stop parsing request bodies on sidecar proxy routes

every multipart upload through /api/<sidecar>/* arrived corrupted. bodyParser ran on
proxy routes and called parseBody for multipart, so hono cached a FormData on the
request; when the proxy then asked for the bytes hono re-serialised them from that
cache with a NEW boundary, while the proxy still forwarded the ORIGINAL content-type
header. header and body disagreed and the far side rejected it with
"Multipart: Unexpected end of form".

bodyParser now skips prefixes owned by createSidecarProxy, which register themselves
so a new sidecar cannot forget. the proxy also forwards the body as a stream instead
of buffering it, which drops the second in-memory copy of every upload.

note the bug report proposed skipping multipart in bodyParser outright; that would
have broken /upload, /file-browser upload and /bug-report, which do read a multipart
body from ctx.get('body').

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/servers/_middlewares/body-parser.ts

@@ -1,7 +1,16 @@
 import type { MiddlewareHandler } from 'hono';
 import * as errors from '../custom-errors';
+import { isProxiedPath } from '../sidecar/proxied-prefixes';
 
 export const bodyParser: () => MiddlewareHandler = () => async (ctx, next) => {
+  // Sidecar proxy routes: the body is forwarded verbatim and never read here. Consuming it would be
+  // pointless for JSON and destructive for multipart — see sidecar/proxied-prefixes.ts for why a parsed
+  // multipart body cannot be forwarded intact.
+  if (isProxiedPath(ctx.req.path)) {
+    ctx.set('body', {});
+    return next();
+  }
+
   if (!['POST', 'PUT', 'PATCH'].includes(ctx.req.method.toUpperCase())) {
     ctx.set('body', {});
     return next();