diff --git a/extensions/nextcloud-talk/src/monitor.replay.test.ts b/extensions/nextcloud-talk/src/monitor.replay.test.ts
index a8bea1a2dab..63325e2fcc1 100644
--- a/extensions/nextcloud-talk/src/monitor.replay.test.ts
+++ b/extensions/nextcloud-talk/src/monitor.replay.test.ts
@@ -1,12 +1,31 @@
-import { describe, expect, it, vi } from "vitest";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import { createMockIncomingRequest } from "../../../test/helpers/mock-incoming-request.js";
 import { WEBHOOK_RATE_LIMIT_DEFAULTS } from "../runtime-api.js";
-import { readNextcloudTalkWebhookBody } from "./monitor.js";
+import {
+  NextcloudTalkRetryableWebhookError,
+  processNextcloudTalkReplayGuardedMessage,
+  readNextcloudTalkWebhookBody,
+} from "./monitor.js";
 import { createSignedCreateMessageRequest } from "./monitor.test-fixtures.js";
 import { startWebhookServer } from "./monitor.test-harness.js";
+import { createNextcloudTalkReplayGuard } from "./replay-guard.js";
 import { generateNextcloudTalkSignature } from "./signature.js";
 import type { NextcloudTalkInboundMessage } from "./types.js";
 
+const tempDirs: string[] = [];
+
+afterEach(() => {
+  while (tempDirs.length > 0) {
+    const dir = tempDirs.pop();
+    if (dir) {
+      fs.rmSync(dir, { recursive: true, force: true });
+    }
+  }
+});
+
 describe("readNextcloudTalkWebhookBody", () => {
   it("reads valid body within max bytes", async () => {
     const req = createMockIncomingRequest(['{"type":"Create"}']);
@@ -71,6 +90,24 @@ describe("createNextcloudTalkWebhookServer backend allowlist", () => {
 });
 
 describe("createNextcloudTalkWebhookServer replay handling", () => {
+  function createReplayAwareProcessMessage(params: {
+    stateDir: string;
+    accountId?: string;
+    handleMessage: (message: NextcloudTalkInboundMessage) => Promise<void>;
+  }) {
+    const replayGuard = createNextcloudTalkReplayGuard({
+      stateDir: params.stateDir,
+    });
+
+    return async (message: NextcloudTalkInboundMessage) =>
+      await processNextcloudTalkReplayGuardedMessage({
+        replayGuard,
+        accountId: params.accountId ?? "acct",
+        message,
+        handleMessage: () => params.handleMessage(message),
+      });
+  }
+
   it("acknowledges replayed requests and skips onMessage side effects", async () => {
     const seen = new Set<string>();
     const onMessage = vi.fn(async () => {});
@@ -107,14 +144,22 @@ describe("createNextcloudTalkWebhookServer replay handling", () => {
   });
 
   it("allows a retry after processMessage fails before replay commit", async () => {
+    const stateDir = fs.mkdtempSync(path.join(os.tmpdir(), "nextcloud-talk-replay-"));
+    tempDirs.push(stateDir);
     let attempts = 0;
     const onError = vi.fn();
-    const processMessage = vi.fn(async () => {
+    const handleMessage = vi.fn(async () => {
       attempts += 1;
       if (attempts === 1) {
-        throw new Error("transient nextcloud failure");
+        throw new NextcloudTalkRetryableWebhookError("transient nextcloud failure");
       }
     });
+    const processMessage = vi.fn(
+      createReplayAwareProcessMessage({
+        stateDir,
+        handleMessage,
+      }),
+    );
     const harness = await startWebhookServer({
       path: "/nextcloud-replay-process",
       processMessage,
@@ -129,6 +174,7 @@ describe("createNextcloudTalkWebhookServer replay handling", () => {
       headers,
       body,
     });
+    await vi.waitFor(() => expect(onError).toHaveBeenCalledTimes(1));
     const second = await fetch(harness.webhookUrl, {
       method: "POST",
       headers,
@@ -137,7 +183,50 @@ describe("createNextcloudTalkWebhookServer replay handling", () => {
 
     expect(first.status).toBe(200);
     expect(second.status).toBe(200);
-    expect(processMessage).toHaveBeenCalledTimes(2);
+    await vi.waitFor(() => expect(handleMessage).toHaveBeenCalledTimes(2));
+    expect(onError).toHaveBeenCalledTimes(1);
+  });
+
+  it("keeps replay committed after a non-retryable processMessage failure", async () => {
+    const stateDir = fs.mkdtempSync(path.join(os.tmpdir(), "nextcloud-talk-replay-"));
+    tempDirs.push(stateDir);
+    const onError = vi.fn();
+    const visibleSideEffect = vi.fn();
+    const handleMessage = vi.fn(async () => {
+      visibleSideEffect();
+      throw new Error("post-send failure");
+    });
+    const processMessage = vi.fn(
+      createReplayAwareProcessMessage({
+        stateDir,
+        handleMessage,
+      }),
+    );
+    const harness = await startWebhookServer({
+      path: "/nextcloud-replay-post-send",
+      processMessage,
+      onMessage: vi.fn(),
+      onError,
+    });
+
+    const { body, headers } = createSignedCreateMessageRequest();
+
+    const first = await fetch(harness.webhookUrl, {
+      method: "POST",
+      headers,
+      body,
+    });
+    await vi.waitFor(() => expect(onError).toHaveBeenCalledTimes(1));
+    const second = await fetch(harness.webhookUrl, {
+      method: "POST",
+      headers,
+      body,
+    });
+
+    expect(first.status).toBe(200);
+    expect(second.status).toBe(200);
+    expect(handleMessage).toHaveBeenCalledTimes(1);
+    expect(visibleSideEffect).toHaveBeenCalledTimes(1);
     expect(onError).toHaveBeenCalledTimes(1);
   });
 });
diff --git a/extensions/nextcloud-talk/src/monitor.ts b/extensions/nextcloud-talk/src/monitor.ts
index 1a45e87ce95..48202750668 100644
--- a/extensions/nextcloud-talk/src/monitor.ts
+++ b/extensions/nextcloud-talk/src/monitor.ts
@@ -16,7 +16,7 @@ import {
 } from "../runtime-api.js";
 import { resolveNextcloudTalkAccount } from "./accounts.js";
 import { handleNextcloudTalkInbound } from "./inbound.js";
-import { createNextcloudTalkReplayGuard } from "./replay-guard.js";
+import { createNextcloudTalkReplayGuard, type NextcloudTalkReplayGuard } from "./replay-guard.js";
 import { getNextcloudTalkRuntime } from "./runtime.js";
 import { extractNextcloudTalkHeaders, verifyNextcloudTalkSignature } from "./signature.js";
 import type {
@@ -64,6 +64,57 @@ const WEBHOOK_ERRORS = {
   internalServerError: "Internal server error",
 } as const;
 
+export class NextcloudTalkRetryableWebhookError extends Error {
+  constructor(message: string, options?: ErrorOptions) {
+    super(message, options);
+    this.name = "NextcloudTalkRetryableWebhookError";
+  }
+}
+
+export async function processNextcloudTalkReplayGuardedMessage(params: {
+  replayGuard: NextcloudTalkReplayGuard;
+  accountId: string;
+  message: NextcloudTalkInboundMessage;
+  handleMessage: () => Promise<void>;
+}): Promise<"processed" | "duplicate"> {
+  const claim = await params.replayGuard.claimMessage({
+    accountId: params.accountId,
+    roomToken: params.message.roomToken,
+    messageId: params.message.messageId,
+  });
+  if (claim !== "claimed") {
+    return "duplicate";
+  }
+
+  try {
+    await params.handleMessage();
+    await params.replayGuard.commitMessage({
+      accountId: params.accountId,
+      roomToken: params.message.roomToken,
+      messageId: params.message.messageId,
+    });
+    return "processed";
+  } catch (error) {
+    if (error instanceof NextcloudTalkRetryableWebhookError) {
+      params.replayGuard.releaseMessage({
+        accountId: params.accountId,
+        roomToken: params.message.roomToken,
+        messageId: params.message.messageId,
+        error,
+      });
+    } else {
+      // Generic failures are treated as non-retryable because the handler may already
+      // have produced a visible side effect, and replaying the webhook would duplicate it.
+      await params.replayGuard.commitMessage({
+        accountId: params.accountId,
+        roomToken: params.message.roomToken,
+        messageId: params.message.messageId,
+      });
+    }
+    throw error;
+  }
+}
+
 function formatError(err: unknown): string {
   if (err instanceof Error) {
     return err.message;
@@ -404,50 +455,36 @@ export async function monitorNextcloudTalkProvider(
       return backendOrigin === expectedBackendOrigin;
     },
     processMessage: async (message) => {
-      const claim = await replayGuard.claimMessage({
+      const result = await processNextcloudTalkReplayGuardedMessage({
+        replayGuard,
         accountId: account.accountId,
-        roomToken: message.roomToken,
-        messageId: message.messageId,
+        message,
+        handleMessage: async () => {
+          core.channel.activity.record({
+            channel: "nextcloud-talk",
+            accountId: account.accountId,
+            direction: "inbound",
+            at: message.timestamp,
+          });
+          if (opts.onMessage) {
+            await opts.onMessage(message);
+          } else {
+            await handleNextcloudTalkInbound({
+              message,
+              account,
+              config: cfg,
+              runtime,
+              statusSink: opts.statusSink,
+            });
+          }
+        },
       });
-      if (claim !== "claimed") {
+      if (result === "duplicate") {
         logger.warn(
           `[nextcloud-talk:${account.accountId}] replayed webhook ignored room=${message.roomToken} messageId=${message.messageId}`,
         );
         return;
       }
-
-      try {
-        core.channel.activity.record({
-          channel: "nextcloud-talk",
-          accountId: account.accountId,
-          direction: "inbound",
-          at: message.timestamp,
-        });
-        if (opts.onMessage) {
-          await opts.onMessage(message);
-        } else {
-          await handleNextcloudTalkInbound({
-            message,
-            account,
-            config: cfg,
-            runtime,
-            statusSink: opts.statusSink,
-          });
-        }
-        await replayGuard.commitMessage({
-          accountId: account.accountId,
-          roomToken: message.roomToken,
-          messageId: message.messageId,
-        });
-      } catch (error) {
-        replayGuard.releaseMessage({
-          accountId: account.accountId,
-          roomToken: message.roomToken,
-          messageId: message.messageId,
-          error,
-        });
-        throw error;
-      }
     },
     onMessage: async () => {},
     onError: (error) => {