refactor: consolidate message delivery API

src/plugins/compat/registry.ts

@@ -758,7 +758,7 @@ export const PLUGIN_COMPAT_RECORDS = [
     surfaces: ["api.runtime.config.loadConfig", "api.runtime.config.writeConfigFile"],
     diagnostics: [
       "plugin runtime compatibility warning",
-      "deprecated internal config API guard",
+      "deprecated API usage guard",
       "runtime channel config boundary guard",
     ],
     tests: [

src/plugins/hook-message.types.ts

@@ -77,6 +77,8 @@ export type PluginHookMessageSendingEvent = {
 export type PluginHookMessageSendingResult = {
   content?: string;
   cancel?: boolean;
+  cancelReason?: string;
+  metadata?: Record<string, unknown>;
 };
 
 export type PluginHookMessageSentEvent = {

src/plugins/hooks.ts

@@ -1045,6 +1045,8 @@ export function createHookRunner(
           return {
             content: lastDefined(acc?.content, next.content),
             cancel: stickyTrue(acc?.cancel, next.cancel),
+            cancelReason: lastDefined(acc?.cancelReason, next.cancelReason),
+            metadata: next.metadata ?? acc?.metadata,
           };
         },
         shouldStop: (result) => result.cancel === true,

src/plugins/wired-hooks-message.test.ts

@@ -47,8 +47,8 @@ describe("message_sending hook runner", () => {
     {
       name: "runMessageSending can cancel message delivery",
       event: { to: "user-123", content: "blocked" },
-      hookResult: { cancel: true },
-      expected: { cancel: true },
+      hookResult: { cancel: true, cancelReason: "policy", metadata: { owner: "agent-2" } },
+      expected: { cancel: true, cancelReason: "policy", metadata: { owner: "agent-2" } },
     },
   ] as const)("$name", async ({ event, hookResult, expected }) => {
     await expectMessageHookCall({