diff --git a/src/plugins/registry.ts b/src/plugins/registry.ts
index 4f24714d4e7..fde8d0e6a6d 100644
--- a/src/plugins/registry.ts
+++ b/src/plugins/registry.ts
@@ -12,7 +12,11 @@ import { resolveUserPath } from "../utils.js";
 import { registerPluginCommand } from "./commands.js";
 import { normalizePluginHttpPath } from "./http-path.js";
 import type { PluginRuntime } from "./runtime/types.js";
-import { isPluginHookName, isPromptInjectionHookName } from "./types.js";
+import {
+  isPluginHookName,
+  isPromptInjectionHookName,
+  stripPromptMutationFieldsFromLegacyHookResult,
+} from "./types.js";
 import type {
   OpenClawPluginApi,
   OpenClawPluginChannelRegistration,
@@ -32,7 +36,6 @@ import type {
   PluginLogger,
   PluginOrigin,
   PluginKind,
-  PluginHookBeforeAgentStartResult,
   PluginHookName,
   PluginHookHandlerMap,
   PluginHookRegistration as TypedPluginHookRegistration,
@@ -146,24 +149,6 @@ type PluginTypedHookPolicy = {
   allowPromptInjection?: boolean;
 };
 
-const stripPromptMutationFieldsFromLegacyHookResult = (
-  result: PluginHookBeforeAgentStartResult | void,
-): PluginHookBeforeAgentStartResult | void => {
-  if (!result || typeof result !== "object") {
-    return result;
-  }
-  const {
-    systemPrompt: _systemPrompt,
-    prependContext: _prependContext,
-    prependSystemContext: _prependSystemContext,
-    appendSystemContext: _appendSystemContext,
-    ...remaining
-  } = result;
-  return Object.keys(remaining).length > 0
-    ? (remaining as PluginHookBeforeAgentStartResult)
-    : undefined;
-};
-
 const constrainLegacyPromptInjectionHook = (
   handler: PluginHookHandlerMap["before_agent_start"],
 ): PluginHookHandlerMap["before_agent_start"] => {
diff --git a/src/plugins/types.ts b/src/plugins/types.ts
index ab0a1a57813..1cb2779e8c2 100644
--- a/src/plugins/types.ts
+++ b/src/plugins/types.ts
@@ -430,6 +430,22 @@ export type PluginHookBeforePromptBuildResult = {
   appendSystemContext?: string;
 };
 
+export const PLUGIN_PROMPT_MUTATION_RESULT_FIELDS = [
+  "systemPrompt",
+  "prependContext",
+  "prependSystemContext",
+  "appendSystemContext",
+] as const satisfies readonly (keyof PluginHookBeforePromptBuildResult)[];
+
+type MissingPluginPromptMutationResultFields = Exclude<
+  keyof PluginHookBeforePromptBuildResult,
+  (typeof PLUGIN_PROMPT_MUTATION_RESULT_FIELDS)[number]
+>;
+type AssertAllPluginPromptMutationResultFieldsListed =
+  MissingPluginPromptMutationResultFields extends never ? true : never;
+const assertAllPluginPromptMutationResultFieldsListed: AssertAllPluginPromptMutationResultFieldsListed = true;
+void assertAllPluginPromptMutationResultFieldsListed;
+
 // before_agent_start hook (legacy compatibility: combines both phases)
 export type PluginHookBeforeAgentStartEvent = {
   prompt: string;
@@ -440,6 +456,26 @@ export type PluginHookBeforeAgentStartEvent = {
 export type PluginHookBeforeAgentStartResult = PluginHookBeforePromptBuildResult &
   PluginHookBeforeModelResolveResult;
 
+export type PluginHookBeforeAgentStartOverrideResult = Omit<
+  PluginHookBeforeAgentStartResult,
+  keyof PluginHookBeforePromptBuildResult
+>;
+
+export const stripPromptMutationFieldsFromLegacyHookResult = (
+  result: PluginHookBeforeAgentStartResult | void,
+): PluginHookBeforeAgentStartOverrideResult | void => {
+  if (!result || typeof result !== "object") {
+    return result;
+  }
+  const remaining: Partial<PluginHookBeforeAgentStartResult> = { ...result };
+  for (const field of PLUGIN_PROMPT_MUTATION_RESULT_FIELDS) {
+    delete remaining[field];
+  }
+  return Object.keys(remaining).length > 0
+    ? (remaining as PluginHookBeforeAgentStartOverrideResult)
+    : undefined;
+};
+
 // llm_input hook
 export type PluginHookLlmInputEvent = {
   runId: string;