diff --git a/.ai/contexts/session-cache.md b/.ai/contexts/session-cache.md
index 34f79e6d..0857b93e 100644
--- a/.ai/contexts/session-cache.md
+++ b/.ai/contexts/session-cache.md
@@ -186,6 +186,18 @@ the exact remote command, and the mutation proofs are in
   delete-then-insert path as the cold-start scan. Parsing 249 MB on the main
   thread would freeze the UI; `refreshFolder` is deliberately not the remote path.
 
+### Remote hosts — busy spinner (issue #242)
+
+Remote transcript-write activity feeds the same `setActivity(sessionId, active, via)`
+dispatcher in `session-activity.js` that local PTY output uses — `remote-activity-ui.js`
+calls `setActivity(sessionId, true, 'remote-watch')` on each `remote-activity` IPC event
+and arms a 20 s decay timer (one per session, reset on each event) that calls
+`setActivity(sessionId, false, 'remote-decay')` when it fires, and `seedRemoteActivity(session)`
+(called from `renderProjects`, before any row is built) applies the same call from
+`session.remoteActiveAt` on first paint so a row rendered inside the decay window starts
+busy without waiting for the next event; the visual is the shared `.cli-busy` braille
+spinner, not a separate indicator.
+
 ### Remote hosts file-level rescan (issue #216, first half)
 
 **The unit of rescan used to be the folder, not the file.** `syncMirror`
diff --git a/eslint.config.js b/eslint.config.js
index c7358ff8..f3a43016 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -141,6 +141,8 @@ const rendererCrossFileGlobals = {
   setActivity: 'readonly',
   trackActivity: 'readonly',
   applyActivityClasses: 'readonly',
+  sessionItemEl: 'readonly',
+  seedRemoteActivity: 'readonly',
   rekeyActivityState: 'readonly',
   reconcileBusyState: 'readonly',
   currentActivitySeq: 'readonly',
diff --git a/main.js b/main.js
index fccd70c4..277163c8 100644
--- a/main.js
+++ b/main.js
@@ -485,7 +485,7 @@ const remoteWatcher = createRemoteWatcher({ log });
 let watchedAliases = new Set();
 function onRemoteWatchEvent(alias) { remoteIndexer.refreshHostNow(alias).catch(() => {}); }
 
-// see .ai/contexts/session-cache.md ("Remote hosts — activity pip")
+// see .ai/contexts/session-cache.md ("Remote hosts — busy spinner (issue #242)")
 const remoteActivityTracker = createRemoteActivityTracker({});
 
 function onRemoteWatchActivity(alias, rel) {
diff --git a/public/remote-activity-ui.js b/public/remote-activity-ui.js
index be5c4e81..a56526b0 100644
--- a/public/remote-activity-ui.js
+++ b/public/remote-activity-ui.js
@@ -1,13 +1,8 @@
-// See .ai/contexts/session-cache.md ("Remote hosts — activity pip").
+// See .ai/contexts/session-cache.md ("Remote hosts — busy spinner (issue #242)").
 
 const PIP_DECAY_MS = 20000;
 const remoteActivityDecayTimers = new Map();
 
-function remoteActivityDotFor(sessionId) {
-  const item = document.querySelector(`.session-item[data-session-id="${sessionId}"]`);
-  return item ? item.querySelector('.remote-activity-dot') : null;
-}
-
 function clearRemoteActivityTimer(sessionId) {
   const t = remoteActivityDecayTimers.get(sessionId);
   if (t) {
@@ -16,23 +11,36 @@ function clearRemoteActivityTimer(sessionId) {
   }
 }
 
+function armRemoteDecayTimer(sessionId, ms) {
+  remoteActivityDecayTimers.set(sessionId, setTimeout(() => {
+    remoteActivityDecayTimers.delete(sessionId);
+    setActivity(sessionId, false, 'remote-decay');
+  }, ms));
+}
+
 function pruneRemoteActivityTimers() {
   for (const sessionId of remoteActivityDecayTimers.keys()) {
-    if (!remoteActivityDotFor(sessionId)) clearRemoteActivityTimer(sessionId);
+    if (!sessionItemEl(sessionId)) clearRemoteActivityTimer(sessionId);
   }
 }
 
 function onRemoteActivityEvent(payload) {
   const sessionId = payload && payload.sessionId;
   if (typeof sessionId !== 'string' || !sessionId) return;
-  const dot = remoteActivityDotFor(sessionId);
-  if (dot) dot.classList.add('active');
+  setActivity(sessionId, true, 'remote-watch');
   clearRemoteActivityTimer(sessionId);
-  remoteActivityDecayTimers.set(sessionId, setTimeout(() => {
-    remoteActivityDecayTimers.delete(sessionId);
-    const el = remoteActivityDotFor(sessionId);
-    if (el) el.classList.remove('active');
-  }, PIP_DECAY_MS));
+  armRemoteDecayTimer(sessionId, PIP_DECAY_MS);
+}
+
+function seedRemoteActivity(session) {
+  if (!session || !session.remoteAlias) return;
+  if (!Number.isFinite(session.remoteActiveAt)) return;
+  const sessionId = session.sessionId;
+  const remaining = session.remoteActiveAt + PIP_DECAY_MS - Date.now();
+  if (remaining <= 0) return;
+  setActivity(sessionId, true, 'remote-seed');
+  if (remoteActivityDecayTimers.has(sessionId)) return;
+  armRemoteDecayTimer(sessionId, remaining);
 }
 
 window.api.onRemoteActivity(onRemoteActivityEvent);
diff --git a/public/sidebar.js b/public/sidebar.js
index a169baeb..9c9b2c8b 100644
--- a/public/sidebar.js
+++ b/public/sidebar.js
@@ -9,9 +9,6 @@
 // showNewSessionPopover, openSettingsViewer, showResumeSessionDialog,
 // showJsonlViewer, forkSession, openSession, loadProjects (app.js/dialogs.js)
 
-// see .ai/contexts/session-cache.md ("Remote hosts — activity pip")
-const REMOTE_ACTIVITY_DECAY_MS = 20000;
-
 function slugId(slug) {
   return 'slug-' + slug.replace(/[^a-zA-Z0-9_-]/g, '_');
 }
@@ -522,6 +519,10 @@ function buildSlugGroup(slug, sessions, subagentIndex) {
 function renderProjects(projects, resort) {
   pruneStaleSubagents();
   pendingSubagentRest.clear();
+  // see .ai/contexts/session-cache.md ("Remote hosts — busy spinner (issue #242)")
+  for (const project of projects) {
+    for (const session of project.sessions) seedRemoteActivity(session);
+  }
   const newSidebar = document.createElement('div');
 
   // Sort project groups using sortedOrder as source of truth
@@ -1302,16 +1303,6 @@ function buildSessionItem(session) {
   const dot = document.createElement('span');
   dot.className = 'session-status-dot' + (activePtyIds.has(session.sessionId) ? ' running' : '');
 
-  // see .ai/contexts/session-cache.md ("Remote hosts — activity pip")
-  let activityDot = null;
-  if (session.remoteAlias) {
-    activityDot = document.createElement('span');
-    const isActive = Number.isFinite(session.remoteActiveAt) &&
-      (Date.now() - session.remoteActiveAt) < REMOTE_ACTIVITY_DECAY_MS;
-    activityDot.className = 'session-status-dot remote-activity-dot' + (isActive ? ' active' : '');
-    activityDot.title = 'Remote session is writing its transcript';
-  }
-
   // Info block
   const info = document.createElement('div');
   info.className = 'session-info';
@@ -1408,7 +1399,6 @@ function buildSessionItem(session) {
 
   row.appendChild(pin);
   row.appendChild(dot);
-  if (activityDot) row.appendChild(activityDot);
   row.appendChild(info);
   row.appendChild(actions);
   item.appendChild(row);
diff --git a/public/style.css b/public/style.css
index c83ddc16..d07b5167 100644
--- a/public/style.css
+++ b/public/style.css
@@ -969,22 +969,6 @@ body { display: flex; flex-direction: column; }
   background: #3ecf5a;
 }
 
-/* see .ai/contexts/session-cache.md ("Remote hosts — activity pip") */
-.remote-activity-dot {
-  background: transparent;
-  margin-left: -4px;
-}
-
-.remote-activity-dot.active {
-  background: #b388ff;
-  animation: remote-activity-pulse 1s ease-in-out infinite;
-}
-
-@keyframes remote-activity-pulse {
-  0%, 100% { opacity: 0.45; transform: scale(0.85); }
-  50% { opacity: 1; transform: scale(1.2); }
-}
-
 /* ---- CLI busy spinner (braille spinner detected) ---- */
 /* needs-attention takes precedence — when both are set, the attention indicator shows */
 /* Braille spinner via content keyframes — see docs/decisions/0002 */
diff --git a/remote-activity.js b/remote-activity.js
index 22cb5a6b..df3789db 100644
--- a/remote-activity.js
+++ b/remote-activity.js
@@ -1,4 +1,4 @@
-// see .ai/contexts/session-cache.md ("Remote hosts — activity pip")
+// see .ai/contexts/session-cache.md ("Remote hosts — busy spinner (issue #242)")
 'use strict';
 
 const SESSION_ID_RE = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i;
diff --git a/test/dom-setup.js b/test/dom-setup.js
index c4966973..e0f276c7 100644
--- a/test/dom-setup.js
+++ b/test/dom-setup.js
@@ -82,9 +82,10 @@ function setupSidebarDom() {
     showTodayOnly: false,
     visibleSessionCount: 10,
     sessionMaxAgeDays: 3650, // generous so fixtures aren't filtered out by age
-    attentionSessions: new Set(),
-    responseReadySessions: new Set(),
-    sessionBusyState: new Map(),
+    // attentionSessions / responseReadySessions / sessionBusyState come from
+    // the real session-activity.js (evaluated below), not a stub here — that
+    // module owns them, and sidebar.js/remote-activity-ui.js must see the
+    // exact same Maps/Sets it mutates.
     cachedProjects: [],
     cachedAllProjects: [],
 
@@ -121,8 +122,19 @@ function setupSidebarDom() {
   evalInWindow(dom, path.join(PUBLIC_DIR, 'icons.js'));
   evalInWindow(dom, path.join(PUBLIC_DIR, 'subagent-timing.js'));
 
-  // Finally, sidebar.js.
+  // session-activity.js owns attentionSessions/responseReadySessions/
+  // sessionBusyState and the setActivity/applyActivityClasses/sessionItemEl
+  // functions sidebar.js and remote-activity-ui.js call — load order mirrors
+  // index.html.
+  evalInWindow(dom, path.join(PUBLIC_DIR, 'session-activity.js'));
+
+  // sidebar.js, then remote-activity-ui.js (seedRemoteActivity, called from
+  // renderProjects).
   evalInWindow(dom, path.join(PUBLIC_DIR, 'sidebar.js'));
+  evalInWindow(dom, path.join(PUBLIC_DIR, 'remote-activity-ui.js'));
+
+  const ctx = dom.getInternalVMContext();
+  const read = (expr) => vm.runInContext(expr, ctx);
 
   return {
     window,
@@ -134,6 +146,12 @@ function setupSidebarDom() {
       folderId: window.folderId,
       showDeleteSessionDialog: window.showDeleteSessionDialog,
     },
+    // The real state owned by session-activity.js — same objects sidebar.js
+    // and remote-activity-ui.js read/mutate as bare identifiers.
+    sessionBusyState: read('sessionBusyState'),
+    attentionSessions: read('attentionSessions'),
+    responseReadySessions: read('responseReadySessions'),
+    setActivity: read('setActivity'),
     // Simulate the main process emitting subagent-spawned/subagent-completed
     // (session-transitions.js) by invoking the callback sidebar.js registered
     // via window.api.onSubagentSpawned/onSubagentCompleted at eval time.
diff --git a/test/dom-sidebar-remote-activity-pip.test.js b/test/dom-sidebar-remote-activity-pip.test.js
index bd5fe13e..0f833bbd 100644
--- a/test/dom-sidebar-remote-activity-pip.test.js
+++ b/test/dom-sidebar-remote-activity-pip.test.js
@@ -1,8 +1,9 @@
-// Issue #242: a rebuilt sidebar (or a fresh launch) must paint the remote
-// activity pip from session.remoteActiveAt without waiting for the next
-// live remote-activity IPC message — see .ai/contexts/session-cache.md
-// ("Remote hosts — activity pip"). The live-update path itself is covered
-// by test/remote-activity-ui.test.js.
+// Issue #242/#243: a rebuilt sidebar (or a fresh launch) must paint a remote
+// session busy — the same braille spinner a local session gets — straight
+// from session.remoteActiveAt, without waiting for the next live
+// remote-activity IPC message. See .ai/contexts/session-cache.md
+// ("Remote hosts — busy spinner (issue #242)"). The live-update path itself
+// is covered by test/remote-activity-ui.test.js.
 
 const test = require('node:test');
 const assert = require('node:assert/strict');
@@ -18,7 +19,41 @@ function remoteProject(session) {
   });
 }
 
-test('a session active within the decay window paints the pip lit on first render', () => {
+// A render function must not arm timers itself — seedRemoteActivity does,
+// and this fake clock drives that timer by hand instead of a real wall-clock
+// wait. Installed on ctx.window BEFORE renderProjects() so the seed's
+// setTimeout call picks it up.
+function installFakeTimers(win) {
+  let elapsed = 0;
+  const timers = [];
+  let nextId = 1;
+  Object.defineProperty(win, 'setTimeout', {
+    value: (fn, ms) => {
+      const t = { id: nextId++, at: elapsed + ms, fn, cleared: false, fired: false };
+      timers.push(t);
+      return t.id;
+    },
+    writable: true, configurable: true,
+  });
+  Object.defineProperty(win, 'clearTimeout', {
+    value: (id) => {
+      const t = timers.find(t => t.id === id);
+      if (t) t.cleared = true;
+    },
+    writable: true, configurable: true,
+  });
+  return {
+    advance(ms) {
+      elapsed += ms;
+      for (const t of timers) {
+        if (!t.cleared && !t.fired && t.at <= elapsed) { t.fired = true; t.fn(); }
+      }
+    },
+    pendingCount: () => timers.filter(t => !t.cleared && !t.fired).length,
+  };
+}
+
+test('a session active within the decay window renders busy on first render', () => {
   const ctx = setupSidebarDom();
   try {
     const session = {
@@ -28,13 +63,13 @@ test('a session active within the decay window paints the pip lit on first rende
     };
     ctx.sidebar.renderProjects([remoteProject(session)], true);
 
-    const dot = ctx.document.querySelector('#si-remote-active .remote-activity-dot');
-    assert.ok(dot, 'a remote session must carry the activity pip element');
-    assert.ok(dot.classList.contains('active'), 'a sighting 5s ago is still inside the 20s decay window');
+    const item = ctx.document.querySelector('#si-remote-active');
+    assert.ok(item, 'the session row must exist');
+    assert.ok(item.classList.contains('cli-busy'), 'a sighting 5s ago is still inside the 20s decay window');
   } finally { ctx.destroy(); }
 });
 
-test('a session last active past the decay window renders the pip off', () => {
+test('a session last active past the decay window renders idle', () => {
   const ctx = setupSidebarDom();
   try {
     const session = {
@@ -44,13 +79,13 @@ test('a session last active past the decay window renders the pip off', () => {
     };
     ctx.sidebar.renderProjects([remoteProject(session)], true);
 
-    const dot = ctx.document.querySelector('#si-remote-stale .remote-activity-dot');
-    assert.ok(dot);
-    assert.ok(!dot.classList.contains('active'), 'a sighting a minute ago is well past the 20s decay window');
+    const item = ctx.document.querySelector('#si-remote-stale');
+    assert.ok(item);
+    assert.ok(!item.classList.contains('cli-busy'), 'a sighting a minute ago is well past the 20s decay window');
   } finally { ctx.destroy(); }
 });
 
-test('a session with no remoteActiveAt at all renders the pip off, not crashing on undefined', () => {
+test('a session with no remoteActiveAt at all renders idle, not crashing on undefined', () => {
   const ctx = setupSidebarDom();
   try {
     const session = {
@@ -60,13 +95,27 @@ test('a session with no remoteActiveAt at all renders the pip off, not crashing
     };
     ctx.sidebar.renderProjects([remoteProject(session)], true);
 
-    const dot = ctx.document.querySelector('#si-remote-never .remote-activity-dot');
-    assert.ok(dot);
-    assert.ok(!dot.classList.contains('active'));
+    const item = ctx.document.querySelector('#si-remote-never');
+    assert.ok(item);
+    assert.ok(!item.classList.contains('cli-busy'));
+  } finally { ctx.destroy(); }
+});
+
+test('no .remote-activity-dot element remains anywhere in the DOM', () => {
+  const ctx = setupSidebarDom();
+  try {
+    const session = {
+      sessionId: 'remote-active', summary: 'live now', modified: '2026-09-06T10:00:00.000Z',
+      starred: false, archived: 0, messageCount: 1,
+      remoteAlias: 'planificator', remoteActiveAt: Date.now() - 5000,
+    };
+    ctx.sidebar.renderProjects([remoteProject(session)], true);
+
+    assert.equal(ctx.document.querySelector('.remote-activity-dot'), null);
   } finally { ctx.destroy(); }
 });
 
-test('a local session carries no activity pip at all', () => {
+test('a local session is not marked busy by the remote paint path', () => {
   const ctx = setupSidebarDom();
   try {
     const project = makeSampleProject({
@@ -77,6 +126,51 @@ test('a local session carries no activity pip at all', () => {
     });
     ctx.sidebar.renderProjects([project], true);
 
-    assert.equal(ctx.document.querySelector('#si-local-1 .remote-activity-dot'), null);
+    const item = ctx.document.querySelector('#si-local-1');
+    assert.ok(item);
+    assert.ok(!item.classList.contains('cli-busy'));
+  } finally { ctx.destroy(); }
+});
+
+test('a seeded remote session goes idle once the remaining decay window elapses, and not before', () => {
+  const ctx = setupSidebarDom();
+  try {
+    const timers = installFakeTimers(ctx.window);
+    const session = {
+      sessionId: 'remote-partial', summary: 'partially aged', modified: '2026-09-06T10:00:00.000Z',
+      starred: false, archived: 0, messageCount: 1,
+      remoteAlias: 'planificator', remoteActiveAt: Date.now() - 15000,
+    };
+    ctx.sidebar.renderProjects([remoteProject(session)], true);
+
+    let item = ctx.document.querySelector('#si-remote-partial');
+    assert.ok(item.classList.contains('cli-busy'), 'seeded busy on first render (15s old, still inside 20s)');
+
+    timers.advance(4000); // total 4000ms — remaining window (~5000ms) not yet elapsed
+    item = ctx.document.querySelector('#si-remote-partial');
+    assert.ok(item.classList.contains('cli-busy'), 'must not decay before the remaining window elapses');
+
+    timers.advance(1001); // total 5001ms — past the ~5000ms remaining window
+    item = ctx.document.querySelector('#si-remote-partial');
+    assert.ok(!item.classList.contains('cli-busy'), 'must go idle once the remaining window elapses');
+  } finally { ctx.destroy(); }
+});
+
+test('seeding the same still-active session again does not stack a second decay timer', () => {
+  const ctx = setupSidebarDom();
+  try {
+    const timers = installFakeTimers(ctx.window);
+    const session = {
+      sessionId: 'remote-rerender', summary: 'live now', modified: '2026-09-06T10:00:00.000Z',
+      starred: false, archived: 0, messageCount: 1,
+      remoteAlias: 'planificator', remoteActiveAt: Date.now() - 5000,
+    };
+    const project = remoteProject(session);
+
+    ctx.sidebar.renderProjects([project], true);
+    assert.equal(timers.pendingCount(), 1, 'exactly one decay timer armed on first seed');
+
+    ctx.sidebar.renderProjects([project], false); // re-render, same session data
+    assert.equal(timers.pendingCount(), 1, 'a repeat seed must not arm a second timer for the same session');
   } finally { ctx.destroy(); }
 });
diff --git a/test/dom-subagent-transcript.test.js b/test/dom-subagent-transcript.test.js
index 20d884c5..008d71a3 100644
--- a/test/dom-subagent-transcript.test.js
+++ b/test/dom-subagent-transcript.test.js
@@ -117,6 +117,10 @@ function setupDom({ readSubagentJsonlResult = { entries: SAMPLE_ENTRIES }, readS
     cachedProjects: [],
     cachedAllProjects: [],
 
+    // remote-activity-ui.js is not loaded in this harness — renderProjects
+    // calls it unconditionally, and no fixture session here is remote.
+    seedRemoteActivity: () => {},
+
     // No-op function stubs (sidebar.js wires these in rebindSidebarEvents;
     // the real spies for openSession / showSubagentTranscript are installed
     // AFTER eval'ing sidebar.js + jsonl-viewer.js so the JS files don't
diff --git a/test/dom-subagent-ttl-tick.test.js b/test/dom-subagent-ttl-tick.test.js
index b5393d43..091ff762 100644
--- a/test/dom-subagent-ttl-tick.test.js
+++ b/test/dom-subagent-ttl-tick.test.js
@@ -66,6 +66,9 @@ function setupCombinedDom() {
     responseReadySessions: new Set(),
     sessionBusyState: new Map(),
     cachedAllProjects: [],
+    // remote-activity-ui.js is not loaded in this harness — renderProjects
+    // calls it unconditionally, and no fixture session here is remote.
+    seedRemoteActivity: () => {},
     pollActiveSessions: () => {},
     showNewSessionPopover: () => {},
     openSettingsViewer: () => {},
diff --git a/test/remote-activity-ui.test.js b/test/remote-activity-ui.test.js
index b0ea4f15..1f2338d5 100644
--- a/test/remote-activity-ui.test.js
+++ b/test/remote-activity-ui.test.js
@@ -1,8 +1,14 @@
 // Tests for public/remote-activity-ui.js — the sidebar's remote
-// transcript-write pip. Evaluated standalone in jsdom, same technique as
-// test/session-activity.test.js: this file was split out precisely so it can
-// be exercised without the rest of app.js (which builds ViewerPanel/xterm at
-// module scope and cannot be eval'd in isolation).
+// transcript-write signal. Since #243 it goes through the same central
+// dispatcher local PTY output uses: session-activity.js's
+// setActivity(sessionId, active, via), which owns sessionBusyState,
+// activitySeq, the response-ready transition and the trace — never a direct
+// write. See .ai/contexts/session-cache.md ("Remote hosts — busy spinner
+// (issue #242)"). Evaluated standalone in jsdom together with the real
+// session-activity.js, same technique as test/session-activity.test.js:
+// split out precisely so it can be exercised without the rest of app.js
+// (which builds ViewerPanel/xterm at module scope and cannot be eval'd in
+// isolation).
 //
 // setTimeout/clearTimeout are stubbed on the jsdom window so the 20s decay
 // is driven by hand instead of a real wall-clock wait.
@@ -15,16 +21,19 @@ const path = require('node:path');
 const vm = require('node:vm');
 const { JSDOM } = require('jsdom');
 
+const ACTIVITY_SRC = path.join(__dirname, '..', 'public', 'session-activity.js');
 const SRC = path.join(__dirname, '..', 'public', 'remote-activity-ui.js');
 
 function setup(sessionIds = ['s1']) {
   const items = sessionIds
-    .map(id => `<div class="session-item" data-session-id="${id}"><span class="remote-activity-dot"></span></div>`)
+    .map(id => `<div class="session-item" data-session-id="${id}"><span class="session-status-dot"></span></div>`)
     .join('');
   const dom = new JSDOM(`<!DOCTYPE html><html><body>${items}</body></html>`,
     { url: 'http://localhost/', runScripts: 'outside-only' });
   const { window } = dom;
 
+  Object.defineProperty(window, 'activeSessionId', { value: null, writable: true, configurable: true });
+
   let onRemoteActivityCb = null;
   Object.defineProperty(window, 'api', {
     value: { onRemoteActivity: (cb) => { onRemoteActivityCb = cb; } },
@@ -50,6 +59,7 @@ function setup(sessionIds = ['s1']) {
   });
 
   const ctx = dom.getInternalVMContext();
+  vm.runInContext(fs.readFileSync(ACTIVITY_SRC, 'utf8'), ctx, { filename: ACTIVITY_SRC });
   vm.runInContext(fs.readFileSync(SRC, 'utf8'), ctx, { filename: SRC });
 
   const read = (expr) => vm.runInContext(expr, ctx);
@@ -58,23 +68,25 @@ function setup(sessionIds = ['s1']) {
     window,
     document: window.document,
     item: (id) => window.document.querySelector(`.session-item[data-session-id="${id}"]`),
-    dot: (id) => window.document.querySelector(`.session-item[data-session-id="${id}"] .remote-activity-dot`),
     emit: (payload) => onRemoteActivityCb(payload),
     scheduled,
     pending: () => scheduled.filter(h => !h.cleared),
     pruneRemoteActivityTimers: read('pruneRemoteActivityTimers'),
     remoteActivityDecayTimers: read('remoteActivityDecayTimers'),
+    sessionBusyState: read('sessionBusyState'),
+    responseReadySessions: read('responseReadySessions'),
     destroy: () => window.close(),
   };
 }
 
-test('a remote-activity event marks the matching row active', () => {
+test('a remote-activity event marks the matching row busy through setActivity', () => {
   const t = setup(['s1']);
-  assert.ok(!t.dot('s1').classList.contains('active'), 'precondition: pip starts off');
+  assert.ok(!t.item('s1').classList.contains('cli-busy'), 'precondition: row starts idle');
 
   t.emit({ alias: 'vps', sessionId: 's1', at: Date.now() });
 
-  assert.ok(t.dot('s1').classList.contains('active'), 'the pip must light up on activity');
+  assert.equal(t.sessionBusyState.get('s1'), true, 'sessionBusyState is set through the central dispatcher');
+  assert.ok(t.item('s1').classList.contains('cli-busy'), 'the row must go busy, same as a local session');
   t.destroy();
 });
 
@@ -84,25 +96,38 @@ test('a payload with no sessionId is ignored', () => {
   t.emit(null);
   t.emit(undefined);
 
-  assert.ok(!t.dot('s1').classList.contains('active'));
+  assert.ok(!t.item('s1').classList.contains('cli-busy'));
   assert.equal(t.scheduled.length, 0, 'a malformed payload must not schedule a decay timer either');
   t.destroy();
 });
 
-test('the pip clears once the decay timer fires, and not before', () => {
+test('.cli-busy clears once the decay timer fires, and not before', () => {
   const t = setup(['s1']);
   t.emit({ sessionId: 's1' });
-  assert.ok(t.dot('s1').classList.contains('active'));
+  assert.ok(t.item('s1').classList.contains('cli-busy'));
 
   const timer = t.pending()[0];
   assert.ok(timer, 'a decay timer must be scheduled');
   assert.equal(timer.ms, 20000, 'the decay window is 20s');
 
-  // Before the timer fires, the pip stays lit.
-  assert.ok(t.dot('s1').classList.contains('active'));
+  // Before the timer fires, the row stays busy.
+  assert.ok(t.item('s1').classList.contains('cli-busy'));
 
   timer.fn(); // simulate the 20s elapsing
-  assert.ok(!t.dot('s1').classList.contains('active'), 'the pip must clear once the decay window elapses');
+  assert.ok(!t.item('s1').classList.contains('cli-busy'), 'the row must go idle once the decay window elapses');
+  t.destroy();
+});
+
+test('decay routes through setActivity: a non-selected remote session lands in responseReadySessions, exactly like a local one', () => {
+  const t = setup(['s1']);
+  t.window.activeSessionId = 's2'; // s1 is not the focused session
+  t.emit({ sessionId: 's1' });
+  assert.ok(!t.responseReadySessions.has('s1'), 'precondition: not response-ready while busy');
+
+  t.pending()[0].fn(); // decay fires
+
+  assert.equal(t.sessionBusyState.get('s1'), false);
+  assert.ok(t.responseReadySessions.has('s1'), 'going idle through setActivity marks the turn as an unread response, like a local session');
   t.destroy();
 });
 
@@ -118,10 +143,10 @@ test('a second event before decay resets the timer instead of stacking one', ()
 
   // Firing the (now-cancelled) first timer's callback would be a stale fire
   // in the real world — clearTimeout prevents that from ever happening — but
-  // confirm the surviving timer is the one that actually clears the pip.
+  // confirm the surviving timer is the one that actually clears the row.
   const second = t.pending()[0];
   second.fn();
-  assert.ok(!t.dot('s1').classList.contains('active'));
+  assert.ok(!t.item('s1').classList.contains('cli-busy'));
   t.destroy();
 });
 
diff --git a/test/remote-activity.test.js b/test/remote-activity.test.js
index a353b8bd..88c5ba6b 100644
--- a/test/remote-activity.test.js
+++ b/test/remote-activity.test.js
@@ -1,8 +1,8 @@
 'use strict';
 
 // remote-activity.js: the uncoalesced transcript-write signal that feeds the
-// sidebar's activity pip. Properties proven here (issue #242, see
-// .ai/contexts/session-cache.md, "Remote hosts — activity pip"):
+// sidebar's busy spinner. Properties proven here (issue #242, see
+// .ai/contexts/session-cache.md, "Remote hosts — busy spinner (issue #242)"):
 //   1. A rel that doesn't decode to a plausible session id is dropped.
 //   2. A first sighting of a session is always forwarded.
 //   3. A second sighting inside the throttle window is swallowed, not forwarded.
diff --git a/test/sidebar-busy-agents-tint.test.js b/test/sidebar-busy-agents-tint.test.js
index 640eb92c..c056841a 100644
--- a/test/sidebar-busy-agents-tint.test.js
+++ b/test/sidebar-busy-agents-tint.test.js
@@ -42,7 +42,7 @@ function projectWithLiveSubagent() {
 test('a busy session with no subagents carries cli-busy alone', () => {
   const ctx = setupSidebarDom();
   try {
-    ctx.window.sessionBusyState.set('s-top-1', true);
+    ctx.sessionBusyState.set('s-top-1', true);
     ctx.sidebar.renderProjects([projectWithLiveSubagent()], true);
 
     const parent = ctx.document.getElementById('si-s-top-1');
@@ -56,7 +56,7 @@ test('a busy session with no subagents carries cli-busy alone', () => {
 test('a busy session with live subagents carries cli-busy AND has-busy-agents at once', () => {
   const ctx = setupSidebarDom();
   try {
-    ctx.window.sessionBusyState.set('s-top-1', true);
+    ctx.sessionBusyState.set('s-top-1', true);
     ctx.sidebar.renderProjects([projectWithLiveSubagent()], true);
     ctx.emitSubagentSpawned({ parentSessionId: 's-top-1', agentId: 'agent-1', subagentType: 'explore' });