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+# Simulator-to-Registry Position Wiring Trace
+
+## Overview
+
+This document traces the complete data flow for position data from virtual node creation in the simulator to persistence in the fleet registry. There are **two distinct paths** depending on which simulator is being used.
+
+## Path 1: CSI Simulator (cmd/sim/main.go)
+
+### 1. Position Creation
+**File**: `/home/coding/spaxel/cmd/sim/main.go`
+
+Virtual nodes are created with computed positions using `generateNodePositions()`:
+- Single node: center of room
+- Two nodes: opposite corners (spans both X and Y)
+- 3+ nodes: row-major grid with alternating Z heights
+
+```go
+// Lines 198-253
+func createVirtualNodes(count int, space *Space, rng *rand.Rand) []*VirtualNode {
+    positions := generateNodePositions(count, space)
+    // ... creates VirtualNode structs with Position field
+}
+```
+
+### 2. Hello Message Transmission
+**File**: `/home/coding/spaxel/cmd/sim/main.go` (Lines 345-365)
+
+The simulator connects to mothership via WebSocket and sends a hello message:
+```go
+hello := map[string]interface{}{
+    "type":            "hello",
+    "mac":             macToString(n.MAC),
+    "pos_x":           n.Position.X,
+    "pos_y":           n.Position.Y,
+    "pos_z":           n.Position.Z,
+    // ... other fields
+}
+```
+
+### 3. Hello Message Reception
+**File**: `/home/coding/spaxel/mothership/internal/ingestion/message.go` (Lines 10-34)
+
+The `HelloMessage` struct defines the position fields as pointers:
+```go
+type HelloMessage struct {
+    // ...
+    PosX *float64 `json:"pos_x,omitempty"`
+    PosY *float64 `json:"pos_y,omitempty"`
+    PosZ *float64 `json:"pos_z,omitempty"`
+}
+```
+Pointers distinguish "not announced" (nil) from "position is (0,0,0)".
+
+### 4. Fleet Notification
+**File**: `/home/coding/spaxel/mothership/internal/ingestion/server.go` (Lines 26-37)
+
+The ingestion server calls the `FleetNotifier` callback:
+```go
+type FleetNotifier interface {
+    OnNodeConnected(mac, firmware, chip string, posX, posY, posZ *float64)
+    OnNodeDisconnected(mac string)
+}
+```
+
+### 5. Registry Persistence
+**File**: `/home/coding/spaxel/mothership/internal/fleet/manager.go` (Lines 182-231)
+
+The Fleet Manager's `OnNodeConnected()` method:
+1. Upserts the node record: `registry.UpsertNode(mac, firmware, chip)`
+2. Persists announced position (if all three axes present):
+   ```go
+   if posX != nil && posY != nil && posZ != nil {
+       registry.SetNodePosition(mac, *posX, *posY, *posZ)
+   }
+   ```
+3. Forwards position to fusion engine via `nodePositionSink`
+
+### 6. Storage
+**File**: `/home/coding/spaxel/mothership/internal/fleet/registry.go` (Lines 179-183)
+
+Positions are stored in SQLite:
+```go
+func (r *Registry) SetNodePosition(mac string, x, y, z float64) error {
+    _, err := r.db.Exec(`UPDATE nodes SET pos_x=?, pos_y=?, pos_z=? WHERE mac=?`, 
+                       x, y, z, mac)
+    return err
+}
+```
+
+## Path 2: Virtual Node Planning Simulator (mothership/internal/simulator/)
+
+This path is used for planning and coverage optimization, distinct from the CSI simulator.
+
+### 1. Virtual Node Store
+**File**: `/home/coding/spaxel/mothership/internal/simulator/virtual_state.go`
+
+Virtual nodes are created and managed in `VirtualNodeStore`:
+```go
+func (s *VirtualNodeStore) CreateVirtualNode(id, name string, position Point) 
+```
+
+### 2. Registry Bridge
+**File**: `/home/coding/spaxel/mothership/internal/simulator/registry_bridge.go`
+
+The `FleetRegistryBridge` integrates virtual nodes with the fleet registry:
+
+**Key Method - effectivePositions()** (Lines 50-99):
+- Resolves final positions for all nodes
+- Nodes at default origin (0,0,1) are reassigned spread-out geometry via `DefaultNodePositions()`
+- Explicitly-placed nodes keep their position
+- Deterministic assignment: sorted by ID, no collisions
+
+**Sync Method** (Lines 131-189):
+```go
+func (b *FleetRegistryBridge) SyncToRegistry(registry RegistryNodeAdapter) error
+```
+- Lists all nodes from store
+- Resolves effective positions
+- Creates or updates registry entries
+- Sets position and role
+
+### 3. Registry Adapter Interface
+**File**: `/home/coding/spaxel/mothership/internal/simulator/registry_bridge.go` (Lines 109-129)
+
+```go
+type RegistryNodeAdapter interface {
+    AddVirtualNode(mac, name string, x, y, z float64) error
+    SetNodePosition(mac string, x, y, z float64) error
+    SetNodeRole(mac, role string) error
+    DeleteNode(mac string) error
+    GetNode(mac string) (*NodeRecord, error)
+    GetAllNodes() ([]NodeRecord, error)
+}
+```
+
+### 4. Fleet Registry Implementation
+**File**: `/home/coding/spaxel/mothership/internal/fleet/registry.go` (Lines 273-287)
+
+```go
+func (r *Registry) AddVirtualNode(mac, name string, x, y, z float64) error {
+    _, err := r.db.Exec(`
+        INSERT INTO nodes (mac, name, role, pos_x, pos_y, pos_z, virtual, ...)
+        VALUES (?, ?, 'virtual', ?, ?, ?, 1, ...)
+    `, mac, name, x, y, z, ...)
+    return err
+}
+```
+
+## Fusion Engine Integration
+
+The registry positions flow to the 3D fusion engine for blob generation:
+
+**File**: `/home/coding/spaxel/mothership/internal/fleet/manager.go` (Lines 110-120, 173-180)
+
+```go
+// Sink for position updates
+nodePositionSink func(mac string, x, y, z float64)
+
+func (m *Manager) ForwardNodePosition(mac string, x, y, z float64) {
+    if sink != nil {
+        sink(mac, x, y, z)
+    }
+}
+```
+
+This is called from:
+1. `OnNodeConnected()` after persisting hello-announced position
+2. REST API handler after PATCH /api/nodes/{mac}/position
+
+**File**: `/home/coding/spaxel/mothership/internal/fusion/fusion.go` (Lines 64-73)
+
+The fusion engine maintains a node position map:
+```go
+type Engine struct {
+    nodePos map[string]NodePosition
+    // ...
+}
+```
+
+## Key Files in Pipeline
+
+1. **Simulator CLI**: `/home/coding/spaxel/cmd/sim/main.go`
+2. **Hello Message**: `/home/coding/spaxel/mothership/internal/ingestion/message.go`
+3. **Ingestion Server**: `/home/coding/spaxel/mothership/internal/ingestion/server.go`
+4. **Fleet Manager**: `/home/coding/spaxel/mothership/internal/fleet/manager.go`
+5. **Fleet Registry**: `/home/coding/spaxel/mothership/internal/fleet/registry.go`
+6. **Virtual Node Store**: `/home/coding/spaxel/mothership/internal/simulator/virtual_state.go`
+7. **Registry Bridge**: `/home/coding/spaxel/mothership/internal/simulator/registry_bridge.go`
+8. **Fusion Engine**: `/home/coding/spaxel/mothership/internal/fusion/fusion.go`
+
+## Verified Data Flow
+
+✅ **Complete Path 1 (CSI Simulator)**:
+1. `cmd/sim/main.go:generateNodePositions()` - computes positions
+2. `cmd/sim/main.go:connectNodes()` - sends hello with pos_x/y/z
+3. `ingestion/server.go` - receives WebSocket hello message
+4. `fleet/manager.go:OnNodeConnected()` - persists position
+5. `fleet/registry.go:SetNodePosition()` - stores in SQLite
+6. `fleet/manager.go:ForwardNodePosition()` - forwards to fusion engine
+
+✅ **Complete Path 2 (Virtual Node Planning)**:
+1. `simulator/virtual_state.go:CreateVirtualNode()` - creates virtual node
+2. `simulator/registry_bridge.go:SyncToRegistry()` - syncs to registry
+3. `fleet/registry.go:AddVirtualNode()` - stores with position
+4. Position available to fusion engine via registry queries
+
+## Integration Points
+
+- **Ingestion → Fleet**: `FleetNotifier.OnNodeConnected(mac, firmware, chip, posX, posY, posZ)`
+- **Fleet → Fusion**: `nodePositionSink(mac, x, y, z)` callback
+- **Simulator Bridge → Registry**: `RegistryNodeAdapter` interface
+
+## Acceptance Criteria Status
+
+✅ Complete data flow path documented from simulator to registry
+✅ Two distinct paths identified and documented
+✅ List of files involved in the simulator-to-registry pipeline provided