Initial implementation of ArtNet remapping proxy

Channel-level DMX remapping between ArtNet universes with:
- TOML configuration with multiple address formats (net.subnet.universe, plain number)
- ArtPoll discovery for output nodes
- Configurable channel ranges for fixture spillover handling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

remap/engine.go

@@ -0,0 +1,94 @@
+package remap
+
+import (
+	"github.com/gopatchy/artmap/artnet"
+	"github.com/gopatchy/artmap/config"
+)
+
+// Output represents a remapped DMX output
+type Output struct {
+	Universe artnet.Universe
+	Data     [512]byte
+}
+
+// Engine handles DMX channel remapping
+type Engine struct {
+	mappings []config.NormalizedMapping
+	// Index mappings by source universe for faster lookup
+	bySource map[artnet.Universe][]config.NormalizedMapping
+}
+
+// NewEngine creates a new remapping engine
+func NewEngine(mappings []config.NormalizedMapping) *Engine {
+	bySource := make(map[artnet.Universe][]config.NormalizedMapping)
+	for _, m := range mappings {
+		bySource[m.FromUniverse] = append(bySource[m.FromUniverse], m)
+	}
+
+	return &Engine{
+		mappings: mappings,
+		bySource: bySource,
+	}
+}
+
+// Remap applies mappings to incoming DMX data and returns outputs
+func (e *Engine) Remap(srcUniverse artnet.Universe, srcData [512]byte) []Output {
+	mappings, ok := e.bySource[srcUniverse]
+	if !ok {
+		return nil
+	}
+
+	// Group outputs by destination universe
+	outputs := make(map[artnet.Universe]*Output)
+
+	for _, m := range mappings {
+		// Get or create output for this destination universe
+		out, ok := outputs[m.ToUniverse]
+		if !ok {
+			out = &Output{
+				Universe: m.ToUniverse,
+			}
+			outputs[m.ToUniverse] = out
+		}
+
+		// Copy channels
+		for i := 0; i < m.Count; i++ {
+			srcChan := m.FromChannel + i
+			dstChan := m.ToChannel + i
+			if srcChan < 512 && dstChan < 512 {
+				out.Data[dstChan] = srcData[srcChan]
+			}
+		}
+	}
+
+	// Convert map to slice
+	result := make([]Output, 0, len(outputs))
+	for _, out := range outputs {
+		result = append(result, *out)
+	}
+
+	return result
+}
+
+// SourceUniverses returns all universes that have mappings
+func (e *Engine) SourceUniverses() []artnet.Universe {
+	result := make([]artnet.Universe, 0, len(e.bySource))
+	for u := range e.bySource {
+		result = append(result, u)
+	}
+	return result
+}
+
+// DestUniverses returns all destination universes
+func (e *Engine) DestUniverses() []artnet.Universe {
+	seen := make(map[artnet.Universe]bool)
+	for _, m := range e.mappings {
+		seen[m.ToUniverse] = true
+	}
+
+	result := make([]artnet.Universe, 0, len(seen))
+	for u := range seen {
+		result = append(result, u)
+	}
+	return result
+}