test: F3.4 semantic collapse + snapshot_idf — 26/26 (23 invariants + 3 known-defeats)

test_swarmmetrics.py

@@ -4,7 +4,7 @@ import sys
 sys.path.insert(0, ".")
 from swarmmetrics import (
     _gini, _half_life_weight, score_reciprocity, score_channels,
-    score_echo, detect_shadows, analyze, shuffle_test
+    score_echo, detect_shadows, analyze, shuffle_test, semantic_collapse
 )
 
 now = time.time()
@@ -408,6 +408,57 @@ def test_genuine_novel_concept_zero_echo():
     # for concepts that have had time to propagate.
 
 
+def test_semantic_collapse_padding():
+    """F3.4: semantic_collapse catches synonym padding attack.
+    50 variants of 'greeting-N' should collapse to ~1 canonical form.
+    This is the defense layer that F3.3 alone lacks."""
+    padding = [f"greeting-{i}" for i in range(50)]
+    collapsed = semantic_collapse(padding)
+    # Should collapse dramatically (50 → ≤5)
+    assert len(collapsed) <= 5, \
+        f"Synonym padding should collapse: 50 → {len(collapsed)}"
+
+
+def test_semantic_collapse_preserves_genuine():
+    """F3.4: semantic_collapse must not collapse genuinely diverse concepts.
+    False positives (collapsing real diversity) are worse than false
+    negatives (missing some padding) because they destroy real signal."""
+    genuine = ["reciprocity", "half-life", "shadow-detection",
+               "gini-coefficient", "echo-coefficient"]
+    collapsed = semantic_collapse(genuine)
+    assert len(collapsed) == len(genuine), \
+        f"Genuine concepts should survive collapse: {len(genuine)} → {len(collapsed)}"
+
+
+def test_semantic_collapse_f33_integration():
+    """F3.4 with F3.3: synonym padding that defeats F3.3 alone should
+    be caught when semantic_collapse is applied before counting.
+
+    Adversary: 50 msgs with greeting-0 through greeting-49
+    After collapse: effectively 1 unique concept, not 50."""
+    msgs = []
+    # Adversary pair with synonym padding
+    hello_synonyms = [f"greeting-{i}" for i in range(50)]
+    for i in range(25):
+        msgs.append({"from_id": "eve", "to_id": "mallory",
+                     "timestamp": now - 2*day + i*60,
+                     "concepts": [hello_synonyms[i], hello_synonyms[i+25]]})
+    for i in range(25):
+        msgs.append({"from_id": "mallory", "to_id": "eve",
+                     "timestamp": now - 1.5*day + i*60,
+                     "concepts": [hello_synonyms[25+i]]})
+
+    # Collect all concepts across the edge, collapse globally, build mapping
+    all_concepts_raw = []
+    for m in msgs:
+        all_concepts_raw.extend(m["concepts"])
+    collapsed_canonical = semantic_collapse(all_concepts_raw)
+
+    # After collapse, all greeting-N should map to ~1 canonical form
+    assert len(collapsed_canonical) <= 5, \
+        f"After collapse, adversary should have ≤5 unique concepts: {len(collapsed_canonical)}"
+
+
 def test_snapshot_idf_vs_corpus_idf():
     """snapshot_idf=True should compute IDF at emission time, not on full corpus.