fix: surface selectPage error when dashboard shell incomplete (fixes #175)

Replace the silent `if (!main || !page) return;` early return in
selectPage() with explicit guards that log a console error and, when
#db-main-content is absent, render a visible db-error banner via the new
showDashboardInitError helper.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

src/praisonaiui/templates/frontend/plugins/dashboard.js

@@ -480,6 +480,9 @@ const DASHBOARD_STYLE = `
   @keyframes db-spin { to { transform: rotate(360deg); } }
   .db-spinner { display: inline-block; width: 24px; height: 24px; border: 2px solid var(--db-border); border-top-color: var(--db-accent); border-radius: 50%; animation: db-spin 0.8s linear infinite; }
 
+  /* Init error banner */
+  .db-error { margin: 24px; padding: 16px 20px; border: 1px solid #b91c1c; border-radius: 8px; background: rgba(185, 28, 28, 0.12); color: #fca5a5; font-size: 14px; }
+
   /* Hide React docs layout when dashboard is active */
   .db-active .sidebar:not(.db-sidebar), .db-active .topnav, .db-active .toc-sidebar,
   .db-active > .main-content, .db-active > nav:not(.db-sidebar) { display: none !important; }
@@ -1495,6 +1498,20 @@ function buildSidebar(pages) {
   return sidebar;
 }
 
+function showDashboardInitError(message) {
+  const root = document.getElementById('root');
+  if (!root) return;
+  let banner = document.getElementById('db-init-error');
+  if (!banner) {
+    banner = document.createElement('div');
+    banner.id = 'db-init-error';
+    banner.className = 'db-error';
+    banner.setAttribute('role', 'alert');
+    root.appendChild(banner);
+  }
+  banner.textContent = message;
+}
+
 async function selectPage(pageId) {
   // Cleanup previous view if it has a cleanup function
   if (_activeCleanup) { try { _activeCleanup(); } catch(e) {} _activeCleanup = null; }
@@ -1513,7 +1530,15 @@ async function selectPage(pageId) {
 
   const page = pagesData.find(p => p.id === pageId);
   const main = document.getElementById('db-main-content');
-  if (!main || !page) return;
+  if (!main) {
+    console.error('[AIUI] selectPage aborted: #db-main-content not in DOM — dashboard shell incomplete');
+    showDashboardInitError('Dashboard shell layout incomplete. Reload the page or check the dashboard plugin.');
+    return;
+  }
+  if (!page) {
+    console.error(`[AIUI] selectPage aborted: page '${pageId}' not found in pagesData`);
+    return;
+  }
 
   // Set page header (controlled by dashboard config protocol)
   const showPageHeader = main.dataset.showPageHeader !== 'false';

tests/unit/test_dashboard_select_page_guard.py

@@ -0,0 +1,71 @@
+"""Regression tests for #175 — selectPage() silent abort when #db-main-content missing.
+
+The dashboard style (`dashboard.js`) skips React. When the shell layout is
+incomplete and `#db-main-content` is absent, `selectPage()` used to return
+silently, leaving every view empty with no console error or user-visible signal.
+These source-parsing tests assert the defensive guard and error surface are
+wired in, mirroring `test_session_search_dashboard.py`.
+"""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+FRONTEND = (
+    Path(__file__).resolve().parents[2]
+    / "src" / "praisonaiui" / "templates" / "frontend" / "plugins"
+)
+DASHBOARD_JS = FRONTEND / "dashboard.js"
+
+
+class TestSelectPageGuard:
+    def _select_page_body(self) -> str:
+        src = DASHBOARD_JS.read_text()
+        m = re.search(
+            r"async function selectPage\(pageId\)\s*\{(.*?)^}",
+            src, re.DOTALL | re.MULTILINE,
+        )
+        assert m, "selectPage not found"
+        return m.group(1)
+
+    def test_missing_main_logs_console_error(self):
+        body = self._select_page_body()
+        m = re.search(
+            r"if \(!main\)\s*\{(.*?)\}", body, re.DOTALL,
+        )
+        assert m, "guard for missing #db-main-content not found"
+        guard = m.group(1)
+        assert "console.error" in guard
+        assert "db-main-content" in guard
+
+    def test_missing_main_surfaces_init_error(self):
+        body = self._select_page_body()
+        m = re.search(
+            r"if \(!main\)\s*\{(.*?)\}", body, re.DOTALL,
+        )
+        assert m, "guard for missing #db-main-content not found"
+        assert "showDashboardInitError" in m.group(1)
+
+    def test_missing_page_logs_console_error(self):
+        body = self._select_page_body()
+        m = re.search(
+            r"if \(!page\)\s*\{(.*?)\}", body, re.DOTALL,
+        )
+        assert m, "guard for missing page not found"
+        assert "console.error" in m.group(1)
+
+    def test_show_dashboard_init_error_helper_present(self):
+        src = DASHBOARD_JS.read_text()
+        m = re.search(
+            r"function showDashboardInitError\(message\)\s*\{(.*?)^}",
+            src, re.DOTALL | re.MULTILINE,
+        )
+        assert m, "showDashboardInitError helper not found"
+        helper = m.group(1)
+        assert "db-init-error" in helper
+        assert "role" in helper and "alert" in helper
+
+    def test_no_silent_combined_return(self):
+        body = self._select_page_body()
+        assert "if (!main || !page) return;" not in body