fix(infonet): reject non-finite gate lock values (#511)

* fix(infonet): reject non-finite gate lock values

* test(infonet): cover non-finite gate lock values

backend/services/infonet/tests/test_gate_lock_nonfinite_values.py

@@ -0,0 +1,66 @@
+"""Regression coverage for non-finite gate lock contributions."""
+
+from services.infonet.config import CONFIG
+from services.infonet.gates import is_locked, validate_lock_request
+from services.infonet.tests._gate_factory import (
+    make_gate_create,
+    make_gate_enter,
+    make_gate_lock,
+)
+
+
+def _gate_with_members() -> tuple[list[dict], list[str]]:
+    base = 1_000_000.0
+    threshold = int(CONFIG["gate_lock_min_members"])
+    members = [f"m{i}" for i in range(threshold)]
+    chain = [make_gate_create("g1", "creator", ts=base, seq=1)]
+    for i, member in enumerate(members):
+        chain.append(make_gate_enter("g1", member, ts=base + 100 + i, seq=2 + i))
+    return chain, members
+
+
+def _append_valid_locks(chain: list[dict], members: list[str]) -> None:
+    cost = int(CONFIG["gate_lock_cost_per_member"])
+    for i, member in enumerate(members):
+        chain.append(
+            make_gate_lock(
+                "g1",
+                member,
+                ts=1_001_000.0 + i,
+                seq=200 + i,
+                lock_cost=cost,
+            )
+        )
+
+
+def test_infinite_lock_cost_does_not_count_toward_threshold():
+    chain, members = _gate_with_members()
+    _append_valid_locks(chain, members[:-1])
+    bad = make_gate_lock("g1", members[-1], ts=1_002_000.0, seq=999)
+    bad["payload"]["lock_cost"] = float("inf")
+    chain.append(bad)
+
+    assert not is_locked("g1", chain)
+
+
+def test_nonfinite_lock_timestamp_does_not_count_toward_threshold():
+    chain, members = _gate_with_members()
+    _append_valid_locks(chain, members[:-1])
+    bad = make_gate_lock("g1", members[-1], ts=float("nan"), seq=999)
+    chain.append(bad)
+
+    assert not is_locked("g1", chain)
+
+
+def test_validate_lock_request_rejects_nonfinite_cost():
+    chain, members = _gate_with_members()
+
+    decision = validate_lock_request(
+        members[0],
+        "g1",
+        chain,
+        lock_cost=float("inf"),  # type: ignore[arg-type]
+    )
+
+    assert not decision.accepted
+    assert decision.reason == "invalid_lock_cost"