feat(phase-2.5): Task 6 cost_kind attribution + fees_eat_alpha threshold CLI

Task 6 del piano Phase 2.5 (deferito → ora completato):
- CostRecord: nuovo campo call_kind (default "hypothesis")
- CostTracker.record: accetta call_kind opzionale, summary include
  by_call_kind breakdown (hypothesis vs mutation)
- Schema cost_records: aggiunta colonna call_kind TEXT NOT NULL DEFAULT
  'hypothesis' + migration soft via ALTER TABLE in init_schema (silently
  catched per DB pre-Task 6)
- Repository.save_cost_record: nuova arg call_kind opzionale
- mutate_prompt_llm: accetta cost_tracker/repo/run_id opzionali e logga
  la call mutator con call_kind="mutation" quando sink presente
- weighted_random_mutate, next_generation: propagano cost sink
- orchestrator.run_phase1: passa cost_tracker+repo+run_id a
  next_generation solo se prompt_mutation_weight > 0

Esposto fees_eat_alpha_threshold come parametro AdversarialAgent
(default 0.5 = comportamento Phase 1.5 invariato), propagato via
RunConfig.fees_eat_alpha_threshold e flag CLI
--fees-eat-alpha-threshold. Abilita ablation con soglia 0.7-0.8 senza
modificare codice — adversarial finding dominante in tutti i run
Phase 2/2.5 (50+ HIGH per run).

Tests (+4 → 186 totale):
- test_cost_tracker: default call_kind="hypothesis"; breakdown
  by_call_kind con hypothesis+mutation
- test_mutation_prompt_llm: logging mutation cost con sink completo;
  backward compat senza sink (no errore)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/test_cost_tracker.py

@@ -61,3 +61,28 @@ def test_tracker_summary_contains_all_five_tiers():
     for tier_letter in ("S", "A", "B", "C", "D"):
         assert tier_letter in summary["by_tier"]
         assert summary["by_tier"][tier_letter]["calls"] == 1
+
+
+def test_tracker_default_call_kind_is_hypothesis():
+    t = CostTracker()
+    rec = t.record(input_tokens=10, output_tokens=10, tier=ModelTier.C, run_id="r", agent_id="a")
+    assert rec.call_kind == "hypothesis"
+    summary = t.summary()
+    assert "hypothesis" in summary["by_call_kind"]
+    assert summary["by_call_kind"]["hypothesis"]["calls"] == 1
+    assert "mutation" not in summary["by_call_kind"]
+
+
+def test_tracker_by_call_kind_breakdown():
+    t = CostTracker()
+    t.record(input_tokens=100, output_tokens=200, tier=ModelTier.C, run_id="r", agent_id="a")
+    t.record(input_tokens=100, output_tokens=200, tier=ModelTier.C, run_id="r", agent_id="a")
+    t.record(
+        input_tokens=50, output_tokens=80, tier=ModelTier.B,
+        run_id="r", agent_id="parent-x", call_kind="mutation",
+    )
+    summary = t.summary()
+    assert summary["by_call_kind"]["hypothesis"]["calls"] == 2
+    assert summary["by_call_kind"]["mutation"]["calls"] == 1
+    assert summary["by_call_kind"]["mutation"]["input_tokens"] == 50
+    assert summary["by_call_kind"]["mutation"]["output_tokens"] == 80