feat: add per-user tenant scoping

internal/tenancy/tenancy.go

@@ -0,0 +1,30 @@
+package tenancy
+
+import (
+	"context"
+	"strings"
+)
+
+type contextKey string
+
+const tenantKeyContextKey contextKey = "tenancy.tenant_key"
+
+// WithTenantKey returns a context scoped to the authenticated tenant boundary.
+// The tenant key is intentionally opaque; today it is the authenticated API key
+// or OAuth client id, and callers should not interpret it as a human username.
+func WithTenantKey(ctx context.Context, tenantKey string) context.Context {
+	tenantKey = strings.TrimSpace(tenantKey)
+	if tenantKey == "" {
+		return ctx
+	}
+	return context.WithValue(ctx, tenantKeyContextKey, tenantKey)
+}
+
+func KeyFromContext(ctx context.Context) (string, bool) {
+	if ctx == nil {
+		return "", false
+	}
+	value, ok := ctx.Value(tenantKeyContextKey).(string)
+	value = strings.TrimSpace(value)
+	return value, ok && value != ""
+}