fix(plugin): verify event hook compatibility with v1.4.0

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/shared/compaction-marker.ts

@@ -0,0 +1,57 @@
+import { existsSync, readdirSync, readFileSync } from "node:fs"
+import { join } from "node:path"
+import { PART_STORAGE } from "./opencode-storage-paths"
+
+type CompactionPartLike = {
+  type?: unknown
+}
+
+type CompactionMessageLike = {
+  agent?: unknown
+  info?: {
+    agent?: unknown
+  }
+  parts?: unknown
+}
+
+function isCompactionPart(part: unknown): boolean {
+  return typeof part === "object" && part !== null && (part as CompactionPartLike).type === "compaction"
+}
+
+export function isCompactionAgent(agent: unknown): boolean {
+  return typeof agent === "string" && agent.trim().toLowerCase() === "compaction"
+}
+
+export function hasCompactionPart(parts: unknown): boolean {
+  return Array.isArray(parts) && parts.some((part) => isCompactionPart(part))
+}
+
+export function isCompactionMessage(message: CompactionMessageLike): boolean {
+  return isCompactionAgent(message.info?.agent ?? message.agent) || hasCompactionPart(message.parts)
+}
+
+export function hasCompactionPartInStorage(messageID: string | undefined): boolean {
+  if (!messageID) {
+    return false
+  }
+
+  const partDir = join(PART_STORAGE, messageID)
+  if (!existsSync(partDir)) {
+    return false
+  }
+
+  try {
+    return readdirSync(partDir)
+      .filter((fileName) => fileName.endsWith(".json"))
+      .some((fileName) => {
+        try {
+          const content = readFileSync(join(partDir, fileName), "utf-8")
+          return isCompactionPart(JSON.parse(content))
+        } catch {
+          return false
+        }
+      })
+  } catch {
+    return false
+  }
+}

src/shared/index.ts

@@ -68,6 +68,7 @@ export * from "./project-discovery-dirs"
 export * from "./normalize-sdk-response"
 export * from "./session-directory-resolver"
 export * from "./prompt-tools"
+export * from "./compaction-marker"
 export * from "./internal-initiator-marker"
 export * from "./plugin-command-discovery"
 export { SessionCategoryRegistry } from "./session-category-registry"