The shell's preloads survive a page's own Link header (#738)

ddiff --git a/server/web/sw.js b/server/web/sw.js
iindex f8bfd37a..ff9d2cf6 100644
---- a/server/web/sw.js
++++ b/server/web/sw.js
@@@ -37,6 +37,20 @@ function earlyHints(res, links) {
      const list = (links || []).filter((l) => l && l.href);
      if (!list.length || !res || res.headersSent) return false;
      const header = list.map((l) => '<' + l.href + '>; rel=preload' + (l.as ? '; as=' + l.as : '')).join(', ');
++    // A page sets its own Link later (the Markdown twin, llms.txt) and replaces the header: the preloads are merged back
++    // in when the head goes out (11-09: production's pages carried only the page's own links).
++    if (typeof res.writeHead === 'function' && typeof res.getHeader === 'function' && !res.ovHintsMerged) {
++        res.ovHintsMerged = true;
++        const writeHead = res.writeHead;
++        res.writeHead = function (...args) {
++            try {
++                const cur = res.getHeader('Link');
++                const now = Array.isArray(cur) ? cur.join(', ') : String(cur || '');
++                if (now.indexOf('rel=preload') < 0) res.setHeader('Link', now ? now + ', ' + header : header);
++            } catch { /* a hint is never worth a page */ }
++            return writeHead.apply(this, args);
++        };
++    }
      try { res.setHeader('Link', header); return true; } catch { return false; }
  }
  
ddiff --git a/test/shell.test.js b/test/shell.test.js
iindex 8f626255..70c467b1 100644
---- a/test/shell.test.js
++++ b/test/shell.test.js
@@@ -9,12 +9,23 @@ try { assets.setSharedDir(require('openvibe-shared/files').dir); } catch { /* */
  const shell = require('../server/web/sw');
  
  function fakeRes() {
--    const res = { headersSent: false, headers: {}, hints: null };
++    const res = { headersSent: false, headers: {}, hints: null, wrote: false };
      res.writeEarlyHints = (h) => { res.hints = h; return true; };
      res.setHeader = (k, v) => { res.headers[k] = v; };
++    res.getHeader = (k) => res.headers[k];
++    res.writeHead = () => { res.wrote = true; return res; };
      return res;
  }
  
++{   // A page that sets its own Link later (the Markdown twin, llms.txt) keeps the preloads too.
++    const res = fakeRes();
++    shell.hints()({ method: 'GET', path: '/', headers: { accept: 'text/html' } }, res, () => { });
++    res.setHeader('Link', '</index.md>; rel="alternate"; type="text/markdown"');
++    res.writeHead(200);
++    assert.ok(res.wrote);
++    assert.ok(/rel="alternate"/.test(res.headers.Link) && /rel=preload; as=script/.test(res.headers.Link), res.headers.Link);
++}
++
  {   // A page is hinted in its Link header; no 103 goes out (nginx 1.28 would send the page as the 103's body).
      const res = fakeRes();
      let nexted = false;