From 76941277fdc0abde874fda17ab0e85bdbd2bb741 Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Thu, 2 Jul 2026 11:44:00 +0000
Subject: [PATCH] otel: child spans in the blog render path (waterfall
 breakdown)

---
 lib/host/blog.sx | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/lib/host/blog.sx b/lib/host/blog.sx
index 52433dc1..adf28cd3 100644
--- a/lib/host/blog.sx
+++ b/lib/host/blog.sx
@@ -2003,7 +2003,9 @@
 (define host/blog-post
   (fn (req)
     (let ((slug (dream-param req "slug")))
-      (let ((r (host/blog-get slug)))
+      ;; child spans nest under the request's root span (from otel/instrument-route),
+      ;; so the waterfall breaks the render down: get → body-fold → relations → …
+      (let ((r (otel/with-span "blog.get" {} (fn () (host/blog-get slug)))))
         (if r
           ;; Compute everything that does durable reads — body, related block, AND
           ;; the auth footer (a durable session read now) — in let bindings BEFORE
@@ -2014,21 +2016,24 @@
                   ;; (default just :body) via the render-fold, in field order, against a
                   ;; context (auth/device/locale + the container). Else the legacy sx_content.
                   (body-html
-                    (let ((ctx (host/blog--comp-ctx principal req slug)))
-                      (let ((rendered (reduce (fn (acc f) (str acc (host/comp-render (host/blog--comp-of slug f) ctx)))
-                                             "" (host/blog--composition-fields slug))))
-                        (if (= rendered "") (host/blog-render r) rendered))))
+                    (otel/with-span "blog.render-body" {}
+                      (fn ()
+                        (let ((ctx (host/blog--comp-ctx principal req slug)))
+                          (let ((rendered (reduce (fn (acc f) (str acc (host/comp-render (host/blog--comp-of slug f) ctx)))
+                                                 "" (host/blog--composition-fields slug))))
+                            (if (= rendered "") (host/blog-render r) rendered))))))
                   ;; all relation blocks (Related, Tags, Types, Tagged-with-this …)
                   ;; come from iterating the registry — one section, registry-driven.
-                  (relations (host/blog--relations-or-hint slug (not (nil? principal))))
+                  (relations (otel/with-span "blog.relations" {}
+                               (fn () (host/blog--relations-or-hint slug (not (nil? principal))))))
                   ;; the typed render-template block (Slice 8c) — field values shown via
                   ;; the post's types' templates. A durable read, so pre-fetch it here.
-                  (typed-block (host/blog--typed-block slug))
+                  (typed-block (otel/with-span "blog.typed-block" {} (fn () (host/blog--typed-block slug))))
                   ;; a TYPE post shows its definition (fields + grammar + relations) publicly —
                   ;; read-only; the edit page has the writable form.
                   (type-def-view (if (host/blog--is-type? slug) (host/blog--type-def-view slug) ""))
                   (type-population (if (host/blog--is-type? slug) (host/blog--type-population slug) ""))
-                  (auth-foot (host/auth-footer req)))
+                  (auth-foot (otel/with-span "blog.auth-footer" {} (fn () (host/auth-footer req)))))
               (host/blog--resp req 200
                 (host/blog--page req (get r :title)
                   (quasiquote