feat(logger): add IntoCtx/FromCtx for per-request loggers

backend/pkg/logger/ctx.go

@@ -0,0 +1,29 @@
+package logger
+
+import (
+	"context"
+
+	"github.com/rs/zerolog"
+)
+
+// ctxKey is unexported so other packages can't collide.
+type ctxKey struct{}
+
+// IntoCtx returns a new context carrying the given logger. Retrieve it later
+// with FromCtx. Middleware that builds a per-request logger should call this
+// once per request.
+func IntoCtx(ctx context.Context, l zerolog.Logger) context.Context {
+	return context.WithValue(ctx, ctxKey{}, l)
+}
+
+// FromCtx returns the logger bound to ctx. If no logger is bound (e.g. the
+// call is outside any middleware, or ctx is nil), it returns the global
+// logger. Never returns a zero-value zerolog.Logger.
+func FromCtx(ctx context.Context) zerolog.Logger {
+	if ctx != nil {
+		if l, ok := ctx.Value(ctxKey{}).(zerolog.Logger); ok {
+			return l
+		}
+	}
+	return Get().Logger
+}

backend/pkg/logger/ctx_test.go

@@ -0,0 +1,42 @@
+package logger
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"github.com/rs/zerolog"
+)
+
+func TestFromCtx_ReturnsBoundLogger(t *testing.T) {
+	var buf bytes.Buffer
+	l := zerolog.New(&buf).With().Str("request_id", "req-1").Logger()
+
+	ctx := IntoCtx(context.Background(), l)
+	got := FromCtx(ctx)
+	got.Info().Msg("hello")
+
+	var parsed map[string]any
+	line := strings.TrimSpace(buf.String())
+	if err := json.Unmarshal([]byte(line), &parsed); err != nil {
+		t.Fatalf("not JSON: %v — %s", err, line)
+	}
+	if parsed["request_id"] != "req-1" {
+		t.Errorf("request_id = %v, want req-1", parsed["request_id"])
+	}
+	if parsed["message"] != "hello" {
+		t.Errorf("message = %v, want hello", parsed["message"])
+	}
+}
+
+func TestFromCtx_NoLoggerFallsBackToDisabled(t *testing.T) {
+	defer func() {
+		if r := recover(); r != nil {
+			t.Fatalf("FromCtx panicked: %v", r)
+		}
+	}()
+	l := FromCtx(context.Background())
+	l.Info().Msg("should not panic")
+}