Add errorToResponse mapper with TDD tests covering all mapping rules

src/routes/error/map.test.ts

@@ -0,0 +1,59 @@
+import { describe, it, expect } from "vitest";
+import { errorToResponse } from "./map.js";
+import { ApiHttpError, ApiTimeoutError } from "@/shared/api/errors";
+
+describe("errorToResponse", () => {
+  it("maps ApiHttpError(404) to not_found", () => {
+    const result = errorToResponse(new ApiHttpError("Not found", 404));
+    expect(result).toEqual({ status: 404, errorCode: "not_found" });
+  });
+
+  it("maps ApiHttpError(500) to internal", () => {
+    const result = errorToResponse(new ApiHttpError("Server error", 500));
+    expect(result).toEqual({ status: 500, errorCode: "internal" });
+  });
+
+  it("maps ApiHttpError(502) to internal", () => {
+    const result = errorToResponse(new ApiHttpError("Bad gateway", 502));
+    expect(result).toEqual({ status: 500, errorCode: "internal" });
+  });
+
+  it("maps ApiHttpError(503) to internal (5xx range)", () => {
+    const result = errorToResponse(new ApiHttpError("Service unavailable", 503));
+    expect(result).toEqual({ status: 500, errorCode: "internal" });
+  });
+
+  it("maps ApiHttpError(599) to internal (5xx boundary)", () => {
+    const result = errorToResponse(new ApiHttpError("Edge case", 599));
+    expect(result).toEqual({ status: 500, errorCode: "internal" });
+  });
+
+  it("maps ApiTimeoutError to unavailable with Retry-After header", () => {
+    const result = errorToResponse(new ApiTimeoutError(5000));
+    expect(result).toEqual({
+      status: 503,
+      headers: { "Retry-After": "30" },
+      errorCode: "unavailable",
+    });
+  });
+
+  it("maps unknown Error to internal", () => {
+    const result = errorToResponse(new Error("something broke"));
+    expect(result).toEqual({ status: 500, errorCode: "internal" });
+  });
+
+  it("maps non-Error value to internal", () => {
+    const result = errorToResponse("string error");
+    expect(result).toEqual({ status: 500, errorCode: "internal" });
+  });
+
+  it("maps null to internal", () => {
+    const result = errorToResponse(null);
+    expect(result).toEqual({ status: 500, errorCode: "internal" });
+  });
+
+  it("maps ApiHttpError with non-5xx/non-404 status to internal", () => {
+    const result = errorToResponse(new ApiHttpError("Forbidden", 403));
+    expect(result).toEqual({ status: 500, errorCode: "internal" });
+  });
+});

src/routes/error/map.ts

@@ -0,0 +1,40 @@
+import { ApiHttpError, ApiTimeoutError } from "@/shared/api/errors";
+
+export interface ErrorResponse {
+  status: 404 | 500 | 503;
+  headers?: Record<string, string>;
+  errorCode: "not_found" | "internal" | "unavailable";
+}
+
+/**
+ * Maps an application error to a structured HTTP-like response.
+ * Consumed by SSR loader paths and error page routing.
+ *
+ * Mapping rules (design spec S4.6):
+ * - ApiHttpError 404       -> { status: 404, errorCode: "not_found" }
+ * - ApiHttpError 500-599   -> { status: 500, errorCode: "internal" }
+ * - ApiTimeoutError        -> { status: 503, Retry-After: 30, errorCode: "unavailable" }
+ * - Everything else        -> { status: 500, errorCode: "internal" }
+ */
+export function errorToResponse(error: unknown): ErrorResponse {
+  if (error instanceof ApiHttpError) {
+    if (error.status === 404) {
+      return { status: 404, errorCode: "not_found" };
+    }
+    if (error.status >= 500 && error.status <= 599) {
+      return { status: 500, errorCode: "internal" };
+    }
+    // Any other HTTP status (e.g. 403) falls through to the default
+    return { status: 500, errorCode: "internal" };
+  }
+
+  if (error instanceof ApiTimeoutError) {
+    return {
+      status: 503,
+      headers: { "Retry-After": "30" },
+      errorCode: "unavailable",
+    };
+  }
+
+  return { status: 500, errorCode: "internal" };
+}