cascade: exponential backoff for session readiness poll

tools/cascade

@@ -23,8 +23,12 @@ model=${MODEL}"
 printf '%s\n' "$kv" > "$OLLIE/s/new" || die "failed to create session"
 
 B="$OLLIE/s/$id"
-deadline=$(( $(date +%s) + 5 ))
-until [ -d "$B" ] || [ "$(date +%s)" -ge "$deadline" ]; do sleep 0.05; done
+wait=0.1
+for _ in 1 2 3 4 5 6 7 8; do
+    [ -d "$B" ] && break
+    sleep "$wait"
+    wait=$(awk "BEGIN{printf \"%.2f\", $wait * 2}")
+done
 [ -d "$B" ] || die "timeout waiting for session $id"
 
 prompt="[parent_session_id=${OLLIE_SESSION_ID}]