diff --git a/src/review/loop-escalation-wire.ts b/src/review/loop-escalation-wire.ts
index b557012c6d..4747153481 100644
--- a/src/review/loop-escalation-wire.ts
+++ b/src/review/loop-escalation-wire.ts
@@ -28,7 +28,9 @@ import { loadRepoFocusManifest } from "../signals/focus-manifest-loader";
 import { resolveLoopOverSelfRepoFullName } from "../config/loopover-repo-focus-manifest";
 import { errorMessage } from "../utils/json";
 
-const ALLOWED_DISCORD_HOSTS = new Set(["discord.com", "discordapp.com"]);
+// Byte-faithful with src/review/alerts.ts and src/services/notify-discord.ts (#9288): the two extra
+// subdomains (canary/ptb) are valid Discord webhook hosts the sibling validators already accept.
+const ALLOWED_DISCORD_HOSTS = new Set(["discord.com", "discordapp.com", "canary.discord.com", "ptb.discord.com"]);
 const DEFAULT_COOLDOWN_MINUTES = 60;
 const AUDIT_EVENT_TYPE = "loop_escalation_notification.discord";
 const AUDIT_TARGET_KEY = "fleet:loop-escalation";
@@ -88,7 +90,7 @@ function envString(env: Env, name: string): string | undefined {
   return typeof fromEnv === "string" && fromEnv.trim().length > 0 ? fromEnv.trim() : undefined;
 }
 
-function isValidDiscordWebhook(url: string): boolean {
+export function isValidDiscordWebhook(url: string): boolean {
   try {
     const parsed = new URL(url);
     if (parsed.protocol !== "https:") return false;
diff --git a/test/unit/loop-escalation-wire.test.ts b/test/unit/loop-escalation-wire.test.ts
index a03a6a70d3..089aefa10b 100644
--- a/test/unit/loop-escalation-wire.test.ts
+++ b/test/unit/loop-escalation-wire.test.ts
@@ -3,6 +3,7 @@ import * as repositories from "../../src/db/repositories";
 import {
   clearLoopEscalationManifestOverrideCacheForTest,
   isLoopEscalationSweepEnabled,
+  isValidDiscordWebhook,
   loadActiveLoopsFromEnv,
   parseActiveLoopFacts,
   resolveLoopEscalationManifestOverride,
@@ -13,6 +14,24 @@ import { createTestEnv } from "../helpers/d1";
 
 const SELF_REPO = "JSONbored/loopover";
 
+describe("isValidDiscordWebhook host allowlist (#9288)", () => {
+  it("accepts all four Discord webhook hosts its sibling validators accept — including canary/ptb", () => {
+    for (const host of ["discord.com", "discordapp.com", "canary.discord.com", "ptb.discord.com"]) {
+      // canary/ptb were rejected before the fix, dropping a valid webhook as invalid_global_webhook.
+      expect(isValidDiscordWebhook(`https://${host}/api/webhooks/123/abc`)).toBe(true);
+      expect(isValidDiscordWebhook(`https://${host.toUpperCase()}/api/webhooks/123/abc`)).toBe(true); // host match is case-insensitive
+    }
+  });
+
+  it("still rejects non-Discord hosts, non-https, and non-webhook paths", () => {
+    expect(isValidDiscordWebhook("https://evil.example.com/api/webhooks/123/abc")).toBe(false);
+    expect(isValidDiscordWebhook("https://notdiscord.com/api/webhooks/123/abc")).toBe(false);
+    expect(isValidDiscordWebhook("http://discord.com/api/webhooks/123/abc")).toBe(false); // not https
+    expect(isValidDiscordWebhook("https://discord.com/not/a/webhook")).toBe(false); // wrong path
+    expect(isValidDiscordWebhook("not a url")).toBe(false);
+  });
+});
+
 describe("isLoopEscalationSweepEnabled (#6349)", () => {
   it("defaults OFF and accepts the standard truthy env forms", () => {
     for (const off of [undefined, "", "false", "no", "0", "off"]) {