fix(backtest): address the second review of the breakeven and book-config work

- The breakeven study grades at the shadow book's capacity AND risk per
  trade, and labels each with where it came from. A missing setting row
  now reads "shadow_book default" instead of crediting the setting; the
  committed report said shadow_book_capacity though the snapshot has no
  such row.
- _production_book_config reads strategies through the same
  _portfolio_monitor_strategies() hook as the monitor.
- breakeven_gate_reset is rejected when there is no post-stop episode or
  cooldown for it to start, and the study skips its diagnostic arm for a
  book without one, so a production config change cannot abort the run.
- identical_to_control is renamed ties_control_on_graded_metrics and needs
  real values: be_2r ties on every graded metric but still changed 2 trades.
- _BookConfig drops an unused field and hashes by identity; the min-R:R
  sweep swaps its gate in with dataclasses.replace instead of passing it.
- New tests cover the parity guard's success path, the no-config fallback
  and the gate-reset check.

The breakeven report is regenerated: every row, diagnostic row and the
parity check are identical; only the labels, the risk fields and the
renamed flag changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/research/breakeven-stop.md

@@ -75,9 +75,11 @@ BACKTEST_BREAKEVEN_STUDY=1 python scripts/run_backtest_snapshot.py \
     --out reports/backtest-20261009-breakeven-stop.json
 ```
 
-The graded capacity is read from the snapshot's `shadow_book_capacity` setting.
-`prod.sqlite` has no such row, so the shadow book's default of 15 applies; the
-report records it as `capacity` / `capacity_source`.
+The graded capacity and risk per trade come from the shadow book's config in the
+database the run reads (`shadow_book_capacity`, `shadow_book_risk_pct`).
+`prod.sqlite` has neither row, so the shadow book's defaults apply: 15
+positions and 1% risk. The report records each value with its source
+(`capacity_source`, `risk_source`), which reads `shadow_book default` here.
 
 ## Result — no change; `be_1r` fails, `be_2r` passes only by being the production exit
 
@@ -201,11 +203,12 @@ and live still agree.
 - `breakeven_r` must be positive and finite, and is rejected for exit policies
   without an ATR trail. Before, a non-positive value moved the stop to entry on
   the first bar, and other policies ignored the setting silently.
-- Each verdict now records `identical_to_control`, which is true for `be_2r`. A
-  pass that is only ties can no longer read as a finding.
-- The graded capacity comes from the shadow book's capacity config (the
-  `shadow_book_capacity` setting in the database the run reads, or its default
-  of 15 when the row is missing) instead of the `SIM_MAX_POSITIONS` constant. On
-  a snapshot that is the snapshot's copy of the setting, not the current live
-  value ([Reproducing](#reproducing)). `capacity_source` reads
-  `shadow_book_capacity` in both cases.
+- Each verdict now records `ties_control_on_graded_metrics`, which is true for
+  `be_2r`. A pass that is only ties can no longer read as a finding. The flag
+  compares the graded metrics only: `be_2r` still changed 2 trades.
+- The graded capacity and risk per trade come from the shadow book's config
+  instead of the `SIM_MAX_POSITIONS` constant and the entry variant's fixed 1%.
+  On a snapshot that is the snapshot's copy of the settings, not the current
+  live values, and a missing row is labeled as the default it fell back to
+  ([Reproducing](#reproducing)). In this run both are defaults, equal to the
+  values the first run used.