fix(timestamp): detect & convert microsecond/nanosecond epochs

src/islands/dev/Timestamp.tsx

@@ -6,6 +6,7 @@ import { Alert } from '@/components/ui/Alert';
 import {
   describeDate,
   parseTimestamp,
+  detectNumericUnit,
   formatInTimeZone,
   listTimeZones,
   getLocalTimeZone,
@@ -19,6 +20,7 @@ export default function Timestamp() {
   const [date, setDate] = useState<Date | null>(null);
   const [timeZone, setTimeZone] = useState(() => getLocalTimeZone());
   const [error, setError] = useState('');
+  const [detectedUnit, setDetectedUnit] = useState('');
   const [pickerValue, setPickerValue] = useState('');
   const [pickerZone, setPickerZone] = useState<'local' | 'utc'>('local');
 
@@ -27,6 +29,7 @@ export default function Timestamp() {
     setPickerValue(value);
     setPickerZone(zone);
     setError('');
+    setDetectedUnit('');
     if (!value) return;
     const parsed = parseDateTimeLocal(value, zone);
     if (parsed) setDate(parsed);
@@ -35,6 +38,7 @@ export default function Timestamp() {
   const convert = () => {
     setError('');
     setDate(null);
+    setDetectedUnit('');
     const trimmed = input.trim();
     if (!trimmed) return;
     const parsed = parseTimestamp(trimmed);
@@ -43,10 +47,13 @@ export default function Timestamp() {
       return;
     }
     setDate(parsed);
+    // Surface how an all-digits value was interpreted (seconds/ms/µs/ns).
+    if (/^\d+$/.test(trimmed)) setDetectedUnit(detectNumericUnit(trimmed));
   };
 
   const now = () => {
     setError('');
+    setDetectedUnit('');
     setDate(new Date());
   };
 
@@ -69,7 +76,7 @@ export default function Timestamp() {
         label="Unix timestamp or date string"
         value={input}
         onChange={e => setInput(e.target.value)}
-        placeholder="1720000000  ·  2026-07-12  ·  Jul 12 2026 10:00"
+        placeholder="1720000000 (s · ms · µs · ns)  ·  2026-07-12  ·  Jul 12 2026 10:00"
         rows={2}
       />
 
@@ -113,13 +120,20 @@ export default function Timestamp() {
           </div>
         </div>
 
-        <Button variant="ghost" onClick={() => { setInput(''); setDate(null); setError(''); setPickerValue(''); }}>
+        <Button variant="ghost" onClick={() => { setInput(''); setDate(null); setError(''); setDetectedUnit(''); setPickerValue(''); }}>
           Clear
         </Button>
       </div>
 
       {error && <Alert variant="error">{error}</Alert>}
 
+      {detectedUnit && (
+        <p className="text-sm text-muted-foreground">
+          Detected numeric input as{' '}
+          <span className="font-bold text-foreground">Unix {detectedUnit}</span>.
+        </p>
+      )}
+
       {date && (
         <>
           <label className="flex flex-wrap items-center gap-2 text-sm">

src/tools/dev/timestamp.lib.test.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest';
 import {
   describeDate,
   parseTimestamp,
+  detectNumericUnit,
   formatInTimeZone,
   listTimeZones,
   getLocalTimeZone,
@@ -21,6 +22,24 @@ describe('parseTimestamp', () => {
     expect(date!.getTime()).toBe(1700000000000);
   });
 
+  it('parses a 16-digit numeric string as Unix microseconds', () => {
+    const date = parseTimestamp('1700000000000000');
+    expect(date).not.toBeNull();
+    expect(date!.getTime()).toBe(1700000000000);
+  });
+
+  it('parses a 19-digit numeric string as Unix nanoseconds', () => {
+    const date = parseTimestamp('1700000000000000000');
+    expect(date).not.toBeNull();
+    expect(date!.getTime()).toBe(1700000000000);
+  });
+
+  it('parses the reported 19-digit nanosecond value instead of erroring', () => {
+    const date = parseTimestamp('1784694237438743460');
+    expect(date).not.toBeNull();
+    expect(date!.getUTCFullYear()).toBe(2026);
+  });
+
   it('parses an ISO date string', () => {
     const date = parseTimestamp('2026-07-12');
     expect(date).not.toBeNull();
@@ -32,6 +51,15 @@ describe('parseTimestamp', () => {
   });
 });
 
+describe('detectNumericUnit', () => {
+  it('maps digit length to the epoch unit', () => {
+    expect(detectNumericUnit('1700000000')).toBe('seconds'); // 10
+    expect(detectNumericUnit('1700000000000')).toBe('milliseconds'); // 13
+    expect(detectNumericUnit('1700000000000000')).toBe('microseconds'); // 16
+    expect(detectNumericUnit('1784694237438743460')).toBe('nanoseconds'); // 19
+  });
+});
+
 describe('describeDate', () => {
   it('describes the Unix epoch', () => {
     const result = describeDate(new Date(0));

src/tools/dev/timestamp.lib.ts

@@ -69,13 +69,40 @@ export function listTimeZones(): string[] {
   return ['UTC', ...zones.filter(zone => zone !== 'UTC')];
 }
 
+export type NumericUnit = 'seconds' | 'milliseconds' | 'microseconds' | 'nanoseconds';
+
+/** Convert a numeric epoch value in the given unit to milliseconds. */
+const TO_MILLIS: Record<NumericUnit, (n: number) => number> = {
+  seconds: n => n * 1000,
+  milliseconds: n => n,
+  microseconds: n => n / 1e3,
+  nanoseconds: n => n / 1e6,
+};
+
+/**
+ * Infer the epoch unit of an all-digits timestamp from its length. Tuned so
+ * present-day values land on the right unit: ~10 digits = seconds,
+ * ~13 = milliseconds, ~16 = microseconds, ~19 = nanoseconds. The seconds/millis
+ * cutoffs (≤10, ≤13) match the tool's original behavior.
+ */
+export function detectNumericUnit(digits: string): NumericUnit {
+  const len = digits.length;
+  if (len <= 10) return 'seconds';
+  if (len <= 13) return 'milliseconds';
+  if (len <= 16) return 'microseconds';
+  return 'nanoseconds';
+}
+
 export function parseTimestamp(input: string): Date | null {
   const trimmed = input.trim();
   let date: Date;
   if (/^\d+$/.test(trimmed)) {
-    // Numeric: treat 10-digit as seconds, 13-digit as milliseconds.
-    const num = Number(trimmed);
-    date = new Date(trimmed.length <= 10 ? num * 1000 : num);
+    // Numeric epoch value: infer the unit (s/ms/µs/ns) from its digit length
+    // and convert to milliseconds for the Date constructor. This lets us accept
+    // high-resolution timestamps (e.g. 19-digit nanoseconds) that would blow
+    // past Date's range if naively treated as milliseconds.
+    const millis = TO_MILLIS[detectNumericUnit(trimmed)](Number(trimmed));
+    date = new Date(millis);
   } else {
     date = new Date(trimmed);
   }