test: 6 phi_accrual tests (32/32 total: 29 invariants + 3 known-defeats)

test_swarmmetrics.py

@@ -4,7 +4,8 @@ import sys
 sys.path.insert(0, ".")
 from swarmmetrics import (
     _gini, _half_life_weight, score_reciprocity, score_channels,
-    score_echo, detect_shadows, analyze, shuffle_test, semantic_collapse
+    score_echo, detect_shadows, analyze, shuffle_test, semantic_collapse,
+    phi_accrual, AgentLiveness
 )
 
 now = time.time()
@@ -603,6 +604,66 @@ def test_colluding_vs_genuine_echo_indistinguishable():
             f"Genuine and colluded should score similarly: alice={alice_echo:.3f}, eve={eve_echo:.3f}, ratio={ratio:.1f}"
 
 
+# ── φ-accrual failure detector tests ──────────────────────
+
+def test_phi_accrual_regular_agent_green():
+    """Agent posting regularly should be green when checked at expected time."""
+    msgs = [{'from_id': 'alice', 'timestamp': now - day * i} for i in range(10, 0, -1)]
+    result = phi_accrual(msgs, t_now=now)
+    assert 'alice' in result
+    assert result['alice'].state == 'green', f"Expected green, got {result['alice'].state} (φ={result['alice'].phi})"
+
+def test_phi_accrual_silent_agent_gray():
+    """Agent silent for 10x its mean interval should be gray (highly suspicious)."""
+    # Agent posts hourly, then goes silent for 10 hours
+    msgs = [{'from_id': 'bob', 'timestamp': now - 3600 * (20 - i)} for i in range(10)]
+    # Last message was at now - 3600*11, t_now = now, so 11 hours of silence vs 1h mean
+    result = phi_accrual(msgs, t_now=now)
+    assert result['bob'].state == 'gray', f"Expected gray, got {result['bob'].state} (φ={result['bob'].phi})"
+
+def test_phi_accrual_too_few_messages():
+    """Agent with < min_messages should be 'unknown'."""
+    msgs = [{'from_id': 'carol', 'timestamp': now - 100}]
+    result = phi_accrual(msgs, t_now=now, min_messages=5)
+    assert result['carol'].state == 'unknown'
+
+def test_phi_accrual_multiple_agents():
+    """Multiple agents get independent suspicion scores."""
+    msgs = []
+    # Alice: posts hourly, recent
+    for i in range(10):
+        msgs.append({'from_id': 'alice', 'timestamp': now - 3600 * i})
+    # Bob: posts hourly, stopped 2 days ago
+    for i in range(10):
+        msgs.append({'from_id': 'bob', 'timestamp': now - day * 2 - 3600 * i})
+    result = phi_accrual(msgs, t_now=now)
+    assert result['alice'].state == 'green'
+    assert result['bob'].state == 'gray'
+
+def test_phi_accrual_monotonic_suspicion():
+    """φ should increase monotonically with silence duration."""
+    msgs = [{'from_id': 'eve', 'timestamp': now - 3600 * (10 - i)} for i in range(10)]
+    # Check at increasing distances from last message
+    phi_values = []
+    for offset in [0, 3600, 7200, 36000, 86400]:
+        result = phi_accrual(msgs, t_now=msgs[-1]['timestamp'] + offset)
+        phi_values.append(result['eve'].phi)
+    # Each should be >= previous
+    for i in range(1, len(phi_values)):
+        assert phi_values[i] >= phi_values[i-1], \
+            f"φ not monotonic: {phi_values[i]} < {phi_values[i-1]} at step {i}"
+
+def test_phi_accrual_silence_vs_stale_green():
+    """Distinguish silence (no messages at all) from stale green (old messages exist).
+    An agent with zero messages shouldn't appear in results.
+    An agent with old messages should be gray, not absent."""
+    msgs = [{'from_id': 'frank', 'timestamp': now - day * 30 - 3600 * i} for i in range(10)]
+    result = phi_accrual(msgs, t_now=now)
+    assert 'nobody' not in result  # truly silent = absent from output
+    assert 'frank' in result
+    assert result['frank'].state == 'gray'  # stale green → gray
+
+
 # Run all tests
 # Split counter: invariants vs known-defeats (per ColonistOne, Colony 2026-07-28)
 # "18/18" mixes "instrument works" with "instrument fails as expected"