Track item updatedBy as readonly metadata and inspect field

docs/item-schema.md

@@ -10,6 +10,7 @@
   "x": 0,
   "y": 0,
   "createdBy": "user-id",
+  "updatedBy": "user-id",
   "createdAt": 1735689600000,
   "updatedAt": 1735689600000,
   "version": 1,
@@ -24,6 +25,7 @@
 - `useSound`: optional client-played one-shot sound when item `use` succeeds; global item field and not user-editable in V1.
 - `emitSound`: optional continuously-looping spatial sound emitted from the item on the grid; global item field and not user-editable in V1.
 - `capabilities`, `useSound`, and `emitSound` are derived from global item-type definitions at runtime (not stored per-instance in persisted state).
+- `updatedBy` tracks the user account that last changed item state.
 - `useCooldownMs`: global per item type (`radio_station=1000`, `dice=1000`, `wheel=4000`, `clock=1000`, `widget=1000`, `piano=1000`), not per-instance editable.
 - `emitRange`: global spatial range default per item type (`radio_station=10`, `dice=15`, `wheel=15`, `clock=10`, `widget=15`, `piano=15`).
   - `radio_station` can override this per instance via `params.emitRange` (`5..20`).
@@ -39,6 +41,7 @@
   "x": 0,
   "y": 0,
   "createdBy": "user-id",
+  "updatedBy": "user-id",
   "createdAt": 1735689600000,
   "updatedAt": 1735689600000,
   "version": 1,

docs/item-types.md

@@ -13,6 +13,7 @@ This is behavior-focused documentation for item types and their defaults.
   - `emitRange` (spatial range in squares)
   - `directional` (directional attenuation enabled)
 - Instance fields are persisted in `server/runtime/items.json`.
+- Read-only inspect fields include `createdBy` and `updatedBy` for ownership/change tracking.
 
 ## `radio_station`
 

docs/protocol-notes.md

@@ -46,7 +46,7 @@ This is a behavior guide for packet semantics beyond raw schemas.
 ## Item Packet Behavior
 
 - `item_upsert` is full-state replacement for one item, not partial patch.
-- `item_upsert.item.display` is server-owned display text for readonly/system properties (for example: `createdAt`, `updatedAt`, `capabilities`, `useSound`, `emitSound`).
+- `item_upsert.item.display` is server-owned display text for readonly/system properties (for example: `createdBy`, `updatedBy`, `createdAt`, `updatedAt`, `capabilities`, `useSound`, `emitSound`).
 - `item_action_result` messages are intended for direct screen-reader/user status feedback.
 - Piano runtime control no longer depends on parsing `item_action_result.message` text.
 - `item_piano_status` carries machine-readable piano events (`use_mode_entered`, record/playback transitions).