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/tests/otel.sx

@@ -202,6 +202,63 @@
 (host-ot-test "empty metrics total 0" (get host-ot-me :total-requests) 0)
 (host-ot-test "empty metrics no routes" (len (get host-ot-me :routes)) 0)
 
+;; ── P6: live dashboard (SSR + SSE) ─────────────────────────────────
+;; Drive two traces through instrumented routes, then check: recent-traces lists
+;; them (newest first); the dashboard SSRs to HTML with the metrics strip + the
+;; latest-trace <svg>; the /otel/stream SSE endpoint emits an SXTP span event.
+(otel/reset!)
+(define host-ot-dapp
+  (dream-router (otel/instrument-routes
+    (list
+      (dream-get "/feed"   (fn (req) (dream-response 200 {} "ok")))
+      (dream-get "/health" (fn (req) (dream-response 200 {} "ok")))))))
+(host-ot-dapp (dream-request "GET" "/feed" {} ""))
+(host-ot-dapp (dream-request "GET" "/health" {} ""))
+
+(host-ot-test "recent-traces lists both" (len (otel/recent-traces)) 2)
+(host-ot-test "recent-traces newest first"
+  (get (first (otel/recent-traces)) :name) "GET /health")
+(host-ot-test "latest-trace is the /health trace"
+  (otel/-trace-root-name (otel/latest-trace)) "GET /health")
+
+;; dashboard SSRs to an HTML string carrying the strip + waterfall + trace list
+(define host-ot-dash (render-to-html (otel/dashboard) {}))
+(host-ot-test "dashboard is a string" (= (type-of host-ot-dash) "string") true)
+(host-ot-test "dashboard has the root id" (contains? host-ot-dash "otel-dashboard") true)
+(host-ot-test "dashboard SSRs the waterfall svg" (contains? host-ot-dash "<svg") true)
+(host-ot-test "dashboard shows a route in the strip" (contains? host-ot-dash "/feed") true)
+(host-ot-test "dashboard declares the SSE subscription" (contains? host-ot-dash "/otel/stream") true)
+
+;; the SSE endpoint emits a span event, SSE-framed
+(define host-ot-sse
+  ((dream-route-handler otel/stream-route) (dream-request "GET" "/otel/stream" {} "")))
+(host-ot-test "sse content type is event-stream"
+  (contains? (str (dream-headers host-ot-sse)) "event-stream") true)
+(host-ot-test "sse body is SSE-framed" (contains? (dream-resp-body host-ot-sse) "data:") true)
+(host-ot-test "sse emits an otel.span event"
+  (contains? (dream-resp-body host-ot-sse) "otel.span") true)
+(host-ot-test "sse event carries the span name"
+  (contains? (dream-resp-body host-ot-sse) "GET /health") true)
+
+;; span-event helper carries the type + span
+(define host-ot-ev (otel/latest-span-event))
+(host-ot-test "latest span event type" (str (get host-ot-ev :type)) "otel.span")
+
+;; mounted through make-app: GET /otel serves the dashboard page
+(otel/reset!)
+(feed/reset!)
+(define host-ot-mapp (host/make-app (list host/feed-routes otel/routes)))
+(define host-ot-otelresp (host-ot-mapp (dream-request "GET" "/otel" {} "")))
+(host-ot-test "GET /otel status 200" (dream-status host-ot-otelresp) 200)
+(host-ot-test "GET /otel serves the dashboard"
+  (contains? (dream-resp-body host-ot-otelresp) "otel-dashboard") true)
+
+;; empty ring → dashboard still SSRs (a placeholder, no svg)
+(otel/reset!)
+(define host-ot-empty-dash (render-to-html (otel/dashboard) {}))
+(host-ot-test "empty dashboard still renders" (contains? host-ot-empty-dash "otel-dashboard") true)
+(host-ot-test "empty stream body is blank" (otel/-stream-body) "")
+
 (define
   host-ot-tests-run!
   (fn