Show talk-circle partners and topic on the location panel and Now tab.

The frame and card share member ids; the client builds the sentence from the directory and locale.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/phases/45-presence-talk.md

@@ -11,18 +11,18 @@
 
 ## Задачи
 
-- [ ] Кадр присутствия: у человека, который в кружке, список id участников и id темы.
+- [x] Кадр присутствия: у человека, который в кружке, список id участников и id темы.
       Имена не строкой. Клиент собирает «говорит с Машей о футболе» из справочника и локали
-- [ ] Версия протокола +1. `ProtocolCodec.cs`, `protocol.ts`, `docs/protocol.md` в одном коммите
+- [x] Версия протокола +1. `ProtocolCodec.cs`, `protocol.ts`, `docs/protocol.md` в одном коммите
-- [ ] Не в кружке — пустой список, как сейчас только id/узел/состояние
+- [x] Не в кружке — пустой список, как сейчас только id/узел/состояние
-- [ ] Вкладка «Сейчас» на карточке согласована с тем же составом
+- [x] Вкладка «Сейчас» на карточке согласована с тем же составом
-- [ ] Старый клиент отваливается Hello, как обычно
+- [x] Старый клиент отваливается Hello, как обычно
 
 ## Тесты, без которых фаза не закрыта
 
-- [ ] Круглый трип и байтовая раскладка человека с кружком и без — на обеих сторонах
+- [x] Круглый трип и байтовая раскладка человека с кружком и без — на обеих сторонах
-- [ ] Имя человека не встречается в кадре присутствия
+- [x] Имя человека не встречается в кадре присутствия
-- [ ] Клиентский тест: локация показывает тему и имя напарника из directory, не из кадра
+- [x] Клиентский тест: локация показывает тему и имя напарника из directory, не из кадра
 
 ## Критерий готовности
 

src/HSchool.Client/src/format/talkCircle.test.ts

@@ -0,0 +1,51 @@
+/**
+ * @vitest-environment happy-dom
+ */
+import { afterEach, describe, expect, it } from 'vitest';
+import { PresenceState, type PresencePerson } from '../net/protocol.ts';
+import { getLocale, setLocale } from '../i18n/locale.ts';
+import { t } from '../i18n/strings.ts';
+import { locationPersonLine, talkCircleText } from './talkCircle.ts';
+
+const initial = getLocale();
+
+afterEach(() => setLocale(initial));
+
+describe('location talk line', () => {
+  it('shows the partner name from the directory and the topic from locale, not from the frame', () => {
+    setLocale('ru');
+    const person: PresencePerson = {
+      id: 'f0.c0',
+      nodeId: 'corridor-1',
+      state: PresenceState.Here,
+      talkMemberIds: ['f0.c0', 'f0.c1'],
+      talkTopicId: 'TopicSport',
+    };
+    const names = new Map([
+      ['f0.c0', 'Иванова Мария'],
+      ['f0.c1', 'Петрова Маша'],
+    ]);
+
+    const line = locationPersonLine(person, names);
+
+    expect(JSON.stringify(person)).not.toContain('Маша');
+    expect(JSON.stringify(person)).not.toContain('Иванова');
+    expect(line).toContain('Петрова Маша');
+    expect(line).toContain(t('talkTopicTopicSport'));
+    expect(line).toBe(`Иванова Мария — ${t('locationTalking', { partners: 'Петрова Маша', topic: t('talkTopicTopicSport') })}`);
+  });
+
+  it('omits talk text when the circle list is empty', () => {
+    const person: PresencePerson = {
+      id: 'f0.c0',
+      nodeId: 'corridor-1',
+      state: PresenceState.Here,
+      talkMemberIds: [],
+      talkTopicId: '',
+    };
+    const names = new Map([['f0.c0', 'Иванова Мария']]);
+
+    expect(locationPersonLine(person, names)).toBe('Иванова Мария');
+    expect(talkCircleText(person.id, person.talkMemberIds, person.talkTopicId, names)).toBe('');
+  });
+});

src/HSchool.Client/src/format/talkCircle.ts

@@ -0,0 +1,64 @@
+import { PresenceState, type PresencePerson } from '../net/protocol.ts';
+import { t, type MessageKey } from '../i18n/strings.ts';
+
+const TOPIC_KEYS: Record<string, MessageKey> = {
+  TopicStudy: 'talkTopicTopicStudy',
+  TopicGames: 'talkTopicTopicGames',
+  TopicFood: 'talkTopicTopicFood',
+  TopicFamily: 'talkTopicTopicFamily',
+  TopicSport: 'talkTopicTopicSport',
+  TopicGossip: 'talkTopicTopicGossip',
+  TopicRude: 'talkTopicTopicRude',
+  TopicAppearance: 'talkTopicTopicAppearance',
+};
+
+export function talkTopicLabel(topicId: string): string {
+  const key = TOPIC_KEYS[topicId];
+  return key === undefined ? topicId : t(key);
+}
+
+export function talkPartnersLabel(
+  selfId: string,
+  memberIds: readonly string[],
+  names: ReadonlyMap<string, string>,
+): string {
+  const others = memberIds
+    .filter((id) => id !== selfId)
+    .map((id) => names.get(id) ?? id);
+  if (others.length === 0) {
+    return '';
+  }
+
+  if (others.length === 1) {
+    return others[0] ?? '';
+  }
+
+  const last = others[others.length - 1] ?? '';
+  const head = others.slice(0, -1).join(', ');
+  return t('talkPartnersJoin', { head, last });
+}
+
+export function talkCircleText(
+  selfId: string,
+  memberIds: readonly string[],
+  topicId: string,
+  names: ReadonlyMap<string, string>,
+): string {
+  if (memberIds.length === 0 || topicId.length === 0) {
+    return '';
+  }
+
+  const partners = talkPartnersLabel(selfId, memberIds, names);
+  if (partners.length === 0) {
+    return '';
+  }
+
+  return t('locationTalking', { partners, topic: talkTopicLabel(topicId) });
+}
+
+export function locationPersonLine(person: PresencePerson, names: ReadonlyMap<string, string>): string {
+  const name = names.get(person.id) ?? person.id;
+  const base = person.state === PresenceState.Walking ? t('locationWalking', { name }) : name;
+  const talk = talkCircleText(person.id, person.talkMemberIds, person.talkTopicId, names);
+  return talk.length > 0 ? `${base} — ${talk}` : base;
+}

src/HSchool.Client/src/i18n/strings.test.ts

@@ -34,6 +34,8 @@ describe('t', () => {
     expect(t('mapHeadcountActivity', { name: 'Класс 101', count: 18, activity: 'Математика · 5А' }))
       .toBe('Класс 101 (18 · Математика · 5А)');
     expect(t('locationWalking', { name: 'Иванов' })).toBe('Иванов (walking)');
+    expect(t('locationTalking', { partners: 'Петрова Маша', topic: t('talkTopicTopicSport') }))
+      .toBe('talking with Петрова Маша about sport');
   });
 });
 

src/HSchool.Client/src/i18n/strings.ts

@@ -335,6 +335,16 @@ const ru = {
   presenceWalking: 'в пути ({name})',
   presenceAway: 'вне школы',
   locationWalking: '{name} (в пути)',
+  locationTalking: 'говорит с {partners} о {topic}',
+  talkPartnersJoin: '{head} и {last}',
+  talkTopicTopicStudy: 'учёбе',
+  talkTopicTopicGames: 'играх',
+  talkTopicTopicFood: 'еде',
+  talkTopicTopicFamily: 'семье',
+  talkTopicTopicSport: 'спорте',
+  talkTopicTopicGossip: 'сплетнях',
+  talkTopicTopicRude: 'грубом',
+  talkTopicTopicAppearance: 'внешности',
   timetableTitle: 'Расписание',
   timetableClass: 'Класс',
   timetableEmpty: 'Нет уроков.',
@@ -692,6 +702,16 @@ const en: Messages = {
   presenceWalking: 'walking ({name})',
   presenceAway: 'off campus',
   locationWalking: '{name} (walking)',
+  locationTalking: 'talking with {partners} about {topic}',
+  talkPartnersJoin: '{head} and {last}',
+  talkTopicTopicStudy: 'schoolwork',
+  talkTopicTopicGames: 'games',
+  talkTopicTopicFood: 'food',
+  talkTopicTopicFamily: 'family',
+  talkTopicTopicSport: 'sport',
+  talkTopicTopicGossip: 'gossip',
+  talkTopicTopicRude: 'rough talk',
+  talkTopicTopicAppearance: 'looks',
   timetableTitle: 'Timetable',
   timetableClass: 'Class',
   timetableEmpty: 'No lessons.',

src/HSchool.Client/src/net/api.ts

@@ -324,6 +324,8 @@ export interface PersonCard {
   readonly needs: readonly NeedStat[];
   readonly activity: string | null;
   readonly activityLabel: string | null;
+  readonly talkCircleMemberIds: readonly string[];
+  readonly talkTopicId: string | null;
   readonly family: {
     readonly parents: readonly PersonRel[];
     readonly children: readonly PersonRel[];

src/HSchool.Client/src/ui/gameScreen.test.ts

@@ -1,9 +1,24 @@
 /**
  * @vitest-environment happy-dom
  */
-import { describe, expect, it, vi } from 'vitest';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { PresenceState } from '../net/protocol.ts';
+import { getLocale, setLocale } from '../i18n/locale.ts';
+import { t } from '../i18n/strings.ts';
 import { GameScreen } from './gameScreen.ts';
 
+vi.mock('../net/api.ts', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('../net/api.ts')>();
+  return {
+    ...actual,
+    fetchDirectory: async () => [],
+  };
+});
+
+const initial = getLocale();
+
+afterEach(() => setLocale(initial));
+
 describe('GameScreen speed buttons', () => {
   it('shows five speed buttons ×½ ×1 ×2 ×5 ×10', () => {
     const onSetSpeed = vi.fn();
@@ -47,3 +62,68 @@ describe('GameScreen speed buttons', () => {
     expect((screen.element.querySelector('.clock__controls') as HTMLElement).hidden).toBe(true);
   });
 });
+
+describe('GameScreen location talk', () => {
+  it('shows talk partners from the directory on the location list, not from the frame', () => {
+    setLocale('ru');
+    const screen = new GameScreen({
+      onLeave: () => {},
+      onSetRunning: () => {},
+      onSetSpeed: () => {},
+      onSkip: () => {},
+    });
+    document.body.append(screen.element);
+    screen.show({
+      id: 1,
+      name: 'Test',
+      gameTime: '2012-03-31T10:00:00.000Z',
+      running: true,
+      speedIndex: 1,
+      seed: 1,
+      mine: true,
+    });
+    screen.applyMap(1, [
+      {
+        kind: 3,
+        id: 'corridor-1',
+        parentId: '',
+        name: 'Коридор',
+        pupilSlots: 0,
+        items: [],
+        positions: [],
+      },
+    ]);
+    const presence = {
+      type: 'presence' as const,
+      schoolId: 1,
+      nodes: [{ id: 'corridor-1', count: 2, activitySubject: '', activityClass: '' }],
+      people: [
+        {
+          id: 'f0.c0',
+          nodeId: 'corridor-1',
+          state: PresenceState.Here,
+          talkMemberIds: ['f0.c0', 'f0.c1'],
+          talkTopicId: 'TopicSport',
+        },
+        {
+          id: 'f0.c1',
+          nodeId: 'corridor-1',
+          state: PresenceState.Here,
+          talkMemberIds: ['f0.c0', 'f0.c1'],
+          talkTopicId: 'TopicSport',
+        },
+      ],
+    };
+    expect(JSON.stringify(presence)).not.toContain('Маша');
+    screen.applyPresence(1, presence);
+    screen.applyDirectory([
+      { id: 'f0.c0', fullName: 'Иванова Мария' },
+      { id: 'f0.c1', fullName: 'Петрова Маша' },
+    ]);
+
+    const items = [...screen.element.querySelectorAll('.panel__list li')].map((item) => item.textContent ?? '');
+    expect(items.some((text) => text.includes('Петрова Маша') && text.includes(t('talkTopicTopicSport')))).toBe(
+      true,
+    );
+  });
+});

src/HSchool.Client/src/ui/gameScreen.ts

@@ -15,7 +15,7 @@ import { fetchDirectory, type School } from '../net/api.ts';
 import { clear, el } from './dom.ts';
 import { ManagementPanel } from './managementPanel.ts';
 import { PeoplePanel } from './peoplePanel.ts';
-import { formatPersonPlace } from './personCard.ts';
+import { locationPersonLine } from '../format/talkCircle.ts';
 
 interface GameScreenOptions {
   readonly onLeave: () => void;
@@ -204,8 +204,7 @@ export class GameScreen {
 
     this.paintSkip();
     this.paintSeed();
-    this.people.setLocate((id) => this.placeOf(id));
+    this.bindPeople();
-    this.management.setLocate((id) => this.placeOf(id));
   }
 
   /** Called when the screen opens, before the first clock frame and snapshot arrive. */
@@ -234,8 +233,7 @@ export class GameScreen {
     this.rebuildTree();
     this.applyClock(new Date(school.gameTime), school.running, school.speedIndex, false, null, null, null);
     this.people.show(school.id);
-    this.people.setLocate((id) => this.placeOf(id));
+    this.bindPeople();
-    this.management.setLocate((id) => this.placeOf(id));
     this.showTab('map');
     this.inspect('location');
     this.showMode('overview');
@@ -267,13 +265,19 @@ export class GameScreen {
     this.presence = message;
     this.paintTreeLabels();
     this.paintSelection();
-    this.people.setLocate((id) => this.placeOf(id));
+    this.bindPeople();
-    this.management.setLocate((id) => this.placeOf(id));
     if (message.people.some((person) => !this.directory.has(person.id))) {
       void this.loadDirectory();
     }
   }
 
+  /** Names for the presence stream. The frame itself never carries display names. */
+  applyDirectory(people: readonly { id: string; fullName: string }[]): void {
+    this.directory = new Map(people.map((person) => [person.id, person.fullName]));
+    this.paintSelection();
+    this.bindPeople();
+  }
+
   update(clock: ClockMessage): void {
     this.applyClock(
       clock.gameTime,
@@ -458,10 +462,7 @@ export class GameScreen {
 
     const names = this.presence.people
       .filter((person) => person.nodeId === id)
-      .map((person) => {
+      .map((person) => locationPersonLine(person, this.directory));
-        const name = this.directory.get(person.id) ?? person.id;
-        return person.state === PresenceState.Walking ? t('locationWalking', { name }) : name;
-      });
     names.sort((left, right) => left.localeCompare(right));
     return names;
   }
@@ -476,6 +477,13 @@ export class GameScreen {
     return formatPersonPlace(person.state === PresenceState.Walking ? 'walking' : 'here', nodeName);
   }
 
+  private bindPeople(): void {
+    this.people.setLocate((id) => this.placeOf(id));
+    this.management.setLocate((id) => this.placeOf(id));
+    this.people.setNames(this.directory);
+    this.management.setNames(this.directory);
+  }
+
   private async loadDirectory(): Promise<void> {
     const schoolId = this.schoolId;
     if (schoolId === null) {
@@ -489,10 +497,7 @@ export class GameScreen {
         return;
       }
 
-      this.directory = new Map(people.map((person) => [person.id, person.fullName]));
+      this.applyDirectory(people);
-      this.paintSelection();
-      this.people.setLocate((id) => this.placeOf(id));
-      this.management.setLocate((id) => this.placeOf(id));
     } catch {
       // Names stay as ids until the next presence frame retries.
     }

src/HSchool.Client/src/ui/managementPanel.test.ts

@@ -67,6 +67,8 @@ function personCard(): PersonCard {
     needs: [],
     activity: null,
     activityLabel: null,
+    talkCircleMemberIds: [],
+    talkTopicId: null,
     family: { parents: [], children: [], siblings: [], partners: [] },
     worn: [],
     carried: [],

src/HSchool.Client/src/ui/managementPanel.ts

@@ -194,6 +194,10 @@ export class ManagementPanel {
     this.cardHost.relocate((id) => this.placeOf(id));
   }
 
+  setNames(names: ReadonlyMap<string, string>): void {
+    this.cardHost.setNames(names);
+  }
+
   private async reload(): Promise<void> {
     const schoolId = this.schoolId;
     if (schoolId === null) {

src/HSchool.Client/src/ui/peoplePanel.ts

@@ -184,6 +184,10 @@ export class PeoplePanel {
     this.cardHost.relocate((id) => this.placeOf(id));
   }
 
+  setNames(names: ReadonlyMap<string, string>): void {
+    this.cardHost.setNames(names);
+  }
+
   private onFilterChange(): void {
     this.page = 1;
     void this.reload();

src/HSchool.Client/src/ui/personCard.test.ts

@@ -33,6 +33,8 @@ function card(overrides: Partial<PersonCard> = {}): PersonCard {
     needs: [],
     activity: null,
     activityLabel: null,
+    talkCircleMemberIds: [],
+    talkTopicId: null,
     family: { parents: [], children: [], siblings: [], partners: [] },
     worn: [
       {
@@ -322,4 +324,26 @@ describe('renderPersonCard', () => {
     expect(root.querySelector('.people__now-activity')?.textContent).toBe(t('peopleAtHome'));
     expect(root.querySelector('.people__now-activity')?.textContent).not.toBe('');
   });
+
+  it('shows the same talk-circle partners on Now as the location line uses', () => {
+    setLocale('ru');
+    const root = document.createElement('div');
+    const names = new Map([
+      ['f0.c0', 'Иванова Мария'],
+      ['f0.c1', 'Петрова Маша'],
+    ]);
+    renderPersonCard(
+      root,
+      card({
+        talkCircleMemberIds: ['f0.c0', 'f0.c1'],
+        talkTopicId: 'TopicSport',
+      }),
+      () => {},
+      { tab: 'now', personNames: names },
+    );
+
+    expect(root.querySelector('.people__now-activity')?.textContent).toBe(
+      t('locationTalking', { partners: 'Петрова Маша', topic: t('talkTopicTopicSport') }),
+    );
+  });
 });

src/HSchool.Client/src/ui/personCard.ts

@@ -10,6 +10,7 @@ import type {
 } from '../net/api.ts';
 import { portraitUrl, type PortraitKind, type PortraitPrompt } from '../net/api.ts';
 import { formatGameTimeOfDay } from '../format/gameTime.ts';
+import { talkCircleText } from '../format/talkCircle.ts';
 import { t, type MessageKey } from '../i18n/strings.ts';
 import { clear, el } from './dom.ts';
 
@@ -46,6 +47,8 @@ export interface RenderPersonCardOptions {
   readonly swarmConfigured?: boolean;
   /** null while checking or when SwarmUI is not configured. */
   readonly swarmConnected?: boolean | null;
+  /** id→fullName from the presence directory; used to label the talk circle on Now. */
+  readonly personNames?: ReadonlyMap<string, string>;
 }
 
 export function roleLabels(roles: readonly string[]): string {
@@ -67,7 +70,21 @@ export function placement(person: Pick<PersonListItem, 'classYear' | 'classLette
   return parts.length > 0 ? parts.join(' · ') : '—';
 }
 
-export function nowActivityText(card: PersonCard, away: boolean): string {
+export function nowActivityText(
+  card: PersonCard,
+  away: boolean,
+  names: ReadonlyMap<string, string> = new Map(),
+): string {
+  const talk = talkCircleText(
+    card.id,
+    card.talkCircleMemberIds,
+    card.talkTopicId ?? '',
+    names,
+  );
+  if (talk.length > 0) {
+    return talk;
+  }
+
   if (away && (card.activityLabel === null || card.activityLabel.length === 0)) {
     return t('peopleAtHome');
   }
@@ -307,7 +324,7 @@ function fillNow(
   log: PersonLogPage | null | undefined,
   options: RenderPersonCardOptions,
 ): void {
-  const activity = nowActivityText(card, away);
+  const activity = nowActivityText(card, away, options.personNames);
   if (activity.length > 0) {
     parent.append(el('p', { class: 'people__now-activity', text: activity }));
   }

src/HSchool.Client/src/ui/personCardHost.ts

@@ -41,6 +41,7 @@ export class PersonCardHost {
   private container: HTMLElement | null = null;
   private onRelative: (id: string) => void = () => {};
   private placeOf: (id: string) => string = () => '';
+  private personNames: ReadonlyMap<string, string> = new Map();
   private onOverviewMounted?: (overview: HTMLElement, card: PersonCard) => void;
   private logQuery: PersonLogQuery = { page: 1, pageSize: 20, dir: 'desc' };
   private logPage: PersonLogPage | null = null;
@@ -172,6 +173,7 @@ export class PersonCardHost {
       onShowPortraitPrompt: (kind) => void this.togglePortraitPrompt(kind),
       swarmConfigured: this.swarmConfigured,
       swarmConnected: this.swarmConnected,
+      personNames: this.personNames,
     });
     const overview = container.querySelector('[data-card-tab="overview"]');
     if (overview instanceof HTMLElement) {
@@ -301,7 +303,20 @@ export class PersonCardHost {
     line.textContent = place;
     const now = this.container?.querySelector('.people__now-activity');
     if (now instanceof HTMLElement) {
-      now.textContent = nowActivityText(this.painted, place === formatPersonPlace('away'));
+      now.textContent = nowActivityText(this.painted, place === formatPersonPlace('away'), this.personNames);
+    }
+  }
+
+  setNames(names: ReadonlyMap<string, string>): void {
+    this.personNames = names;
+    if (this.painted === null) {
+      return;
+    }
+
+    const now = this.container?.querySelector('.people__now-activity');
+    if (now instanceof HTMLElement) {
+      const place = this.placeOf(this.painted.id);
+      now.textContent = nowActivityText(this.painted, place === formatPersonPlace('away'), names);
     }
   }
 }

src/HSchool.Server/Api/PeopleModels.cs

@@ -82,7 +82,9 @@ internal sealed record PersonCardResponse(
     bool HasCustom = false,
     bool HasFullBody = false,
     string? CustomPortraitPrompt = null,
-    PersonConnectionsResponse? Connections = null);
+    PersonConnectionsResponse? Connections = null,
+    IReadOnlyList<string>? TalkCircleMemberIds = null,
+    string? TalkTopicId = null);
 
 internal sealed record WornItemResponse(
     string DefName,

src/HSchool.Server/Game/PersonCardReader.cs

@@ -60,6 +60,8 @@ internal static class PersonCardReader
             activityLabel = activityId;
         }
 
+        var circle = school.TalkCircleOf(personId);
+
         return new PersonCardResponse(
             person.Id,
             person.Name.Full,
@@ -89,7 +91,9 @@ internal static class PersonCardReader
             person.LockerRoomId is not null
                 || person.Items.Any(item => item.Location.Equals(ItemLocations.Locker, StringComparison.Ordinal)),
             person.Items.Count(item => item.Location.Equals(ItemLocations.Home, StringComparison.Ordinal)),
-            Connections: Connections(roster, person, catalog, locale));
+            Connections: Connections(roster, person, catalog, locale),
+            TalkCircleMemberIds: circle?.MemberIds ?? [],
+            TalkTopicId: circle?.TopicId);
     }
 
     private static IReadOnlyDictionary<string, float>? LiveNeeds(World world, string personId)

src/HSchool.Server/Game/PresenceFrame.cs

@@ -25,10 +25,13 @@ internal static class PresenceFrame
             }
 
             var walking = row.Path.Count > 0 || row.RemainingMinutes > 0;
+            var circle = school.TalkCircleOf(row.PersonId);
             people.Add(new PresencePerson(
                 row.PersonId,
                 row.NodeId,
-                walking ? PresenceState.Walking : PresenceState.Here));
+                walking ? PresenceState.Walking : PresenceState.Here,
+                circle?.MemberIds ?? [],
+                circle?.TopicId ?? ""));
             counts[row.NodeId] = counts.GetValueOrDefault(row.NodeId) + 1;
         }
 

src/HSchool.Simulation/PresenceSystem.cs

@@ -621,3 +621,6 @@ public sealed record PresenceSnapshot(
     string? GoalId = null,
     float GoalWeight = 0f,
     string? GoalAction = null);
+
+/// <summary>Ids of an active talk circle. Names are resolved by the client, not here.</summary>
+public sealed record TalkCirclePresence(string TopicId, IReadOnlyList<string> MemberIds);

src/HSchool.Simulation/School.cs

@@ -218,6 +218,23 @@ public sealed class School : IDisposable
 
     public IReadOnlyList<PresenceSnapshot> CapturePresence() => PresenceSystem.Capture(this);
 
+    /// <summary>
+    /// Live circle for the presence frame and the person card. Null when this person is not talking.
+    /// Member ids include self and are sorted; names stay off the wire.
+    /// </summary>
+    public TalkCirclePresence? TalkCircleOf(string personId)
+    {
+        if (!TalkCircleByPerson.TryGetValue(personId, out var circleId)
+            || !TalkCirclesById.TryGetValue(circleId, out var circle))
+        {
+            return null;
+        }
+
+        var members = circle.Members.ToArray();
+        Array.Sort(members, StringComparer.Ordinal);
+        return new TalkCirclePresence(circle.TopicId, members);
+    }
+
     public void RestorePresence(IReadOnlyList<PresenceSnapshot>? saved) => PresenceSystem.Restore(this, saved);
 
     public bool IsCampusEmpty() => PresenceSystem.IsEmpty(this);

tests/HSchool.Simulation.Tests/TalkCircleTests.cs

@@ -26,6 +26,13 @@ public class TalkCircleTests
             var rows = school.CapturePresence();
             Assert.Equal(TalkActions.Chat, rows.Single(row => row.PersonId == first.Id).ActionId);
             Assert.Equal(TalkActions.Chat, rows.Single(row => row.PersonId == second.Id).ActionId);
+            var circle = school.TalkCircleOf(first.Id);
+            Assert.NotNull(circle);
+            Assert.Contains(first.Id, circle.MemberIds);
+            Assert.Contains(second.Id, circle.MemberIds);
+            Assert.False(string.IsNullOrEmpty(circle.TopicId));
+            Assert.Equal(circle.MemberIds, school.TalkCircleOf(second.Id)?.MemberIds);
+            Assert.Null(school.TalkCircleOf("missing"));
         }
     }