fix(theseus): chrome height sync must not wait for an animation frame

syncHeight queued its measurement in requestAnimationFrame, and frames
stop whenever the window is occluded — so a prompt closing, or a row
hiding, while another window covered Theseus left the chrome at its
old height until the window came back. A zero timeout coalesces the
same way and always runs. The open-prompt allowance now lives in
syncHeight itself, so any re-measure while a prompt is up keeps its
room, and the growth helper simply defers to it.

chrome.html

@@ -522,7 +522,22 @@
 <script>
   const $ = (id) => document.getElementById(id);
   const T = window.theseus;
-  function syncHeight() { requestAnimationFrame(() => T.setChromeHeight(document.body.scrollHeight)); }
+  // Every caller (tab events, window resize, prompts) funnels through here,
+  // so an open prompt keeps its room no matter what else re-measures the
+  // chrome while it is up — a fixed mask never counts toward scrollHeight.
+  // Coalesced with a zero timeout, not requestAnimationFrame: frames stop
+  // whenever the window is occluded, and a height change queued then (a
+  // prompt closing, a row hiding) would only land when the window came back.
+  let syncHeightTimer = 0;
+  function syncHeight() {
+    clearTimeout(syncHeightTimer);
+    syncHeightTimer = setTimeout(() => {
+      let h = document.body.scrollHeight;
+      const box = document.querySelector(".promptmask .promptbox");
+      if (box) h = Math.max(h, Math.ceil(box.getBoundingClientRect().height) + 56);
+      T.setChromeHeight(h);
+    }, 0);
+  }
   // Reserve room for the native window-controls overlay at the right of the
   // tab row (Windows only — the frame is hidden there, see main.js). Use the
   // overlay's real geometry when Chromium exposes it to this view; otherwise
@@ -1111,13 +1126,7 @@
   // cut off at the view's edge (the two-field favorites form lost its title
   // and buttons). Grow the view to fit the box while a prompt is open;
   // done() calls syncHeight() to shrink it back.
-  function growForPrompt(mask) {
+  function growForPrompt() { syncHeight(); }
-    try {
-      const box = mask.querySelector(".promptbox");
-      const need = box ? Math.ceil(box.getBoundingClientRect().height) + 56 : 0;
-      T.setChromeHeight(Math.max(document.body.scrollHeight, need));
-    } catch {}
-  }
   function inPrompt(label, initial) {
     return new Promise((resolve) => {
       const mask = document.createElement("div"); mask.className = "promptmask";