feat(desktop): platforms.changed broadcast retires the Messaging page's 6s status poll

The change watcher (#73673) missed one always-on-while-mounted timer: the
Messaging page polled /api/messaging/platforms every 6s for connection
status. The gateway already persists platform connect/disconnect/health to
gateway_state.json, so watch that file's mtime and broadcast
platforms.changed (floored to 5s — the gateway also rewrites the file for
in-flight-count bookkeeping), route it through live-sync like its
siblings, and refresh the page on the tick. Older backends keep the
legacy visible-tab poll verbatim.

Finishes the always-on poll sweep for #73618.

apps/desktop/src/app/messaging/index.tsx

@@ -1,3 +1,4 @@
+import { useStore } from '@nanostores/react'
 import type * as React from 'react'
 import { useCallback, useEffect, useMemo, useState } from 'react'
 
@@ -20,6 +21,7 @@ import { openExternalLink } from '@/lib/external-link'
 import { ExternalLink, Save, Trash2 } from '@/lib/icons'
 import { normalize } from '@/lib/text'
 import { cn } from '@/lib/utils'
+import { $changeEventsAvailable, $platformsChangeTick } from '@/store/live-sync'
 import { notify, notifyError } from '@/store/notifications'
 import { runGatewayRestart } from '@/store/system-actions'
 
@@ -141,9 +143,26 @@ export function MessagingView({ setStatusbarItemGroup: _setStatusbarItemGroup, .
     void refreshPlatforms()
   }, [refreshPlatforms])
 
-  // Auto-poll while the user is on the messaging page so connection status
-  // updates without a manual "check" click. Pause when the tab is hidden.
+  const changeEventsAvailable = useStore($changeEventsAvailable)
+  const platformsChangeTick = useStore($platformsChangeTick)
+
+  // Connection status updates without a manual "check" click. platforms.changed
+  // (the gateway persisting connect/disconnect/health to gateway_state.json)
+  // drives the refresh on event-capable backends — no timer; older backends
+  // keep the legacy visible-tab poll.
   useEffect(() => {
+    if (!changeEventsAvailable || platformsChangeTick === 0 || document.hidden) {
+      return
+    }
+
+    void refreshPlatforms(true)
+  }, [changeEventsAvailable, platformsChangeTick, refreshPlatforms])
+
+  useEffect(() => {
+    if (changeEventsAvailable) {
+      return
+    }
+
     let cancelled = false
 
     function tick() {
@@ -160,7 +179,7 @@ export function MessagingView({ setStatusbarItemGroup: _setStatusbarItemGroup, .
       cancelled = true
       window.clearInterval(id)
     }
-  }, [refreshPlatforms])
+  }, [changeEventsAvailable, refreshPlatforms])
 
   const selected = useMemo(() => {
     if (!platforms) {

apps/desktop/src/app/session/hooks/use-message-stream/gateway-event.ts

@@ -27,6 +27,7 @@ import { applyGoalStatusText } from '@/store/goals'
 import {
   notifyCronChanged,
   notifyPetChanged,
+  notifyPlatformsChanged,
   notifySessionsChanged,
   type PetChangeMeta,
   setChangeEventsAvailable
@@ -298,7 +299,12 @@ export function useGatewayEventHandler(deps: GatewayEventDeps) {
         }
 
         return
-      } else if (event.type === 'pet.changed' || event.type === 'cron.changed' || event.type === 'sessions.changed') {
+      } else if (
+        event.type === 'pet.changed' ||
+        event.type === 'cron.changed' ||
+        event.type === 'sessions.changed' ||
+        event.type === 'platforms.changed'
+      ) {
         // Change-watcher broadcasts (server._broadcast_watched_changes): the
         // backend's on-disk signature moved. Route to the live-sync ticks the
         // former pollers now subscribe to. Only the active profile's changes
@@ -311,6 +317,8 @@ export function useGatewayEventHandler(deps: GatewayEventDeps) {
             notifyPetChanged(payload as PetChangeMeta | undefined)
           } else if (event.type === 'cron.changed') {
             notifyCronChanged()
+          } else if (event.type === 'platforms.changed') {
+            notifyPlatformsChanged()
           } else {
             notifySessionsChanged()
           }

apps/desktop/src/store/live-sync.ts

@@ -18,6 +18,7 @@ export const $changeEventsAvailable = atom(false)
 
 export const $cronChangeTick = atom(0)
 export const $sessionsChangeTick = atom(0)
+export const $platformsChangeTick = atom(0)
 
 /** `pet.info.meta`-shaped payload carried on `pet.changed` — lets the pet skip
  *  the heavy sprite refetch when the broadcast already says enabled=false. */
@@ -47,6 +48,10 @@ export function notifySessionsChanged(): void {
   $sessionsChangeTick.set($sessionsChangeTick.get() + 1)
 }
 
+export function notifyPlatformsChanged(): void {
+  $platformsChangeTick.set($platformsChangeTick.get() + 1)
+}
+
 /** Reset on gateway wipe/reconnect — a new backend re-advertises capability on
  *  its own gateway.ready, and stale ticks must not fire refreshes into stores
  *  the wipe just cleared. */

tests/tui_gateway/test_change_watcher.py

@@ -62,6 +62,16 @@ def test_state_db_move_broadcasts_sessions_changed(watcher_home):
     assert ("sessions.changed", {}) in events
 
 
+def test_gateway_state_move_broadcasts_platforms_changed(watcher_home):
+    home, events = watcher_home
+    server._broadcast_watched_changes(now=0.0)
+
+    (home / "gateway_state.json").write_text('{"platforms": {}}')
+    server._broadcast_watched_changes(now=10.0)
+
+    assert ("platforms.changed", {}) in events
+
+
 def test_sessions_floor_coalesces_burst_but_keeps_trailing_edge(watcher_home):
     home, events = watcher_home
     server._broadcast_watched_changes(now=0.0)

tui_gateway/server.py

@@ -3072,6 +3072,16 @@ def _sessions_sig():
     return sig
 
 
+def _platforms_sig():
+    """mtime of gateway_state.json — the messaging gateway process persists
+    platform connect/disconnect/health there, so its movement is the
+    "connection status changed" signal for the Messaging page."""
+    try:
+        return (_watcher_home() / "gateway_state.json").stat().st_mtime_ns
+    except OSError:
+        return None
+
+
 # Watched change signals: event → (check interval, signature fn, payload fn).
 # Signatures are stat/dict-lookup cheap, same bar as the skin watcher; the
 # check interval keeps the pricier probes (pet resolves the active sheet off
@@ -3080,12 +3090,14 @@ _CHANGE_WATCHES: dict[str, tuple[float, Any, Any]] = {
     "pet.changed": (2.0, _pet_sig, _pet_changed_payload),
     "cron.changed": (1.0, _cron_sig, lambda: {}),
     "sessions.changed": (0.5, _sessions_sig, lambda: {}),
+    "platforms.changed": (2.0, _platforms_sig, lambda: {}),
 }
 
-# state.db moves on every message append during a streaming turn; the floor
-# coalesces that burst to one broadcast per window (trailing edge included —
-# a floored change keeps its old signature and re-fires next tick).
-_CHANGE_BROADCAST_FLOOR_S = {"sessions.changed": 2.0}
+# state.db moves on every message append during a streaming turn, and the
+# gateway rewrites gateway_state.json for in-flight-count bookkeeping; the
+# floor coalesces those bursts to one broadcast per window (trailing edge
+# included — a floored change keeps its old signature and re-fires next tick).
+_CHANGE_BROADCAST_FLOOR_S = {"sessions.changed": 2.0, "platforms.changed": 5.0}
 
 _change_sigs: dict[str, Any] = {}
 _change_checked_at: dict[str, float] = {}