Trigger update checks off WS reconnect, not just the hourly poll (#42)

A backend restart during a deploy kills every open WebSocket, and the
chat socket's existing reconnect-with-backoff already re-fires onopen
within seconds -- reuse that as a reliable "the server just restarted"
signal to check for a new service worker version, instead of waiting up
to an hour for UpdateBanner's poll. The hourly poll stays as a fallback.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/components/UpdateBanner.tsx

@@ -1,4 +1,5 @@
 import { useRegisterSW } from 'virtual:pwa-register/react'
+import { checkForUpdate, setSwRegistration } from '../lib/swUpdate'
 import './UpdateBanner.css'
 
 // The service worker (registerType: 'prompt', sw.ts) already installs and
@@ -6,7 +7,11 @@ import './UpdateBanner.css'
 // never navigates, and a page only checks for a new SW on navigation by
 // default, so a tab left open for hours could sit on a stale check
 // indefinitely. This polls explicitly so "reload available" shows up
-// without the user having to close and reopen the app first.
+// without the user having to close and reopen the app first. It's now a
+// fallback, not the primary trigger -- useChatSocket.ts also calls
+// checkForUpdate() on every WS reconnect, which reliably fires within
+// seconds of a deploy (the backend restart that ships a new version also
+// kills every open WS connection) rather than waiting up to an hour.
 const UPDATE_CHECK_INTERVAL_MS = 60 * 60 * 1000
 
 export function UpdateBanner() {
@@ -16,7 +21,8 @@ export function UpdateBanner() {
   } = useRegisterSW({
     onRegisteredSW(_url, registration) {
       if (!registration) return
-      setInterval(() => registration.update(), UPDATE_CHECK_INTERVAL_MS)
+      setSwRegistration(registration)
+      setInterval(checkForUpdate, UPDATE_CHECK_INTERVAL_MS)
     },
   })
 

frontend/src/lib/swUpdate.ts

@@ -0,0 +1,14 @@
+// Bridges the service worker registration (owned by UpdateBanner, which
+// mounts outside ChatSocketProvider -- see App.tsx) out to code that has no
+// other way to reach it, namely useChatSocket.ts's reconnect handler, which
+// wants to trigger an update check whenever the WS reconnects (a reliable
+// signal the backend just restarted, i.e. a deploy happened).
+let registration: ServiceWorkerRegistration | null = null
+
+export function setSwRegistration(reg: ServiceWorkerRegistration): void {
+  registration = reg
+}
+
+export function checkForUpdate(): void {
+  void registration?.update()
+}

frontend/src/ws/useChatSocket.ts

@@ -1,4 +1,5 @@
 import { useCallback, useEffect, useRef, useState } from 'react'
+import { checkForUpdate } from '../lib/swUpdate'
 import type { ServerEnvelope } from '../types'
 
 interface UseChatSocketOptions {
@@ -42,6 +43,13 @@ export function useChatSocket({ onUnauthenticated }: UseChatSocketOptions) {
     let stopped = false
     let reconnectDelay = RECONNECT_BASE_DELAY_MS
     let reconnectTimer: ReturnType<typeof setTimeout> | null = null
+    // False only for the very first connect() of this effect's lifetime --
+    // every connect() after that was triggered by onclose's retry logic,
+    // i.e. this is a genuine reconnect. A reconnect reliably means the
+    // backend process just restarted (a deploy kills every open WS), so
+    // it's used as the trigger for an out-of-band SW update check instead
+    // of waiting on UpdateBanner's hourly poll -- see lib/swUpdate.ts.
+    let hasConnectedBefore = false
 
     function connect() {
       const protocol = location.protocol === 'https:' ? 'wss' : 'ws'
@@ -56,6 +64,8 @@ export function useChatSocket({ onUnauthenticated }: UseChatSocketOptions) {
         // socket's callbacks can stomp on state that the second (real)
         // socket already owns.
         if (socketRef.current !== ws) return
+        if (hasConnectedBefore) checkForUpdate()
+        hasConnectedBefore = true
         reconnectDelay = RECONNECT_BASE_DELAY_MS
         setConnected(true)
         // Re-join whatever rooms were joined before a reconnect -- the