Snapshot PINK DITAv2 system + Sprint 0 flaw-fix verification

First commit of the previously-untracked PINK-on-DITAv2 migration system
(execution moves to the Rust kernel; policy stays on legacy DITA, so Alpha
Engine algorithmic integrity is preserved). BLUE is untouched.

Sprint 0 (safety snapshot + flaw-fix verification, MARKET single-leg scope):
- Verified Rust FSM fixes (flaws 2,4,10,11,13) by source read of lib.rs.
- Hardened 5 vacuous/guarded assertions in test_flaws.py so each flaw test
  genuinely exercises its fix. Most important: Flaw 5 now asserts capital
  moves by EXACTLY realized PnL (was entering/exiting at the same price).
- Offline suites: 533 passed, 0 failed (35 flaws + 402 kernel/accounting/
  bridge + 96 runtime/persistence/multi-exit/restart/seams).
- GATE PASS: MARKET-path-critical flaws 1,2,5 confirmed fixed + green.
- Added SPRINT0_FLAW_VERIFICATION.md report and _rust_kernel/.gitignore
  (excludes Rust target/ build artifacts).

LIMIT/partial-fill remain explicitly out of scope (MARKET-only bring-up).

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

prod/tests/test_pink_ditav2_rate_limit_contract.py

@@ -0,0 +1,71 @@
+"""Rate-limit classification + downstream emission tests for PINK + DITAv2."""
+
+from __future__ import annotations
+
+from datetime import datetime, timezone
+import unittest
+
+from prod.clean_arch.dita_v2 import (
+    ControlUpdate,
+    ExecutionKernel,
+    InMemoryControlPlane,
+    InMemoryZincPlane,
+    KernelCommandType,
+    KernelDiagnosticCode,
+    KernelIntent,
+    KernelMode,
+    MockVenueAdapter,
+    MockVenueScenario,
+    TradeSide,
+)
+
+
+class TestRateLimitContract(unittest.TestCase):
+    """Verify the kernel handles venue rejections without corrupting state."""
+
+    def setUp(self):
+        self.control = InMemoryControlPlane()
+        self.control.update(ControlUpdate(
+            mode=KernelMode.DEBUG, trace_transitions=True,
+        ))
+        self.venue = MockVenueAdapter(
+            MockVenueScenario(
+                reject_entries=True,
+                reject_exits=False,
+                partial_fill_ratio=0.0,
+                cancel_reject=False,
+            )
+        )
+        self.kernel = ExecutionKernel(
+            max_slots=1,
+            control_plane=self.control,
+            venue=self.venue,
+            zinc_plane=InMemoryZincPlane(),
+        )
+
+    def _make_intent(self, action: KernelCommandType = KernelCommandType.ENTER) -> KernelIntent:
+        return KernelIntent(
+            timestamp=datetime.now(timezone.utc),
+            intent_id="rate-test-001",
+            trade_id="rate-trade-001",
+            slot_id=0,
+            asset="BTCUSDT",
+            side=TradeSide.SHORT,
+            action=action,
+            reference_price=65000.0,
+            target_size=0.01,
+            leverage=2.0,
+            reason="rate_limit_test",
+        )
+
+    def test_kernel_state_unaffected_by_rejection(self):
+        """Slot returns to free/IDLE after venue rejects entry."""
+        intent = self._make_intent(KernelCommandType.ENTER)
+        self.kernel.process_intent(intent)
+        slot = self.kernel.slot(0)
+        self.assertTrue(slot.is_free(),
+                        f"Slot should be free after reject, got {slot.fsm_state}")
+
+
+if __name__ == "__main__":
+    unittest.main()