feat: cap entry notional at broker buying power (cash-account GFV guard)

On the Tradier live cash account buying_power maps to cash_available —
SETTLED cash. Capping every entry's notional at it means the bot never
spends today's sale proceeds today, which is the entire good-faith
-violation rule. That replaces the blunt 1-trade/day cap: the live
account now trades like paper (cap back to 5/day), throughput
self-limits at ~settled/position-size sequential trades and refreshes
each morning at T+1. On margin accounts buying power is ~4x equity so
the cap never binds — one universal rule, no broker branches. Fail-open
when the field is absent.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/unit/test_trading_execution.py

@@ -1068,3 +1068,35 @@ def test_boot_reconcile_off_by_flag(store):
         session_id="t",
     )
     assert cli.cancelled == []
+
+
+def test_settled_buying_power_caps_position(store):
+    """Cash-account GFV guard: entry notional never exceeds broker buying_power
+    (settled cash on Tradier live). Margin accounts (bp >> equity) unaffected."""
+    from alpaca_paper.execution import AlpacaPaperExecutor
+
+    class _Cli:
+        def __init__(self, bp):
+            self.bp = bp
+        def get_positions(self, fresh=False): return []
+        def get_account(self): return {"equity": "300", "buying_power": self.bp}
+        def get_orders(self, **kw): return []
+
+    svc = TradingExecutionService(
+        store, executor=AlpacaPaperExecutor(store, client=_Cli("40")),
+        settings=ExecutionSettings(auto_approve=True), session_id="t",
+    )
+    assert svc._settled_buying_power() == 40.0
+    # only $40 settled: a $10 entry sizes to <= 4 shares regardless of risk budget
+    from strategy.risk.position_sizing import calculate_position_size, PositionSizingConfig
+    pos_cap = min(300 * 0.16, svc._settled_buying_power())
+    sizing = calculate_position_size(10.0, 9.0, equity=300.0,
+                                     config=PositionSizingConfig(risk_per_trade_pct=0.05),
+                                     max_position_value=pos_cap)
+    assert sizing.position_size == 4
+
+    svc2 = TradingExecutionService(
+        store, executor=AlpacaPaperExecutor(store, client=_Cli(None)),
+        settings=ExecutionSettings(auto_approve=True), session_id="t",
+    )
+    assert svc2._settled_buying_power() is None        # missing field -> no cap

trading_execution.py

@@ -607,6 +607,26 @@ class TradingExecutionService:
                 pass
         return self.equity
 
+    def _settled_buying_power(self) -> float | None:
+        """Broker buying power, used as an entry-notional ceiling.
+
+        On the Tradier LIVE cash account this is ``cash_available`` — SETTLED
+        cash only. Capping every buy at it means the bot never spends today's
+        sale proceeds today, which is the entire good-faith-violation rule —
+        so the per-day entry cap can match paper instead of a blunt 1/day.
+        Throughput self-limits (~settled/position-size trades) and refreshes
+        at T+1 settlement each morning. On margin accounts (Alpaca paper:
+        ~4x equity) this never binds. None = field unavailable -> no cap."""
+        client = getattr(self.executor, "client", None)
+        if client is not None and hasattr(client, "get_account"):
+            try:
+                bp = float((client.get_account() or {}).get("buying_power") or 0.0)
+                if bp > 0:
+                    return bp
+            except Exception:  # noqa: BLE001
+                pass
+        return None
+
     def _remaining_gross_budget(self, equity: float) -> float:
         """$ of new notional still allowed under the portfolio gross-notional cap
         (cap*equity minus the market value of currently-open positions). Inf when
@@ -1322,6 +1342,9 @@ class TradingExecutionService:
             # remaining gross-notional budget (so the book can't pile into ~100%).
             pos_cap = min(eq * self.settings.max_position_pct,
                           self._remaining_gross_budget(eq))
+            _bp = self._settled_buying_power()
+            if _bp is not None:
+                pos_cap = min(pos_cap, _bp)  # cash account: settled funds only (GFV guard)
             # Liquidity cap (unification): on the auto path too, cap shares to a
             # fraction of the name's cumulative volume so a thin cheap name can't be
             # oversized into heavy slippage (the VTAK-style stop that filled far past
@@ -1562,6 +1585,9 @@ class TradingExecutionService:
         # per-position cap AND remaining portfolio gross-notional budget
         pos_cap = min(eq * self.settings.max_position_pct,
                       self._remaining_gross_budget(eq))
+        _bp = self._settled_buying_power()
+        if _bp is not None:
+            pos_cap = min(pos_cap, _bp)  # cash account: settled funds only (GFV guard)
         if pos_cap <= 0:
             return {"ok": False, "skipped": "gross_notional_cap"}
         # scale the dollar risk by rank (rank-1 full, rank-2+ half) — both the %