Add resource node persistence

Docs/PersistenceDesignDocument.md

@@ -441,12 +441,19 @@ This document defines:
 
 Implementation work remains tracked separately in the roadmap.
 
+The MVP resource-node implementation stores depletion as existing map/tile
+actor state. Each `AAgrarianResourceNode` may define a stable
+`PersistenceNodeId`; otherwise the actor name is used as a fallback. Save files
+capture `RemainingHarvests` for resource nodes present in the loaded world and
+restore only matching existing nodes. This deliberately avoids spawning resource
+nodes from saves, keeping tile-authored resources owned by tile content while
+letting persistence remember depletion for active tiles.
+
 ## Open Questions
 
 - Should the first playable MVP use `USaveGame`, JSON, or a hybrid save
   backend?
 - What is the first stable `SaveFormatVersion` value?
-- Which resource nodes should persist depletion in Ground Zero?
 - Should disconnected players remain in world physically or be removed?
 - How much inventory should death/respawn preserve?
 - When do saves move from file-based records to database-backed records?

Docs/TechnicalDesignDocument.md

@@ -458,6 +458,15 @@ plants remain pure bare-hand gathering. Later nodes can disable
 `bAllowBareHandGathering` when the game has proper tool equipment, durability,
 and feedback UI.
 
+Resource node persistence is map/tile state, not a spawned-actor replay path.
+`UAgrarianSaveGame` stores `FAgrarianSavedResourceNode` records keyed by
+`AAgrarianResourceNode::PersistenceNodeId`, with the actor name as a fallback.
+`UAgrarianPersistenceSubsystem` captures only resource nodes that exist in the
+currently loaded world and restores matching existing nodes by stable id. This
+keeps the MVP compatible with later Earth-scale tiles: a tile contributes
+resource depletion state only when its resource actors actually exist, and tile
+generation/placement scripts should assign deterministic node ids.
+
 ### Wildlife Navigation
 
 MVP wildlife movement is server authoritative. `AAgrarianWildlifeBase` uses an

Docs/Terrain/GroundZeroResourcePass.md

@@ -69,6 +69,15 @@ immediate benefit:
 The rule is inventory-based until equipment slots, durability, and explicit
 active-hand state are implemented.
 
+## Persistence
+
+Ground Zero resource actors receive stable `PersistenceNodeId` values matching
+their placement labels. The persistence subsystem captures and restores only
+resource nodes that exist in the loaded world, so depletion records stay scoped
+to active map/tile content. Future generated Earth-scale tiles should follow the
+same rule: assign deterministic resource node IDs during placement and let the
+save system record depletion only for tiles whose resource actors are present.
+
 ## Follow-Up
 
 Future passes should replace the prototype meshes with real coastal scrub,