Initial commit: shared Go utilities (ssr, stringsx)

Extracted from sweeper to share across Go projects:
- ssr: template caching and SSR writer
- stringsx: string helpers

go.mod

@@ -0,0 +1,5 @@
+module sxgo
+
+go 1.25.5
+
+require github.com/cespare/xxhash/v2 v2.3.0

go.sum

@@ -0,0 +1,2 @@
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=

ssr/ssr.go

@@ -0,0 +1,71 @@
+package ssr
+
+import (
+	"errors"
+	"html/template"
+	"io"
+	"sync"
+
+	"github.com/cespare/xxhash/v2"
+)
+
+type Writer struct {
+	err   error
+	w     io.Writer
+	cache *TmplCache
+}
+
+func NewWriter(w io.Writer, cache *TmplCache) *Writer {
+	return &Writer{w: w, cache: cache}
+}
+
+func (w *Writer) Raw(s string) error {
+	_, err := w.w.Write([]byte(s))
+	w.err = errors.Join(w.err, err)
+	return w.err
+}
+
+func (w *Writer) Tmpl(data any, tmpl string) error {
+	t, err := w.cache.GetOrCompile(tmpl)
+	if err != nil {
+		w.err = errors.Join(w.err, err)
+		return w.err
+	}
+
+	err = t.Execute(w.w, data)
+	w.err = errors.Join(w.err, err)
+	return w.err
+}
+
+func (w *Writer) Error() error {
+	return w.err
+}
+
+type TmplCache struct {
+	funcs template.FuncMap
+	cache sync.Map // uint64 -> *template.Template
+}
+
+func NewTmplCache(funcs template.FuncMap) *TmplCache {
+	return &TmplCache{funcs: funcs}
+}
+
+func (t *TmplCache) GetOrCompile(content string) (*template.Template, error) {
+	key := xxhash.Sum64String(content)
+
+	if cached, ok := t.cache.Load(key); ok {
+		return cached.(*template.Template), nil
+	}
+
+	tmpl, err := template.New("").Funcs(t.funcs).Parse(content)
+	if err != nil {
+		return nil, err
+	}
+
+	t.cache.Store(key, tmpl)
+	return tmpl, nil
+}
+
+type Renderable interface {
+	Render(sw *Writer) error
+}

stringsx/stringsx.go

@@ -0,0 +1,9 @@
+// Package stringsx provides string-related helpers.
+package stringsx
+
+import "strings"
+
+// IsBlank reports whether a string contains only whitespace.
+func IsBlank(s string) bool {
+	return strings.TrimSpace(s) == ""
+}