diff --git a/archify.zip b/archify.zip
index 59b525489..7b14ffcb5 100644
Binary files a/archify.zip and b/archify.zip differ
diff --git a/archify/renderers/waterfall/render-waterfall.mjs b/archify/renderers/waterfall/render-waterfall.mjs
index 54d334d2e..ad16256d7 100644
--- a/archify/renderers/waterfall/render-waterfall.mjs
+++ b/archify/renderers/waterfall/render-waterfall.mjs
@@ -66,6 +66,9 @@ for (const [index, span] of raw.entries()) {
   const hasDuration = Number.isFinite(span.duration);
   const timing = (message, fixes) => fail('waterfall/invalid-timing', `Span "${span.id}" ${message}`, { path: `/spans/${index}`, nodeId: span.id },
     { start: span.start, end: span.end ?? null, duration: span.duration ?? null, status: span.status ?? 'ok' }, fixes);
+  if (hasDuration && !Number.isFinite(span.start + span.duration)) {
+    timing('has a derived end outside the finite numeric range.', ['Rescale the recorded timing and unit to a representable range.']);
+  }
   if (hasEnd && span.end < span.start) timing(`ends (${span.end}) before it starts (${span.start}).`, ['Correct start or end from the recorded timing.']);
   if (hasEnd && hasDuration && Math.abs(span.end - span.start - span.duration) > 1e-9) {
     timing(`states end ${span.end} and duration ${span.duration}, which disagree with start ${span.start}.`, ['Keep only one of end or duration.']);
@@ -126,7 +129,7 @@ const rows = [];
 }(spans.filter((span) => span.parent === undefined), 0));
 
 function number(value) {
-  const rounded = Math.round(value * 100) / 100;
+  const rounded = Math.abs(value) > Number.MAX_VALUE / 100 ? value : Math.round(value * 100) / 100;
   return rounded.toLocaleString('en-US', { maximumFractionDigits: 2 });
 }
 const formatDuration = (value) => `${number(value)} ${unitLabel}`;
@@ -157,6 +160,11 @@ const labelW = Math.ceil(Math.max(140, ...rows.map(nameWidth)));
 const axisX0 = layout.margin + labelW + layout.columnGap;
 const axisX1 = axisX0 + layout.axisWidth;
 const scale = wall > 0 ? layout.axisWidth / wall : 0;
+if (!Number.isFinite(scale)) {
+  fail('waterfall/invalid-timing', 'The recorded range cannot form a finite axis scale.',
+    { path: '/spans' }, { start: t0, end: t1, wall }, ['Rescale the recorded timing and unit to a representable range.']);
+  throwDiagnosticProblems('Waterfall validation failed', problems, { diagnostics: details });
+}
 const xOf = (t) => Math.round((axisX0 + (t - t0) * scale) * 100) / 100;
 const rowsTop = layout.top + layout.axisH;
 
@@ -171,7 +179,14 @@ const tickStep = (() => {
   }
 })();
 const ticks = [];
-for (let t = Math.ceil(t0 / tickStep) * tickStep; t <= t1 + 1e-9; t += tickStep) ticks.push({ t, x: xOf(t) });
+const firstTick = Math.ceil(t0 / tickStep) * tickStep;
+const tickCount = Math.max(0, Math.floor((t1 - firstTick) / tickStep + 1e-9) + 1);
+for (let index = 0; index < tickCount; index += 1) {
+  const t = firstTick + index * tickStep;
+  // Large timestamps can round adjacent ticks to the same double. Index-based
+  // iteration remains bounded even when adding tickStep cannot advance t.
+  if (ticks.at(-1)?.t !== t) ticks.push({ t, x: xOf(t) });
+}
 
 const LABEL_GAP = 7;
 const parentIds = new Set(rows.map((row) => row.parent).filter((id) => id !== undefined));
diff --git a/test/waterfall-rendering.test.mjs b/test/waterfall-rendering.test.mjs
index d7c3340f0..10cb376a5 100644
--- a/test/waterfall-rendering.test.mjs
+++ b/test/waterfall-rendering.test.mjs
@@ -19,7 +19,7 @@ function run(diagram, extra = []) {
   const input = path.join(directory, 'candidate.waterfall.json');
   const output = path.join(directory, 'candidate.html');
   fs.writeFileSync(input, JSON.stringify(diagram));
-  return { ...spawnSync(process.execPath, [renderer, input, output, ...extra], { cwd: directory, encoding: 'utf8' }), output };
+  return { ...spawnSync(process.execPath, [renderer, input, output, ...extra], { cwd: directory, encoding: 'utf8', timeout: 10000 }), input, output };
 }
 function layoutOf(diagram) {
   const result = run(diagram, ['--layout-json']);
@@ -58,6 +58,48 @@ test('waterfall: bar geometry is exactly the recorded timing on one axis', () =>
   assert.deepEqual(report.rows.map((row) => row.id), ['request', 'auth', 'inventory', 'discount', 'payment', 'save']);
 });
 
+test('waterfall: large timestamps terminate when tick increments are below floating-point resolution', () => {
+  const diagram = clone(small);
+  diagram.spans = [{ id: 'request', name: 'Request', start: 1e16, end: 1e16 + 2 }];
+  const result = run(diagram, ['--layout-json']);
+  assert.equal(result.status, 0, result.stderr || result.error?.message);
+  const report = JSON.parse(result.stdout);
+  assert.equal(report.wall, 2);
+  assert.equal(report.rows[0].label, '2 ms');
+  assert.ok(Number.isFinite(report.rows[0].x0));
+  assert.ok(Number.isFinite(report.rows[0].x1));
+  assert.ok(report.rows[0].x1 > report.rows[0].x0);
+});
+
+test('waterfall: unrepresentable derived timing is rejected without writing invalid geometry', () => {
+  for (const span of [
+    { id: 'request', name: 'Request', start: 1e308, duration: 1e308 },
+    { id: 'request', name: 'Request', start: 0, duration: Number.MIN_VALUE },
+  ]) {
+    const diagram = clone(small);
+    diagram.spans = [span];
+    const result = run(diagram);
+    assert.equal(result.status, 1, result.stderr || result.error?.message);
+    assert.match(result.stderr, /finite/);
+    assert.equal(fs.existsSync(result.output), false);
+    const cli = spawnSync(process.execPath, [path.join(skillRoot, 'bin/archify.mjs'), 'validate', 'waterfall', result.input, '--json'], { encoding: 'utf8', timeout: 10000 });
+    assert.equal(cli.status, 1, cli.stderr || cli.stdout);
+    const receipt = JSON.parse(cli.stdout);
+    const diagnostic = receipt.diagnostics.find(({ code }) => code === 'waterfall/invalid-timing');
+    assert.ok(diagnostic, cli.stdout);
+    assert.ok(diagnostic.supportedFixes.length > 0, cli.stdout);
+  }
+});
+
+test('waterfall: finite very large timing labels do not overflow while formatting', () => {
+  const diagram = clone(small);
+  diagram.spans = [{ id: 'request', name: 'Request', start: 1e307, end: 1.1e307 }];
+  const result = run(diagram);
+  assert.equal(result.status, 0, result.stderr || result.error?.message);
+  const html = fs.readFileSync(result.output, 'utf8');
+  assert.doesNotMatch(html, /(?:NaN|Infinity|∞)/);
+});
+
 test('waterfall: percentages name their denominator and are never summed into the parent', () => {
   const html = fs.readFileSync(run(small).output, 'utf8');
   assert.match(html, /data-node-id="payment"[^>]*aria-label="[^"]*400–1,050 ms · 650 ms · 54% of 1,200 ms wall-clock/);