fix: add rate-limiting semaphores to audit script

The audit script was flooding RIPE Stat and PeeringDB with unthrottled
parallel requests, causing 429 rate-limits that resulted in auth=0
false negatives (inflating the failure count).

Changes:
- Added threading.Semaphore for RIPE Stat (max 3) and PeeringDB (max 2)
- Added retry logic to _fetch_ripe (was fire-and-forget)
- Increased PDB retries from 2 to 3 with longer backoff (2s, 4s, 6s)
- Increased ASN stagger from 2s to 3s

Results: Accuracy 84% -> 87% (trend: 77% -> 87%, +10%)

audit/audit.py

@@ -12,7 +12,7 @@ Reports dir:   /opt/peercortex-app/audit/reports/YYYY-MM-DD.json
 Latest text:   /opt/peercortex-app/audit/latest_report.txt
 """
 
-import json, os, sys, time, datetime, urllib.request, urllib.error
+import json, os, sys, time, datetime, urllib.request, urllib.error, threading
 from concurrent.futures import ThreadPoolExecutor, as_completed
 from pathlib import Path
 
@@ -89,6 +89,13 @@ SEED_ASNS = [
     1, 64512, 65000, 0, 4294967295,
 ]
 
+# ─── Rate-limiting semaphores ────────────────────────────────────────────────
+# Prevents 429 errors from RIPE Stat and PeeringDB by limiting concurrent requests.
+# Without this, the audit floods both APIs and gets rate-limited, causing auth=0
+# false negatives that inflate the failure count.
+_ripe_sem = threading.Semaphore(3)   # max 3 concurrent RIPE Stat requests
+_pdb_sem  = threading.Semaphore(2)   # max 2 concurrent PeeringDB requests
+
 # ─── HTTP helpers ─────────────────────────────────────────────────────────────
 def _fetch(url, timeout=30, headers=None):
     """GET url → parsed JSON dict, or None on any error."""
@@ -101,24 +108,39 @@ def _fetch(url, timeout=30, headers=None):
     except Exception:
         return None
 
-def _fetch_pdb(path, timeout=30, retries=2):
-    """Fetch PeeringDB with API key and retry on 429 / failures."""
+def _fetch_pdb(path, timeout=30, retries=3):
+    """Fetch PeeringDB with API key, semaphore throttling, and retry on 429."""
     headers = {}
     if PEERINGDB_KEY:
         headers["Authorization"] = "Api-Key " + PEERINGDB_KEY
     url = PDB_BASE + path
     for attempt in range(retries + 1):
+        _pdb_sem.acquire()
+        try:
             result = _fetch(url, timeout=timeout, headers=headers)
+        finally:
+            _pdb_sem.release()
+        if result is not None:
+            return result
+        if attempt < retries:
+            time.sleep(2.0 * (attempt + 1))   # 2s, 4s, 6s backoff
+    return None
+
+def _fetch_ripe(endpoint, asn, timeout=30, retries=2):
+    """Fetch RIPE Stat with semaphore throttling and retry on failure."""
+    url = f"{RIPE_BASE}/{endpoint}/data.json?resource=AS{asn}"
+    for attempt in range(retries + 1):
+        _ripe_sem.acquire()
+        try:
+            result = _fetch(url, timeout=timeout)
+        finally:
+            _ripe_sem.release()
         if result is not None:
             return result
         if attempt < retries:
             time.sleep(1.5 * (attempt + 1))   # 1.5s, 3s backoff
     return None
 
-def _fetch_ripe(endpoint, asn, timeout=30):
-    url = f"{RIPE_BASE}/{endpoint}/data.json?resource=AS{asn}"
-    return _fetch(url, timeout=timeout)
-
 def _fetch_pc(asn, timeout=90):
     return _fetch(f"{PEERCORTEX_URL}/api/lookup?asn={asn}", timeout=timeout)
 
@@ -186,8 +208,7 @@ def _fetch_auth(asn):
     net     = ((pdb_net or {}).get("data") or [{}])[0]
     net_id  = net.get("id")
 
-    # RIPE Stat (run in parallel via threads)
-    from concurrent.futures import ThreadPoolExecutor
+    # RIPE Stat + PDB IX/Fac (run in parallel via threads, throttled by semaphores)
     with ThreadPoolExecutor(max_workers=4) as pool:
         f_pfx = pool.submit(_fetch_ripe, "announced-prefixes", asn, TIMEOUT_AUTH)
         f_nb  = pool.submit(_fetch_ripe, "asn-neighbours",     asn, TIMEOUT_AUTH)
@@ -414,12 +435,13 @@ def main():
 
     results = []
     with ThreadPoolExecutor(max_workers=CONCURRENCY) as pool:
-        # Stagger submissions by 2s so PeerCortex's internal PDB requests
-        # don't all fire simultaneously (9+ concurrent PDB calls → rate limit).
+        # Stagger submissions by 3s so PeerCortex's internal PDB requests
+        # don't all fire simultaneously (semaphore limits concurrent API calls,
+        # but staggering avoids burst pressure on rate-limit windows).
         futures = {}
         for idx, asn in enumerate(batch):
             if idx > 0:
-                time.sleep(2)
+                time.sleep(3)
             futures[pool.submit(_audit_asn, asn)] = asn
         for i, future in enumerate(as_completed(futures), 1):
             asn = futures[future]