Improve 500 error logging with actual error details and correct log levels

pino-http was logging 500s at INFO level with a generic "failed with status
code 500" message. Now 500s log at ERROR level and include the actual error
(message, stack, name) via res.locals handoff from the error handler.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/middleware/error-handler.ts

@@ -26,6 +26,9 @@ export function errorHandler(
     ? { message: err.message, stack: err.stack, name: err.name }
     : { raw: err };
 
+  // Attach the real error so pino-http can include it in its response log
+  res.locals.serverError = errObj;
+
   logger.error(
     { err: errObj, method: req.method, url: req.originalUrl },
     "Unhandled error: %s %s — %s",

server/src/middleware/logger.ts

@@ -2,8 +2,20 @@ import path from "node:path";
 import fs from "node:fs";
 import pino from "pino";
 import { pinoHttp } from "pino-http";
+import { readConfigFile } from "../config-file.js";
+import { resolveDefaultLogsDir, resolveHomeAwarePath } from "../home-paths.js";
 
-const logDir = path.resolve(process.cwd(), ".paperclip", "logs");
+function resolveServerLogDir(): string {
+  const envOverride = process.env.PAPERCLIP_LOG_DIR?.trim();
+  if (envOverride) return resolveHomeAwarePath(envOverride);
+
+  const fileLogDir = readConfigFile()?.logging.logDir?.trim();
+  if (fileLogDir) return resolveHomeAwarePath(fileLogDir);
+
+  return resolveDefaultLogsDir();
+}
+
+const logDir = resolveServerLogDir();
 fs.mkdirSync(logDir, { recursive: true });
 
 const logFile = path.join(logDir, "server.log");
@@ -32,10 +44,22 @@ export const logger = pino({
 
 export const httpLogger = pinoHttp({
   logger,
+  customLogLevel(_req, res, err) {
+    if (err || res.statusCode >= 500) return "error";
+    if (res.statusCode >= 400) return "warn";
+    return "info";
+  },
   customSuccessMessage(req, res) {
     return `${req.method} ${req.url} ${res.statusCode}`;
   },
   customErrorMessage(req, res) {
     return `${req.method} ${req.url} ${res.statusCode}`;
   },
+  customProps(_req, res) {
+    const serverError = (res as any).locals?.serverError;
+    if (serverError) {
+      return { serverError };
+    }
+    return {};
+  },
 });