Look up Stringer context values using the original key

builder.go

@@ -433,7 +433,7 @@ func (b OopsErrorBuilder) WithContext(ctx context.Context, keys ...any) OopsErro
 	for _, k := range keys {
 		switch k := k.(type) {
 		case fmt.Stringer:
-			snap[k.String()] = contextValueOrNil(ctx, k.String())
+			snap[k.String()] = contextValueOrNil(ctx, k)
 		case string:
 			snap[k] = contextValueOrNil(ctx, k)
 		case *string:

context_stringer_test.go

@@ -0,0 +1,26 @@
+package oops
+
+import (
+	"context"
+	"testing"
+)
+
+type stringerContextKey int
+
+func (k stringerContextKey) String() string { return "request_id" }
+
+func TestWithContextPreservesStringerKeyIdentity(t *testing.T) {
+	t.Parallel()
+	key := stringerContextKey(1)
+	ctx := context.WithValue(context.Background(), key, "typed value")
+	// A string key with the same display name must not shadow the typed key.
+	ctx = context.WithValue(ctx, "request_id", "string value") //nolint:staticcheck,revive
+	wrapped := WithContext(ctx, key).Errorf("failed")
+	err, ok := wrapped.(OopsError)
+	if !ok {
+		t.Fatalf("unexpected error type: %T", wrapped)
+	}
+	if got := err.context["request_id"]; got != "typed value" {
+		t.Fatalf("context value = %v", got)
+	}
+}