fix(router): map middleware errors like handler errors

internal/router/router_impl.go

@@ -658,8 +658,14 @@ func applyMiddleware(h http.Handler, middleware []Middleware, container vessel.V
 			if errorHandler != nil {
 				_ = errorHandler.HandleError(ctx.Context(), err)
 			} else {
-				// Default error handling
-				http.Error(w, err.Error(), http.StatusInternalServerError)
+				// Same mapping the typed-handler path uses, so an error
+				// carries its status and envelope whether it was returned
+				// from a handler or from middleware. Falling back to
+				// http.Error here turned every middleware error into a
+				// 500 with a plain-text body — a middleware returning
+				// Unauthorized produced a 500, which pushed callers into
+				// hand-writing ctx.JSON responses instead.
+				handleError(ctx, err)
 			}
 		}
 	})
@@ -738,8 +744,14 @@ func applyMiddlewareAndInterceptors(
 			if errorHandler != nil {
 				_ = errorHandler.HandleError(ctx.Context(), err)
 			} else {
-				// Default error handling
-				http.Error(w, err.Error(), http.StatusInternalServerError)
+				// Same mapping the typed-handler path uses, so an error
+				// carries its status and envelope whether it was returned
+				// from a handler or from middleware. Falling back to
+				// http.Error here turned every middleware error into a
+				// 500 with a plain-text body — a middleware returning
+				// Unauthorized produced a 500, which pushed callers into
+				// hand-writing ctx.JSON responses instead.
+				handleError(ctx, err)
 			}
 		}
 	})
@@ -770,8 +782,9 @@ func convertForgeMiddlewareToHTTP(mw Middleware, container vessel.Vessel, errorH
 				if errorHandler != nil {
 					_ = errorHandler.HandleError(ctx.Context(), err)
 				} else {
-					// Default error handling
-					http.Error(w, err.Error(), http.StatusInternalServerError)
+					// See applyMiddleware — global middleware maps errors
+					// the same way route middleware does.
+					handleError(ctx, err)
 				}
 			}
 		})

middleware_error_mapping_test.go

@@ -0,0 +1,110 @@
+package forge_test
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/xraph/forge"
+)
+
+type meReq struct{}
+type meResp struct {
+	OK bool `json:"ok"`
+}
+
+// post drives a route that either returns err from middleware or from the
+// handler, so the two paths can be compared directly.
+func post(t *testing.T, fromMiddleware bool, err error) *httptest.ResponseRecorder {
+	t.Helper()
+	r := forge.NewRouter()
+
+	handler := func(ctx forge.Context, _ *meReq) (*meResp, error) {
+		if fromMiddleware {
+			return &meResp{OK: true}, nil
+		}
+		return nil, err
+	}
+
+	opts := []forge.RouteOption{}
+	if fromMiddleware {
+		opts = append(opts, forge.WithMiddleware(func(next forge.Handler) forge.Handler {
+			return func(ctx forge.Context) error { return err }
+		}))
+	}
+	if regErr := r.POST("/x", handler, opts...); regErr != nil {
+		t.Fatalf("register route: %v", regErr)
+	}
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(context.Background(), "POST", "/x",
+		bytes.NewReader([]byte(`{}`)))
+	req.Header.Set("Content-Type", "application/json")
+	r.ServeHTTP(rec, req)
+	return rec
+}
+
+// An error returned from middleware must produce the same status and body as
+// the same error returned from a handler.
+//
+// Previously the middleware path fell back to http.Error, so a
+// forge.Unauthorized became a 500 with a plain-text body. Callers worked
+// around it by hand-writing ctx.JSON responses in middleware, which
+// duplicates the envelope and drifts from the handler-side shape.
+func TestMiddlewareError_MapsLikeHandlerError(t *testing.T) {
+	cases := []struct {
+		name string
+		err  error
+		want int
+	}{
+		{"unauthorized", forge.Unauthorized("nope"), http.StatusUnauthorized},
+		{"forbidden", forge.Forbidden("denied"), http.StatusForbidden},
+		{"bad request", forge.BadRequest("bad"), http.StatusBadRequest},
+		{"not found", forge.NotFound("gone"), http.StatusNotFound},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			fromHandler := post(t, false, tc.err)
+			fromMiddleware := post(t, true, tc.err)
+
+			if fromHandler.Code != tc.want {
+				t.Fatalf("handler: got %d, want %d (body %q)",
+					fromHandler.Code, tc.want, fromHandler.Body.String())
+			}
+			if fromMiddleware.Code != tc.want {
+				t.Errorf("middleware: got %d, want %d (body %q)",
+					fromMiddleware.Code, tc.want, fromMiddleware.Body.String())
+			}
+			if fromMiddleware.Body.String() != fromHandler.Body.String() {
+				t.Errorf("bodies differ:\n  handler:    %q\n  middleware: %q",
+					fromHandler.Body.String(), fromMiddleware.Body.String())
+			}
+		})
+	}
+}
+
+// The body must be the JSON envelope, not a plain-text dump.
+func TestMiddlewareError_ProducesJSONEnvelope(t *testing.T) {
+	rec := post(t, true, forge.Unauthorized("nope"))
+
+	var body map[string]any
+	if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
+		t.Fatalf("middleware error body is not JSON: %q", rec.Body.String())
+	}
+	if body["error"] != "nope" {
+		t.Errorf("error field: got %v, want %q", body["error"], "nope")
+	}
+}
+
+// A plain error carries no status, so it must still be a 500 — the fix
+// promotes typed errors, it does not swallow untyped ones.
+func TestMiddlewareError_UntypedStaysInternalError(t *testing.T) {
+	rec := post(t, true, context.DeadlineExceeded)
+	if rec.Code != http.StatusInternalServerError {
+		t.Errorf("got %d, want 500 (body %q)", rec.Code, rec.Body.String())
+	}
+}