feat(fase1): spike B - magentic unbounded + concurrent state isolation [skip-docs]

tests/spikes/test_b_footguns.py

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+"""Spike B tests — Magentic unbounded footgun (G1/B4) + fan-out state isolation (G2/B7).
+
+These drive the real GA builders with the fake client (no endpoint), de-risked by the
+Step 2 builder smoke. Pattern: tests/test_backends.py.
+"""
+
+from portfolio_optimiser.reference_domain import load_reference_projects
+from spikes.b_footguns import (
+    bounded_magentic_terminates,
+    fresh_instance_call_counts,
+    shared_instance_max_calls,
+    unbounded_magentic_self_terminates,
+)
+
+
+async def test_unbounded_magentic_does_not_self_terminate() -> None:
+    # max_round_count=None never finalizes — only the external guard stops it (B4).
+    self_terminated = await unbounded_magentic_self_terminates(guard_rounds=8)
+    assert self_terminated is False  # the guard fired, not a natural stop
+
+
+async def test_bounded_magentic_terminates_within_limit() -> None:
+    # An explicit max_round_count makes the same never-satisfied manager stop cleanly.
+    assert await bounded_magentic_terminates(max_round_count=2) is True
+
+
+async def test_shared_instance_bleeds_state_across_projects() -> None:
+    ids = [p.id for p in load_reference_projects()]
+    assert len(ids) == 3
+    bled = await shared_instance_max_calls(ids)
+    # One shared instance reused across all 3 projects -> calls accumulate -> bleed.
+    assert bled == len(ids)
+
+
+async def test_fresh_instance_zero_bleed_across_projects() -> None:
+    ids = [p.id for p in load_reference_projects()]
+    counts = await fresh_instance_call_counts(ids)
+    # A fresh instance per project -> each run sees exactly one call -> zero bleed.
+    assert counts == [1, 1, 1]