diff --git a/lib/__tests__/plugin-app-side-panel.test.ts b/lib/__tests__/plugin-app-side-panel.test.ts
index ce8fafbda..9f53bd284 100644
--- a/lib/__tests__/plugin-app-side-panel.test.ts
+++ b/lib/__tests__/plugin-app-side-panel.test.ts
@@ -5,6 +5,8 @@ import { isFillableSlot } from '@/lib/plugin-sandbox/slot-layout';
 import { ALL_PERMISSIONS, type InstalledPlugin, type Permission } from '@/lib/plugin-types';
 import { slotSpec } from '@/lib/plugin-slot-catalog';
 import { assistantFeatures } from '@/lib/plugin-sandbox/assistant';
+import { runPluginAction } from '@/lib/plugin-sandbox/actions';
+import { deregister, register, type ActivePlugin } from '@/lib/plugin-sandbox/registry';
 import { APP_SIDE_PANEL_CONTEXT_FIELDS } from '@/lib/plugin-sandbox/assistant/f.types';
 
 // The app-side-panel slot (area f of the assistant's host APIs): a side
@@ -62,11 +64,28 @@ describe('app-side-panel', () => {
     expect(Object.keys(all.context as object).sort()).toEqual(Object.keys(APP_SIDE_PANEL_CONTEXT_FIELDS).sort());
   });
 
-  it('cuts the context the same way in an action click (the dialog on a phone)', () => {
-    const visible = slotPropsFor(plugin(['ui:side-panel', 'calendar:read']), 'app-side-panel', { view: 'contacts', context: { contact: context.contact, page: context.page } });
-    expect(visible).toEqual({ view: 'contacts', context: { page: context.page } });
+  it("cuts the context the same way in the click that asks the plugin for its dialog (the loader's dispatcher)", async () => {
+    // Importing the loader installs its action dispatcher, as in the app.
+    await import('@/lib/plugin-sandbox/loader');
+    const invokeHook = vi.fn(async () => undefined);
+    register({ plugin: plugin(['ui:side-panel', 'calendar:read']), code: '', tier: 'untrusted', background: { invokeHook }, slotOffers: [], hookDisposables: [] } as unknown as ActivePlugin);
+    try {
+      await runPluginAction('p', 'app-side-panel', 'open', { view: 'contacts', context: { contact: context.contact, page: context.page, secret: 'x' } });
+      expect(invokeHook).toHaveBeenCalledWith('onAction', [{ surface: 'app-side-panel', actionId: 'open', context: { view: 'contacts', context: { page: context.page } } }]);
+    } finally {
+      deregister('p');
+    }
     // Garbage in the context is dropped, not passed on.
     expect(slotPropsFor(plugin(['ui:side-panel']), 'app-side-panel', { context: 'x' }).context).toEqual({});
+    // The loader's import is slow under load.
+  }, 30_000);
+
+  it('tells each plugin whether it may show the panel (sidePanel follows its grant)', () => {
+    expect(assistantFeatures(plugin(['ui:side-panel'])).sidePanel).toBe(true);
+    // Enabled before an update added the permission: not granted yet.
+    const notGranted = { ...plugin(['ui:side-panel']), grantedPermissions: [] };
+    expect(assistantFeatures(notGranted).sidePanel).toBe(false);
+    expect(assistantFeatures(plugin([])).sidePanel).toBe(false);
   });
 
   it('routes api.ui.openPanel for it to the view that shows it, and nowhere else', () => {
diff --git a/lib/__tests__/plugin-host-features.test.ts b/lib/__tests__/plugin-host-features.test.ts
index 9db8a0e83..d85e4443c 100644
--- a/lib/__tests__/plugin-host-features.test.ts
+++ b/lib/__tests__/plugin-host-features.test.ts
@@ -19,8 +19,8 @@ import {
 } from '@/lib/plugin-sandbox/host-features';
 import { assistantFeatures } from '@/lib/plugin-sandbox/assistant';
 
-/** The AI assistant's flags (lib/plugin-sandbox/assistant) come on top; their own tests check them. */
-const withAssistant = (core: Record<string, boolean>) => ({ ...core, ...assistantFeatures() });
+/** The AI assistant's flags (lib/plugin-sandbox/assistant) come on top, as `plugin` sees them; their own tests check them. */
+const withAssistant = (core: Record<string, boolean>, plugin?: never) => ({ ...core, ...assistantFeatures(plugin) });
 
 function setExternalMail(patch: Partial<typeof DEFAULT_ORGANISATION_POLICY.externalMail>) {
   usePolicyStore.setState({
@@ -85,21 +85,21 @@ describe('host bridge', () => {
     const plugin = { id: 'p', name: 'P', version: '1.0.0', permissions: [], settings: {}, settingsSchema: {} } as never;
     const instance = createBackgroundInstance({ plugin, tier: 'privileged', code: '', locale: 'en' });
     const pending = (instance as unknown as { pendingInit: { hostFeatures?: unknown } | null }).pendingInit;
-    expect(pending?.hostFeatures).toEqual(withAssistant({ externalSenderLabel: true, externalRecipientWarning: false, noThirdPartyTraffic: false }));
+    expect(pending?.hostFeatures).toEqual(withAssistant({ externalSenderLabel: true, externalRecipientWarning: false, noThirdPartyTraffic: false }, plugin));
 
     // Before init has gone out a change lands in the payload ...
     setExternalMail({});
-    expect(pending?.hostFeatures).toEqual(withAssistant({ externalSenderLabel: false, externalRecipientWarning: false, noThirdPartyTraffic: false }));
+    expect(pending?.hostFeatures).toEqual(withAssistant({ externalSenderLabel: false, externalRecipientWarning: false, noThirdPartyTraffic: false }, plugin));
 
     // ... after it, as a host-change message.
     const sent: unknown[] = [];
     (instance as unknown as { pendingInit: unknown }).pendingInit = null;
     (instance as unknown as { send: (m: unknown) => void }).send = (m) => sent.push(m);
     setExternalMail({ recipientWarning: true });
-    expect(sent).toEqual([{ type: 'host-change', features: withAssistant({ externalSenderLabel: false, externalRecipientWarning: true, noThirdPartyTraffic: false }) }]);
+    expect(sent).toEqual([{ type: 'host-change', features: withAssistant({ externalSenderLabel: false, externalRecipientWarning: true, noThirdPartyTraffic: false }, plugin) }]);
     // The admin turns third-party traffic off: running plugins hear it.
     setNoThirdPartyTraffic(true);
-    expect(sent[1]).toEqual({ type: 'host-change', features: withAssistant({ externalSenderLabel: false, externalRecipientWarning: true, noThirdPartyTraffic: true }) });
+    expect(sent[1]).toEqual({ type: 'host-change', features: withAssistant({ externalSenderLabel: false, externalRecipientWarning: true, noThirdPartyTraffic: true }, plugin) });
     setNoThirdPartyTraffic(false);
     instance.destroy();
   }, 30_000);
diff --git a/lib/plugin-sandbox/assistant/f.ts b/lib/plugin-sandbox/assistant/f.ts
index c4cccac8f..e125c0cc6 100644
--- a/lib/plugin-sandbox/assistant/f.ts
+++ b/lib/plugin-sandbox/assistant/f.ts
@@ -5,6 +5,7 @@
 // the whole host side, mounted by components/plugins/app-side-panel.tsx.
 
 import type { InstalledPlugin, Permission } from '../../plugin-types';
+import { mayOfferSlot } from '../permissions';
 import { NOT_MINE } from './not-mine';
 import type { AreaHostFeaturesF } from './f.types';
 
@@ -16,7 +17,13 @@ export async function dispatch(_plugin: InstalledPlugin, _method: string, _args:
   return NOT_MINE;
 }
 
-/** This area's flags in api.host.features, right now. */
-export function features(): AreaHostFeaturesF {
-  return { sidePanel: true };
+/**
+ * This area's flags in api.host.features, right now. For one plugin,
+ * sidePanel says whether it may show the panel (ui:side-panel granted; a
+ * plugin enabled before an update that added it lacks it until turned off
+ * and on), so it can tell the user instead of offering a switch that does
+ * nothing.
+ */
+export function features(plugin?: InstalledPlugin): AreaHostFeaturesF {
+  return { sidePanel: plugin ? mayOfferSlot(plugin, 'app-side-panel') : true };
 }
diff --git a/lib/plugin-sandbox/assistant/index.ts b/lib/plugin-sandbox/assistant/index.ts
index 9d73e4a8d..f98ac68a4 100644
--- a/lib/plugin-sandbox/assistant/index.ts
+++ b/lib/plugin-sandbox/assistant/index.ts
@@ -23,7 +23,10 @@ export async function dispatchAssistant(plugin: InstalledPlugin, method: string,
   return NOT_MINE;
 }
 
-/** Every area's api.host.features flags, right now. */
-export function assistantFeatures(): AssistantHostFeatures {
-  return Object.assign({}, ...AREAS.map((a) => a.features()));
+/**
+ * Every area's api.host.features flags, right now; with `plugin`, as that
+ * plugin's frames see them (a flag may depend on what it was granted).
+ */
+export function assistantFeatures(plugin?: InstalledPlugin): AssistantHostFeatures {
+  return Object.assign({}, ...AREAS.map((a) => (a.features as (p?: InstalledPlugin) => object)(plugin)));
 }
diff --git a/lib/plugin-sandbox/host-bridge.ts b/lib/plugin-sandbox/host-bridge.ts
index a780c3e7b..617dffabe 100644
--- a/lib/plugin-sandbox/host-bridge.ts
+++ b/lib/plugin-sandbox/host-bridge.ts
@@ -14,6 +14,7 @@ export type { RegionalSnapshot };
 import { withBasePath } from '../browser-navigation';
 import { snapshotHostTheme, type ThemeSnapshot } from './host-theme';
 import { snapshotHostFeatures, watchHostFeatures } from './host-features';
+import { assistantFeatures } from './assistant';
 import { effectiveSettings } from '../plugin-settings';
 import { clampSlotHeight, clampSlotWidth, isInlineSlot, MAX_INLINE_SLOT_WIDTH } from './slot-layout';
 import { resolveDateLocale } from '../utils';
@@ -257,7 +258,8 @@ function pushThemeToFrames(): void {
 /** Every frame hears about a Bulwark feature that replaces plugins turning on or off. */
 function pushHostFeaturesToFrames(features: HostFeaturesView): void {
   for (const instance of liveInstances) {
-    try { instance.setHostFeatures(features); } catch { /* one broken iframe must not stop the rest */ }
+    // Some of the assistant's flags depend on the plugin's grants (host-features.ts).
+    try { instance.setHostFeatures({ ...features, ...instance.ownHostFeatures() }); } catch { /* one broken iframe must not stop the rest */ }
   }
 }
 
@@ -672,6 +674,11 @@ export class SandboxInstance {
   }
 
   /** Push what api.host.features says now; before init it goes into the init payload. */
+  /** The flags of api.host.features that depend on this plugin. */
+  ownHostFeatures(): Partial<HostFeaturesView> {
+    return assistantFeatures(this.plugin);
+  }
+
   setHostFeatures(features: HostFeaturesView): void {
     if (this.destroyed) return;
     if (this.pendingInit) {
@@ -782,7 +789,7 @@ export function createBackgroundInstance(opts: BackgroundOptions): SandboxInstan
     code: opts.code,
     locale: opts.locale,
     regional: opts.regional ?? snapshotRegionalSettings(opts.locale),
-    hostFeatures: snapshotHostFeatures(),
+    hostFeatures: snapshotHostFeatures(opts.plugin),
   };
   return new SandboxInstance(
     opts.plugin,
@@ -812,7 +819,7 @@ export function createSlotInstance(opts: SlotOptions): SandboxInstance {
     locale: opts.locale,
     regional: opts.regional ?? snapshotRegionalSettings(opts.locale),
     theme: snapshotHostTheme(),
-    hostFeatures: snapshotHostFeatures(),
+    hostFeatures: snapshotHostFeatures(opts.plugin),
   };
   return new SandboxInstance(opts.plugin, payload, opts.hostContainer, opts.onResize, opts.onFloatingDropdown);
 }
diff --git a/lib/plugin-sandbox/host-features.ts b/lib/plugin-sandbox/host-features.ts
index 0d82ac618..0b679d28c 100644
--- a/lib/plugin-sandbox/host-features.ts
+++ b/lib/plugin-sandbox/host-features.ts
@@ -10,7 +10,7 @@
 
 import { usePolicyStore } from '@/stores/policy-store';
 import { noThirdPartyTraffic, subscribeThirdPartyMode } from '@/lib/third-party-mode';
-import type { HostFeaturesView } from '../plugin-types';
+import type { HostFeaturesView, InstalledPlugin } from '../plugin-types';
 import type { OrganisationPolicy } from '@/lib/admin/organisation-policy';
 import { assistantFeatures } from './assistant';
 
@@ -26,11 +26,11 @@ export function hostFeaturesFor(externalMail: OrganisationPolicy['externalMail']
   };
 }
 
-export function snapshotHostFeatures(): HostFeaturesView {
+export function snapshotHostFeatures(plugin?: InstalledPlugin): HostFeaturesView {
   return {
     ...hostFeaturesFor(usePolicyStore.getState().getOrganisation().externalMail, noThirdPartyTraffic()),
     // The AI assistant's host APIs this webmail offers (lib/plugin-sandbox/assistant).
-    ...assistantFeatures(),
+    ...assistantFeatures(plugin),
   };
 }