diff --git a/frontend/src/settings/traces/TraceWaterfall.tsx b/frontend/src/settings/traces/TraceWaterfall.tsx
index f7f70f05..fba28239 100644
--- a/frontend/src/settings/traces/TraceWaterfall.tsx
+++ b/frontend/src/settings/traces/TraceWaterfall.tsx
@@ -90,10 +90,10 @@ export default function TraceWaterfall({ trace }: { trace: Trace }) {
           {SCALE_STEPS.map((step) => (
             <span
               key={step}
-              className="absolute top-0 -translate-x-1/2 tabular-nums first:translate-x-0 last:-translate-x-full"
+              className="absolute top-0 -translate-x-1/2 whitespace-nowrap tabular-nums first:translate-x-0 last:-translate-x-full"
               style={{ left: `${step * 100}%` }}
             >
-              {formatDurationMs(totalMs * step)}
+              {step === 0 ? '0' : formatDurationMs(totalMs * step)}
             </span>
           ))}
         </div>
diff --git a/tests/e2e/specs/tier-a/execution-traces.spec.ts b/tests/e2e/specs/tier-a/execution-traces.spec.ts
new file mode 100644
index 00000000..2f1f4653
--- /dev/null
+++ b/tests/e2e/specs/tier-a/execution-traces.spec.ts
@@ -0,0 +1,181 @@
+/**
+ * Execution traces — a chat turn's steps are stored and shown in the Logs UI.
+ *
+ * One `/stream` turn with a tool call writes a `request_traces` row holding
+ * the agent run, every LLM call and the tool call. The Logs row links to it
+ * through `request_id` (stamped into `user_logs.data`), carries a trace
+ * summary, and "View trace" opens the waterfall.
+ *
+ * // Silent-break covered: the Logs row loses its trace link. If the
+ *    request id stops reaching `user_logs` (or the stored trace), the row
+ *    silently renders without the "View trace" button and nothing errors.
+ */
+
+import * as playwright from '@playwright/test';
+const { expect, test } = playwright;
+
+import { dirname, resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+import { authedRequest } from '../../helpers/api.js';
+import { newUserContext } from '../../helpers/auth.js';
+import { pg } from '../../helpers/db.js';
+import { resetDb } from '../../helpers/reset.js';
+import {
+  multipartContext,
+  postUpload,
+  waitForTask,
+} from '../../helpers/uploads.js';
+
+const HERE = dirname(fileURLToPath(import.meta.url));
+const README_MD = resolve(HERE, '..', '..', 'fixtures', 'docs', 'readme.md');
+
+/** `memory_view` ships in DEFAULT_CHAT_TOOLS, so every user can run it. */
+const TOOL_DIRECTIVE = '[[MOCK_LLM_TOOLCALL:memory_view:once]]';
+
+interface TraceRow {
+  source: string;
+  status: string;
+  request_id: string | null;
+  message_id: string | null;
+  // pg parses JSONB to JS values
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  spans: any[];
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  summary: any;
+}
+
+async function tracesFor(userId: string): Promise<TraceRow[]> {
+  const { rows } = await pg.query<TraceRow>(
+    `SELECT source, status, request_id, message_id::text AS message_id, spans, summary
+       FROM request_traces WHERE user_id = $1 ORDER BY started_at`,
+    [userId],
+  );
+  return rows;
+}
+
+test.describe('tier-a · execution traces', () => {
+  test.beforeEach(async () => {
+    await resetDb();
+  });
+
+  test('a chat turn with a tool call is traced and opens from the Logs page', async ({
+    browser,
+  }) => {
+    const { context, sub, token } = await newUserContext(browser);
+    const api = await authedRequest(playwright, token);
+    try {
+      const res = await api.post('/stream', {
+        data: {
+          question: `what do you remember about me? ${TOOL_DIRECTIVE}`,
+          save_conversation: true,
+        },
+        timeout: 180_000,
+      });
+      expect(res.ok()).toBeTruthy();
+      expect(await res.text()).toContain('"type": "end"');
+
+      // Stored trace: one row for the turn, linked to its message.
+      const traces = await tracesFor(sub);
+      expect(traces).toHaveLength(1);
+      const [trace] = traces;
+      expect(trace.source).toBe('stream');
+      expect(trace.request_id).toBeTruthy();
+      expect(trace.message_id).toBeTruthy();
+      const kinds = new Set(trace.spans.map((s) => s.kind));
+      expect(kinds.has('agent')).toBe(true);
+      expect(kinds.has('llm')).toBe(true);
+      expect(kinds.has('tool')).toBe(true);
+      expect(trace.summary.llm_calls).toBeGreaterThan(0);
+      const tool = trace.spans.find((s) => s.kind === 'tool');
+      expect(tool.attributes['gen_ai.tool.name']).toBe('memory_view');
+
+      // The Logs API links the row to the trace.
+      const logsRes = await api.post('/api/get_user_logs', {
+        data: { page: 1, page_size: 10, event_type: 'chat' },
+      });
+      const logs = (await logsRes.json()).logs;
+      expect(logs[0].request_id).toBe(trace.request_id);
+      expect(logs[0].trace.ref).toEqual({
+        field: 'request_id',
+        value: trace.request_id,
+      });
+
+      // And the UI opens it.
+      const page = await context.newPage();
+      await page.goto('/settings/logs');
+      await page.getByText('what do you remember about me?').first().click();
+      await page.getByRole('button', { name: 'View trace' }).click();
+      const sheet = page.getByRole('dialog');
+      await expect(sheet.getByText('Execution trace')).toBeVisible();
+      await expect(sheet.getByText('execute_tool memory_view').first()).toBeVisible();
+      await sheet.getByText('execute_tool memory_view').first().click();
+      await expect(sheet.getByText('Arguments')).toBeVisible();
+      if (process.env.TRACE_SCREENSHOT) {
+        await page.screenshot({ path: process.env.TRACE_SCREENSHOT, fullPage: false });
+      }
+    } finally {
+      await api.dispose();
+      await context.close();
+    }
+  });
+
+  test('a RAG turn records the retrieval, its query embedding and each source search', async ({
+    browser,
+  }) => {
+    const { context, sub, token } = await newUserContext(browser);
+    const api = await authedRequest(playwright, token);
+    const multi = await multipartContext(token);
+    try {
+      const taskId = await postUpload(multi, README_MD, {
+        user: sub,
+        name: 'trace-docs',
+        mimeType: 'text/markdown',
+      });
+      expect((await waitForTask(api, taskId, 120_000)).status).toBe('SUCCESS');
+      const { rows } = await pg.query<{ id: string }>(
+        `SELECT id::text AS id FROM sources WHERE user_id = $1 ORDER BY date DESC LIMIT 1`,
+        [sub],
+      );
+      const sourceId = rows[0].id;
+
+      const res = await api.post('/stream', {
+        data: {
+          question: 'how do I get started?',
+          active_docs: sourceId,
+          save_conversation: true,
+        },
+        timeout: 180_000,
+      });
+      expect(await res.text()).toContain('"type": "end"');
+
+      const [trace] = await tracesFor(sub);
+      const byKind = (kind: string) => trace.spans.filter((s) => s.kind === kind);
+      const retrieval = byKind('retrieval');
+      expect(retrieval.length).toBeGreaterThan(0);
+      expect(byKind('embedding').length).toBeGreaterThan(0);
+      const searches = byKind('search');
+      expect(searches.map((s) => s.attributes['gen_ai.data_source.id'])).toContain(sourceId);
+      // Retrieval ran before the agent answered, inside the same trace.
+      const agent = byKind('agent')[0];
+      expect(retrieval[0].offset_ms).toBeLessThan(agent.offset_ms);
+      expect(trace.summary.retrieval_calls).toBeGreaterThan(0);
+
+      const page = await context.newPage();
+      await page.goto('/settings/logs');
+      await page.getByText('how do I get started?').first().click();
+      await page.getByRole('button', { name: 'View trace' }).click();
+      const sheet = page.getByRole('dialog');
+      await expect(sheet.getByText('Execution trace')).toBeVisible();
+      await sheet.getByText(/^retrieval/).first().click();
+      await expect(sheet.getByText('Retrieved chunks')).toBeVisible();
+      if (process.env.TRACE_SCREENSHOT_RAG) {
+        await page.screenshot({ path: process.env.TRACE_SCREENSHOT_RAG, fullPage: false });
+      }
+    } finally {
+      await multi.dispose();
+      await api.dispose();
+      await context.close();
+    }
+  });
+});