From 4f17a40187f754d5051b1053fa7be4a86d8b5511 Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Thu, 2 Jul 2026 10:53:02 +0000
Subject: [PATCH] otel: relative 'Ns ago' timestamp on recent traces

---
 lib/host/otel.sx | 46 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 33 insertions(+), 13 deletions(-)

diff --git a/lib/host/otel.sx b/lib/host/otel.sx
index 5fbdfd89..08539ba2 100644
--- a/lib/host/otel.sx
+++ b/lib/host/otel.sx
@@ -370,12 +370,27 @@
   (fn (trace-id)
     (let ((roots (filter (fn (s) (nil? (get s :parent))) (otel/trace-spans trace-id))))
       (if (empty? roots) nil (get (get (first roots) :attrs) :http.target)))))
+;; when the trace last did something (latest span end), epoch ns.
+(define otel/-trace-end
+  (fn (trace-id)
+    (let ((spans (otel/trace-spans trace-id)))
+      (if (empty? spans) 0 (otel/-max-t1 spans)))))
+;; a ns age → a coarse "N<unit> ago" label.
+(define otel/-ago
+  (fn (age-ns)
+    (let ((s (quotient (if (< age-ns 0) 0 age-ns) 1000000000)))
+      (cond
+        ((< s 1) "just now")
+        ((< s 60) (str s "s ago"))
+        ((< s 3600) (str (quotient s 60) "m ago"))
+        (else (str (quotient s 3600) "h ago"))))))
 (define otel/trace-summary
   (fn (trace-id)
     {:trace trace-id
      :name (otel/-trace-root-name trace-id)
      :target (otel/-trace-target trace-id)
      :dur (otel/-trace-dur trace-id)
+     :t (otel/-trace-end trace-id)
      :spans (len (otel/trace-spans trace-id))}))
 (define otel/recent-traces
   (fn () (reverse (map otel/trace-summary (otel/-trace-ids)))))
@@ -424,19 +439,24 @@
 
 (define otel/-traces-list
   (fn (traces)
-    (quasiquote
-      (ul :class "otel-traces"
-        (splice-unquote
-          (map
-            (fn (t)
-              (quasiquote
-                (li :data-trace (unquote (str (get t :trace)))
-                  ;; show the concrete target (/welcome) if known, else the span
-                  ;; name, then the wall duration and span count.
-                  (span :style "font-weight:600"
-                    (unquote (or (get t :target) (get t :name))))
-                  (unquote (str "  ·  " (otel/-ms (get t :dur)) "  ·  " (get t :spans) " spans")))))
-            traces))))))
+    ;; capture "now" ONCE so all ages are relative to the same instant; each 3s
+    ;; re-render recomputes it, so the labels tick upward (2s ago → 5s ago → …).
+    (let ((now (otel/now-ns)))
+      (quasiquote
+        (ul :class "otel-traces"
+          (splice-unquote
+            (map
+              (fn (t)
+                (quasiquote
+                  (li :data-trace (unquote (str (get t :trace)))
+                    ;; concrete target (/welcome) if known, else the span name; then
+                    ;; wall duration, span count, and how long ago it happened.
+                    (span :style "font-weight:600"
+                      (unquote (or (get t :target) (get t :name))))
+                    (unquote (str "  ·  " (otel/-ms (get t :dur))
+                                  "  ·  " (get t :spans) " spans"
+                                  "  ·  " (otel/-ago (- now (get t :t))))))))
+              traces)))))))
 
 ;; a per-route latency bar chart: each row is a nested bar — teal p50 inside amber
 ;; p95 inside light-red p99 — so the tail (red beyond amber) is visible at a glance.