swarm: HTTP-backed primitive retrieval + live-engram integration test

- primitive_attend retrieves over HTTP (POST /api/search) when ENGRAM_URL is
  set — the location-independent worker model — falling back to the in-process
  store otherwise. Proven against the isolated :8901 clone: CCR compiled a
  bounded context from REAL mind content (VBD/intellectual-dna).
- gate the engram work-tracking mirror behind SWARM_MIRROR=1; the durable
  substrate is always the JSONL journal, so a swarm never depends on the mind
  to track its work. (Repeated POST /api/nodes mirror writes were observed to
  crash the isolated daemon — a daemon-side write-path robustness issue;
  retrieval POST /api/search is solid. Prod :8742 never touched.)
- integ_engram: CCR real-retrieval + full swarm completion against live clone.

lang/swarm/worktrack.el

@@ -106,6 +106,15 @@ fn worktrack_append(kind: String, corr_id: String, subject: String, payload: Str
 // No-op unless ENGRAM_URL is set. Failures are swallowed (tracking must not
 // depend on the mind being reachable).
 fn worktrack_mirror_engram(rec: String, corr_id: String, kind: String, subject: String) -> Bool {
+    // Opt-in: the durable substrate is the JSONL journal (always written). The
+    // engram mirror is an additional convenience, enabled with SWARM_MIRROR=1,
+    // so a swarm never depends on — or loads — the mind just to track its work.
+    if str_eq(env("SWARM_MIRROR"), "1") {
+        // enabled — fall through to the mirror POST
+        let _go: Int = 1
+    } else {
+        return false
+    }
     let url: String = env("ENGRAM_URL")
     if str_eq(url, "") {
         return false
@@ -121,7 +130,7 @@ fn worktrack_mirror_engram(rec: String, corr_id: String, kind: String, subject:
     let body: String = json_build_object(body_kv)
     let key: String = env("ENGRAM_API_KEY")
     let body2: String = json_set_str(body, "_auth", key)
-    let resp: String = http_post(url + "/api/node", body2)
+    let resp: String = http_post(url + "/api/nodes", body2)
     return true
 }