PINK: fix multi-leg exit residual — carry kernel leg-index into legacy position

Root cause (harness multi_leg, ~14-TRX residual): pink_direct rebuilds the legacy
TradePosition from the kernel slot every step, but left exit_leg_index=0, so
IntentEngine.next_exit_ratio() consumed ratio[0] (0.5) on EVERY leg and never
advanced to the final leg's 1.0:
  leg1: 0.5×53 ≈ 26 closed -> 27 remain
  leg2: 0.5×27 ≈ 13 closed -> 14 RESIDUAL  (kernel believes flat, exchange isn't)

Fix: propagate the kernel slot's authoritative active_leg_index into the rebuilt
legacy position's exit_leg_index, so the intent engine consumes the correct leg
ratio. The final leg now closes the full remaining -> fully flattens.

Verified: offline 18 green (no regression); live VST harness multi_leg now closes
fully (XPASS) — residual gone, all 6 capital invariants hold. xfail mark removed;
capital-accounting battery is now fully green (7/7) on testnet.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

prod/tests/test_pink_capital_harness.py

@@ -319,16 +319,7 @@ _TRADING_SCENARIOS = {
 }
 
 
-@pytest.mark.parametrize("name", [
-    "round_trip",
-    pytest.param("multi_leg", marks=pytest.mark.xfail(
-        reason="KNOWN capital/sizing finding: multi-leg partial reduce-only exits leave a "
-               "lot-step rounding residual on the venue (kernel believes flat, exchange has a "
-               "remainder). To be fixed in the capital/sizing-path rework.",
-        strict=False)),
-    "sequential",
-    "exit_then_reentry",
-])
+@pytest.mark.parametrize("name", list(_TRADING_SCENARIOS))
 def test_pink_capital(name):
     ratios, scenario = _TRADING_SCENARIOS[name]