fix: use monitor-side checked_at timestamp instead of coordinator arrival time

apps/api/src/routes/pings.ts

@@ -65,13 +65,15 @@ export const ingest = new Elysia()
     const meta = body.meta ? { ...body.meta } : {};
     if (body.cert_expiry_days != null) meta.cert_expiry_days = body.cert_expiry_days;
 
+    const checkedAt = body.checked_at ? new Date(body.checked_at) : null;
     const scheduledAt = body.scheduled_at ? new Date(body.scheduled_at) : 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, region, run_id)
+      INSERT INTO pings (monitor_id, checked_at, scheduled_at, jitter_ms, status_code, latency_ms, up, error, meta, region, run_id)
       VALUES (
         ${body.monitor_id},
+        ${checkedAt ?? sql`now()`},
         ${scheduledAt},
         ${jitterMs},
         ${body.status_code ?? null},
@@ -93,6 +95,7 @@ export const ingest = new Elysia()
   }, {
     body: t.Object({
       monitor_id:       t.String(),
+      checked_at:       t.Optional(t.Nullable(t.String())),
       scheduled_at:     t.Optional(t.Nullable(t.String())),
       jitter_ms:        t.Optional(t.Nullable(t.Number())),
       status_code:      t.Optional(t.Nullable(t.Number())),

apps/monitor/src/runner.rs

@@ -100,6 +100,7 @@ pub async fn fetch_and_run(
                 Ok(r) => r,
                 Err(_) => PingResult {
                     monitor_id: monitor.id.clone(),
+                    checked_at: Some(chrono::Utc::now().to_rfc3339()),
                     scheduled_at: scheduled_at_iso.clone(),
                     jitter_ms: None,
                     status_code: None,
@@ -125,6 +126,9 @@ pub async fn fetch_and_run(
 }
 
 async fn run_check(client: &reqwest::Client, monitor: &Monitor, scheduled_at: Option<String>, region: &str, run_id: &str) -> PingResult {
+    // Record when the check actually started (used as checked_at in the ping)
+    let checked_at = chrono::Utc::now().to_rfc3339();
+
     // Compute jitter: how late we actually started vs when we were scheduled
     let jitter_ms: Option<i64> = scheduled_at.as_deref().and_then(|s| {
         let scheduled = chrono::DateTime::parse_from_rfc3339(s).ok()?;
@@ -175,6 +179,7 @@ async fn run_check(client: &reqwest::Client, monitor: &Monitor, scheduled_at: Op
             debug!("{} check error: {e}", monitor.url);
             PingResult {
                 monitor_id: monitor.id.clone(),
+                checked_at: Some(checked_at.clone()),
                 scheduled_at,
                 jitter_ms,
                 status_code: None,
@@ -236,6 +241,7 @@ async fn run_check(client: &reqwest::Client, monitor: &Monitor, scheduled_at: Op
 
             PingResult {
                 monitor_id: monitor.id.clone(),
+                checked_at: Some(checked_at),
                 scheduled_at,
                 jitter_ms,
                 status_code: Some(status),

apps/monitor/src/types.rs

@@ -33,6 +33,7 @@ pub struct Monitor {
 #[derive(Debug, Serialize)]
 pub struct PingResult {
     pub monitor_id:       String,
+    pub checked_at:       Option<String>,
     pub scheduled_at:     Option<String>,
     pub jitter_ms:        Option<i64>,
     pub status_code:      Option<u16>,