diff --git a/plugins/voyage/playground/voyage-playground.html b/plugins/voyage/playground/voyage-playground.html
index 853d43a..6be85c3 100644
--- a/plugins/voyage/playground/voyage-playground.html
+++ b/plugins/voyage/playground/voyage-playground.html
@@ -1422,6 +1422,163 @@ playground first-run shows a complete round-trip-able artifact.
         announce('Dashboard lastet — ' + tiles.length + ' artifacts vist.');
       }
 
+      // ---- v4.3 Step 15 — drill-down + back-nav + URL routing ----------
+      // Click on a fleet-tile drills into renderArtifactDetail; the
+      // back-to-dashboard button (or breadcrumb-click) returns to the
+      // dashboard without state-loss. URL parameter `?project=` is
+      // additive: at page-load we surface a guide-panel hint because
+      // webkitdirectory cannot be triggered without a user-gesture.
+      // popstate handler keeps browser back/forward in sync with view-state.
+
+      function resolveArtifactEntry(a, key) {
+        if (!a) return null;
+        if (key === 'brief')    return a.brief;
+        if (key === 'plan')     return a.plan;
+        if (key === 'review')   return a.review;
+        if (key === 'progress') return a.progress;
+        if (key === 'research') return (a.research && a.research.length) ? a.research[0] : null;
+        return null;
+      }
+
+      function renderArtifactDetail(artifactKey) {
+        var a = __voyageCurrentArtifacts;
+        if (!a) return;
+        var slot = $('voyage-detail');
+        if (!slot) return;
+
+        var entry = resolveArtifactEntry(a, artifactKey);
+        var bodyHtml;
+        if (artifactKey === 'research') {
+          if (a.research && a.research.length) {
+            bodyHtml = '<ul class="voyage-research-list">' + a.research.map(function (r) {
+              var fm = r.frontmatter || {};
+              var title = fm.title || r.path;
+              return '<li><div class="fleet-tile__name">' + escapeHtml(title) +
+                '</div><div class="fleet-tile__stat">' + escapeHtml(r.path) + '</div></li>';
+            }).join('') + '</ul>';
+          } else {
+            bodyHtml = '<p><em>Ingen research-briefs i prosjektet.</em></p>';
+          }
+        } else if (!entry) {
+          bodyHtml = '<p><em>Artifact mangler i prosjektmappen.</em></p>';
+        } else if (artifactKey === 'progress') {
+          bodyHtml = '<pre><code>' + escapeHtml(entry.content || '') + '</code></pre>';
+        } else {
+          bodyHtml = renderArtifact(entry.content || '');
+        }
+
+        var titleMap = { brief: 'Brief', plan: 'Plan', review: 'Review',
+                         research: 'Research', progress: 'Progress' };
+        var artifactName = titleMap[artifactKey] || artifactKey;
+        var projectName = shortenBasePath(a.basePath);
+
+        slot.innerHTML = renderPageShell({
+          eyebrow: 'Artifact detail',
+          title: artifactName,
+          lede: 'Project: ' + projectName,
+          meta: entry ? ('path: ' + (entry.path || '')) : 'mangler'
+        }, '<button type="button" class="voyage-back-btn" data-action="back-to-dashboard" aria-label="Tilbake til dashboard">← Tilbake til dashboard</button>' + bodyHtml);
+        slot.hidden = false;
+
+        // Hide dashboard + paste-flow stages.
+        var dash = $('voyage-dashboard');             if (dash) dash.hidden = true;
+        var emptyState = $('empty-state');            if (emptyState) emptyState.hidden = true;
+        var pasteRow = document.querySelector('.paste-import-row'); if (pasteRow) pasteRow.hidden = true;
+        var layout = document.querySelector('.voyage-layout');      if (layout) layout.hidden = true;
+
+        renderTopbar([
+          { label: 'Voyage', href: '#' },
+          { label: projectName, href: '#' },
+          { label: artifactName }
+        ]);
+        announce('Detail-visning: ' + artifactName);
+      }
+
+      function showDashboardFromState() {
+        if (!__voyageCurrentArtifacts) return;
+        var detail = $('voyage-detail'); if (detail) detail.hidden = true;
+        renderDashboard(__voyageCurrentArtifacts);
+      }
+
+      function pushDashboardURL() {
+        try {
+          if (!window.history || !window.history.pushState) return;
+          var a = __voyageCurrentArtifacts;
+          var params = new URLSearchParams(window.location.search);
+          if (a && a.basePath) params.set('project', a.basePath);
+          params.delete('artifact');
+          var qs = params.toString();
+          var url = window.location.pathname + (qs ? ('?' + qs) : '');
+          window.history.pushState({ view: 'dashboard', basePath: a ? a.basePath : null }, '', url);
+        } catch (_) { /* file:// + privatmodus */ }
+      }
+
+      function pushDetailURL(artifactKey) {
+        try {
+          if (!window.history || !window.history.pushState) return;
+          var a = __voyageCurrentArtifacts;
+          var params = new URLSearchParams(window.location.search);
+          if (a && a.basePath) params.set('project', a.basePath);
+          params.set('artifact', artifactKey);
+          var qs = params.toString();
+          var url = window.location.pathname + (qs ? ('?' + qs) : '');
+          window.history.pushState({ view: 'detail', basePath: a ? a.basePath : null, artifact: artifactKey }, '', url);
+        } catch (_) { /* file:// + privatmodus */ }
+      }
+
+      function wireDashboardNavigation() {
+        document.addEventListener('click', function (e) {
+          var tile = e.target && e.target.closest && e.target.closest('.fleet-tile[data-artifact]');
+          if (tile) {
+            e.preventDefault();
+            var key = tile.getAttribute('data-artifact');
+            if (key) {
+              renderArtifactDetail(key);
+              pushDetailURL(key);
+            }
+            return;
+          }
+          var back = e.target && e.target.closest && e.target.closest('[data-action="back-to-dashboard"]');
+          if (back) {
+            e.preventDefault();
+            showDashboardFromState();
+            pushDashboardURL();
+          }
+        });
+        // Browser back/forward → restore view from history state.
+        window.addEventListener('popstate', function (e) {
+          var s = e.state;
+          if (!s || !__voyageCurrentArtifacts) return;
+          if (s.view === 'detail' && s.artifact) {
+            renderArtifactDetail(s.artifact);
+          } else if (s.view === 'dashboard') {
+            showDashboardFromState();
+          }
+        });
+      }
+
+      function maybeShowProjectURLHint() {
+        // Caveat per Step 15 spec: webkitdirectory cannot be triggered
+        // programmatically without a user-gesture, so a `?project=` URL
+        // surfaces a guide-panel hint instead of attempting auto-load.
+        try {
+          var qs = new URLSearchParams(window.location.search);
+          var projectQ = qs.get('project');
+          if (!projectQ) return;
+          var emptyState = $('empty-state');
+          if (!emptyState) return;
+          var titleEl = emptyState.querySelector('.guide-panel__title');
+          var bodyEl = emptyState.querySelector('.guide-panel__body');
+          if (titleEl) titleEl.textContent = 'Project deep-link oppdaget';
+          if (bodyEl) {
+            bodyEl.innerHTML = '<p>URL inneholder <code>?project=' +
+              escapeHtml(projectQ) + '</code>. Browseren krever et bruker-klikk ' +
+              'før prosjektmappen kan leses; bruk knappen <strong>«Last prosjektmappe»</strong> ' +
+              'eller dra mappen til vinduet for å fortsette.</p>';
+          }
+        } catch (_) { /* file:// + privatmodus */ }
+      }
+
       // ---- DOM wiring ----------------------------------------------------
       function $(id) { return document.getElementById(id); }
 
@@ -2139,6 +2296,11 @@ playground first-run shows a complete round-trip-able artifact.
         // Step 12 (v4.3) — drag-drop overlay with webkitGetAsEntry recursive
         // walker + Firefox 150 Windows UA-guard.
         wireDragDrop();
+
+        // Step 15 (v4.3) — fleet-tile click delegation, back-to-dashboard
+        // handler, popstate restoration, and ?project= URL deep-link hint.
+        wireDashboardNavigation();
+        maybeShowProjectURLHint();
       }
 
       function setThemeLabel(theme) {
diff --git a/plugins/voyage/tests/playground/voyage-playground.test.mjs b/plugins/voyage/tests/playground/voyage-playground.test.mjs
index 1718b7a..e724ab6 100644
--- a/plugins/voyage/tests/playground/voyage-playground.test.mjs
+++ b/plugins/voyage/tests/playground/voyage-playground.test.mjs
@@ -176,3 +176,27 @@ test('voyage-playground.html declares dashboard status vocabulary (v4.3 Step 14)
   assert.match(text, /'missing'/, 'status missing required');
   assert.match(text, /'stale'/, 'status stale required');
 });
+
+test('voyage-playground.html declares renderArtifactDetail JS function (v4.3 Step 15 drill-down)', () => {
+  const text = readFileSync(HTML, 'utf-8');
+  assert.match(text, /function renderArtifactDetail\b/, 'renderArtifactDetail function required for drill-down');
+});
+
+test('voyage-playground.html declares URLSearchParams routing (v4.3 Step 15)', () => {
+  const text = readFileSync(HTML, 'utf-8');
+  // Presence-only: URLSearchParams already used at line 810 for project-key
+  // derivation; Step 15 adds ?project= dashboard/detail routing.
+  assert.match(text, /URLSearchParams/, 'URLSearchParams required for ?project= routing');
+});
+
+test('voyage-playground.html declares data-action="back-to-dashboard" (v4.3 Step 15 back-nav)', () => {
+  const text = readFileSync(HTML, 'utf-8');
+  // Stricter than Step 14 wording — must appear as data-action attribute
+  // somewhere in the JS template, not only in HTML comments.
+  assert.match(text, /data-action="back-to-dashboard"/, 'data-action="back-to-dashboard" required for return-nav handler');
+});
+
+test('voyage-playground.html declares popstate handler (v4.3 Step 15 back/forward)', () => {
+  const text = readFileSync(HTML, 'utf-8');
+  assert.match(text, /'popstate'/, 'popstate listener required for browser back/forward');
+});