFileSync(join(messageDir, file), "utf-8")
+        const msg = JSON.parse(content) as StoredMessage
+        if (msg.agent && msg.model?.providerID && msg.model?.modelID) {
+          return msg
+        }
+      } catch {
+        continue
+      }
+    }
+  } catch {
+    return null
+  }
+  return null
+}
+
+function generateMessageId(): string {
+  const timestamp = Date.now().toString(16)
+  const random = Math.random().toString(36).substring(2, 14)
+  return `msg_${timestamp}${random}`
+}
+
+function generatePartId(): string {
+  const timestamp = Date.now().toString(16)
+  const random = Math.random().toString(36).substring(2, 10)
+  return `prt_${timestamp}${random}`
+}
+
+function getOrCreateMessageDir(sessionID: string): string {
+  if (!existsSync(MESSAGE_STORAGE)) {
+    mkdirSync(MESSAGE_STORAGE, { recursive: true })
+  }
+
+  const directPath = join(MESSAGE_STORAGE, sessionID)
+  if (existsSync(directPath)) {
+    return directPath
+  }
+
+  for (const dir of readdirSync(MESSAGE_STORAGE)) {
+    const sessionPath = join(MESSAGE_STORAGE, dir, sessionID)
+    if (existsSync(sessionPath)) {
+      return sessionPath
+    }
+  }
+
+  mkdirSync(directPath, { recursive: true })
+  return directPath
+}
+
+export function injectHookMessage(
+  sessionID: string,
+  hookContent: string,
+  originalMessage: OriginalMessageContext
+): boolean {
+  const messageDir = getOrCreateMessageDir(sessionID)
+
+  const needsFallback =
+    !originalMessage.agent ||
+    !originalMessage.model?.providerID ||
+    !originalMessage.model?.modelID
+
+  const fallback = needsFallback ? findNearestMessageWithFields(messageDir) : null
+
+  const now = Date.now()
+  const messageID = generateMessageId()
+  const partID = generatePartId()
+
+  const resolvedAgent = originalMessage.agent ?? fallback?.agent ?? "general"
+  const resolvedModel =
+    originalMessage.model?.providerID && originalMessage.model?.modelID
+      ? { providerID: originalMessage.model.providerID, modelID: originalMessage.model.modelID }
+      : fallback?.model?.providerID && fallback?.model?.modelID
+        ? { providerID: fallback.model.providerID, modelID: fallback.model.modelID }
+        : undefined
+  const resolvedTools = originalMessage.tools ?? fallback?.tools
+
+  const messageMeta: MessageMeta = {
+    id: messageID,
+    sessionID,
+    role: "user",
+    time: {
+      created: now,
+    },
+    agent: resolvedAgent,
+    model: resolvedModel,
+    path:
+      originalMessage.path?.cwd
+        ? {
+            cwd: originalMessage.path.cwd,
+            root: originalMessage.path.root ?? "/",
+          }
+        : undefined,
+    tools: resolvedTools,
+  }
+
+  const textPart: TextPart = {
+    id: partID,
+    type: "text",
+    text: hookContent,
+    synthetic: true,
+    time: {
+      start: now,
+      end: now,
+    },
+    messageID,
+    sessionID,
+  }
+
+  try {
+    writeFileSync(join(messageDir, `${messageID}.json`), JSON.stringify(messageMeta, null, 2))
+
+    const partDir = join(PART_STORAGE, messageID)
+    if (!existsSync(partDir)) {
+      mkdirSync(partDir, { recursive: true })
+    }
+    writeFileSync(join(partDir, `${partID}.json`), JSON.stringify(textPart, null, 2))
+
+    return true
+  } catch {
+    return false
+  }
+}

src/features/hook-message-injector/types.ts

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+export interface MessageMeta {
+  id: string
+  sessionID: string
+  role: "user" | "assistant"
+  time: {
+    created: number
+    completed?: number
+  }
+  agent?: string
+  model?: {
+    providerID: string
+    modelID: string
+  }
+  path?: {
+    cwd: string
+    root: string
+  }
+  tools?: Record<string, boolean>
+}
+
+export interface OriginalMessageContext {
+  agent?: string
+  model?: {
+    providerID?: string
+    modelID?: string
+  }
+  path?: {
+    cwd?: string
+    root?: string
+  }
+  tools?: Record<string, boolean>
+}
+
+export interface TextPart {
+  id: string
+  type: "text"
+  text: string
+  synthetic: boolean
+  time: {
+    start: number
+    end: number
+  }
+  messageID: string
+  sessionID: string
+}