fix: jitter_ms now measured in Rust at check start, excludes latency and return trip

apps/web/src/routes/pings.ts

@@ -57,7 +57,7 @@ export const ingest = new Elysia()
     if (body.cert_expiry_days != null) meta.cert_expiry_days = body.cert_expiry_days;
 
     const scheduledAt = body.scheduled_at ? new Date(body.scheduled_at) : null;
-    const jitterMs = scheduledAt ? Math.max(0, Date.now() - scheduledAt.getTime()) : null;
+    const jitterMs = body.jitter_ms ?? null;
 
     const [ping] = await sql`
       INSERT INTO pings (monitor_id, scheduled_at, jitter_ms, status_code, latency_ms, up, error, meta)
@@ -83,6 +83,7 @@ export const ingest = new Elysia()
     body: t.Object({
       monitor_id:       t.String(),
       scheduled_at:     t.Optional(t.Nullable(t.String())),
+      jitter_ms:        t.Optional(t.Nullable(t.Number())),
       status_code:      t.Optional(t.Number()),
       latency_ms:       t.Optional(t.Number()),
       up:               t.Boolean(),