otel P7: OTLP-JSON export + injected transport

otel/export-otlp folds spans → OTLP/JSON envelope (resourceSpans → scopeSpans →
spans) with hex traceId(32)/spanId(16)/parentSpanId, uint64-as-string nano
timestamps, typed attributes (stringValue/intValue), and span kind
(SERVER/INTERNAL). otel/export-otlp-json encodes via dream-json-encode;
otel/post-otlp POSTs through an injected transport (testable without a live
collector).

lib/host/tests/otel.sx

@@ -259,6 +259,69 @@
 (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) "")
 
+;; ── P7: OTLP-JSON export ───────────────────────────────────────────
+;; Serialize spans to OTLP/JSON: resourceSpans → scopeSpans → spans with hex
+;; traceId/spanId/parentSpanId, string nano timestamps, typed attributes. POST
+;; via an injected transport (testable without a live collector).
+(otel/reset!)
+(otel/record! {:trace "trace-1" :span "span-1" :parent nil :name "GET /feed"
+               :t0 1000 :t1 5000 :attrs {:http.method "GET" :http.status 200} :events (list)})
+(otel/record! {:trace "trace-1" :span "span-2" :parent "span-1" :name "db"
+               :t0 2000 :t1 3000 :attrs {} :events (list)})
+
+(define host-ot-otlp (otel/export-otlp (otel/recent)))
+(define host-ot-rss (get host-ot-otlp :resourceSpans))
+(host-ot-test "one resourceSpans" (len host-ot-rss) 1)
+(define host-ot-ss (get (first host-ot-rss) :scopeSpans))
+(host-ot-test "one scopeSpans" (len host-ot-ss) 1)
+(define host-ot-ospans (get (first host-ot-ss) :spans))
+(host-ot-test "two otlp spans" (len host-ot-ospans) 2)
+
+(define host-ot-oroot (first host-ot-ospans))
+(host-ot-test "traceId is 32 hex chars" (len (get host-ot-oroot :traceId)) 32)
+(host-ot-test "traceId value" (get host-ot-oroot :traceId) "00000000000000000000000000000001")
+(host-ot-test "spanId is 16 hex chars" (len (get host-ot-oroot :spanId)) 16)
+(host-ot-test "spanId value" (get host-ot-oroot :spanId) "0000000000000001")
+(host-ot-test "otlp name" (get host-ot-oroot :name) "GET /feed")
+(host-ot-test "startTimeUnixNano is a string" (get host-ot-oroot :startTimeUnixNano) "1000")
+(host-ot-test "endTimeUnixNano is a string" (get host-ot-oroot :endTimeUnixNano) "5000")
+(host-ot-test "server span kind 2" (get host-ot-oroot :kind) 2)
+(host-ot-test "root has no parentSpanId" (has-key? host-ot-oroot :parentSpanId) false)
+
+;; typed attributes: strings → stringValue, numbers → intValue
+(define host-ot-oattrs (get host-ot-oroot :attributes))
+(host-ot-test "two attributes" (len host-ot-oattrs) 2)
+(define host-ot-mattr (first (filter (fn (a) (= (get a :key) "http.method")) host-ot-oattrs)))
+(host-ot-test "attr key" (get host-ot-mattr :key) "http.method")
+(host-ot-test "string attr uses stringValue" (get (get host-ot-mattr :value) :stringValue) "GET")
+(define host-ot-sattr (first (filter (fn (a) (= (get a :key) "http.status")) host-ot-oattrs)))
+(host-ot-test "int attr uses intValue" (get (get host-ot-sattr :value) :intValue) "200")
+
+;; child carries parentSpanId = root spanId, and internal kind
+(define host-ot-ochild (nth host-ot-ospans 1))
+(host-ot-test "child parentSpanId is root spanId" (get host-ot-ochild :parentSpanId) "0000000000000001")
+(host-ot-test "child spanId" (get host-ot-ochild :spanId) "0000000000000002")
+(host-ot-test "internal span kind 1" (get host-ot-ochild :kind) 1)
+
+;; JSON string + injected transport
+(host-ot-test "export-otlp-json contains resourceSpans"
+  (contains? (otel/export-otlp-json (otel/recent)) "resourceSpans") true)
+(define host-ot-cap {})
+(define host-ot-transport (fn (req) (begin (set! host-ot-cap req) req)))
+(otel/post-otlp "http://collector:4318/v1/traces" (otel/recent) host-ot-transport)
+(host-ot-test "transport got a POST" (get host-ot-cap :method) "POST")
+(host-ot-test "transport got the endpoint" (get host-ot-cap :url) "http://collector:4318/v1/traces")
+(host-ot-test "transport got json content-type"
+  (get (get host-ot-cap :headers) :content-type) "application/json")
+(host-ot-test "transport body carries the hex traceId"
+  (contains? (get host-ot-cap :body) "00000000000000000000000000000001") true)
+
+;; empty spans still yield the OTLP envelope with an empty spans list
+(host-ot-test "empty export has resourceSpans"
+  (len (get (otel/export-otlp (list)) :resourceSpans)) 1)
+(host-ot-test "empty export has zero spans"
+  (len (get (first (get (first (get (otel/export-otlp (list)) :resourceSpans)) :scopeSpans)) :spans)) 0)
+
 (define
   host-ot-tests-run!
   (fn