diff --git a/lib/host/otel.sx b/lib/host/otel.sx
index 43bc5558..d80017ff 100644
--- a/lib/host/otel.sx
+++ b/lib/host/otel.sx
@@ -383,3 +383,82 @@
     (fn (req)
       (dream-response 200 {:content-type "text/event-stream"} (otel/-stream-body)))))
 (define otel/routes (list otel/dashboard-route otel/stream-route))
+
+;; ── P7: OTLP-JSON export ──────────────────────────────────────────────
+;; Serialize spans to the OTLP/JSON schema (resourceSpans → scopeSpans → spans)
+;; for interop with Jaeger/Grafana. traceId/spanId/parentSpanId are hex strings;
+;; timestamps are uint64-as-string; attributes are typed {key,value}. Export is a
+;; fold (span → OTLP span); POST goes through an INJECTED transport so it's
+;; testable without a live collector.
+
+;; our "trace-N"/"span-N" ids → a fixed-width lowercase-hex id (real OTLP widths:
+;; traceId 16 bytes = 32 hex, spanId 8 bytes = 16 hex). Deterministic from the id.
+(define otel/-id-num
+  (fn (id)
+    (let ((n (string->number (last (split id "-")))))
+      (if (nil? n) 0 n))))
+(define otel/-zeros
+  (fn (k) (if (<= k 0) "" (str "0" (otel/-zeros (- k 1))))))
+(define otel/-pad-hex
+  (fn (n width)
+    (let ((h (number->string n 16)))
+      (str (otel/-zeros (- width (len h))) h))))
+(define otel/-trace-hex (fn (id) (otel/-pad-hex (otel/-id-num id) 32)))
+(define otel/-span-hex  (fn (id) (otel/-pad-hex (otel/-id-num id) 16)))
+
+;; a value → OTLP AnyValue: numbers are intValue (uint64-as-string), else stringValue.
+(define otel/-otlp-value
+  (fn (v)
+    (if (= (type-of v) "number")
+      {:intValue (str v)}
+      {:stringValue (str v)})))
+(define otel/-otlp-attrs
+  (fn (attrs)
+    (map (fn (k) {:key (str k) :value (otel/-otlp-value (get attrs k))}) (keys attrs))))
+
+;; span kind: 2 = SERVER for an instrumented request (has http.method), else
+;; 1 = INTERNAL.
+(define otel/-otlp-kind
+  (fn (attrs) (if (get attrs :http.method) 2 1)))
+
+(define otel/-otlp-span
+  (fn (s)
+    (let ((attrs (or (get s :attrs) {})))
+      (let ((base
+              {:traceId (otel/-trace-hex (get s :trace))
+               :spanId (otel/-span-hex (get s :span))
+               :name (get s :name)
+               :kind (otel/-otlp-kind attrs)
+               :startTimeUnixNano (str (get s :t0))
+               :endTimeUnixNano (str (get s :t1))
+               :attributes (otel/-otlp-attrs attrs)}))
+        (if (nil? (get s :parent))
+          base
+          (assoc base :parentSpanId (otel/-span-hex (get s :parent))))))))
+
+;; spans → the OTLP export envelope (a JSON-shaped SX value).
+(define otel/export-otlp
+  (fn (spans)
+    {:resourceSpans
+      (list
+        {:resource
+          {:attributes (list {:key "service.name"
+                              :value {:stringValue "rose-ash-host"}})}
+         :scopeSpans
+          (list
+            {:scope {:name "otel-on-sx" :version "0.1.0"}
+             :spans (map otel/-otlp-span spans)})})}))
+
+(define otel/export-otlp-json
+  (fn (spans) (dream-json-encode (otel/export-otlp spans))))
+
+;; POST the OTLP payload through an injected transport. `transport` is a fn taking
+;; a request dict {:method :url :headers :body} — real deploys pass an http POST;
+;; tests pass a recorder. Returns whatever the transport returns.
+(define otel/post-otlp
+  (fn (endpoint spans transport)
+    (transport
+      {:method "POST"
+       :url endpoint
+       :headers {:content-type "application/json"}
+       :body (otel/export-otlp-json spans)})))
diff --git a/lib/host/tests/otel.sx b/lib/host/tests/otel.sx
index c3a84231..d71ee27a 100644
--- a/lib/host/tests/otel.sx
+++ b/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