refactor(hooks): remove beast-mode system integration

Remove the beast-mode-system hook and all transform wiring so Copilot-specific prompt injection is fully eliminated from the runtime pipeline.

src/plugin/hooks/create-transform-hooks.ts

@@ -5,7 +5,6 @@ import {
   createClaudeCodeHooksHook,
   createKeywordDetectorHook,
   createThinkingBlockValidatorHook,
-  createBeastModeSystemHook,
 } from "../../hooks"
 import {
   contextCollector,
@@ -18,7 +17,6 @@ export type TransformHooks = {
   keywordDetector: ReturnType<typeof createKeywordDetectorHook> | null
   contextInjectorMessagesTransform: ReturnType<typeof createContextInjectorMessagesTransformHook>
   thinkingBlockValidator: ReturnType<typeof createThinkingBlockValidatorHook> | null
-  beastModeSystem: ReturnType<typeof createBeastModeSystemHook> | null
 }
 
 export function createTransformHooks(args: {
@@ -65,19 +63,10 @@ export function createTransformHooks(args: {
       )
     : null
 
-  const beastModeSystem = isHookEnabled("beast-mode-system")
-    ? safeCreateHook(
-        "beast-mode-system",
-        () => createBeastModeSystemHook(),
-        { enabled: safeHookEnabled },
-      )
-    : null
-
   return {
     claudeCodeHooks,
     keywordDetector,
     contextInjectorMessagesTransform,
     thinkingBlockValidator,
-    beastModeSystem,
   }
 }

src/plugin/system-transform.ts

@@ -1,12 +1,6 @@
-import type { CreatedHooks } from "../create-hooks"
-
-export function createSystemTransformHandler(args: {
-  hooks: CreatedHooks
-}): (input: { sessionID: string }, output: { system: string[] }) => Promise<void> {
-  return async (input, output): Promise<void> => {
-    await args.hooks.beastModeSystem?.["experimental.chat.system.transform"]?.(
-      input,
-      output,
-    )
-  }
+export function createSystemTransformHandler(): (
+  input: { sessionID: string },
+  output: { system: string[] },
+) => Promise<void> {
+  return async (): Promise<void> => {}
 }