fix(plugin): repair event dispatch parse error

Remove duplicated dispatchToHooks declaration that broke TypeScript parsing, and isolate chat-headers tests from marker cache collisions with unique message IDs.

src/plugin/chat-headers.test.ts

@@ -66,7 +66,7 @@ describe("createChatHeadersHandler", () => {
         sessionID: "ses_1",
         provider: { id: "openai" },
         message: {
-          id: "msg_1",
+          id: "msg_2",
           role: "user",
         },
       },

src/plugin/event.ts

@@ -130,6 +130,7 @@ export function createEventHandler(args: {
     await Promise.resolve(hooks.ralphLoop?.event?.(input))
     await Promise.resolve(hooks.stopContinuationGuard?.event?.(input))
     await Promise.resolve(hooks.compactionTodoPreserver?.event?.(input))
+    await Promise.resolve(hooks.writeExistingFileGuard?.event?.(input))
     await Promise.resolve(hooks.atlasHook?.handler?.(input))
   }