fix(ui): keep the Slack page usable on an unreadable check time

- Guard the last-checked timestamp with isValid before formatting
- Fall back to the never-checked rendering instead of the error boundary

ui/__tests__/msw/handlers/slack.fixtures.ts

@@ -193,6 +193,17 @@ export const connectedSlackFixture = (
     ...overrides,
   });
 
+const configuredInstall = (): SlackInstallFixture => ({
+  id: SLACK_INTEGRATION_ID,
+  connected: true,
+  connectionLastCheckedAt: "2026-08-10T09:30:00Z",
+  workspace: {
+    ...PROWLER_HQ,
+    channelId: SLACK_DEFAULT_CHANNEL.id,
+    channelName: SLACK_DEFAULT_CHANNEL.name,
+  },
+});
+
 /**
  * A workspace connected *and* a channel on record. Anything the API refuses
  * until a channel exists (the connection check) needs this fixture.
@@ -200,16 +211,17 @@ export const connectedSlackFixture = (
 export const configuredSlackFixture = (
   overrides: Partial<SlackFixture> = {},
 ): SlackFixture =>
+  connectedSlackFixture({ install: configuredInstall(), ...overrides });
+
+/**
+ * The same finished setup, with a check time no parser can read: a zero date
+ * from a bad write or a serializer change. The contract types the attribute as
+ * a string and rules nothing else out.
+ */
+export const unreadableCheckTimeSlackFixture = (): SlackFixture =>
   connectedSlackFixture({
     install: {
-      id: SLACK_INTEGRATION_ID,
-      connected: true,
-      connectionLastCheckedAt: "2026-08-10T09:30:00Z",
-      workspace: {
-        ...PROWLER_HQ,
-        channelId: SLACK_DEFAULT_CHANNEL.id,
-        channelName: SLACK_DEFAULT_CHANNEL.name,
-      },
+      ...configuredInstall(),
+      connectionLastCheckedAt: "0000-00-00T00:00:00Z",
     },
-    ...overrides,
   });

ui/app/(prowler)/integrations/slack/slack-integration.harness.ts

@@ -240,6 +240,17 @@ export class SlackIntegrationHarness extends BrowserHarness<SlackFixture> {
     return this.containsText(/Choosing a destination channel is the next step/);
   }
 
+  /**
+   * The "last checked" line as rendered, or null when the page shows none —
+   * which is what a workspace whose connection was never checked shows.
+   */
+  lastCheckedLine(): string | null {
+    const line = Array.from(
+      this.container.querySelectorAll<HTMLElement>("p"),
+    ).find((p) => /^Last checked:/.test((p.textContent ?? "").trim()));
+    return line ? (line.textContent ?? "").trim() : null;
+  }
+
   async testConnection(): Promise<ConnectionOutcome> {
     await this.clickButton(/Test connection/);
 

ui/app/(prowler)/integrations/slack/slack-page.integration.test.tsx

@@ -13,6 +13,7 @@ import {
   connectedSlackFixture,
   INTEGRATIONS_SERVER_ERROR_DETAIL,
   slackFixture,
+  unreadableCheckTimeSlackFixture,
 } from "@/__tests__/msw/handlers/slack.fixtures";
 
 import {
@@ -190,6 +191,23 @@ describe("a connected workspace", () => {
     expect(badge).not.toMatch(/Disconnected/);
   }, 30000);
 
+  it("keeps the page usable when the recorded check time is one no parser can read", async () => {
+    // Given — a finished setup whose `connection_last_checked_at` is a zero
+    // date. `date-fns` throws a RangeError on it, which would replace the whole
+    // page with the route's error boundary.
+    const harness = new SlackIntegrationHarness(
+      unreadableCheckTimeSlackFixture(),
+    );
+
+    await harness.mount();
+
+    expect(await harness.connectedWorkspaceName()).toBe(WORKSPACE_NAME);
+    expect(await harness.connectionBadge()).toBe("Connected");
+    // Nothing to show, so nothing is shown: the same line a workspace that was
+    // never checked renders.
+    expect(harness.lastCheckedLine()).toBeNull();
+  }, 30000);
+
   it("does not offer a connection check the API is bound to refuse", async () => {
     // Given — a workspace connected and no destination channel recorded.
     const harness = new SlackIntegrationHarness(connectedSlackFixture());

ui/components/integrations/slack/slack-integration-manager.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { format } from "date-fns";
+import { format, isValid, parseISO } from "date-fns";
 import { TestTube } from "lucide-react";
 import { useState } from "react";
 
@@ -73,6 +73,14 @@ export const SlackIntegrationManager = ({
   // Absent until a channel is chosen, never present-and-null.
   const channelId = configuration?.channel_id ?? null;
 
+  const checkedAt = integration?.attributes.connection_last_checked_at;
+  const checkedOn = checkedAt ? parseISO(checkedAt) : null;
+  // `format` throws a RangeError on an unreadable value, which would replace
+  // the page with the route's error boundary: show nothing instead, as for a
+  // connection that was never checked.
+  const lastCheckedOn =
+    checkedOn && isValid(checkedOn) ? format(checkedOn, "yyyy/MM/dd") : null;
+
   return (
     <div className="flex flex-col gap-6">
       {rateLimitMessage && (
@@ -118,15 +126,10 @@ export const SlackIntegrationManager = ({
           <CardContent className="pt-0">
             <div className="flex flex-col gap-3 sm:flex-row sm:items-center sm:justify-between">
               <div className="text-xs text-gray-500 dark:text-gray-300">
-                {integration.attributes.connection_last_checked_at && (
+                {lastCheckedOn && (
                   <p>
                     <span className="font-medium">Last checked:</span>{" "}
-                    {format(
-                      new Date(
-                        integration.attributes.connection_last_checked_at,
-                      ),
-                      "yyyy/MM/dd",
-                    )}
+                    {lastCheckedOn}
                   </p>
                 )}
                 {!channelId && (