diff --git a/crates/giskard-server/static/app.css b/crates/giskard-server/static/app.css
index 8eaa0b0..dcdac8c 100644
--- a/crates/giskard-server/static/app.css
+++ b/crates/giskard-server/static/app.css
@@ -99,7 +99,12 @@
   .thread.subagent-thread { font-size:12px; }
   .thread.subagent-thread::before { content:"sub"; flex:none; color:var(--muted); font-size:10px; }
   .thread:hover { background:var(--panel2); }
-  .thread.active { background:var(--panel2); color:var(--fg); }
+  /* Selected thread: a whisper of accent tint over the neutral raised fill plus a thin accent
+     rail, no bold. The ~9% tint gives selection a hint of color that a plain hover (bare --panel2)
+     lacks, so the two separate cleanly at a glance while staying restrained and editor-like. */
+  .thread.active { background:var(--panel2); background:color-mix(in srgb, var(--accent) 9%, var(--panel2)); color:var(--fg); box-shadow:inset 2px 0 0 var(--accent); }
+  .thread.active:hover { background:var(--panel2); background:color-mix(in srgb, var(--accent) 13%, var(--panel2)); }
+  .thread.active .thread-title { color:var(--fg); }
   .thread-status { flex:none; width:10px; text-align:center; color:var(--muted); font-weight:700; }
   .thread-title { min-width:0; overflow:hidden; text-overflow:ellipsis; white-space:nowrap; }
   .thread.has-activity .thread-title { color:var(--fg); }
diff --git a/crates/giskard-server/static/app.js b/crates/giskard-server/static/app.js
index 1c04ce3..0d4ed00 100644
--- a/crates/giskard-server/static/app.js
+++ b/crates/giskard-server/static/app.js
@@ -756,6 +756,7 @@ function threadRow(pid, t) {
   const title = t.title || t.id.slice(0,8);
   const el = document.createElement("div"); el.className="thread mono";
   applyThreadTitleToElement(el, pid, t.id, title);
+  markThreadRowActive(el, !!state.threadId && String(t.id) === String(state.threadId));
 
   const menuBtn = document.createElement("button");
   menuBtn.type = "button"; menuBtn.className = "thread-menu-btn";
@@ -939,6 +940,25 @@ function renderAllThreadActivityIndicators() {
   document.querySelectorAll(".thread").forEach(el => renderThreadActivityIndicator(el.dataset.tid));
 }
 
+// Mark a single thread row as the selected one (or not). `aria-current` mirrors the visual state for
+// assistive tech and gives the CSS a stable hook.
+function markThreadRowActive(el, active) {
+  if (!el) return;
+  el.classList.toggle("active", active);
+  if (active) el.setAttribute("aria-current", "true");
+  else el.removeAttribute("aria-current");
+}
+
+// Derive the sidebar selection from `state.threadId` rather than tracking it imperatively. Thread
+// rows are rebuilt whenever the list reloads, so any highlight set by hand goes stale on the next
+// re-render (leaving a previously selected row looking selected); recomputing from the single source
+// of truth keeps exactly one row active.
+function syncActiveThreadHighlight() {
+  const tid = state.threadId ? String(state.threadId) : null;
+  document.querySelectorAll(".thread").forEach(el =>
+    markThreadRowActive(el, tid !== null && String(el.dataset.tid) === tid));
+}
+
 function setThreadActivity(tid, activity) {
   if (!tid || !activity) return;
   const key = String(tid);
@@ -1503,7 +1523,7 @@ function openDraftThread(pid, defaultModel) {
   state.awaitingInitialThreadState = false;
   state.awaitingThreadResync = false;
   resetRenderState();
-  document.querySelectorAll(".thread").forEach(e => e.classList.remove("active"));
+  syncActiveThreadHighlight();   // state.threadId is null for a draft, so this clears any selection
   $("thrHeader").style.display="flex"; $("composer").style.display="flex";
   $("pickerBar").style.display="flex";
   setThreadTitle("New thread");
@@ -1571,7 +1591,7 @@ async function openThread(pid, tid, title, opts) {
   state.awaitingThreadResync = false;
   state.awaitingIncrementalResync = false; state.resyncStickBottom = false;
   resetRenderState();
-  document.querySelectorAll(".thread").forEach(e => e.classList.toggle("active", e.dataset.tid===tid));
+  syncActiveThreadHighlight();
   renderAllThreadActivityIndicators();
   $("thrHeader").style.display="flex"; $("composer").style.display="flex";
   $("pickerBar").style.display="flex";
diff --git a/docs/screenshots/ide-desktop.png b/docs/screenshots/ide-desktop.png
index 5087e6e..d09d163 100644
Binary files a/docs/screenshots/ide-desktop.png and b/docs/screenshots/ide-desktop.png differ
diff --git a/docs/screenshots/ide-mobile.png b/docs/screenshots/ide-mobile.png
index 21dd1b2..34c39d3 100644
Binary files a/docs/screenshots/ide-mobile.png and b/docs/screenshots/ide-mobile.png differ
diff --git a/tests/e2e/tests/thread-selection.spec.ts b/tests/e2e/tests/thread-selection.spec.ts
new file mode 100644
index 0000000..5e9464d
--- /dev/null
+++ b/tests/e2e/tests/thread-selection.spec.ts
@@ -0,0 +1,66 @@
+import { test, expect } from "@playwright/test";
+import { SCRIPTED_REPLY, login } from "./helpers";
+
+// The selected thread must be unmistakable in the sidebar, and switching threads must move the
+// highlight — a previously selected row that stays highlighted (e.g. because the thread list was
+// rebuilt and the imperative highlight went stale) is the regression guarded here.
+//
+// The replay server is shared and stateful across the suite, so earlier specs may have left threads
+// in the Demo project. The assertions therefore never assume a clean slate: they rely on the
+// invariant that exactly one row is active and identify the threads under test by their own ids.
+test.describe("sidebar thread selection", () => {
+  test.beforeEach(async ({ page }) => {
+    await login(page);
+  });
+
+  // Create a thread from a fresh draft and return the id of the row that becomes selected.
+  async function createThread(page, message: string): Promise<string> {
+    await page.locator(".proj", { hasText: "Demo" }).locator(".project-add").click();
+    const input = page.locator("#input");
+    await expect(input).toBeVisible();
+    await input.fill(message);
+    await page.locator("#sendBtn").click();
+    await expect(
+      page.locator("#transcript .msg.agent", { hasText: SCRIPTED_REPLY }),
+    ).toBeVisible();
+    // The just-opened thread is the only active one.
+    await expect(page.locator(".thread.active")).toHaveCount(1);
+    const tid = await page.locator(".thread.active").getAttribute("data-tid");
+    expect(tid).toBeTruthy();
+    return tid as string;
+  }
+
+  test("highlights exactly one thread and moves it when switching", async ({ page }) => {
+    const tid1 = await createThread(page, "Alpha thread about the login flow");
+    const tid2 = await createThread(page, "Bravo thread about the cache layer");
+    expect(tid2).not.toBe(tid1);
+
+    // Switch back to the first thread.
+    await page.locator(`.thread[data-tid="${tid1}"]`).click();
+    await expect(page.locator(`.thread[data-tid="${tid1}"]`)).toHaveClass(/\bactive\b/);
+    // The previously selected thread must lose the highlight — exactly one active row remains.
+    await expect(page.locator(".thread.active")).toHaveCount(1);
+    await expect(page.locator(`.thread[data-tid="${tid2}"]`)).not.toHaveClass(/\bactive\b/);
+
+    // The selection is visually reinforced with an accent bar (inset box-shadow), not just a
+    // background tint, so it reads clearly even in a long list.
+    const shadow = await page
+      .locator(`.thread[data-tid="${tid1}"]`)
+      .evaluate((el) => getComputedStyle(el).boxShadow);
+    expect(shadow).not.toBe("none");
+    // aria-current mirrors the visual selection for assistive tech.
+    await expect(page.locator(`.thread[data-tid="${tid1}"]`)).toHaveAttribute(
+      "aria-current",
+      "true",
+    );
+
+    // A reload rebuilds the whole thread list from scratch. The selection is derived from the
+    // restored thread rather than an imperative highlight, so exactly one row — the restored one —
+    // must come back active, with no stale highlight left on the other.
+    await page.reload();
+    await expect(page.locator("#app")).toHaveClass(/open/);
+    await expect(page.locator(`.thread[data-tid="${tid1}"]`)).toHaveClass(/\bactive\b/);
+    await expect(page.locator(".thread.active")).toHaveCount(1);
+    await expect(page.locator(`.thread[data-tid="${tid2}"]`)).not.toHaveClass(/\bactive\b/);
+  });
+});