From 38afbcad365bff143235392697f22c6194b793a1 Mon Sep 17 00:00:00 2001
From: Leonid Pershin <lpershin@syntellect.ru>
Date: Tue, 18 Aug 2026 17:21:16 +0300
Subject: [PATCH] Update wire protocol to version 5, introducing pupil slots
 and item counts in map snapshots. Enhance UI components to display pupil
 slots and item counts in game screens and map editors. Revise localization
 strings for improved user guidance. Update tests to validate new
 functionalities and ensure robustness in handling room and item data.

---
 docs/protocol.md                              | 13 +++-
 src/HSchool.Client/src/i18n/strings.test.ts   |  1 +
 src/HSchool.Client/src/i18n/strings.ts        |  4 ++
 src/HSchool.Client/src/net/api.ts             |  4 +-
 src/HSchool.Client/src/net/protocol.test.ts   | 63 ++++++++++++++++++-
 src/HSchool.Client/src/net/protocol.ts        | 29 +++++++--
 src/HSchool.Client/src/style.css              | 11 ++++
 src/HSchool.Client/src/ui/gameScreen.ts       | 14 ++++-
 src/HSchool.Client/src/ui/mapEditor.ts        | 25 ++++++--
 src/HSchool.Content/CatalogLoader.cs          | 10 +++
 src/HSchool.Content/Defs.cs                   |  6 ++
 src/HSchool.Content/MapLayout.cs              |  6 ++
 src/HSchool.Content/MapValidator.cs           |  5 ++
 src/HSchool.Content/MapView.cs                | 46 +++++++++++---
 src/HSchool.Protocol/Messages.cs              |  8 ++-
 src/HSchool.Protocol/ProtocolCodec.cs         | 16 +++--
 src/HSchool.Protocol/ProtocolConstants.cs     |  2 +-
 src/HSchool.Server/Api/ModEndpoints.cs        | 15 +++--
 src/HSchool.Server/Game/SchoolWorker.cs       |  9 ++-
 .../mods/core/defs/rooms/academic.jsonc       |  2 +
 .../mods/core/defs/things/furniture.jsonc     |  4 +-
 .../mods/core/maps/default.jsonc              | 27 ++++----
 .../HSchool.AppHost.Tests/GameSocketTests.cs  |  4 ++
 tests/HSchool.Content.Tests/MapViewTests.cs   | 19 +++++-
 .../HSchool.Content.Tests/VanillaCoreTests.cs | 12 ++++
 .../ProtocolCodecTests.cs                     | 58 ++++++++++++++---
 26 files changed, 349 insertions(+), 64 deletions(-)

diff --git a/docs/protocol.md b/docs/protocol.md
index 4d0fcce..00b8781 100644
--- a/docs/protocol.md
+++ b/docs/protocol.md
@@ -1,4 +1,4 @@
-# Wire protocol v4
+# Wire protocol v5
 
 The client talks to the server two ways:
 
@@ -65,6 +65,10 @@ Placeable (non-abstract) types plus labels in `lang`, and the last-wins `maps/de
 `core` plus the listed extras. The server always prepends `core`. `mods` is a comma-separated
 list of extra pack ids; omit it for vanilla. Unknown extras return `400` `unknown-mod`.
 
+Room slots include a `count` (how many of the default thing the def places). Things carry
+`pupilSlots` — how many pupils that thing hosts for lessons. The create editor copies both onto
+the map instance; the snapshot's per-node pupil-slot total is computed on the server.
+
 `lang` is the same value Hello carries — not `Accept-Language`. Anything other than `en` is
 Russian.
 
@@ -243,9 +247,12 @@ Each node:
 | string | instance id |
 | string | parent id (empty for the yard) |
 | string | display name |
-| `u8` | item count, then that many strings |
+| `u16` | pupil slots — how many pupils can take a lesson here. Summed from things on the server. |
+| `u8` | item count, then that many records of: string name + `u8` count |
 | `u8` | position count, then that many strings |
 
+Item `count` is how many of that thing stand in the room (`Парта ×16` is one record, not sixteen). The client must not recompute pupil slots from items.
+
 ## Guarantees and limits
 
 - **Inbound** frames larger than 8 KiB are refused with close status `1009 MessageTooBig`. That
@@ -258,7 +265,7 @@ Each node:
   the oldest, because a stale clock is worthless once a newer one exists.
 - The map snapshot uses a separate reliable queue so ticks cannot crowd it out.
 
-## Not in v4 yet
+## Not in v5 yet
 
 Authentication, Sit orders, an event log, and `OpenLocation` on the server — the tree is filtered
 on the client from the snapshot. The school's ECS world is created but still empty.
diff --git a/src/HSchool.Client/src/i18n/strings.test.ts b/src/HSchool.Client/src/i18n/strings.test.ts
index 117e602..fcd17d8 100644
--- a/src/HSchool.Client/src/i18n/strings.test.ts
+++ b/src/HSchool.Client/src/i18n/strings.test.ts
@@ -20,6 +20,7 @@ describe('t', () => {
   it('interpolates placeholders', () => {
     setLocale('en');
     expect(t('schoolCount', { current: 2, max: 6 })).toBe('Schools: 2 of 6.');
+    expect(t('pupilSlots', { count: 16 })).toBe('Pupil places: 16');
   });
 });
 
diff --git a/src/HSchool.Client/src/i18n/strings.ts b/src/HSchool.Client/src/i18n/strings.ts
index 1a1fb62..b0408ac 100644
--- a/src/HSchool.Client/src/i18n/strings.ts
+++ b/src/HSchool.Client/src/i18n/strings.ts
@@ -62,6 +62,7 @@ const ru = {
   addRoom: 'Добавить комнату',
   removeRoom: 'Удалить комнату',
   slotEmpty: '— пусто —',
+  slotCount: 'Количество',
 
   backToMenu: '← В главное меню',
   pause: 'Пауза',
@@ -76,6 +77,7 @@ const ru = {
   locationActivities: 'Сейчас',
   locationPositions: 'Должности',
   itemsEmpty: 'Пусто.',
+  pupilSlots: 'Ученических мест: {count}',
   charactersEmpty: 'Никого нет.',
   activitiesEmpty: 'Ничего не происходит.',
   positionsEmpty: 'Нет должностей.',
@@ -145,6 +147,7 @@ const en: Messages = {
   addRoom: 'Add room',
   removeRoom: 'Remove room',
   slotEmpty: '— empty —',
+  slotCount: 'Count',
 
   backToMenu: '← Main menu',
   pause: 'Pause',
@@ -159,6 +162,7 @@ const en: Messages = {
   locationActivities: 'Now',
   locationPositions: 'Positions',
   itemsEmpty: 'Empty.',
+  pupilSlots: 'Pupil places: {count}',
   charactersEmpty: 'Nobody here.',
   activitiesEmpty: 'Nothing is happening.',
   positionsEmpty: 'No positions.',
diff --git a/src/HSchool.Client/src/net/api.ts b/src/HSchool.Client/src/net/api.ts
index fd193ec..cb482de 100644
--- a/src/HSchool.Client/src/net/api.ts
+++ b/src/HSchool.Client/src/net/api.ts
@@ -71,11 +71,13 @@ export interface ModInfo {
 export interface DefInfo {
   readonly defName: string;
   readonly label: string;
+  readonly pupilSlots?: number;
 }
 
 export interface RoomSlotInfo {
   readonly key: string;
   readonly thing: string;
+  readonly count: number;
 }
 
 export interface RoomInfo {
@@ -95,7 +97,7 @@ export interface MapLayout {
     building: string;
     floor: string;
     label?: string;
-    slots?: { key: string; thing: string }[];
+    slots?: { key: string; thing: string; count?: number }[];
   }[];
   links: { a: string; b: string }[];
 }
diff --git a/src/HSchool.Client/src/net/protocol.test.ts b/src/HSchool.Client/src/net/protocol.test.ts
index 573957d..940414d 100644
--- a/src/HSchool.Client/src/net/protocol.test.ts
+++ b/src/HSchool.Client/src/net/protocol.test.ts
@@ -129,7 +129,7 @@ describe('decodeServerMessage', () => {
     const id = encoder.encode('yard');
     const parent = encoder.encode('');
     const name = encoder.encode('Двор');
-    const buffer = new ArrayBuffer(7 + 1 + 2 + id.length + 2 + parent.length + 2 + name.length + 1 + 1);
+    const buffer = new ArrayBuffer(7 + 1 + 2 + id.length + 2 + parent.length + 2 + name.length + 2 + 1 + 1);
     const view = new DataView(buffer);
     view.setUint8(0, MessageType.ServerMapSnapshot);
     view.setInt32(1, 7, true);
@@ -147,6 +147,8 @@ describe('decodeServerMessage', () => {
     offset += 2;
     new Uint8Array(buffer).set(name, offset);
     offset += name.length;
+    view.setUint16(offset, 0, true);
+    offset += 2;
     view.setUint8(offset, 0);
     offset += 1;
     view.setUint8(offset, 0);
@@ -155,7 +157,64 @@ describe('decodeServerMessage', () => {
       type: 'map-snapshot',
       schoolId: 7,
       nodes: [
-        { kind: 0, id: 'yard', parentId: '', name: 'Двор', items: [], positions: [] },
+        { kind: 0, id: 'yard', parentId: '', name: 'Двор', pupilSlots: 0, items: [], positions: [] },
+      ],
+    });
+  });
+
+  it('reads stacked items and pupil slots at the documented offsets', () => {
+    const encoder = new TextEncoder();
+    const id = encoder.encode('classroom-1a');
+    const parent = encoder.encode('floor-1');
+    const name = encoder.encode('Класс 1A');
+    const itemName = encoder.encode('Парта');
+    const buffer = new ArrayBuffer(
+      7 + 1 + 2 + id.length + 2 + parent.length + 2 + name.length + 2 + 1 + 2 + itemName.length + 1 + 1,
+    );
+    const view = new DataView(buffer);
+    view.setUint8(0, MessageType.ServerMapSnapshot);
+    view.setInt32(1, 1, true);
+    view.setUint16(5, 1, true);
+    let offset = 7;
+    view.setUint8(offset, 3);
+    offset += 1;
+    view.setUint16(offset, id.length, true);
+    offset += 2;
+    new Uint8Array(buffer).set(id, offset);
+    offset += id.length;
+    view.setUint16(offset, parent.length, true);
+    offset += 2;
+    new Uint8Array(buffer).set(parent, offset);
+    offset += parent.length;
+    view.setUint16(offset, name.length, true);
+    offset += 2;
+    new Uint8Array(buffer).set(name, offset);
+    offset += name.length;
+    view.setUint16(offset, 16, true);
+    offset += 2;
+    view.setUint8(offset, 1);
+    offset += 1;
+    view.setUint16(offset, itemName.length, true);
+    offset += 2;
+    new Uint8Array(buffer).set(itemName, offset);
+    offset += itemName.length;
+    view.setUint8(offset, 16);
+    offset += 1;
+    view.setUint8(offset, 0);
+
+    expect(decodeServerMessage(buffer)).toEqual({
+      type: 'map-snapshot',
+      schoolId: 1,
+      nodes: [
+        {
+          kind: 3,
+          id: 'classroom-1a',
+          parentId: 'floor-1',
+          name: 'Класс 1A',
+          pupilSlots: 16,
+          items: [{ name: 'Парта', count: 16 }],
+          positions: [],
+        },
       ],
     });
   });
diff --git a/src/HSchool.Client/src/net/protocol.ts b/src/HSchool.Client/src/net/protocol.ts
index 6aa312d..cb01956 100644
--- a/src/HSchool.Client/src/net/protocol.ts
+++ b/src/HSchool.Client/src/net/protocol.ts
@@ -5,7 +5,7 @@
  * changed together and documented in `docs/protocol.md`. All numbers are little-endian.
  */
 
-export const PROTOCOL_VERSION = 4;
+export const PROTOCOL_VERSION = 5;
 
 export const MessageType = {
   ClientHello: 0x01,
@@ -69,12 +69,18 @@ export const MapNodeKind = {
   Room: 3,
 } as const;
 
+export interface MapSnapshotItem {
+  readonly name: string;
+  readonly count: number;
+}
+
 export interface MapSnapshotNode {
   readonly kind: number;
   readonly id: string;
   readonly parentId: string;
   readonly name: string;
-  readonly items: readonly string[];
+  readonly pupilSlots: number;
+  readonly items: readonly MapSnapshotItem[];
   readonly positions: readonly string[];
 }
 
@@ -236,13 +242,18 @@ function decodeMapSnapshot(view: DataView): MapSnapshotMessage {
     offset = parentId.next;
     const name = readString(view, offset);
     offset = name.next;
+    ensure(view, offset + 2);
+    const pupilSlots = view.getUint16(offset, true);
+    offset += 2;
     const itemCount = readU8(view, offset);
     offset += 1;
-    const items: string[] = [];
+    const items: MapSnapshotItem[] = [];
     for (let item = 0; item < itemCount; item++) {
       const value = readString(view, offset);
-      items.push(value.text);
       offset = value.next;
+      const count = readU8(view, offset);
+      offset += 1;
+      items.push({ name: value.text, count });
     }
 
     const positionCount = readU8(view, offset);
@@ -254,7 +265,15 @@ function decodeMapSnapshot(view: DataView): MapSnapshotMessage {
       offset = value.next;
     }
 
-    nodes.push({ kind, id: id.text, parentId: parentId.text, name: name.text, items, positions });
+    nodes.push({
+      kind,
+      id: id.text,
+      parentId: parentId.text,
+      name: name.text,
+      pupilSlots,
+      items,
+      positions,
+    });
   }
 
   return { type: 'map-snapshot', schoolId, nodes };
diff --git a/src/HSchool.Client/src/style.css b/src/HSchool.Client/src/style.css
index cec7cae..df43785 100644
--- a/src/HSchool.Client/src/style.css
+++ b/src/HSchool.Client/src/style.css
@@ -317,6 +317,12 @@ body {
   font-size: 13px;
 }
 
+.panel__meta {
+  margin: 6px 0 0;
+  color: var(--text-muted);
+  font-size: 13px;
+}
+
 .tree {
   margin: 0;
   padding: 0;
@@ -542,6 +548,11 @@ body {
   flex: 1;
 }
 
+.field__row > .input--count {
+  flex: 0 0 4.5rem;
+  width: 4.5rem;
+}
+
 .field .hint {
   margin: 0;
   font-size: 13px;
diff --git a/src/HSchool.Client/src/ui/gameScreen.ts b/src/HSchool.Client/src/ui/gameScreen.ts
index 6fa5140..c1c90a0 100644
--- a/src/HSchool.Client/src/ui/gameScreen.ts
+++ b/src/HSchool.Client/src/ui/gameScreen.ts
@@ -1,4 +1,4 @@
-import { CLOCK_SPEEDS, type ClockMessage, type MapSnapshotNode } from '../net/protocol.ts';
+import { CLOCK_SPEEDS, type ClockMessage, type MapSnapshotItem, type MapSnapshotNode } from '../net/protocol.ts';
 import { formatGameDate, formatGameTimeOfDay, formatGameWeekday } from '../format/gameTime.ts';
 import { t } from '../i18n/strings.ts';
 import type { School } from '../net/api.ts';
@@ -36,6 +36,7 @@ export class GameScreen {
   private readonly itemsHeading = el('h3', { class: 'panel__section-title' });
   private readonly itemsEmpty = el('p', { class: 'panel__empty' });
   private readonly itemsList = el('ul', { class: 'panel__list' });
+  private readonly pupilSlotsLine = el('p', { class: 'panel__meta' });
   private readonly charactersHeading = el('h3', { class: 'panel__section-title' });
   private readonly charactersEmpty = el('p', { class: 'panel__empty' });
   private readonly activitiesHeading = el('h3', { class: 'panel__section-title' });
@@ -101,7 +102,7 @@ export class GameScreen {
             'div',
             { class: 'panel__body' },
             this.locationName,
-            el('div', { class: 'panel__section' }, this.itemsHeading, this.itemsEmpty, this.itemsList),
+            el('div', { class: 'panel__section' }, this.itemsHeading, this.itemsEmpty, this.itemsList, this.pupilSlotsLine),
             el('div', { class: 'panel__section' }, this.charactersHeading, this.charactersEmpty),
             el('div', { class: 'panel__section' }, this.activitiesHeading, this.activitiesEmpty),
             el('div', { class: 'panel__section' }, this.positionsHeading, this.positionsEmpty, this.positionsList),
@@ -210,7 +211,10 @@ export class GameScreen {
 
     const node = this.nodes.find((candidate) => candidate.id === this.selectedId);
     this.locationName.textContent = node?.name ?? '';
-    paintList(this.itemsList, this.itemsEmpty, node?.items ?? []);
+    paintList(this.itemsList, this.itemsEmpty, (node?.items ?? []).map(formatItem));
+    const pupilSlots = node?.pupilSlots ?? 0;
+    this.pupilSlotsLine.hidden = pupilSlots <= 0;
+    this.pupilSlotsLine.textContent = pupilSlots > 0 ? t('pupilSlots', { count: pupilSlots }) : '';
     paintList(this.positionsList, this.positionsEmpty, node?.positions ?? []);
   }
 
@@ -236,6 +240,10 @@ function childrenOf(nodes: readonly MapSnapshotNode[], parentId: string): MapSna
   return nodes.filter((node) => node.parentId === parentId);
 }
 
+function formatItem(item: MapSnapshotItem): string {
+  return item.count === 1 ? item.name : `${item.name} ×${item.count}`;
+}
+
 function paintList(list: HTMLUListElement, empty: HTMLParagraphElement, values: readonly string[]): void {
   clear(list);
   empty.hidden = values.length > 0;
diff --git a/src/HSchool.Client/src/ui/mapEditor.ts b/src/HSchool.Client/src/ui/mapEditor.ts
index 18b7c61..e5104d1 100644
--- a/src/HSchool.Client/src/ui/mapEditor.ts
+++ b/src/HSchool.Client/src/ui/mapEditor.ts
@@ -116,15 +116,29 @@ export function mapEditor(options: MapEditorOptions): {
 
       const fill = (room.slots ?? []).find((candidate) => candidate.key === slot.key);
       select.value = fill?.thing ?? '';
-      select.addEventListener('change', () => {
+
+      const countInput = el('input', { class: 'input input--count', type: 'number' });
+      countInput.min = '1';
+      countInput.max = '255';
+      countInput.step = '1';
+      countInput.value = String(fill?.count ?? slot.count ?? 1);
+      countInput.title = t('slotCount');
+
+      const writeSlot = (): void => {
         const slots = [...(room.slots ?? [])].filter((candidate) => candidate.key !== slot.key);
         if (select.value !== '') {
-          slots.push({ key: slot.key, thing: select.value });
+          const parsed = Number.parseInt(countInput.value, 10);
+          const count = Number.isFinite(parsed) ? Math.min(255, Math.max(1, parsed)) : (slot.count ?? 1);
+          countInput.value = String(count);
+          slots.push({ key: slot.key, thing: select.value, count });
         }
 
         room.slots = slots;
         emit();
-      });
+      };
+
+      select.addEventListener('change', writeSlot);
+      countInput.addEventListener('change', writeSlot);
 
       rows.push(
         el(
@@ -132,6 +146,7 @@ export function mapEditor(options: MapEditorOptions): {
           { class: 'field__row' },
           el('span', { class: 'field__label', text: slot.key }),
           select,
+          countInput,
         ),
       );
     }
@@ -288,8 +303,8 @@ function hasLink(map: MapLayout, a: string, b: string): boolean {
   );
 }
 
-function defaultSlots(def: RoomInfo): { key: string; thing: string }[] {
-  return def.slots.map((slot) => ({ key: slot.key, thing: slot.thing }));
+function defaultSlots(def: RoomInfo): { key: string; thing: string; count: number }[] {
+  return def.slots.map((slot) => ({ key: slot.key, thing: slot.thing, count: slot.count }));
 }
 
 function nextId(prefix: string, used: Set<string>): string {
diff --git a/src/HSchool.Content/CatalogLoader.cs b/src/HSchool.Content/CatalogLoader.cs
index b4bd9af..721a23c 100644
--- a/src/HSchool.Content/CatalogLoader.cs
+++ b/src/HSchool.Content/CatalogLoader.cs
@@ -352,6 +352,11 @@ public sealed class CatalogLoader
     {
         foreach (var thing in catalog.Things.Values)
         {
+            if (thing.PupilSlots < 0 || thing.PupilSlots > byte.MaxValue)
+            {
+                throw new ContentLoadException($"ThingDef '{thing.DefName}' pupilSlots must be 0–{byte.MaxValue}.");
+            }
+
             foreach (var action in thing.Actions)
             {
                 if (!catalog.Actions.ContainsKey(action))
@@ -369,6 +374,11 @@ public sealed class CatalogLoader
                 {
                     throw new ContentLoadException($"RoomDef '{room.DefName}' slot '{slot.Key}' references unknown ThingDef '{slot.Thing}'.");
                 }
+
+                if (slot.Count < 0 || slot.Count > byte.MaxValue)
+                {
+                    throw new ContentLoadException($"RoomDef '{room.DefName}' slot '{slot.Key}' count must be 0–{byte.MaxValue}.");
+                }
             }
 
             foreach (var position in room.Positions)
diff --git a/src/HSchool.Content/Defs.cs b/src/HSchool.Content/Defs.cs
index b00286d..24864cc 100644
--- a/src/HSchool.Content/Defs.cs
+++ b/src/HSchool.Content/Defs.cs
@@ -27,6 +27,12 @@ public sealed class ActionDef : Def;
 public sealed class ThingDef : Def
 {
     public IReadOnlyList<string> Actions { get; init; } = [];
+
+    /// <summary>
+    /// How many pupils this thing hosts for lessons. Zero for teacher's furniture — a chair
+    /// must not inflate class size just because someone sits in it.
+    /// </summary>
+    public int PupilSlots { get; init; }
 }
 
 public sealed class PositionDef : Def;
diff --git a/src/HSchool.Content/MapLayout.cs b/src/HSchool.Content/MapLayout.cs
index dd18dee..ec0ef11 100644
--- a/src/HSchool.Content/MapLayout.cs
+++ b/src/HSchool.Content/MapLayout.cs
@@ -63,6 +63,12 @@ public sealed class SlotFill
     public required string Key { get; init; }
 
     public required string Thing { get; init; }
+
+    /// <summary>
+    /// How many of <see cref="Thing"/> occupy this slot. Missing or non-positive JSON is 1, so
+    /// older maps without a count still round-trip.
+    /// </summary>
+    public int Count { get; init; } = 1;
 }
 
 public sealed class MapLink
diff --git a/src/HSchool.Content/MapValidator.cs b/src/HSchool.Content/MapValidator.cs
index b916970..fe8ef2d 100644
--- a/src/HSchool.Content/MapValidator.cs
+++ b/src/HSchool.Content/MapValidator.cs
@@ -140,6 +140,11 @@ public static class MapValidator
             {
                 throw new MapValidationException($"Room '{room.Id}' slot '{fill.Key}' uses unknown or abstract ThingDef '{fill.Thing}'.");
             }
+
+            if (fill.Count > byte.MaxValue)
+            {
+                throw new MapValidationException($"Room '{room.Id}' slot '{fill.Key}' count {fill.Count} is above {byte.MaxValue}.");
+            }
         }
     }
 
diff --git a/src/HSchool.Content/MapView.cs b/src/HSchool.Content/MapView.cs
index d7fefc6..b861f90 100644
--- a/src/HSchool.Content/MapView.cs
+++ b/src/HSchool.Content/MapView.cs
@@ -21,11 +21,17 @@ public sealed class MapViewNode
 
     public required string Name { get; init; }
 
-    public IReadOnlyList<string> Items { get; init; } = [];
+    public IReadOnlyList<MapViewItem> Items { get; init; } = [];
+
+    /// <summary>Sum of <c>ThingDef.PupilSlots × fill count</c> for this node. Zero off rooms.</summary>
+    public int PupilSlots { get; init; }
 
     public IReadOnlyList<string> Positions { get; init; } = [];
 }
 
+/// <summary>One stacked thing in a room. The client formats <c>Парта ×16</c>; this is the data.</summary>
+public sealed record MapViewItem(string Name, int Count);
+
 /// <summary>
 /// Builds the location tree the client draws. Labels come from the frozen catalog in the
 /// requested locale; people and in-place activities are not part of this view.
@@ -47,6 +53,7 @@ public static class MapView
                 parentId: string.Empty,
                 LabelOf(catalog, locale, DefKind.Territory, territory.Def),
                 items: [],
+                pupilSlots: 0,
                 PositionsOf(catalog, locale, DefKind.Territory, territory.Def)),
         };
 
@@ -58,6 +65,7 @@ public static class MapView
                 territory.Id,
                 LabelOf(catalog, locale, DefKind.Building, building.Def),
                 [],
+                pupilSlots: 0,
                 PositionsOf(catalog, locale, DefKind.Building, building.Def)));
         }
 
@@ -69,23 +77,20 @@ public static class MapView
                 floor.Building,
                 FloorName(catalog, locale, floor),
                 [],
+                pupilSlots: 0,
                 PositionsOf(catalog, locale, DefKind.Floor, floor.Def)));
         }
 
         foreach (var room in map.Rooms)
         {
-            var items = new List<string>(room.Slots.Count);
-            foreach (var fill in room.Slots)
-            {
-                items.Add(LabelOf(catalog, locale, DefKind.Thing, fill.Thing));
-            }
-
+            var (items, pupilSlots) = RoomContents(catalog, locale, room);
             nodes.Add(Node(
                 MapNodeKind.Room,
                 room.Id,
                 room.Floor,
                 RoomName(catalog, locale, room),
                 items,
+                pupilSlots,
                 PositionsOf(catalog, locale, DefKind.Room, room.Def)));
         }
 
@@ -97,7 +102,8 @@ public static class MapView
         string id,
         string parentId,
         string name,
-        IReadOnlyList<string> items,
+        IReadOnlyList<MapViewItem> items,
+        int pupilSlots,
         IReadOnlyList<string> positions) =>
         new()
         {
@@ -106,9 +112,33 @@ public static class MapView
             ParentId = parentId,
             Name = name,
             Items = items,
+            PupilSlots = pupilSlots,
             Positions = positions,
         };
 
+    private static (IReadOnlyList<MapViewItem> Items, int PupilSlots) RoomContents(
+        DefCatalog catalog,
+        string locale,
+        RoomNode room)
+    {
+        var items = new List<MapViewItem>(room.Slots.Count);
+        var pupilSlots = 0L;
+        foreach (var fill in room.Slots)
+        {
+            var count = SlotQuantity(fill.Count);
+            items.Add(new MapViewItem(LabelOf(catalog, locale, DefKind.Thing, fill.Thing), count));
+            if (catalog.Things.TryGetValue(fill.Thing, out var thing) && thing.PupilSlots > 0)
+            {
+                pupilSlots += (long)thing.PupilSlots * count;
+            }
+        }
+
+        return (items, (int)Math.Clamp(pupilSlots, 0, ushort.MaxValue));
+    }
+
+    private static int SlotQuantity(int count) =>
+        count < 1 ? 1 : Math.Min(count, byte.MaxValue);
+
     /// <summary>
     /// A floor's <see cref="FloorNode.Label"/> is its designation, not a replacement name — the
     /// vanilla map says "1". On its own that is a stray digit in the client's tree, so it follows
diff --git a/src/HSchool.Protocol/Messages.cs b/src/HSchool.Protocol/Messages.cs
index cb852b2..d6e1b3e 100644
--- a/src/HSchool.Protocol/Messages.cs
+++ b/src/HSchool.Protocol/Messages.cs
@@ -44,15 +44,21 @@ public readonly record struct ServerSchoolGoneMessage(int SchoolId);
 /// <summary>
 /// Tree node in a map snapshot. Kind is <c>0</c> territory, <c>1</c> building, <c>2</c> floor, <c>3</c> room.
 /// <paramref name="ParentId"/> is empty for the yard.
+/// <paramref name="PupilSlots"/> is how many pupils can take a lesson here — summed from things
+/// on the server, not by the client.
 /// </summary>
 public sealed record MapSnapshotNode(
     byte Kind,
     string Id,
     string ParentId,
     string Name,
-    IReadOnlyList<string> Items,
+    ushort PupilSlots,
+    IReadOnlyList<MapSnapshotItem> Items,
     IReadOnlyList<string> Positions);
 
+/// <summary>One stacked thing in a room. <paramref name="Count"/> is 1–255.</summary>
+public sealed record MapSnapshotItem(string Name, byte Count);
+
 /// <summary>
 /// One school's map, labelled in the Hello locale. Sent once when that school is opened, not every tick.
 /// People and in-place activities are omitted — the client keeps those sections empty.
diff --git a/src/HSchool.Protocol/ProtocolCodec.cs b/src/HSchool.Protocol/ProtocolCodec.cs
index a9b3971..2200130 100644
--- a/src/HSchool.Protocol/ProtocolCodec.cs
+++ b/src/HSchool.Protocol/ProtocolCodec.cs
@@ -116,11 +116,12 @@ public static class ProtocolCodec
         {
             size += sizeof(byte);
             size += StringSize(node.Id) + StringSize(node.ParentId) + StringSize(node.Name);
+            size += sizeof(ushort);
 
             size += sizeof(byte);
             foreach (var item in node.Items)
             {
-                size += StringSize(item);
+                size += StringSize(item.Name) + sizeof(byte);
             }
 
             size += sizeof(byte);
@@ -156,10 +157,12 @@ public static class ProtocolCodec
             writer.WriteString(node.Id);
             writer.WriteString(node.ParentId);
             writer.WriteString(node.Name);
+            writer.WriteUInt16(node.PupilSlots);
             writer.WriteByte((byte)node.Items.Count);
             foreach (var item in node.Items)
             {
-                writer.WriteString(item);
+                writer.WriteString(item.Name);
+                writer.WriteByte(item.Count);
             }
 
             writer.WriteByte((byte)node.Positions.Count);
@@ -263,11 +266,14 @@ public static class ProtocolCodec
             var id = reader.ReadString();
             var parentId = reader.ReadString();
             var name = reader.ReadString();
+            var pupilSlots = reader.ReadUInt16();
             var itemCount = reader.ReadByte();
-            var items = new string[itemCount];
+            var items = new MapSnapshotItem[itemCount];
             for (var item = 0; item < itemCount; item++)
             {
-                items[item] = reader.ReadString();
+                var itemName = reader.ReadString();
+                var count = reader.ReadByte();
+                items[item] = new MapSnapshotItem(itemName, count);
             }
 
             var positionCount = reader.ReadByte();
@@ -277,7 +283,7 @@ public static class ProtocolCodec
                 positions[position] = reader.ReadString();
             }
 
-            nodes[i] = new MapSnapshotNode(kind, id, parentId, name, items, positions);
+            nodes[i] = new MapSnapshotNode(kind, id, parentId, name, pupilSlots, items, positions);
         }
 
         return new ServerMapSnapshotMessage(schoolId, nodes);
diff --git a/src/HSchool.Protocol/ProtocolConstants.cs b/src/HSchool.Protocol/ProtocolConstants.cs
index 1455f02..dcd7dae 100644
--- a/src/HSchool.Protocol/ProtocolConstants.cs
+++ b/src/HSchool.Protocol/ProtocolConstants.cs
@@ -4,7 +4,7 @@ namespace HSchool.Protocol;
 public static class ProtocolConstants
 {
     /// <summary>Bumped on every breaking change to the binary layout.</summary>
-    public const byte Version = 4;
+    public const byte Version = 5;
 
     /// <summary>Upper bound for a single WebSocket frame accepted by the server.</summary>
     public const int MaxMessageSize = 8 * 1024;
diff --git a/src/HSchool.Server/Api/ModEndpoints.cs b/src/HSchool.Server/Api/ModEndpoints.cs
index 848b38a..7ecffa5 100644
--- a/src/HSchool.Server/Api/ModEndpoints.cs
+++ b/src/HSchool.Server/Api/ModEndpoints.cs
@@ -94,7 +94,7 @@ internal sealed record CatalogResponse(
             Placeable(catalog.Buildings.Values, catalog, locale),
             Placeable(catalog.Floors.Values, catalog, locale),
             PlaceableRooms(catalog, locale),
-            Placeable(catalog.Things.Values, catalog, locale),
+            PlaceableThings(catalog, locale),
             map);
 
     private static IReadOnlyList<DefInfoResponse> Placeable<T>(IEnumerable<T> defs, DefCatalog catalog, string locale)
@@ -105,6 +105,13 @@ internal sealed record CatalogResponse(
             .Select(def => new DefInfoResponse(def.DefName, catalog.Label(locale, def)))
             .ToArray();
 
+    private static IReadOnlyList<DefInfoResponse> PlaceableThings(DefCatalog catalog, string locale) =>
+        catalog.Things.Values
+            .Where(def => !def.Abstract)
+            .OrderBy(def => def.DefName, StringComparer.Ordinal)
+            .Select(def => new DefInfoResponse(def.DefName, catalog.Label(locale, def), def.PupilSlots))
+            .ToArray();
+
     private static IReadOnlyList<RoomInfoResponse> PlaceableRooms(DefCatalog catalog, string locale) =>
         catalog.Rooms.Values
             .Where(def => !def.Abstract)
@@ -112,12 +119,12 @@ internal sealed record CatalogResponse(
             .Select(def => new RoomInfoResponse(
                 def.DefName,
                 catalog.Label(locale, def),
-                def.Slots.Select(slot => new RoomSlotInfo(slot.Key, slot.Thing)).ToArray(),
+                def.Slots.Select(slot => new RoomSlotInfo(slot.Key, slot.Thing, slot.Count)).ToArray(),
                 def.Positions.ToArray()))
             .ToArray();
 }
 
-internal sealed record DefInfoResponse(string DefName, string Label);
+internal sealed record DefInfoResponse(string DefName, string Label, int PupilSlots = 0);
 
 internal sealed record RoomInfoResponse(
     string DefName,
@@ -125,4 +132,4 @@ internal sealed record RoomInfoResponse(
     IReadOnlyList<RoomSlotInfo> Slots,
     IReadOnlyList<string> Positions);
 
-internal sealed record RoomSlotInfo(string Key, string Thing);
+internal sealed record RoomSlotInfo(string Key, string Thing, int Count);
diff --git a/src/HSchool.Server/Game/SchoolWorker.cs b/src/HSchool.Server/Game/SchoolWorker.cs
index 6664573..b6851b5 100644
--- a/src/HSchool.Server/Game/SchoolWorker.cs
+++ b/src/HSchool.Server/Game/SchoolWorker.cs
@@ -449,12 +449,19 @@ internal sealed class SchoolWorker
         for (var i = 0; i < view.Count; i++)
         {
             var node = view[i];
+            var items = new MapSnapshotItem[node.Items.Count];
+            for (var item = 0; item < node.Items.Count; item++)
+            {
+                items[item] = new MapSnapshotItem(node.Items[item].Name, (byte)node.Items[item].Count);
+            }
+
             nodes[i] = new MapSnapshotNode(
                 (byte)node.Kind,
                 node.Id,
                 node.ParentId,
                 node.Name,
-                node.Items,
+                (ushort)node.PupilSlots,
+                items,
                 node.Positions);
         }
 
diff --git a/src/HSchool.Server/mods/core/defs/rooms/academic.jsonc b/src/HSchool.Server/mods/core/defs/rooms/academic.jsonc
index 25cc2f8..3ea58de 100644
--- a/src/HSchool.Server/mods/core/defs/rooms/academic.jsonc
+++ b/src/HSchool.Server/mods/core/defs/rooms/academic.jsonc
@@ -4,6 +4,7 @@
     "slots": [
       { "key": "board", "thing": "Blackboard" },
       { "key": "teacherDesk", "thing": "Desk" },
+      { "key": "teacherChair", "thing": "Chair" },
       { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
     ],
     "positions": ["Teacher"],
@@ -22,6 +23,7 @@
     "defName": "ComputerLab",
     "slots": [
       { "key": "teacherDesk", "thing": "Desk" },
+      { "key": "teacherChair", "thing": "Chair" },
       { "key": "computers", "thing": "Computer", "count": 12 },
     ],
     "positions": ["Teacher"],
diff --git a/src/HSchool.Server/mods/core/defs/things/furniture.jsonc b/src/HSchool.Server/mods/core/defs/things/furniture.jsonc
index 5876694..1f9825b 100644
--- a/src/HSchool.Server/mods/core/defs/things/furniture.jsonc
+++ b/src/HSchool.Server/mods/core/defs/things/furniture.jsonc
@@ -1,10 +1,10 @@
 [
   { "defName": "Blackboard" },
-  { "defName": "StudentDesk", "parent": "Desk", "actions": ["Sit"] },
+  { "defName": "StudentDesk", "parent": "Desk", "actions": ["Sit"], "pupilSlots": 1 },
   { "defName": "Bookshelf" },
   { "defName": "DiningTable" },
   { "defName": "Bench", "actions": ["Sit"] },
-  { "defName": "Computer" },
+  { "defName": "Computer", "pupilSlots": 1 },
   { "defName": "MedicalCouch" },
   { "defName": "Locker" },
 ]
diff --git a/src/HSchool.Server/mods/core/maps/default.jsonc b/src/HSchool.Server/mods/core/maps/default.jsonc
index 15e18ff..44252fa 100644
--- a/src/HSchool.Server/mods/core/maps/default.jsonc
+++ b/src/HSchool.Server/mods/core/maps/default.jsonc
@@ -23,7 +23,7 @@
       "slots": [
         { "key": "directorChair", "thing": "DirectorsChair" },
         { "key": "desk", "thing": "Desk" },
-        { "key": "guestChair", "thing": "Chair" },
+        { "key": "guestChair", "thing": "Chair", "count": 2 },
       ],
     },
     {
@@ -43,7 +43,7 @@
       "floor": "floor-1",
       "slots": [
         { "key": "table", "thing": "DiningTable" },
-        { "key": "chairs", "thing": "Chair" },
+        { "key": "chairs", "thing": "Chair", "count": 6 },
       ],
     },
     {
@@ -55,7 +55,8 @@
       "slots": [
         { "key": "board", "thing": "Blackboard" },
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "studentDesks", "thing": "StudentDesk" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
       ],
     },
     {
@@ -67,7 +68,8 @@
       "slots": [
         { "key": "board", "thing": "Blackboard" },
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "studentDesks", "thing": "StudentDesk" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
       ],
     },
     {
@@ -77,7 +79,7 @@
       "floor": "floor-1",
       "slots": [
         { "key": "counter", "thing": "DiningTable" },
-        { "key": "seats", "thing": "Chair" },
+        { "key": "seats", "thing": "Chair", "count": 8 },
       ],
     },
     { "id": "restroom-1", "def": "Restroom", "building": "main", "floor": "floor-1", "label": "1" },
@@ -102,7 +104,8 @@
       "slots": [
         { "key": "board", "thing": "Blackboard" },
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "studentDesks", "thing": "StudentDesk" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
       ],
     },
     {
@@ -114,7 +117,8 @@
       "slots": [
         { "key": "board", "thing": "Blackboard" },
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "studentDesks", "thing": "StudentDesk" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "studentDesks", "thing": "StudentDesk", "count": 16 },
       ],
     },
     {
@@ -124,7 +128,7 @@
       "floor": "floor-2",
       "slots": [
         { "key": "desk", "thing": "Desk" },
-        { "key": "shelves", "thing": "Bookshelf" },
+        { "key": "shelves", "thing": "Bookshelf", "count": 4 },
       ],
     },
     {
@@ -134,7 +138,8 @@
       "floor": "floor-2",
       "slots": [
         { "key": "teacherDesk", "thing": "Desk" },
-        { "key": "computers", "thing": "Computer" },
+        { "key": "teacherChair", "thing": "Chair" },
+        { "key": "computers", "thing": "Computer", "count": 12 },
       ],
     },
     { "id": "restroom-2", "def": "Restroom", "building": "main", "floor": "floor-2", "label": "2" },
@@ -144,7 +149,7 @@
       "building": "gym",
       "floor": "gym-floor",
       "slots": [
-        { "key": "benches", "thing": "Bench" },
+        { "key": "benches", "thing": "Bench", "count": 4 },
       ],
     },
     {
@@ -153,7 +158,7 @@
       "building": "gym",
       "floor": "gym-floor",
       "slots": [
-        { "key": "lockers", "thing": "Locker" },
+        { "key": "lockers", "thing": "Locker", "count": 12 },
       ],
     },
   ],
diff --git a/tests/HSchool.AppHost.Tests/GameSocketTests.cs b/tests/HSchool.AppHost.Tests/GameSocketTests.cs
index 2f723a1..f47f643 100644
--- a/tests/HSchool.AppHost.Tests/GameSocketTests.cs
+++ b/tests/HSchool.AppHost.Tests/GameSocketTests.cs
@@ -106,6 +106,10 @@ public class GameSocketTests(AppHostFixture fixture)
         Assert.Equal("floor-1", office.ParentId);
         Assert.Contains("Директор", office.Positions);
         Assert.NotEmpty(office.Items);
+        var classroom = Assert.Single(snapshot.Nodes, node => node.Id == "classroom-1a");
+        Assert.Equal(16, classroom.PupilSlots);
+        Assert.Contains(classroom.Items, item => item.Name == "Парта" && item.Count == 16);
+        Assert.Contains(classroom.Items, item => item.Name == "Стул" && item.Count == 1);
     }
 
     [Fact]
diff --git a/tests/HSchool.Content.Tests/MapViewTests.cs b/tests/HSchool.Content.Tests/MapViewTests.cs
index e0aef1f..a46e08f 100644
--- a/tests/HSchool.Content.Tests/MapViewTests.cs
+++ b/tests/HSchool.Content.Tests/MapViewTests.cs
@@ -23,12 +23,17 @@ public class MapViewTests
 
         var officeRu = ru.Single(node => node.Id == "principals-office");
         Assert.Equal("Кабинет директора", officeRu.Name);
-        Assert.Equal(["Кресло директора", "Стол", "Стул"], officeRu.Items);
+        Assert.Equal(
+            [new MapViewItem("Кресло директора", 1), new MapViewItem("Стол", 1), new MapViewItem("Стул", 2)],
+            officeRu.Items);
+        Assert.Equal(0, officeRu.PupilSlots);
         Assert.Equal(["Директор"], officeRu.Positions);
 
         var officeEn = en.Single(node => node.Id == "principals-office");
         Assert.Equal("Principal's office", officeEn.Name);
-        Assert.Equal(["Principal's chair", "Desk", "Chair"], officeEn.Items);
+        Assert.Equal(
+            [new MapViewItem("Principal's chair", 1), new MapViewItem("Desk", 1), new MapViewItem("Chair", 2)],
+            officeEn.Items);
         Assert.Equal(["Principal"], officeEn.Positions);
 
         var corridor = ru.Single(node => node.Id == "corridor-1");
@@ -38,7 +43,15 @@ public class MapViewTests
 
         var classroom = ru.Single(node => node.Id == "classroom-1a");
         Assert.Equal("Класс 1A", classroom.Name);
-        Assert.Equal(["Доска", "Стол", "Парта"], classroom.Items);
+        Assert.Equal(
+            [
+                new MapViewItem("Доска", 1),
+                new MapViewItem("Стол", 1),
+                new MapViewItem("Стул", 1),
+                new MapViewItem("Парта", 16),
+            ],
+            classroom.Items);
+        Assert.Equal(16, classroom.PupilSlots);
         Assert.Equal(["Учитель"], classroom.Positions);
         Assert.Equal("Classroom 1A", en.Single(node => node.Id == "classroom-1a").Name);
     }
diff --git a/tests/HSchool.Content.Tests/VanillaCoreTests.cs b/tests/HSchool.Content.Tests/VanillaCoreTests.cs
index 1a2ed05..2e4bec9 100644
--- a/tests/HSchool.Content.Tests/VanillaCoreTests.cs
+++ b/tests/HSchool.Content.Tests/VanillaCoreTests.cs
@@ -25,8 +25,20 @@ public class VanillaCoreTests
         Assert.True(catalog.Rooms.ContainsKey("Classroom"));
         Assert.Equal("Класс", catalog.Label("ru", catalog.Rooms["Classroom"]));
         Assert.Equal(["Teacher"], catalog.PositionsFor(DefKind.Room, "Classroom"));
+        Assert.Equal(1, catalog.Things["StudentDesk"].PupilSlots);
+        Assert.Equal(1, catalog.Things["Computer"].PupilSlots);
+        Assert.Equal(0, catalog.Things["Desk"].PupilSlots);
+        Assert.Equal(0, catalog.Things["Chair"].PupilSlots);
+        Assert.Contains(catalog.Rooms["Classroom"].Slots, slot => slot.Key == "teacherChair" && slot.Thing == "Chair");
+        Assert.Equal(16, catalog.Rooms["Classroom"].Slots.Single(slot => slot.Key == "studentDesks").Count);
         Assert.Equal(2, map.Buildings.Count);
         Assert.True(map.Rooms.Count >= 18, "Vanilla layout should look like a small school, not a stub.");
         Assert.Contains(map.Rooms, room => room.Id == "classroom-1a" && room.Label == "1A");
+        Assert.Equal(
+            16,
+            map.Rooms.Single(room => room.Id == "classroom-1a").Slots.Single(slot => slot.Key == "studentDesks").Count);
+        Assert.Contains(
+            map.Rooms.Single(room => room.Id == "classroom-1a").Slots,
+            slot => slot.Key == "teacherChair" && slot.Thing == "Chair");
     }
 }
diff --git a/tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs b/tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs
index f435b1f..0f41ca9 100644
--- a/tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs
+++ b/tests/HSchool.Protocol.Tests/ProtocolCodecTests.cs
@@ -137,8 +137,15 @@ public class ProtocolCodecTests
     public void MapSnapshot_RoundTripsAndWritesHeaderOffsets()
     {
         var message = new ServerMapSnapshotMessage(7, [
-            new MapSnapshotNode(0, "yard", "", "Двор", [], []),
-            new MapSnapshotNode(3, "office", "floor-1", "Кабинет директора", ["Стул"], ["Директор"]),
+            new MapSnapshotNode(0, "yard", "", "Двор", 0, [], []),
+            new MapSnapshotNode(
+                3,
+                "office",
+                "floor-1",
+                "Кабинет директора",
+                0,
+                [new MapSnapshotItem("Стул", 2)],
+                ["Директор"]),
         ]);
         var buffer = new byte[ProtocolConstants.MaxMessageSize];
 
@@ -154,17 +161,47 @@ public class ProtocolCodecTests
         Assert.Equal("yard", read.Nodes[0].Id);
         Assert.Equal("", read.Nodes[0].ParentId);
         Assert.Equal("Двор", read.Nodes[0].Name);
-        Assert.Equal(["Стул"], read.Nodes[1].Items);
+        Assert.Equal(0, read.Nodes[0].PupilSlots);
+        Assert.Equal([new MapSnapshotItem("Стул", 2)], read.Nodes[1].Items);
         Assert.Equal(["Директор"], read.Nodes[1].Positions);
     }
 
+    [Fact]
+    public void MapSnapshot_WritesPupilSlotsAndStackedItemCount()
+    {
+        var message = new ServerMapSnapshotMessage(1, [
+            new MapSnapshotNode(
+                3,
+                "classroom-1a",
+                "floor-1",
+                "Класс 1A",
+                16,
+                [new MapSnapshotItem("Парта", 16)],
+                []),
+        ]);
+        var buffer = new byte[ProtocolCodec.MapSnapshotSize(message)];
+
+        var length = ProtocolCodec.WriteMapSnapshot(buffer, message);
+        var read = ProtocolCodec.ReadMapSnapshot(buffer.AsSpan(0, length));
+
+        Assert.Equal(16, read.Nodes[0].PupilSlots);
+        Assert.Equal([new MapSnapshotItem("Парта", 16)], read.Nodes[0].Items);
+    }
+
     [Fact]
     public void MapSnapshotSize_IsExactlyWhatTheWriterProduces()
     {
         var message = new ServerMapSnapshotMessage(7, [
-            new MapSnapshotNode(0, "yard", "", "Двор", [], []),
-            new MapSnapshotNode(2, "floor-1", "main", "Этаж 1", [], []),
-            new MapSnapshotNode(3, "office", "floor-1", "Кабинет директора", ["Стол", "Стул"], ["Директор"]),
+            new MapSnapshotNode(0, "yard", "", "Двор", 0, [], []),
+            new MapSnapshotNode(2, "floor-1", "main", "Этаж 1", 0, [], []),
+            new MapSnapshotNode(
+                3,
+                "office",
+                "floor-1",
+                "Кабинет директора",
+                0,
+                [new MapSnapshotItem("Стол", 1), new MapSnapshotItem("Стул", 2)],
+                ["Директор"]),
         ]);
 
         var size = ProtocolCodec.MapSnapshotSize(message);
@@ -179,7 +216,7 @@ public class ProtocolCodecTests
         // A player who keeps clicking "Add room" in the create editor gets past 8 KiB somewhere
         // around sixty furnished rooms. Sizing the buffer from the message is what keeps that
         // school openable instead of killing its worker thread on the first snapshot.
-        var nodes = new List<MapSnapshotNode> { new(0, "yard", "", "Двор", [], []) };
+        var nodes = new List<MapSnapshotNode> { new(0, "yard", "", "Двор", 0, [], []) };
         for (var i = 1; i <= 200; i++)
         {
             nodes.Add(new MapSnapshotNode(
@@ -187,7 +224,8 @@ public class ProtocolCodecTests
                 $"principals-office-{i}",
                 "floor-1",
                 "Кабинет директора",
-                ["Кресло директора", "Стол", "Стул"],
+                0,
+                [new MapSnapshotItem("Кресло директора", 1), new MapSnapshotItem("Стол", 1), new MapSnapshotItem("Стул", 2)],
                 ["Директор"]));
         }
 
@@ -201,7 +239,9 @@ public class ProtocolCodecTests
 
         Assert.Equal(nodes.Count, read.Nodes.Count);
         Assert.Equal("principals-office-200", read.Nodes[^1].Id);
-        Assert.Equal(["Кресло директора", "Стол", "Стул"], read.Nodes[^1].Items);
+        Assert.Equal(
+            [new MapSnapshotItem("Кресло директора", 1), new MapSnapshotItem("Стол", 1), new MapSnapshotItem("Стул", 2)],
+            read.Nodes[^1].Items);
     }
 
     [Fact]