feat(lab): phase 4 -- hash-router for sim deep-links

URL #sim/<name> deep-links: F5 restores sim, browser back/forward
switches between sims, click on sim-card updates URL.

34 sims mapped via _SIM_HASH_MAP (built dynamically from SIMS array).
Unknown hash -> console.warn fallback.
Recursion guard prevents double-activation on programmatic navigate.
closeSim clears hash via history.pushState (no hashchange loop).
Embed mode excluded from hash updates (?embed=1 workflow unaffected).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/js/labs/lab-glue.js

@@ -818,8 +818,71 @@
       } else {
         renderSims();
         if (_autoSim) openSim(_autoSim);
+        // hash-router: activate sim from URL fragment after catalogue renders
+        else _activateFromHash();
       }
     });
     lucide.createIcons();
     LS.notif.init();
   }
+
+  /* ─── Hash router for sim deep-links ─────────────────────────────────────
+     URL pattern: /lab#sim/<name>
+     <name> matches SIMS[i].id (e.g. 'projectile', 'graph', 'chemsandbox').
+     F5 restores sim. Browser back/forward switches between sims.
+     Click on sim-card updates URL via wrapped openSim.
+  ──────────────────────────────────────────────────────────────────────── */
+
+  // Build valid-id set from SIMS catalogue (filters out "coming soon" entries)
+  const _SIM_HASH_MAP = {};
+  SIMS.forEach(function(s) { if (s.id) { _SIM_HASH_MAP[s.id] = s.id; } });
+
+  var _routerNavigating = false;
+
+  function _activateFromHash() {
+    var m = (location.hash || '').match(/^#sim\/([\w-]+)/);
+    if (!m) return false;
+    var simName = m[1];
+    if (!_SIM_HASH_MAP[simName]) {
+      // eslint-disable-next-line no-console
+      window.console && window.console.warn('lab-router: unknown sim', simName);
+      return false;
+    }
+    openSim(simName);
+    return true;
+  }
+
+  // Intercept openSim to push URL hash on user-initiated navigation
+  var _origOpenSim = openSim;
+  openSim = function(id) {
+    _origOpenSim(id);
+    if (!_routerNavigating && !_embedMode) {
+      var baseId = id.includes(':') ? id.split(':')[0] : id;
+      if (_SIM_HASH_MAP[baseId]) {
+        _routerNavigating = true;
+        location.hash = '#sim/' + baseId;
+        // use setTimeout so hashchange fires after flag is set
+        setTimeout(function() { _routerNavigating = false; }, 0);
+      }
+    }
+  };
+
+  // Intercept closeSim to clear hash when returning to home grid
+  var _origCloseSim = closeSim;
+  closeSim = function() {
+    _origCloseSim();
+    if (!_embedMode) {
+      _routerNavigating = true;
+      history.pushState(null, '', location.pathname + location.search);
+      setTimeout(function() { _routerNavigating = false; }, 0);
+    }
+  };
+
+  // Browser back/forward navigation
+  window.addEventListener('hashchange', function() {
+    if (_routerNavigating) return;
+    var hasHash = _activateFromHash();
+    if (!hasHash && document.getElementById('lab-sim').classList.contains('open')) {
+      _origCloseSim();
+    }
+  });