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>

cmd/envc/get.go

@@ -0,0 +1,83 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/eslider/go-config/internal/bytesutil"
+	"github.com/eslider/go-config/internal/keymap"
+)
+
+// RunGet implements: envc get --from F --path p [input].
+func RunGet(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("get", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	from := fs.String("from", "", "format: yaml|json|ini|env")
+	path := fs.String("path", "", "dot-separated path (e.g. service.subservice.name)")
+	if err := fs.Parse(args); err != nil {
+		return 2
+	}
+	if *from == "" || *path == "" {
+		_, _ = fmt.Fprintln(stderr, "get: --from and --path are required")
+		return 2
+	}
+	pos := fs.Args()
+	input := "-"
+	if len(pos) > 0 {
+		input = pos[0]
+	}
+	ctx := context.Background()
+	src := openSource(input, stdin)
+	b, err := bytesutil.ReadAll(ctx, src)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "get: read: %v\n", err)
+		return 1
+	}
+	m, err := loadMapFromBytes(ctx, *from, b)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "get: parse: %v\n", err)
+		return 1
+	}
+	v, err := walkPath(m, strings.Split(*path, "."))
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "get: %v\n", err)
+		return 1
+	}
+	switch val := v.(type) {
+	case string, bool, float64, int, int64, nil:
+		_, _ = fmt.Fprintln(stdout, val)
+	default:
+		enc := json.NewEncoder(stdout)
+		enc.SetIndent("", "  ")
+		if err := enc.Encode(val); err != nil {
+			_, _ = fmt.Fprintf(stderr, "get: encode: %v\n", err)
+			return 1
+		}
+	}
+	return 0
+}
+
+func walkPath(m map[string]any, parts []string) (any, error) {
+	var cur any = m
+	for i, p := range parts {
+		if p == "" {
+			continue
+		}
+		pk := keymap.LowerAlnum(p)
+		switch t := cur.(type) {
+		case map[string]any:
+			nx, ok := t[pk]
+			if !ok {
+				return nil, fmt.Errorf("missing key %q (normalized %q) at segment %d", p, pk, i)
+			}
+			cur = nx
+		default:
+			return nil, fmt.Errorf("not a map at segment %d", i)
+		}
+	}
+	return cur, nil
+}