fix: terminal input reaches the shell in the order it was typed

internal/server/web/templates/terminal.html

@@ -162,11 +162,42 @@
     term.write('\r\n\x1b[33m' + msg + '\x1b[0m\r\n');
   }
 
-  function send(data) {
+  // Input goes out one request at a time, so on a slow link a keystroke can
+  // never overtake the one before it; what is typed meanwhile is sent together
+  // next. A request that fails goes again under the same number, and the
+  // server drops one it already has.
+  let inSeq = 0, inBusy = false;
+  const inQueue = [];
+  function queueIn(m) {
     if (closed || !sid) return;
-    const bytes = new TextEncoder().encode(data);
-    post(base + sid + '/in', { t: 'i', d: bytesToB64(bytes) });
+    const last = inQueue[inQueue.length - 1];
+    if (last && last.t === 'i' && m.t === 'i') last.text += m.text;
+    else if (last && last.t === 'r' && m.t === 'r') inQueue[inQueue.length - 1] = m;
+    else inQueue.push(m);
+    pumpIn();
   }
+  async function pumpIn() {
+    if (inBusy || !inQueue.length) return;
+    inBusy = true;
+    while (inQueue.length && !closed) {
+      const m = inQueue.shift();
+      const body = m.t === 'i'
+        ? { t: 'i', d: bytesToB64(new TextEncoder().encode(m.text)), seq: ++inSeq }
+        : { t: 'r', cols: m.cols, rows: m.rows, seq: ++inSeq };
+      for (let wait = 300; !closed; wait = Math.min(wait * 2, 5000)) {
+        let r = null;
+        try {
+          r = await fetch(base + sid + '/in', {
+            method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify(body)
+          });
+        } catch (e) { /* no answer: send it again */ }
+        if (r && r.status < 500) break; // taken, or refused for good
+        await new Promise(res => setTimeout(res, wait));
+      }
+    }
+    inBusy = false;
+  }
+  function send(data) { queueIn({ t: 'i', text: data }); }
   // What the keyboard types gets the CTRL / ALT of the extra keys, if armed.
   term.onData(function (data) { send(withMods(data)); });
 
@@ -240,10 +271,7 @@
     b.addEventListener('contextmenu', function (e) { e.preventDefault(); });
   });
 
-  function sendResize() {
-    if (closed || !sid) return;
-    post(base + sid + '/in', { t: 'r', cols: term.cols, rows: term.rows });
-  }
+  function sendResize() { queueIn({ t: 'r', cols: term.cols, rows: term.rows }); }
   function refit() {
     if (touch && window.visualViewport) {
       // Follow the visible area, so the extra keys sit right above the