otel P6: live dashboard — GET /otel SSR + /otel/stream SSE

otel/dashboard SSRs the metrics strip + latest-trace waterfall + recent-traces
list as HTML carrying Datastar-style data-on-load subscribing to /otel/stream,
the SSE feed of SXTP otel.span events. Routes otel/dashboard-route +
otel/stream-route (otel/routes) mount via make-app. recent-traces/latest-trace
+ otel/span-event helpers.

lib/host/otel.sx

@@ -273,3 +273,113 @@
 
 ;; convenience: metrics over the current ring.
 (define otel/metrics-recent (fn () (otel/metrics (otel/recent))))
+
+;; ── P6: live dashboard (SSR + SSE) ────────────────────────────────────
+;; GET /otel renders a dashboard — metrics strip + the latest trace's waterfall +
+;; a recent-traces list — as server-rendered HTML carrying Datastar-style reactive
+;; attributes that subscribe to GET /otel/stream, the SSE feed of new span events
+;; (SXTP events, the host's Datastar-borrowed wire format). SSR + declarative
+;; reactive attrs + SSE patches IS the reactive-island model here. (Live client
+;; hydration is a deploy concern; SSR, the event feed, and the data are tested.)
+
+;; recent traces, newest-first: {:trace :name :spans}. root name = the parentless
+;; span (fallback: first recorded).
+(define otel/-trace-ids
+  (fn () (otel/-distinct (map (fn (s) (get s :trace)) (otel/recent)))))
+(define otel/-trace-root-name
+  (fn (trace-id)
+    (let ((spans (otel/trace-spans trace-id)))
+      (let ((roots (filter (fn (s) (nil? (get s :parent))) spans)))
+        (cond
+          ((not (empty? roots)) (get (first roots) :name))
+          ((not (empty? spans)) (get (first spans) :name))
+          (else ""))))))
+(define otel/trace-summary
+  (fn (trace-id)
+    {:trace trace-id
+     :name (otel/-trace-root-name trace-id)
+     :spans (len (otel/trace-spans trace-id))}))
+(define otel/recent-traces
+  (fn () (reverse (map otel/trace-summary (otel/-trace-ids)))))
+(define otel/latest-trace
+  (fn ()
+    (let ((r (otel/recent)))
+      (if (empty? r) nil (get (last r) :trace)))))
+
+;; ── SSE span events (SXTP) ────────────────────────────────────────────
+(define otel/span-event
+  (fn (s)
+    (sxtp/event "otel.span"
+      {:id (get s :span)
+       :body {:trace (get s :trace) :span (get s :span) :parent (get s :parent)
+              :name (get s :name) :t0 (get s :t0) :t1 (get s :t1)
+              :attrs (get s :attrs)}
+       :time (get s :t1)})))
+(define otel/latest-span-event
+  (fn ()
+    (let ((r (otel/recent)))
+      (if (empty? r) nil (otel/span-event (last r))))))
+;; one SSE frame: `event: otel.span\n data: <sxtp event>\n\n`; "" when no spans.
+(define otel/-stream-body
+  (fn ()
+    (let ((e (otel/latest-span-event)))
+      (if (nil? e)
+        ""
+        (str "event: otel.span\ndata: " (sxtp/serialize e) "\n\n")))))
+
+;; ── dashboard markup (plain HTML tags → render-to-html SSRs cleanly) ──
+(define otel/-metrics-strip
+  (fn (m)
+    (quasiquote
+      (table :class "otel-metrics"
+        (tr (th "route") (th "count") (th "p50") (th "p95") (th "p99"))
+        (splice-unquote
+          (map
+            (fn (r)
+              (quasiquote
+                (tr (td (unquote (str (get r :route))))
+                    (td (unquote (str (get r :count))))
+                    (td (unquote (str (get r :p50))))
+                    (td (unquote (str (get r :p95))))
+                    (td (unquote (str (get r :p99)))))))
+            (get m :routes)))))))
+
+(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)))
+                  (unquote (str (get t :name) " — " (get t :spans) " spans")))))
+            traces))))))
+
+(define otel/dashboard
+  (fn ()
+    (let ((m (otel/metrics (otel/recent)))
+          (lt (otel/latest-trace))
+          (traces (otel/recent-traces)))
+      (quasiquote
+        (div :id "otel-dashboard" :data-on-load "@get('/otel/stream')"
+          (h1 "OpenTelemetry")
+          (h2 "metrics")
+          (unquote (otel/-metrics-strip m))
+          (h2 "latest trace")
+          (unquote
+            (if (nil? lt)
+              (quasiquote (p :class "otel-empty" "no traces yet"))
+              (otel/waterfall lt)))
+          (h2 "recent traces")
+          (unquote (otel/-traces-list traces)))))))
+
+;; ── routes ────────────────────────────────────────────────────────────
+(define otel/dashboard-route
+  (dream-get "/otel"
+    (fn (req) (dream-html (render-to-html (otel/dashboard) {})))))
+(define otel/stream-route
+  (dream-get "/otel/stream"
+    (fn (req)
+      (dream-response 200 {:content-type "text/event-stream"} (otel/-stream-body)))))
+(define otel/routes (list otel/dashboard-route otel/stream-route))