feat(kevin): KevinStrategy standalone decision logic

Stateless: mention + account_state -> KevinDecision. Conviction-weighted
sizing, time_horizon-derived hold periods, hard per-ticker cap. The
bridge and the backtest mini-engine both call evaluate_mention so
behaviour cannot drift.

tests/shared/strategies/test_kevin_strategy.py

@@ -0,0 +1,304 @@
+"""KevinStrategy tests — one behaviour per test, full conviction x action x held grid."""
+
+from datetime import datetime, timedelta, timezone
+from decimal import Decimal
+
+import pytest
+
+from shared.schemas.kevin import KevinAccountState, KevinDecisionType
+from shared.schemas.meet_kevin import TickerAction, TimeHorizon
+from shared.strategies.kevin import KevinStrategy, KevinStrategyConfig
+
+
+@pytest.fixture
+def cfg() -> KevinStrategyConfig:
+    return KevinStrategyConfig(
+        min_conviction=Decimal("0.6"),
+        max_mention_age_hours=48,
+        base_position_pct=Decimal("0.04"),
+        min_trade_usd=Decimal("500"),
+        max_trade_usd=Decimal("5000"),
+        max_per_ticker_usd=Decimal("7500"),
+        hold_days_by_horizon={
+            "days": 3,
+            "weeks": 10,
+            "months": 45,
+            "long_term": 90,
+            "unspecified": 10,
+        },
+        avoid_closes_longs=True,
+        avoid_blocks_days=7,
+    )
+
+
+@pytest.fixture
+def state() -> KevinAccountState:
+    return KevinAccountState(
+        equity_usd=Decimal("100000"),
+        cash_usd=Decimal("100000"),
+        held_positions={},
+        blocklisted_symbols=set(),
+        daily_trade_count=0,
+        daily_alloc_usd=Decimal("0"),
+        paused=False,
+    )
+
+
+def _mention(symbol="NVDA", action="buy", conviction="0.7", horizon="weeks", age_hours=1):
+    """Lightweight stub matching KevinStockMention attribute access."""
+    return type(
+        "M",
+        (),
+        {
+            "id": 1,
+            "symbol": symbol,
+            "action": TickerAction(action) if isinstance(action, str) else action,
+            "conviction": Decimal(conviction),
+            "time_horizon": TimeHorizon(horizon),
+            "rationale_quote": "test",
+            "created_at": datetime.now(timezone.utc) - timedelta(hours=age_hours),
+        },
+    )
+
+
+async def test_buy_high_conviction_emits_open_long(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="buy", conviction="0.8"),
+        state,
+        effective_conviction=Decimal("0.8"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.OPEN_LONG
+    assert d.symbol == "NVDA"
+    # 4% * (0.5 + 0.5*(0.8-0.6)/0.4) = 4% * 0.75 = 3% of 100k = $3000
+    assert d.target_dollars == Decimal("3000.00")
+    assert d.holding_days == 10  # weeks
+
+
+async def test_buy_conviction_at_floor_emits_minimum_size(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="buy", conviction="0.6"),
+        state,
+        effective_conviction=Decimal("0.6"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    # 4% * 0.5 = 2% of 100k = $2000
+    assert d.target_dollars == Decimal("2000.00")
+
+
+async def test_buy_below_min_conviction_is_no_op(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="buy", conviction="0.5"),
+        state,
+        effective_conviction=Decimal("0.5"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+    assert "min_conviction" in d.rationale.lower()
+
+
+async def test_buy_mention_too_old_is_no_op(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(age_hours=72),
+        state,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+    assert "age" in d.rationale.lower()
+
+
+async def test_buy_non_tradable_is_no_op(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(symbol="OTCXX"),
+        state,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("1"),
+        is_tradable=False,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+    assert "tradable" in d.rationale.lower()
+
+
+async def test_buy_intraday_horizon_is_no_op(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(horizon="intraday"),
+        state,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+
+
+async def test_buy_when_blocklisted_is_no_op(cfg, state):
+    state_b = state.model_copy(update={"blocklisted_symbols": {"NVDA"}})
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(),
+        state_b,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+    assert "blocklist" in d.rationale.lower()
+
+
+async def test_buy_at_per_ticker_cap_is_no_op(cfg, state):
+    state_full = state.model_copy(
+        update={"held_positions": {"NVDA": Decimal("7500")}}
+    )
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(),
+        state_full,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+    assert "cap" in d.rationale.lower()
+
+
+async def test_buy_held_below_cap_tops_up_to_cap(cfg, state):
+    state_p = state.model_copy(
+        update={"held_positions": {"NVDA": Decimal("5000")}}
+    )
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(conviction="1.0"),
+        state_p,
+        effective_conviction=Decimal("1.0"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.OPEN_LONG
+    # full target = $4000 (4% of 100k clamped at 5k cap), but per-ticker cap = $7500,
+    # already held $5000 -> top up min(4000, 2500) = $2500
+    assert d.target_dollars == Decimal("2500.00")
+
+
+async def test_sell_with_held_emits_close_long(cfg, state):
+    state_p = state.model_copy(
+        update={"held_positions": {"NVDA": Decimal("3000")}}
+    )
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="sell"),
+        state_p,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.CLOSE_LONG
+
+
+async def test_sell_without_held_is_no_op(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="sell"),
+        state,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+
+
+async def test_avoid_with_held_emits_close_long(cfg, state):
+    state_p = state.model_copy(
+        update={"held_positions": {"NVDA": Decimal("3000")}}
+    )
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="avoid"),
+        state_p,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.CLOSE_LONG
+
+
+async def test_avoid_without_held_is_no_op_but_blocklists(cfg, state):
+    # The strategy itself returns NO_OP; the bridge applies the blocklist
+    # side-effect. We assert rationale reflects intent.
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="avoid"),
+        state,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+    assert "blocklist" in d.rationale.lower() or "avoid" in d.rationale.lower()
+
+
+async def test_hold_action_never_trades(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="hold"),
+        state,
+        effective_conviction=Decimal("0.9"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+
+
+async def test_watch_action_never_trades(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(action="watch"),
+        state,
+        effective_conviction=Decimal("0.9"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.decision == KevinDecisionType.NO_OP
+
+
+async def test_size_clamps_to_min_trade_usd(cfg, state):
+    # Equity small enough that 2% < $500 floor
+    small_state = state.model_copy(update={"equity_usd": Decimal("10000")})
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(conviction="0.6"),
+        small_state,
+        effective_conviction=Decimal("0.6"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    # 2% of $10k = $200 -> clamped to $500
+    assert d.target_dollars == Decimal("500.00")
+
+
+async def test_size_clamps_to_max_trade_usd(cfg, state):
+    big_state = state.model_copy(update={"equity_usd": Decimal("1000000")})
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(conviction="1.0"),
+        big_state,
+        effective_conviction=Decimal("1.0"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    # 4% of $1M = $40k -> clamped to $5k
+    assert d.target_dollars == Decimal("5000.00")
+
+
+async def test_horizon_long_term_maps_to_90_days(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(horizon="long_term"),
+        state,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.holding_days == 90
+
+
+async def test_horizon_unspecified_defaults_to_weeks(cfg, state):
+    d = await KevinStrategy(cfg).evaluate_mention(
+        _mention(horizon="unspecified"),
+        state,
+        effective_conviction=Decimal("0.7"),
+        current_price=Decimal("100"),
+        is_tradable=True,
+    )
+    assert d.holding_days == 10