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/merge.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"io"
+
+	"github.com/eslider/go-config/internal/bytesutil"
+	"github.com/eslider/go-config/internal/merge"
+	"github.com/eslider/go-config/internal/source"
+)
+
+// RunMerge implements: envc merge --from F --to T [--output] inputs...
+func RunMerge(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("merge", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	from := fs.String("from", "", "input format: yaml|json|ini|env")
+	to := fs.String("to", "", "output format: yaml|json|ini|env")
+	output := fs.String("output", "-", "output path or - for stdout")
+	if err := fs.Parse(args); err != nil {
+		return 2
+	}
+	if *from == "" || *to == "" {
+		_, _ = fmt.Fprintln(stderr, "merge: --from and --to are required")
+		return 2
+	}
+	inputs := fs.Args()
+	if len(inputs) == 0 {
+		_, _ = fmt.Fprintln(stderr, "merge: at least one input file or URL required")
+		return 2
+	}
+	ctx := context.Background()
+	acc := make(map[string]any)
+	for _, in := range inputs {
+		var src source.Source
+		if in == "-" {
+			b, err := io.ReadAll(stdin)
+			if err != nil {
+				_, _ = fmt.Fprintf(stderr, "merge: stdin: %v\n", err)
+				return 1
+			}
+			src = source.Bytes{Data: b, Name: "stdin"}
+		} else {
+			src = openSource(in, stdin)
+		}
+		b, err := bytesutil.ReadAll(ctx, src)
+		if err != nil {
+			_, _ = fmt.Fprintf(stderr, "merge: read %s: %v\n", in, err)
+			return 1
+		}
+		m, err := loadMapFromBytes(ctx, *from, b)
+		if err != nil {
+			_, _ = fmt.Fprintf(stderr, "merge: parse %s: %v\n", in, err)
+			return 1
+		}
+		merge.DeepMerge(acc, m)
+	}
+	outb, err := marshalMap(*to, acc)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "merge: marshal: %v\n", err)
+		return 1
+	}
+	out, err := openOutput(*output, stdout)
+	if err != nil {
+		_, _ = fmt.Fprintf(stderr, "merge: output: %v\n", err)
+		return 1
+	}
+	defer func() { _ = out.Close() }()
+	if _, err := out.Write(outb); err != nil {
+		_, _ = fmt.Fprintf(stderr, "merge: write: %v\n", err)
+		return 1
+	}
+	if *output == "-" || *output == "" {
+		if len(outb) > 0 && outb[len(outb)-1] != '\n' {
+			_, _ = out.Write([]byte("\n"))
+		}
+	}
+	return 0
+}