perf(dlp): replace O(n*m) proximity check with O(n log n) sorted scan

Sort all match positions and scan linearly instead of checking every
a-b pair. Early-exits on overlap (gap=0) or once the gap drops below
the threshold.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bot_bottle/dlp_detectors.py

@@ -112,19 +112,33 @@ JAILBREAK_PHRASES: tuple[re.Pattern[str], ...] = (
 PROXIMITY_CHARS = 500
 
 
-def _min_distance(
+def _nearby(
     a_matches: list[re.Match[str]],
     b_matches: list[re.Match[str]],
+    threshold: int,
 ) -> int | None:
-    """Smallest char distance between any pair of matches."""
+    """Return the smallest char gap between any a–b pair, or None if
+    both lists are empty.  O(n log n) via sort + linear scan."""
     if not a_matches or not b_matches:
         return None
-    best = None
-    for a in a_matches:
-        for b in b_matches:
-            gap = max(0, max(a.start(), b.start()) - min(a.end(), b.end()))
+    events = sorted(
+        [(m.start(), m.end(), "a") for m in a_matches]
+        + [(m.start(), m.end(), "b") for m in b_matches],
+    )
+    best: int | None = None
+    prev_end: int | None = None
+    prev_tag: str | None = None
+    for start, end, tag in events:
+        if prev_tag is not None and prev_tag != tag and prev_end is not None:
+            gap = max(0, start - prev_end)
             if best is None or gap < best:
                 best = gap
+                if best == 0:
+                    return 0
+                if best <= threshold:
+                    return best
+        prev_end = end if prev_end is None else max(prev_end, end)
+        prev_tag = tag
     return best
 
 
@@ -133,7 +147,7 @@ def scan_naive_injection(text: str) -> ScanResult | None:
     jailbreak_hits = [m for p in JAILBREAK_PHRASES for m in p.finditer(text)]
 
     if disclosure_hits and jailbreak_hits:
-        dist = _min_distance(disclosure_hits, jailbreak_hits)
+        dist = _nearby(disclosure_hits, jailbreak_hits, PROXIMITY_CHARS)
         if dist is not None and dist <= PROXIMITY_CHARS:
             return ScanResult(
                 severity="block",