diff --git a/TASKS.md b/TASKS.md
index 78a9ff4..1e067e0 100644
--- a/TASKS.md
+++ b/TASKS.md
@@ -2,18 +2,18 @@
 
 ## Current
 
-### `feat/frontend-css-state-cleanup`
+### `feat/frontend-performance-polish`
 
 Status: in_progress
 
 DoD:
-- button and control state visuals move from inline `element.style` mutations into CSS classes
-- wizard navigation and similar interactive UI use semantic state classes instead of manual style strings
-- existing UI e2e coverage stays green after the CSS-state cleanup
+- repeated O(n) filtering in hot render paths is removed
+- tab counts and similar derived UI metrics use cached/derived snapshots instead of recomputing the same filters
+- existing UI e2e coverage stays green after the performance polish
 
 ## Next
 
-- `feat/frontend-performance-polish`
+- `feat/frontend-observability-and-testability`
 
 ## Backlog
 
diff --git a/apps/ui/css/pages.css b/apps/ui/css/pages.css
index 22338dc..748f103 100644
--- a/apps/ui/css/pages.css
+++ b/apps/ui/css/pages.css
@@ -69,6 +69,19 @@
   box-shadow: 0 0 0 3px var(--accent-ring);
 }
 
+.btn-primary:disabled,
+.btn-primary.is-disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+  box-shadow: none;
+}
+
+.btn-primary:disabled:hover,
+.btn-primary.is-disabled:hover {
+  background: var(--accent);
+  box-shadow: none;
+}
+
 .btn-secondary {
   display: inline-flex;
   align-items: center;
diff --git a/apps/ui/css/wizard.css b/apps/ui/css/wizard.css
index a074bd6..4657ac4 100644
--- a/apps/ui/css/wizard.css
+++ b/apps/ui/css/wizard.css
@@ -989,6 +989,17 @@
   border-color: var(--bg-muted);
 }
 
+.btn-back:disabled {
+  opacity: 0.35;
+  cursor: not-allowed;
+}
+
+.btn-back:disabled:hover {
+  background: var(--bg-overlay);
+  color: var(--text-secondary);
+  border-color: var(--border);
+}
+
 .btn-save-draft {
   background: none;
   color: var(--text-muted);
@@ -1044,6 +1055,20 @@
   box-shadow: 0 1px 4px rgba(13, 148, 136, 0.3);
 }
 
+.btn-continue.is-final-step {
+  background: #3fb950;
+  border-color: #2ea043;
+  box-shadow: 0 1px 4px rgba(63, 185, 80, 0.4);
+}
+
+.btn-continue.is-final-step:hover {
+  background: #2ea043;
+  border-color: transparent;
+  box-shadow:
+    0 2px 10px rgba(63, 185, 80, 0.45),
+    0 0 0 3px rgba(63, 185, 80, 0.18);
+}
+
 /* ── Code editor ── */
 .code-block {
   border: 1px solid var(--border);
diff --git a/apps/ui/css/workspace-setup.css b/apps/ui/css/workspace-setup.css
index 3638106..669ca11 100644
--- a/apps/ui/css/workspace-setup.css
+++ b/apps/ui/css/workspace-setup.css
@@ -203,6 +203,11 @@
   gap: 10px;
   margin-top: 24px;
 }
+
+.ws-submit-btn {
+  padding: 9px 22px;
+  font-size: 13px;
+}
 .ws-setup-footer-note {
   font-size: 12px;
   color: var(--text-muted);
diff --git a/apps/ui/html/wizard/index.html b/apps/ui/html/wizard/index.html
index f58d2ae..b1b9ef6 100644
--- a/apps/ui/html/wizard/index.html
+++ b/apps/ui/html/wizard/index.html
@@ -201,7 +201,7 @@
     <div class="action-bar" role="toolbar" aria-label="Wizard navigation">
       <div class="action-bar-inner">
 
-        <button class="btn btn-back" type="button" disabled style="opacity: 0.35; cursor: not-allowed;">
+        <button class="btn btn-back" type="button" disabled>
           <svg width="13" height="13" viewBox="0 0 16 16" fill="currentColor">
             <path d="M9.78 12.78a.75.75 0 01-1.06 0L4.47 8.53a.75.75 0 010-1.06l4.25-4.25a.75.75 0 011.06 1.06L6.06 8l3.72 3.72a.75.75 0 010 1.06z"/>
           </svg>
diff --git a/apps/ui/html/workspace-setup.html b/apps/ui/html/workspace-setup.html
index 5900b2d..5035eac 100644
--- a/apps/ui/html/workspace-setup.html
+++ b/apps/ui/html/workspace-setup.html
@@ -286,7 +286,7 @@
       <!-- ── Actions ── -->
       <div class="ws-setup-actions">
         <a href="javascript:history.back()" class="btn-ghost-sm" style="padding:9px 18px;font-size:13px;text-decoration:none;color:var(--text-secondary);" data-i18n="btn.cancel">Cancel</a>
-        <button class="btn-primary" id="submit-btn" type="button" onclick="submitForm()" style="padding:9px 22px;font-size:13px;" data-i18n="workspace_setup.actions.save">Save changes</button>
+        <button class="btn-primary ws-submit-btn" id="submit-btn" type="button" onclick="submitForm()" data-i18n="workspace_setup.actions.save">Save changes</button>
       </div>
 
       <div class="ws-setup-footer-note" id="footer-note" style="display:none;">
diff --git a/apps/ui/js/wizard-shell.js b/apps/ui/js/wizard-shell.js
index 92f0be7..8cbb680 100644
--- a/apps/ui/js/wizard-shell.js
+++ b/apps/ui/js/wizard-shell.js
@@ -84,15 +84,7 @@
 
     var backButton = document.querySelector('.btn-back');
     if (backButton) {
-      if (step === 1) {
-        backButton.disabled = true;
-        backButton.style.opacity = '0.35';
-        backButton.style.cursor = 'not-allowed';
-      } else {
-        backButton.disabled = false;
-        backButton.style.opacity = '';
-        backButton.style.cursor = '';
-      }
+      backButton.disabled = step === 1;
     }
 
     var continueButton = document.querySelector('.btn-continue');
@@ -100,10 +92,10 @@
       if (step === TOTAL_STEPS) {
         var finalLabel = window.wizardMode === 'edit' ? tKey('wizard.button.save_changes') : tKey('wizard.button.create');
         continueButton.innerHTML = finalLabel + ' ' + ARROW_SVG;
-        continueButton.style.cssText = 'background:#3fb950;border-color:#2ea043;box-shadow:0 1px 4px rgba(63,185,80,0.4);';
+        continueButton.classList.add('is-final-step');
       } else {
         continueButton.innerHTML = tKey('wizard.button.continue') + ' ' + ARROW_SVG;
-        continueButton.style.cssText = '';
+        continueButton.classList.remove('is-final-step');
       }
     }
 
diff --git a/apps/ui/js/workspace-setup.js b/apps/ui/js/workspace-setup.js
index 5eb7a62..b32154d 100644
--- a/apps/ui/js/workspace-setup.js
+++ b/apps/ui/js/workspace-setup.js
@@ -231,12 +231,12 @@ function updatePageMode() {
     document.getElementById('footer-note').style.display = '';
     submit.textContent = tKey('workspace_setup.actions.create');
     submit.disabled = true;
-    submit.style.opacity = '0.5';
-    submit.style.cursor = 'not-allowed';
+    submit.classList.add('is-disabled');
   } else {
     document.getElementById('section-members').style.display = '';
     document.getElementById('section-danger').style.display = '';
     submit.textContent = tKey('workspace_setup.actions.save');
+    submit.classList.remove('is-disabled');
   }
 }
 
@@ -276,8 +276,7 @@ function validateCreateForm() {
   var elements = formElements();
   var valid = Boolean(elements.name.value.trim() && elements.slug.value.trim());
   elements.submit.disabled = !valid;
-  elements.submit.style.opacity = valid ? '1' : '0.5';
-  elements.submit.style.cursor = valid ? 'pointer' : 'not-allowed';
+  elements.submit.classList.toggle('is-disabled', !valid);
 }
 
 function inviteRows() {