tooltip: kill stuck tips with watchdog + pointermove sanity

Tooltips could strand on screen when pointerleave didn't fire — fast
flicks off the target, re-renders that yanked the element out mid-
hover, or the tab losing focus. Three guards:

  - 5s max-life watchdog on every show, so the worst case is a late
    fade rather than a permanent overlay
  - pointermove check: if the pointer is no longer over the tip's
    owning target (or the target got detached from the DOM), hide
  - window blur + visibilitychange also hide immediately

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/js/modules/tooltip.js

@@ -5,11 +5,13 @@
 
 const SHOW_DELAY = 400;
 const HIDE_DELAY = 100;
+const MAX_LIFE   = 5000;  // watchdog: tooltip never outlives this
 const OFFSET = 8;
 
 let tipEl = null;
 let showTimer = null;
 let hideTimer = null;
+let lifeTimer = null;
 let currentTarget = null;
 
 function create() {
@@ -63,10 +65,18 @@ function show(target) {
     tipEl.style.top = top + 'px';
     tipEl.style.left = left + 'px';
     tipEl.style.visibility = '';
+
+    // Watchdog: if pointerleave never fires (fast flick off the
+    // element, target removed from the DOM mid-hover, focus taken by
+    // another window), the tooltip would sit forever. Force-hide
+    // after MAX_LIFE regardless.
+    clearTimeout(lifeTimer);
+    lifeTimer = setTimeout(hide, MAX_LIFE);
 }
 
 function hide() {
     currentTarget = null;
+    clearTimeout(lifeTimer);
     if (tipEl) tipEl.style.display = 'none';
 }
 
@@ -91,3 +101,20 @@ document.addEventListener('pointerleave', onLeave, true);
 document.addEventListener('pointerdown', () => { clearTimeout(showTimer); hide(); }, true);
 document.addEventListener('keydown', () => { clearTimeout(showTimer); hide(); }, true);
 document.addEventListener('scroll', () => { clearTimeout(showTimer); hide(); }, true);
+
+// Belt-and-suspenders sanity check on every move: if the pointer is
+// no longer over the tip-owning target (or the target has been
+// detached from the DOM since show time), hide. Catches fast flicks
+// that skip the expected pointerleave and DOM churn that yanks the
+// element out from under us.
+document.addEventListener('pointermove', (e) => {
+    if (!currentTarget) return;
+    if (!currentTarget.isConnected) { hide(); return; }
+    const el = document.elementFromPoint(e.clientX, e.clientY);
+    if (!el || !currentTarget.contains(el)) hide();
+}, true);
+
+// Window losing focus / tab hidden — nothing to hover over while
+// we're not there, kill any lingering tip.
+window.addEventListener('blur', () => { clearTimeout(showTimer); hide(); });
+document.addEventListener('visibilitychange', () => { if (document.hidden) { clearTimeout(showTimer); hide(); } });