chore: establish local platform baseline

internal/developmentembedding/embedding.go

@@ -0,0 +1,49 @@
+package developmentembedding
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+)
+
+const Dimensions = 1536
+
+// Vector is a deterministic local-development projection. It is not a
+// production semantic embedding and exists only to exercise the storage,
+// filtering and lifecycle contracts without an external model account.
+func Vector(content string) []float64 {
+	values := make([]float64, Dimensions)
+	for block := 0; block < Dimensions/32; block++ {
+		digest := sha256.Sum256([]byte(fmt.Sprintf("%d:%s", block, content)))
+		for index, value := range digest {
+			values[block*32+index] = (float64(value) - 127.5) / 127.5
+		}
+	}
+	var squared float64
+	for _, value := range values {
+		squared += value * value
+	}
+	norm := math.Sqrt(squared)
+	if norm != 0 {
+		for index := range values {
+			values[index] /= norm
+		}
+	}
+	return values
+}
+
+func Literal(values []float64) string {
+	var builder strings.Builder
+	builder.Grow(len(values) * 12)
+	builder.WriteByte('[')
+	for index, value := range values {
+		if index > 0 {
+			builder.WriteByte(',')
+		}
+		builder.WriteString(strconv.FormatFloat(value, 'g', 8, 64))
+	}
+	builder.WriteByte(']')
+	return builder.String()
+}