feat(go-config): multi-format codecs, envc CLI, fixtures, ASRs

- Module github.com/eslider/go-config with env/yaml/json/ini packages
- internal: source, keymap, merge, structconv, bytesutil
- cmd/envc: convert, get, merge
- docs/asr ASR-0001..0008, README/CHANGELOG/AGENTS refresh
- golangci-lint v2 config; tests + fixtures

Co-authored-by: Cursor <cursoragent@cursor.com>

env/options.go

@@ -0,0 +1,105 @@
+package env
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"os"
+
+	"github.com/eslider/go-config/internal/keymap"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+	"github.com/go-viper/mapstructure/v2"
+)
+
+// Option configures a Codec.
+type Option func(*Codec)
+
+// WithCurrentEnvironment appends the process environment as a source (read at Map time).
+func WithCurrentEnvironment() Option {
+	return func(c *Codec) {
+		c.layers = append(c.layers, func(_ context.Context) (map[string]string, error) {
+			return flatFromEnviron(os.Environ()), nil
+		})
+	}
+}
+
+// WithFile appends a dotenv file path as a source.
+func WithFile(path string) Option {
+	return withSource(source.File{Path: path}, path)
+}
+
+// WithBytes appends raw dotenv bytes as a source.
+func WithBytes(b []byte) Option {
+	return withSource(source.Bytes{Data: b, Name: "bytes"}, "bytes")
+}
+
+// WithReader appends dotenv content from r (read fully on each Map call).
+func WithReader(r io.Reader) Option {
+	return withSource(source.Reader{R: r, Name: "reader"}, "reader")
+}
+
+// WithURL appends an HTTP(S) URL returning dotenv content. Use WithHTTPHeader /
+// WithHTTPClient before WithURL so they apply to this request.
+func WithURL(raw string) Option {
+	return func(c *Codec) {
+		var hdr http.Header
+		if c.urlHeader != nil {
+			hdr = c.urlHeader.Clone()
+		}
+		s := source.URL{Raw: raw, Header: hdr, HTTPClient: c.httpClient}
+		withSource(s, raw)(c)
+	}
+}
+
+// WithHTTPClient sets the HTTP client used by subsequent WithURL sources.
+func WithHTTPClient(client *http.Client) Option {
+	return func(c *Codec) { c.httpClient = client }
+}
+
+// WithHTTPHeader adds a header for subsequent WithURL sources.
+func WithHTTPHeader(k, v string) Option {
+	return func(c *Codec) {
+		if c.urlHeader == nil {
+			c.urlHeader = make(http.Header)
+		}
+		c.urlHeader.Add(k, v)
+	}
+}
+
+// WithPrefix strips prefix from variable names before path splitting.
+func WithPrefix(prefix string) Option {
+	return func(c *Codec) { c.prefix = prefix }
+}
+
+// WithKeyNormalizer sets key normalizer after merge (nil disables).
+func WithKeyNormalizer(n keymap.Normalizer) Option {
+	return func(c *Codec) { c.normalizer = n }
+}
+
+// WithSliceMerge sets slice merge strategy when merging sources.
+func WithSliceMerge(s merge.SliceStrategy) Option {
+	return func(c *Codec) { c.sliceStrat = s }
+}
+
+// WithTrim toggles struct string trim via mapstructure hook.
+func WithTrim(enable bool) Option {
+	return func(c *Codec) { c.structOpts.Trim = enable }
+}
+
+// WithWeaklyTyped toggles weak typing for struct decode.
+func WithWeaklyTyped(enable bool) Option {
+	return func(c *Codec) { c.structOpts.WeaklyTyped = enable }
+}
+
+// WithTagName sets the struct tag name for mapstructure.
+func WithTagName(name string) Option {
+	return func(c *Codec) { c.structOpts.TagName = name }
+}
+
+// WithDecodeHook appends a decode hook.
+func WithDecodeHook(h mapstructure.DecodeHookFunc) Option {
+	return func(c *Codec) {
+		c.structOpts.ExtraHooks = append(c.structOpts.ExtraHooks, h)
+	}
+}