diff --git a/client/src/items/types/behaviorRegistry.ts b/client/src/items/types/behaviorRegistry.ts
index 17a1f50..037bc0e 100644
--- a/client/src/items/types/behaviorRegistry.ts
+++ b/client/src/items/types/behaviorRegistry.ts
@@ -1,26 +1,14 @@
 import { type IncomingMessage } from '../../network/protocol';
 import { type GameMode, type WorldItem } from '../../state/gameState';
-import { createClockBehavior } from './clock/behavior';
-import { createDiceBehavior } from './dice/behavior';
 import { createPianoBehavior } from './piano/behavior';
-import { createRadioStationBehavior } from './radioStation/behavior';
 import { type ItemBehavior, type ItemBehaviorDeps } from './runtimeShared';
-import { createWheelBehavior } from './wheel/behavior';
-import { createWidgetBehavior } from './widget/behavior';
 
 /** Runtime registry that composes all per-item client behavior modules. */
 export class ItemBehaviorRegistry {
   private readonly behaviors: ItemBehavior[];
 
   constructor(deps: ItemBehaviorDeps) {
-    this.behaviors = [
-      createClockBehavior(deps),
-      createDiceBehavior(deps),
-      createPianoBehavior(deps),
-      createRadioStationBehavior(deps),
-      createWheelBehavior(deps),
-      createWidgetBehavior(deps),
-    ];
+    this.behaviors = [createPianoBehavior(deps)];
   }
 
   /** Runs per-item initialization hooks after app bootstrap. */
diff --git a/client/src/items/types/clock/behavior.ts b/client/src/items/types/clock/behavior.ts
deleted file mode 100644
index b2484e5..0000000
--- a/client/src/items/types/clock/behavior.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-import { type ItemBehavior, type ItemBehaviorDeps } from '../runtimeShared';
-
-/** Creates runtime behavior hooks for clock items. */
-export function createClockBehavior(_deps: ItemBehaviorDeps): ItemBehavior {
-  return {};
-}
-
diff --git a/client/src/items/types/clock/definition.ts b/client/src/items/types/clock/definition.ts
deleted file mode 100644
index 5ec042b..0000000
--- a/client/src/items/types/clock/definition.ts
+++ /dev/null
@@ -1,63 +0,0 @@
-import { type ItemTypeClientDefinition } from '../shared';
-
-export const CLOCK_TIME_ZONE_OPTIONS = [
-  'America/Anchorage',
-  'America/Argentina/Buenos_Aires',
-  'America/Chicago',
-  'America/Detroit',
-  'America/Halifax',
-  'America/Indiana/Indianapolis',
-  'America/Kentucky/Louisville',
-  'America/Los_Angeles',
-  'America/St_Johns',
-  'Asia/Bangkok',
-  'Asia/Dhaka',
-  'Asia/Dubai',
-  'Asia/Hong_Kong',
-  'Asia/Kabul',
-  'Asia/Karachi',
-  'Asia/Kathmandu',
-  'Asia/Kolkata',
-  'Asia/Seoul',
-  'Asia/Singapore',
-  'Asia/Tehran',
-  'Asia/Tokyo',
-  'Asia/Yangon',
-  'Atlantic/Azores',
-  'Atlantic/South_Georgia',
-  'Australia/Brisbane',
-  'Australia/Darwin',
-  'Australia/Eucla',
-  'Australia/Lord_Howe',
-  'Europe/Berlin',
-  'Europe/Helsinki',
-  'Europe/London',
-  'Europe/Moscow',
-  'Pacific/Apia',
-  'Pacific/Auckland',
-  'Pacific/Chatham',
-  'Pacific/Honolulu',
-  'Pacific/Kiritimati',
-  'Pacific/Noumea',
-  'Pacific/Pago_Pago',
-  'UTC',
-] as const;
-
-/** Default client-side UI definition for clock items. */
-export const clockDefinition: ItemTypeClientDefinition = {
-  type: 'clock',
-  label: 'clock',
-  editableProperties: ['title', 'timeZone', 'use24Hour'],
-  globalProperties: {
-    useSound: 'none',
-    emitSound: 'sounds/clock.ogg',
-    useCooldownMs: 1000,
-    emitRange: 10,
-    directional: false,
-    emitSoundSpeed: 50,
-    emitSoundTempo: 50,
-  },
-  propertyOptions: {
-    timeZone: [...CLOCK_TIME_ZONE_OPTIONS],
-  },
-};
diff --git a/client/src/items/types/clock/index.ts b/client/src/items/types/clock/index.ts
deleted file mode 100644
index 27de3d4..0000000
--- a/client/src/items/types/clock/index.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export { clockDefinition, CLOCK_TIME_ZONE_OPTIONS } from './definition';
-
diff --git a/client/src/items/types/dice/behavior.ts b/client/src/items/types/dice/behavior.ts
deleted file mode 100644
index 60ec35b..0000000
--- a/client/src/items/types/dice/behavior.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-import { type ItemBehavior, type ItemBehaviorDeps } from '../runtimeShared';
-
-/** Creates runtime behavior hooks for dice items. */
-export function createDiceBehavior(_deps: ItemBehaviorDeps): ItemBehavior {
-  return {};
-}
-
diff --git a/client/src/items/types/dice/definition.ts b/client/src/items/types/dice/definition.ts
deleted file mode 100644
index 3bd11df..0000000
--- a/client/src/items/types/dice/definition.ts
+++ /dev/null
@@ -1,17 +0,0 @@
-import { type ItemTypeClientDefinition } from '../shared';
-
-/** Default client-side UI definition for dice items. */
-export const diceDefinition: ItemTypeClientDefinition = {
-  type: 'dice',
-  label: 'dice',
-  editableProperties: ['title', 'sides', 'number'],
-  globalProperties: {
-    useSound: 'sounds/roll.ogg',
-    emitSound: 'none',
-    useCooldownMs: 1000,
-    emitRange: 15,
-    directional: false,
-    emitSoundSpeed: 50,
-    emitSoundTempo: 50,
-  },
-};
diff --git a/client/src/items/types/dice/index.ts b/client/src/items/types/dice/index.ts
deleted file mode 100644
index 578fc14..0000000
--- a/client/src/items/types/dice/index.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export { diceDefinition } from './definition';
-
diff --git a/client/src/items/types/index.ts b/client/src/items/types/index.ts
deleted file mode 100644
index 290a05b..0000000
--- a/client/src/items/types/index.ts
+++ /dev/null
@@ -1,21 +0,0 @@
-import { type ItemType } from '../../state/gameState';
-import { clockDefinition } from './clock';
-import { diceDefinition } from './dice';
-import { pianoDefinition } from './piano';
-import { radioStationDefinition } from './radioStation';
-import { wheelDefinition } from './wheel';
-import { widgetDefinition } from './widget';
-import { type ItemTypeClientDefinition } from './shared';
-
-/** Ordered default client item definitions used before server UI definitions arrive. */
-export const DEFAULT_ITEM_TYPE_DEFINITIONS: ItemTypeClientDefinition[] = [
-  clockDefinition,
-  diceDefinition,
-  pianoDefinition,
-  radioStationDefinition,
-  wheelDefinition,
-  widgetDefinition,
-];
-
-/** Default add-item menu ordering derived from local item definitions. */
-export const DEFAULT_ITEM_TYPE_SEQUENCE: ItemType[] = DEFAULT_ITEM_TYPE_DEFINITIONS.map((definition) => definition.type);
diff --git a/client/src/items/types/piano/definition.ts b/client/src/items/types/piano/definition.ts
deleted file mode 100644
index 2f5bf98..0000000
--- a/client/src/items/types/piano/definition.ts
+++ /dev/null
@@ -1,22 +0,0 @@
-import { PIANO_INSTRUMENT_OPTIONS } from '../../../audio/pianoSynth';
-import { type ItemTypeClientDefinition } from '../shared';
-
-/** Default client-side UI definition for piano items. */
-export const pianoDefinition: ItemTypeClientDefinition = {
-  type: 'piano',
-  label: 'piano',
-  editableProperties: ['title', 'instrument', 'voiceMode', 'octave', 'attack', 'decay', 'release', 'brightness', 'emitRange'],
-  globalProperties: {
-    useSound: 'none',
-    emitSound: 'none',
-    useCooldownMs: 1000,
-    emitRange: 15,
-    directional: false,
-    emitSoundSpeed: 50,
-    emitSoundTempo: 50,
-  },
-  propertyOptions: {
-    instrument: [...PIANO_INSTRUMENT_OPTIONS],
-    voiceMode: ['poly', 'mono'],
-  },
-};
diff --git a/client/src/items/types/piano/index.ts b/client/src/items/types/piano/index.ts
deleted file mode 100644
index 10c9275..0000000
--- a/client/src/items/types/piano/index.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export { pianoDefinition } from './definition';
-export { createPianoBehavior } from './behavior';
diff --git a/client/src/items/types/radioStation/behavior.ts b/client/src/items/types/radioStation/behavior.ts
deleted file mode 100644
index 1b30836..0000000
--- a/client/src/items/types/radioStation/behavior.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-import { type ItemBehavior, type ItemBehaviorDeps } from '../runtimeShared';
-
-/** Creates runtime behavior hooks for radio_station items. */
-export function createRadioStationBehavior(_deps: ItemBehaviorDeps): ItemBehavior {
-  return {};
-}
-
diff --git a/client/src/items/types/radioStation/definition.ts b/client/src/items/types/radioStation/definition.ts
deleted file mode 100644
index 76cb78c..0000000
--- a/client/src/items/types/radioStation/definition.ts
+++ /dev/null
@@ -1,23 +0,0 @@
-import { RADIO_CHANNEL_OPTIONS } from '../../../audio/radioStationRuntime';
-import { EFFECT_SEQUENCE } from '../../../audio/effects';
-import { type ItemTypeClientDefinition } from '../shared';
-
-/** Default client-side UI definition for radio_station items. */
-export const radioStationDefinition: ItemTypeClientDefinition = {
-  type: 'radio_station',
-  label: 'radio',
-  editableProperties: ['title', 'streamUrl', 'enabled', 'mediaVolume', 'mediaChannel', 'mediaEffect', 'mediaEffectValue', 'facing', 'emitRange'],
-  globalProperties: {
-    useSound: 'none',
-    emitSound: 'none',
-    useCooldownMs: 1000,
-    emitRange: 20,
-    directional: true,
-    emitSoundSpeed: 50,
-    emitSoundTempo: 50,
-  },
-  propertyOptions: {
-    mediaEffect: EFFECT_SEQUENCE.map((effect) => effect.id),
-    mediaChannel: [...RADIO_CHANNEL_OPTIONS],
-  },
-};
diff --git a/client/src/items/types/radioStation/index.ts b/client/src/items/types/radioStation/index.ts
deleted file mode 100644
index ae80d4f..0000000
--- a/client/src/items/types/radioStation/index.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export { radioStationDefinition } from './definition';
-
diff --git a/client/src/items/types/shared.ts b/client/src/items/types/shared.ts
deleted file mode 100644
index d58bc7a..0000000
--- a/client/src/items/types/shared.ts
+++ /dev/null
@@ -1,14 +0,0 @@
-import { type ItemType } from '../../state/gameState';
-import { type ItemPropertyMetadata } from '../itemRegistry';
-
-/** Static client-side definition for one item type's UI/config defaults. */
-export type ItemTypeClientDefinition = {
-  type: ItemType;
-  label: string;
-  tooltip?: string;
-  editableProperties: string[];
-  globalProperties: Record<string, string | number | boolean>;
-  propertyOptions?: Record<string, string[]>;
-  propertyMetadata?: Record<string, ItemPropertyMetadata>;
-};
-
diff --git a/client/src/items/types/wheel/behavior.ts b/client/src/items/types/wheel/behavior.ts
deleted file mode 100644
index 0f57435..0000000
--- a/client/src/items/types/wheel/behavior.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-import { type ItemBehavior, type ItemBehaviorDeps } from '../runtimeShared';
-
-/** Creates runtime behavior hooks for wheel items. */
-export function createWheelBehavior(_deps: ItemBehaviorDeps): ItemBehavior {
-  return {};
-}
-
diff --git a/client/src/items/types/wheel/definition.ts b/client/src/items/types/wheel/definition.ts
deleted file mode 100644
index adad777..0000000
--- a/client/src/items/types/wheel/definition.ts
+++ /dev/null
@@ -1,17 +0,0 @@
-import { type ItemTypeClientDefinition } from '../shared';
-
-/** Default client-side UI definition for wheel items. */
-export const wheelDefinition: ItemTypeClientDefinition = {
-  type: 'wheel',
-  label: 'wheel',
-  editableProperties: ['title', 'spaces'],
-  globalProperties: {
-    useSound: 'sounds/spin.ogg',
-    emitSound: 'none',
-    useCooldownMs: 4000,
-    emitRange: 15,
-    directional: false,
-    emitSoundSpeed: 50,
-    emitSoundTempo: 50,
-  },
-};
diff --git a/client/src/items/types/wheel/index.ts b/client/src/items/types/wheel/index.ts
deleted file mode 100644
index 08db340..0000000
--- a/client/src/items/types/wheel/index.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export { wheelDefinition } from './definition';
-
diff --git a/client/src/items/types/widget/behavior.ts b/client/src/items/types/widget/behavior.ts
deleted file mode 100644
index 98e7ec0..0000000
--- a/client/src/items/types/widget/behavior.ts
+++ /dev/null
@@ -1,7 +0,0 @@
-import { type ItemBehavior, type ItemBehaviorDeps } from '../runtimeShared';
-
-/** Creates runtime behavior hooks for widget items. */
-export function createWidgetBehavior(_deps: ItemBehaviorDeps): ItemBehavior {
-  return {};
-}
-
diff --git a/client/src/items/types/widget/definition.ts b/client/src/items/types/widget/definition.ts
deleted file mode 100644
index 37afe26..0000000
--- a/client/src/items/types/widget/definition.ts
+++ /dev/null
@@ -1,34 +0,0 @@
-import { EFFECT_SEQUENCE } from '../../../audio/effects';
-import { type ItemTypeClientDefinition } from '../shared';
-
-/** Default client-side UI definition for widget items. */
-export const widgetDefinition: ItemTypeClientDefinition = {
-  type: 'widget',
-  label: 'widget',
-  editableProperties: [
-    'title',
-    'enabled',
-    'directional',
-    'facing',
-    'emitRange',
-    'emitVolume',
-    'emitSoundSpeed',
-    'emitSoundTempo',
-    'emitEffect',
-    'emitEffectValue',
-    'useSound',
-    'emitSound',
-  ],
-  globalProperties: {
-    useSound: 'none',
-    emitSound: 'none',
-    useCooldownMs: 1000,
-    emitRange: 15,
-    directional: false,
-    emitSoundSpeed: 50,
-    emitSoundTempo: 50,
-  },
-  propertyOptions: {
-    emitEffect: EFFECT_SEQUENCE.map((effect) => effect.id),
-  },
-};
diff --git a/client/src/items/types/widget/index.ts b/client/src/items/types/widget/index.ts
deleted file mode 100644
index 7c28e49..0000000
--- a/client/src/items/types/widget/index.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export { widgetDefinition } from './definition';
-
diff --git a/docs/item-schema.md b/docs/item-schema.md
index 1e7b2d5..149b1ef 100644
--- a/docs/item-schema.md
+++ b/docs/item-schema.md
@@ -49,7 +49,7 @@
 
 - Persisted state stores only instance data.
 - Global/type-level properties are loaded from server registry in `server/app/item_catalog.py`.
-- Per-type use/update validation and message behavior are implemented in per-item modules under `server/app/items/`, discovered via plugins in `server/app/items/types/*/plugin.py`.
+- Per-type use/update validation and message behavior are implemented in per-item modules under `server/app/items/types/*/module.py`, discovered via plugins in `server/app/items/types/*/plugin.py`.
 - Client-side add/edit metadata is consumed from `welcome.uiDefinitions` via `client/src/items/itemRegistry.ts` (no local fallback definitions).
 - End-to-end add-item template: `docs/item-type-template.md`.
 
diff --git a/docs/item-type-template.md b/docs/item-type-template.md
index 21d62db..71f2f78 100644
--- a/docs/item-type-template.md
+++ b/docs/item-type-template.md
@@ -1,50 +1,54 @@
 # Item Type Template
 
-This page is a practical template for adding a new item type with the current per-item module + single registry system.
+This page is the practical template for the current plugin-driven item architecture.
 
 ## Plain-English Flow
 
-When a new item type is added, wire it in these places:
+When adding a new item type:
 
-1. Server item module (`server/app/items/<name>.py`)
-- Define item metadata constants:
-  - label/tooltip
-  - editable properties
-  - defaults/capabilities/sounds/cooldown/range/directional
-  - property metadata
+1. Server item module
+- Add `server/app/items/types/<item_type>/module.py`.
+- Define metadata/constants:
+  - `LABEL`, `TOOLTIP`
+  - `EDITABLE_PROPERTIES`
+  - `CAPABILITIES`
+  - `USE_SOUND`, `EMIT_SOUND`
+  - `USE_COOLDOWN_MS`, `EMIT_RANGE`, `DIRECTIONAL`
+  - `DEFAULT_TITLE`, `DEFAULT_PARAMS`
+  - `PROPERTY_METADATA`
 - Implement behavior:
   - `validate_update(item, next_params)`
   - `use_item(item, nickname, clock_formatter)`
 
-2. Server registry (`server/app/items/registry.py`)
-- Add one module entry in `ITEM_MODULES`.
-- Update `ITEM_TYPE_ORDER` if needed.
+2. Server plugin file
+- Add `server/app/items/types/<item_type>/plugin.py` exporting:
+  - `type`
+  - `order`
+  - `module`
 
-3. Shared item type unions
+3. Shared item-type unions
 - Add the type in:
   - `server/app/models.py`
   - `client/src/network/protocol.ts`
   - `client/src/state/gameState.ts`
 
-4. Client fallback metadata
-- Add defaults in `client/src/items/itemRegistry.ts`:
-  - `DEFAULT_ITEM_TYPE_SEQUENCE`
-  - `DEFAULT_ITEM_TYPE_EDITABLE_PROPERTIES`
-  - `DEFAULT_ITEM_TYPE_GLOBAL_PROPERTIES`
+4. Client runtime behavior (optional)
+- Default: no item-specific client module needed.
+- Add `client/src/items/types/<item_type>/behavior.ts` only if this item needs custom client runtime UX/audio logic (for example piano mode).
 
 That is enough for a first working item type.
 
 ## Minimal Server Module Example: `counter`
 
-`server/app/items/counter.py`:
+`server/app/items/types/counter/module.py`:
 
 ```py
 from __future__ import annotations
 
 from typing import Callable
 
-from ..item_types import ItemUseResult
-from ..models import WorldItem
+from ...item_types import ItemUseResult
+from ...models import WorldItem
 
 LABEL = "counter"
 TOOLTIP = "Counts up each time you use it."
@@ -84,19 +88,15 @@ def use_item(item: WorldItem, nickname: str, _clock_formatter: Callable[[dict],
     )
 ```
 
-Then register it in `server/app/items/registry.py`:
+Then add plugin registration in `server/app/items/types/counter/plugin.py`:
 
 ```py
-from . import clock, counter, dice, radio, wheel
+from . import module
 
-ITEM_TYPE_ORDER: tuple[str, ...] = ("clock", "counter", "dice", "radio_station", "wheel")
-
-ITEM_MODULES: dict[str, ItemModule] = {
-    "clock": clock,
-    "counter": counter,
-    "dice": dice,
-    "radio_station": radio,
-    "wheel": wheel,
+ITEM_TYPE_PLUGIN = {
+    "type": "counter",
+    "order": 25,
+    "module": module,
 }
 ```
 
diff --git a/docs/item-types.md b/docs/item-types.md
index 9f9184c..61d8eb8 100644
--- a/docs/item-types.md
+++ b/docs/item-types.md
@@ -42,7 +42,7 @@ This is behavior-focused documentation for item types and their defaults.
 - `mediaVolume`: integer `0..100`
 - `mediaEffect`: `reverb | echo | flanger | high_pass | low_pass | off`
 - `mediaEffectValue`: number `0..100` with `0.1` precision
-- `facing`: number `0..360` with `0.1` precision
+- `facing`: number `0..360` with step `1`
 - `emitRange`: integer `5..20`
 
 ## `dice`
@@ -141,7 +141,7 @@ This is behavior-focused documentation for item types and their defaults.
 ### Validation
 - `enabled`: boolean or on/off style input
 - `directional`: boolean or on/off style input
-- `facing`: number `0..360` with `0.1` precision
+- `facing`: number `0..360` with step `1`
 - `emitRange`: integer `1..20`
 - `emitVolume`: integer `0..100`
 - `emitSoundSpeed`: integer `0..100` (`0=0.5x`, `50=1.0x`, `100=2.0x`) for speed/pitch
@@ -193,7 +193,7 @@ Server is the source of truth for item type definitions and metadata. The client
 
 For a full copy/paste example with plain-English explanation, see `docs/item-type-template.md`.
 
-1. Server item module: add a new file under `server/app/items/` with:
+1. Server item module: add a new file under `server/app/items/types/<item_type>/module.py` with:
    - defaults/capabilities
    - property metadata/options
    - `validate_update` and `use_item`
@@ -204,7 +204,7 @@ For a full copy/paste example with plain-English explanation, see `docs/item-typ
    The server auto-discovers plugins at boot, so no central registry edit is needed.
 3. Server models: extend `ItemType` literals in `server/app/models.py` and any packet enums that list item types.
 4. Client protocol/state types: update item-type unions in `client/src/network/protocol.ts` and `client/src/state/gameState.ts`.
-5. Client runtime behavior: add `client/src/items/types/<item_type>/behavior.ts` only if custom client runtime is needed.
+5. Client runtime behavior: add `client/src/items/types/<item_type>/behavior.ts` only if custom client runtime is needed (for example piano mode).
 6. Tests: add or update server tests under `server/tests/` for use/update validation, unknown-key stripping, and `uiDefinitions` completeness.
 
 ### Example Shape
diff --git a/plans/item-architecture-refactor-plan.md b/plans/item-architecture-refactor-plan.md
new file mode 100644
index 0000000..396168b
--- /dev/null
+++ b/plans/item-architecture-refactor-plan.md
@@ -0,0 +1,302 @@
+# Server-First Item Architecture Refactor Plan
+
+## Goal
+Make the **server the only source of truth** for item definitions, schema, defaults, options, validation rules, and editable behavior. The client should consume server definitions and provide UX/rendering/audio only.
+
+This plan removes client fallback definitions and introduces a repeatable, consistent item authoring structure so adding new item types is low-risk and uniform.
+
+## Target End State
+
+### 1) Source of truth
+- Server owns, for each item type:
+  - Type id, label, tooltip
+  - Full property schema (value type, required/optional, min/max/step, maxLength, enum options)
+  - Defaults (global + per-item initial params)
+  - Editability and read-only behavior
+  - Validation, normalization, migration policy (if any)
+  - Runtime actions (`use`, optional custom actions)
+  - Capability list
+- Server sends this as canonical `uiDefinitions` + schema metadata on `welcome` (or equivalent bootstrap).
+
+### 2) Client model
+- Client has no static fallback item definitions.
+- If schema payload is missing/invalid, item features are unavailable (explicit error/status), not silently guessed.
+- Client property editor and item menus are metadata-driven.
+- Client runtime behavior modules remain for UX/audio only (e.g., piano local mode), keyed by server type ids.
+
+### 3) Repeatable item authoring
+Adding an item type uses one standard server folder/template and a short checklist, with **auto-discovery** on server boot (no manual registry edits).
+
+---
+
+## Proposed Architecture
+
+## A) Server: Item Type Package Contract (Auto-Discovered)
+Create/standardize per-item server packages under something like:
+- `server/app/items/types/<item_type>/`
+
+Each item type package exports the same contract:
+- `definition.py`
+  - `type_id`, `label`, `tooltip`
+  - `schema` (properties + metadata)
+  - `defaults`
+  - `editable_properties`
+  - `capabilities`
+- `validator.py`
+  - `validate_create(params) -> normalized_params`
+  - `validate_update(existing, patch) -> normalized_params`
+  - Must drop unknown keys by default.
+- `actions.py`
+  - `use(context, item, client, payload?) -> result`
+  - optional `custom_actions` handlers
+- `ui.py` (optional if definition is enough)
+  - transforms schema -> `uiDefinitions` payload fragments
+
+A central loader in server scans `server/app/items/types/*` at boot and imports one plugin entrypoint per folder (for example `plugin.py` with `ITEM_TYPE_PLUGIN` export).
+
+The discovered plugins are then assembled into an in-memory registry object exposing:
+- validation hooks
+- defaults
+- ui definitions
+- capabilities
+- action dispatch
+
+This means:
+- adding a new item folder + plugin file is sufficient for server registration
+- no hand-edited master list is required
+
+## B) Server: Strict Params Hygiene
+In update flow:
+- Build next params by applying patch into current params.
+- Run through type validator that:
+  - strips unknown keys
+  - normalizes known keys
+  - enforces types/ranges/options
+- Persist only validated output.
+
+No raw client params should persist.
+
+## C) Server: Save Strategy
+Replace synchronous `save_state()` every mutation with coalesced writes:
+- mark dirty on mutation
+- debounce write (e.g., 100-300ms)
+- cap max delay (e.g., 1-2s)
+- flush on shutdown/signal
+
+This preserves durability while reducing event-loop blocking.
+
+## D) Client: Schema-Driven UI Runtime
+Refactor client item registry/editor to consume server schema only.
+
+Client keeps:
+- Presentation helpers
+- Generic item behavior path driven only by schema/metadata
+- Optional per-item UX runtime modules only where needed (example: piano key mode)
+
+Client removes:
+- static defaults/options/editability lists as authority
+- fallback-driven assumptions
+- requirement for per-item client modules when behavior is generic
+
+Property editor logic becomes generic:
+- `valueType: boolean` -> toggle
+- `valueType: list` + `options` -> list select
+- `valueType: number` + `range` -> numeric editor/stepper
+- `valueType: text/sound` + `maxLength` -> text editor
+- `readonly` -> blocked edit with status
+
+Special-case handlers only for UX extras (e.g., live preview for certain fields).
+
+### D.1) Dependent Property Rules
+Add dependency metadata to server schema so client can hide dependent fields generically.
+
+Recommended metadata fields per property:
+- `visibleWhen`: simple predicate (for example `{ directional: true }`)
+
+Example:
+- `facing` has `visibleWhen: { directional: true }`
+- when `directional` is `false`, `facing` is hidden
+- when a controlling property changes, the property menu is recomputed immediately so visibility updates live
+
+## E) Protocol Shape (Recommended)
+Ensure `welcome.uiDefinitions` includes enough to be complete:
+- `itemTypes[]`
+  - `type`, `label`, `tooltip`
+  - `editableProperties[]`
+  - `propertyMetadata{ key -> { valueType, tooltip, range, maxLength, options?, readonly?, visibleWhen? } }`
+  - `globalProperties`
+  - `capabilities`
+- `itemTypeOrder[]`
+
+Optional future:
+- `schemaVersion` for compatibility checks.
+
+---
+
+## Phased Implementation Plan
+
+## Phase 0: Preconditions and guardrails
+1. Document canonical schema contract in `docs/item-schema.md`.
+2. Add tests asserting unknown keys are rejected/stripped per type.
+3. Add tests asserting `uiDefinitions` completeness for all registered types.
+
+Deliverable:
+- Locked schema contract and tests before heavy refactor.
+
+## Phase 1: Server type package standardization + auto-discovery
+1. Standardize all existing item types to same package contract.
+2. Move any remaining type-specific logic out of generic server paths into per-type packages.
+3. Add auto-discovery loader APIs:
+- `get_type_definition(type_id)`
+- `validate_update(type_id, existing, patch)`
+- `build_ui_definitions()`
+4. Loader scans item folders at startup and registers plugins automatically.
+
+Deliverable:
+- Uniform server-side item modules for all current item types.
+
+## Phase 2: Strict validation and unknown-key stripping
+1. Enforce strict allowed-key filtering in per-type validators.
+2. Fail/strip behavior decision:
+- recommended: strip unknown keys on load/update, optionally log at debug level.
+3. Backfill tests for each type.
+
+Deliverable:
+- No unsupported params can persist.
+
+## Phase 3: Client removes authority/fallback definitions
+1. Remove client hardcoded item defaults/options as authoritative data.
+2. Keep only bootstrap guards:
+- if schema missing/invalid, fail item UX with explicit status (no fallback behavior).
+3. Refactor `itemRegistry` to be a runtime cache of server definitions.
+
+Deliverable:
+- Client item UI driven entirely by server payload.
+
+## Phase 4: Metadata-driven property editor + visibility dependencies
+1. Replace key-specific submit/toggle/list branches with generic metadata-based handlers.
+2. Keep a small optional hook map:
+- `onPropertyPreviewChange(type,key,value)` for UX preview.
+3. Implement `visibleWhen` semantics with live menu recompute when controlling values change.
+4. Verify all current item properties work with generic editor.
+
+Deliverable:
+- Adding a new field usually requires server changes only.
+
+## Phase 5: Behavior registry completion (optional modules)
+1. Keep one generic behavior path that works for items with no special runtime.
+2. Keep per-item behavior modules only when UX/audio runtime is truly custom.
+3. Ensure all runtime hooks are accessed via registry interfaces.
+4. Remove any remaining type checks in `main.ts` and shared handlers.
+
+Deliverable:
+- `main.ts` stays orchestration-only.
+
+## Phase 6: Coalesced persistence
+1. Implement debounced save queue in server item service.
+2. Add durability tests (flush on shutdown).
+3. Add config knobs (debounce ms, max delay).
+
+Deliverable:
+- lower save overhead under bursty updates.
+
+---
+
+## Repeatable New Item Template
+
+When adding a new item type:
+
+1. Server
+- Create `server/app/items/types/<new_type>/`
+- Implement:
+  - `definition.py`
+  - `validator.py`
+  - `actions.py`
+  - `plugin.py` (entrypoint export for auto-discovery)
+- Add tests:
+  - create defaults
+  - update validation (valid + invalid + unknown keys)
+  - `use` behavior
+  - `uiDefinitions` fields present
+
+2. Client
+- Add `client/src/items/types/<newType>/behavior.ts` only if custom UX runtime exists.
+- Prefer zero client type-specific code for generic items.
+- If behavior module is needed, register via behavior loader pattern.
+- No hardcoded property logic in editor.
+
+3. Docs
+- Update `docs/item-types.md`
+- Update `docs/item-schema.md`
+- Update controls docs if keybindings changed.
+
+---
+
+## Risks and Mitigations
+
+1. Risk: temporary client breakage when fallback removed.
+- Mitigation: explicit schema-required startup check and clear status error.
+
+2. Risk: inconsistent schema during deploy rollover.
+- Mitigation: include `schemaVersion` and reject incompatible client/server combinations with clear reconnect message.
+
+3. Risk: over-generalized editor misses edge-case UX.
+- Mitigation: keep small per-item preview hooks while generic editor handles core commit logic.
+
+4. Risk: debounced persistence data loss on crash.
+- Mitigation: short debounce + max-delay + flush on shutdown.
+
+---
+
+## Suggested Execution Order for Your Repo (Practical)
+1. Implement strict unknown-key stripping on server (highest impact, lowest UX risk).
+2. Implement server plugin auto-discovery for item type folders.
+3. Convert client item registry to require server schema payload (remove fallback authority).
+4. Make item property editor fully metadata-driven with dependency rules.
+5. Finalize optional client behavior modules (only for custom UX items like piano).
+6. Add coalesced persistence.
+
+---
+
+## Definition of Done
+- Server item validators fully define accepted params and drop unknowns.
+- Server item types are boot-loaded from folder plugins (no manual master registry edits).
+- `uiDefinitions` is complete and authoritative for all item UI config.
+- Client contains no authoritative item defaults/options/editability outside server payload.
+- Client has no fallback schema path.
+- New item addition follows one template with predictable files/tests.
+- `main.ts` has no item-type-specific runtime branches.
+
+---
+
+## Implementation Update (2026-02-24)
+
+### Completed
+- Phase 0:
+  - Added server-side contract coverage for `uiDefinitions` completeness.
+  - Added/kept tests for unknown-key stripping and validation behavior.
+- Phase 1:
+  - Server item plugins are auto-discovered from `server/app/items/types/*/plugin.py`.
+  - Registry now builds type order/modules from discovered plugins.
+- Phase 2:
+  - Unknown params are stripped by validators and use-path updates are revalidated before persist.
+- Phase 3:
+  - Client item registry now requires server `uiDefinitions`; no fallback item-definition authority.
+  - Missing/invalid schema now disables item menus with explicit status.
+- Phase 4:
+  - Property editor behavior is metadata-driven by `valueType/range/options/maxLength`.
+  - `visibleWhen` is supported and item property rows recompute live after updates.
+- Phase 5:
+  - Client runtime behavior remains modular per item via behavior registry; `main.ts` orchestration no longer carries item-specific business branches.
+- Phase 6:
+  - Coalesced/debounced state saving implemented.
+  - Flush-on-shutdown implemented.
+  - Save timing now configurable via:
+    - `storage.state_save_debounce_ms`
+    - `storage.state_save_max_delay_ms`
+
+### Notes
+- Client item-specific runtime is now reduced to only `piano`; simple items (`dice`, `wheel`, `clock`, `radio_station`, `widget`) run through generic client flows with no custom behavior module.
+- Server item implementations now live inside per-type folders (`server/app/items/types/*/module.py`) and plugins point directly to those modules.
+- Remaining optional future work:
+  - split server type modules into `definition.py`/`validator.py`/`actions.py` files per type if we want finer-grained plugin internals.
diff --git a/server/app/item_catalog.py b/server/app/item_catalog.py
index bb3213f..00cbfce 100644
--- a/server/app/item_catalog.py
+++ b/server/app/item_catalog.py
@@ -5,7 +5,6 @@ from __future__ import annotations
 from dataclasses import dataclass
 from typing import Literal, cast
 
-from .items import clock, piano, radio
 from .items.registry import ITEM_MODULES, ITEM_TYPE_ORDER
 
 ItemType = Literal["radio_station", "dice", "wheel", "clock", "widget", "piano"]
@@ -15,12 +14,12 @@ ITEM_TYPE_EDITABLE_PROPERTIES: dict[ItemType, tuple[str, ...]] = {
     item_type: ITEM_MODULES[item_type].EDITABLE_PROPERTIES for item_type in ITEM_TYPE_SEQUENCE
 }
 
-CLOCK_DEFAULT_TIME_ZONE = clock.DEFAULT_TIME_ZONE
-CLOCK_TIME_ZONE_OPTIONS = clock.TIME_ZONE_OPTIONS
-RADIO_EFFECT_OPTIONS = radio.EFFECT_OPTIONS
-RADIO_CHANNEL_OPTIONS = radio.CHANNEL_OPTIONS
-PIANO_INSTRUMENT_OPTIONS = piano.INSTRUMENT_OPTIONS
-PIANO_VOICE_MODE_OPTIONS = piano.VOICE_MODE_OPTIONS
+CLOCK_DEFAULT_TIME_ZONE = cast(str, ITEM_MODULES["clock"].DEFAULT_TIME_ZONE)
+CLOCK_TIME_ZONE_OPTIONS = cast(tuple[str, ...], ITEM_MODULES["clock"].TIME_ZONE_OPTIONS)
+RADIO_EFFECT_OPTIONS = cast(tuple[str, ...], ITEM_MODULES["radio_station"].EFFECT_OPTIONS)
+RADIO_CHANNEL_OPTIONS = cast(tuple[str, ...], ITEM_MODULES["radio_station"].CHANNEL_OPTIONS)
+PIANO_INSTRUMENT_OPTIONS = cast(tuple[str, ...], ITEM_MODULES["piano"].INSTRUMENT_OPTIONS)
+PIANO_VOICE_MODE_OPTIONS = cast(tuple[str, ...], ITEM_MODULES["piano"].VOICE_MODE_OPTIONS)
 
 
 @dataclass(frozen=True)
diff --git a/server/app/items/__init__.py b/server/app/items/__init__.py
index 37d3683..d2375e7 100644
--- a/server/app/items/__init__.py
+++ b/server/app/items/__init__.py
@@ -1,2 +1 @@
-"""Per-item modules containing item-specific schema and behavior."""
-
+"""Item subsystem package (shared helpers + type-plugin loader)."""
diff --git a/server/app/items/clock.py b/server/app/items/types/clock/module.py
similarity index 95%
rename from server/app/items/clock.py
rename to server/app/items/types/clock/module.py
index 8018789..f886406 100644
--- a/server/app/items/clock.py
+++ b/server/app/items/types/clock/module.py
@@ -4,9 +4,9 @@ from __future__ import annotations
 
 from typing import Callable
 
-from ..item_types import ItemUseResult
-from ..models import WorldItem
-from .helpers import keep_only_known_params, parse_bool_like_or_none
+from ....item_types import ItemUseResult
+from ....models import WorldItem
+from ...helpers import keep_only_known_params, parse_bool_like_or_none
 
 LABEL = "clock"
 TOOLTIP = "It tells the time. What did you think it did?"
diff --git a/server/app/items/types/clock/plugin.py b/server/app/items/types/clock/plugin.py
index 10026e2..52d5b6b 100644
--- a/server/app/items/types/clock/plugin.py
+++ b/server/app/items/types/clock/plugin.py
@@ -2,10 +2,10 @@
 
 from __future__ import annotations
 
-from ... import clock
+from . import module
 
 ITEM_TYPE_PLUGIN = {
     "type": "clock",
     "order": 10,
-    "module": clock,
+    "module": module,
 }
diff --git a/server/app/items/dice.py b/server/app/items/types/dice/module.py
similarity index 95%
rename from server/app/items/dice.py
rename to server/app/items/types/dice/module.py
index 0b283ba..2e85929 100644
--- a/server/app/items/dice.py
+++ b/server/app/items/types/dice/module.py
@@ -5,9 +5,9 @@ from __future__ import annotations
 import random
 from typing import Callable
 
-from ..item_types import ItemUseResult
-from ..models import WorldItem
-from .helpers import keep_only_known_params
+from ....item_types import ItemUseResult
+from ....models import WorldItem
+from ...helpers import keep_only_known_params
 
 LABEL = "dice"
 TOOLTIP = "Great for drinking games or boredom."
diff --git a/server/app/items/types/dice/plugin.py b/server/app/items/types/dice/plugin.py
index cdfa9c6..241bddc 100644
--- a/server/app/items/types/dice/plugin.py
+++ b/server/app/items/types/dice/plugin.py
@@ -2,10 +2,10 @@
 
 from __future__ import annotations
 
-from ... import dice
+from . import module
 
 ITEM_TYPE_PLUGIN = {
     "type": "dice",
     "order": 20,
-    "module": dice,
+    "module": module,
 }
diff --git a/server/app/items/piano.py b/server/app/items/types/piano/module.py
similarity index 98%
rename from server/app/items/piano.py
rename to server/app/items/types/piano/module.py
index 8f9e07d..11523c4 100644
--- a/server/app/items/piano.py
+++ b/server/app/items/types/piano/module.py
@@ -4,9 +4,9 @@ from __future__ import annotations
 
 from typing import Callable
 
-from ..item_types import ItemUseResult
-from ..models import WorldItem
-from .helpers import keep_only_known_params
+from ....item_types import ItemUseResult
+from ....models import WorldItem
+from ...helpers import keep_only_known_params
 
 LABEL = "piano"
 TOOLTIP = "Playable keyboard instrument with multiple synth voices."
diff --git a/server/app/items/types/piano/plugin.py b/server/app/items/types/piano/plugin.py
index 9824d2f..cd829d2 100644
--- a/server/app/items/types/piano/plugin.py
+++ b/server/app/items/types/piano/plugin.py
@@ -2,10 +2,10 @@
 
 from __future__ import annotations
 
-from ... import piano
+from . import module
 
 ITEM_TYPE_PLUGIN = {
     "type": "piano",
     "order": 30,
-    "module": piano,
+    "module": module,
 }
diff --git a/server/app/items/radio.py b/server/app/items/types/radio_station/module.py
similarity index 97%
rename from server/app/items/radio.py
rename to server/app/items/types/radio_station/module.py
index 6be9c9b..8cc5385 100644
--- a/server/app/items/radio.py
+++ b/server/app/items/types/radio_station/module.py
@@ -4,9 +4,9 @@ from __future__ import annotations
 
 from typing import Callable
 
-from ..item_types import ItemUseResult
-from ..models import WorldItem
-from .helpers import keep_only_known_params, toggle_bool_param
+from ....item_types import ItemUseResult
+from ....models import WorldItem
+from ...helpers import keep_only_known_params, toggle_bool_param
 
 LABEL = "radio"
 TOOLTIP = "Can play stations from the Internet. Tune multiple to the same station and they will sync up."
diff --git a/server/app/items/types/radio_station/plugin.py b/server/app/items/types/radio_station/plugin.py
index 382fdd5..487a012 100644
--- a/server/app/items/types/radio_station/plugin.py
+++ b/server/app/items/types/radio_station/plugin.py
@@ -2,10 +2,10 @@
 
 from __future__ import annotations
 
-from ... import radio
+from . import module
 
 ITEM_TYPE_PLUGIN = {
     "type": "radio_station",
     "order": 40,
-    "module": radio,
+    "module": module,
 }
diff --git a/server/app/items/wheel.py b/server/app/items/types/wheel/module.py
similarity index 95%
rename from server/app/items/wheel.py
rename to server/app/items/types/wheel/module.py
index d7dc2ce..8009d1d 100644
--- a/server/app/items/wheel.py
+++ b/server/app/items/types/wheel/module.py
@@ -5,9 +5,9 @@ from __future__ import annotations
 import random
 from typing import Callable
 
-from ..item_types import ItemUseResult
-from ..models import WorldItem
-from .helpers import keep_only_known_params
+from ....item_types import ItemUseResult
+from ....models import WorldItem
+from ...helpers import keep_only_known_params
 
 LABEL = "wheel"
 TOOLTIP = "Spin to win fabulous prizes."
diff --git a/server/app/items/types/wheel/plugin.py b/server/app/items/types/wheel/plugin.py
index 1e413fd..8fbc863 100644
--- a/server/app/items/types/wheel/plugin.py
+++ b/server/app/items/types/wheel/plugin.py
@@ -2,10 +2,10 @@
 
 from __future__ import annotations
 
-from ... import wheel
+from . import module
 
 ITEM_TYPE_PLUGIN = {
     "type": "wheel",
     "order": 50,
-    "module": wheel,
+    "module": module,
 }
diff --git a/server/app/items/widget.py b/server/app/items/types/widget/module.py
similarity index 98%
rename from server/app/items/widget.py
rename to server/app/items/types/widget/module.py
index 2eda0ad..5d4d931 100644
--- a/server/app/items/widget.py
+++ b/server/app/items/types/widget/module.py
@@ -4,9 +4,9 @@ from __future__ import annotations
 
 from typing import Callable
 
-from ..item_types import ItemUseResult
-from ..models import WorldItem
-from .helpers import keep_only_known_params, parse_bool_like, toggle_bool_param
+from ....item_types import ItemUseResult
+from ....models import WorldItem
+from ...helpers import keep_only_known_params, parse_bool_like, toggle_bool_param
 
 LABEL = "widget"
 TOOLTIP = "A basic item. Make it a beacon or whatever you want."
diff --git a/server/app/items/types/widget/plugin.py b/server/app/items/types/widget/plugin.py
index 25a435a..f0f7fb3 100644
--- a/server/app/items/types/widget/plugin.py
+++ b/server/app/items/types/widget/plugin.py
@@ -2,10 +2,10 @@
 
 from __future__ import annotations
 
-from ... import widget
+from . import module
 
 ITEM_TYPE_PLUGIN = {
     "type": "widget",
     "order": 60,
-    "module": widget,
+    "module": module,
 }