diff --git a/server/src/__tests__/error-handler.test.ts b/server/src/__tests__/error-handler.test.ts
new file mode 100644
index 00000000..d01a8c3c
--- /dev/null
+++ b/server/src/__tests__/error-handler.test.ts
@@ -0,0 +1,53 @@
+import type { NextFunction, Request, Response } from "express";
+import { describe, expect, it, vi } from "vitest";
+import { HttpError } from "../errors.js";
+import { errorHandler } from "../middleware/error-handler.js";
+
+function makeReq(): Request {
+  return {
+    method: "GET",
+    originalUrl: "/api/test",
+    body: { a: 1 },
+    params: { id: "123" },
+    query: { q: "x" },
+  } as unknown as Request;
+}
+
+function makeRes(): Response {
+  const res = {
+    status: vi.fn(),
+    json: vi.fn(),
+  } as unknown as Response;
+  (res.status as unknown as ReturnType<typeof vi.fn>).mockReturnValue(res);
+  return res;
+}
+
+describe("errorHandler", () => {
+  it("attaches the original Error to res.err for 500s", () => {
+    const req = makeReq();
+    const res = makeRes() as any;
+    const next = vi.fn() as unknown as NextFunction;
+    const err = new Error("boom");
+
+    errorHandler(err, req, res, next);
+
+    expect(res.status).toHaveBeenCalledWith(500);
+    expect(res.json).toHaveBeenCalledWith({ error: "Internal server error" });
+    expect(res.err).toBe(err);
+    expect(res.__errorContext?.error?.message).toBe("boom");
+  });
+
+  it("attaches HttpError instances for 500 responses", () => {
+    const req = makeReq();
+    const res = makeRes() as any;
+    const next = vi.fn() as unknown as NextFunction;
+    const err = new HttpError(500, "db exploded");
+
+    errorHandler(err, req, res, next);
+
+    expect(res.status).toHaveBeenCalledWith(500);
+    expect(res.json).toHaveBeenCalledWith({ error: "db exploded" });
+    expect(res.err).toBe(err);
+    expect(res.__errorContext?.error?.message).toBe("db exploded");
+  });
+});
diff --git a/server/src/middleware/error-handler.ts b/server/src/middleware/error-handler.ts
index 293c42ab..7f86dfd0 100644
--- a/server/src/middleware/error-handler.ts
+++ b/server/src/middleware/error-handler.ts
@@ -11,6 +11,25 @@ export interface ErrorContext {
   reqQuery?: unknown;
 }
 
+function attachErrorContext(
+  req: Request,
+  res: Response,
+  payload: ErrorContext["error"],
+  rawError?: Error,
+) {
+  (res as any).__errorContext = {
+    error: payload,
+    method: req.method,
+    url: req.originalUrl,
+    reqBody: req.body,
+    reqParams: req.params,
+    reqQuery: req.query,
+  } satisfies ErrorContext;
+  if (rawError) {
+    (res as any).err = rawError;
+  }
+}
+
 export function errorHandler(
   err: unknown,
   req: Request,
@@ -19,14 +38,12 @@ export function errorHandler(
 ) {
   if (err instanceof HttpError) {
     if (err.status >= 500) {
-      (res as any).__errorContext = {
-        error: { message: err.message, stack: err.stack, name: err.name, details: err.details },
-        method: req.method,
-        url: req.originalUrl,
-        reqBody: req.body,
-        reqParams: req.params,
-        reqQuery: req.query,
-      } satisfies ErrorContext;
+      attachErrorContext(
+        req,
+        res,
+        { message: err.message, stack: err.stack, name: err.name, details: err.details },
+        err,
+      );
     }
     res.status(err.status).json({
       error: err.message,
@@ -40,16 +57,15 @@ export function errorHandler(
     return;
   }
 
-  (res as any).__errorContext = {
-    error: err instanceof Error
+  const rootError = err instanceof Error ? err : new Error(String(err));
+  attachErrorContext(
+    req,
+    res,
+    err instanceof Error
       ? { message: err.message, stack: err.stack, name: err.name }
-      : { message: String(err), raw: err },
-    method: req.method,
-    url: req.originalUrl,
-    reqBody: req.body,
-    reqParams: req.params,
-    reqQuery: req.query,
-  } satisfies ErrorContext;
+      : { message: String(err), raw: err, stack: rootError.stack, name: rootError.name },
+    rootError,
+  );
 
   res.status(500).json({ error: "Internal server error" });
 }
diff --git a/server/src/middleware/logger.ts b/server/src/middleware/logger.ts
index dd826c06..be47e3c5 100644
--- a/server/src/middleware/logger.ts
+++ b/server/src/middleware/logger.ts
@@ -62,7 +62,7 @@ export const httpLogger = pinoHttp({
       const ctx = (res as any).__errorContext;
       if (ctx) {
         return {
-          err: ctx.error,
+          errorContext: ctx.error,
           reqBody: ctx.reqBody,
           reqParams: ctx.reqParams,
           reqQuery: ctx.reqQuery,