exec(unified): UnifiedExecutor — initial-submit pipeline + S2 pain-fence

executor.py composes the built parts into one execute(request, snapshot): S-grade fence →
router.decide → placer.pre_submit → submit → register working. The initial-submit half that
complements DriveLoop's expiry half (analogue of pink_direct.py:1645-1700).

Composition rulings encoded + tested:
- S2/S3 pain-fence (§15.2): refused WHOLE, loudly, below T14 — never silently sliced.
- placer declines (spread gate) → cross ONLY if urgency crosses on expiry; ACQUIRE ABANDONS
  (a missed entry is free, §4-1). Both mutation-verified RED.
- TTL from urgency discipline: PROTECT 2s / ROTATE deadline_ms / ACQUIRE quote-lifetime.

contract.py: SGrade enum (S0-S3) + s_grade/parent_request_id fields. _constants: MAKER_QUOTE_TTL_S.

FIX (real bug, not just test): drive_loop._is_resolved EXIT was trade_id-based (a PINK
artifact — PINK reused the position's trade_id for exits). The agnostic layer never gets
the position id, so exit-done is now SIZE-based. Kept ENTER on clientOrderId match.

Full exec_unified suite: 94 green, mutation-litmus verified.

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

prod/exec_unified/contract.py

@@ -47,6 +47,24 @@ class UrgencyClass(Enum):
                          UrgencyClass.HARVEST, UrgencyClass.ROTATE)
 
 
+class SGrade(Enum):
+    """Size axis — orthogonal to the T-tier smartness ladder (spec §15.2).
+
+    Computed at intake from Appendix E's power-law depth model (per-asset, stress-adjusted),
+    or supplied by the caller. Below T14 the layer executes S0/S1 directly and REFUSES S2+
+    whole (the pain-fence) so nobody meets the large-size pain class by accident.
+    """
+
+    S0 = 0  # size << top-of-book depth (walk < 1 tick) — any tier executes directly
+    S1 = 1  # walks visible levels (expected walk >= spread) — T2+ prices the walk
+    S2 = 2  # exceeds book capacity in the urgency window — must be SLICED; refused below T14
+    S3 = 3  # size IS the market (footprint moves MM behaviour) — MALKHUT/VIBRASS territory
+
+    @property
+    def needs_slicing(self) -> bool:
+        return self in (SGrade.S2, SGrade.S3)
+
+
 @dataclass(frozen=True)
 class ProtectiveSpec:
     """Attach-a-dead-man's-stop geometry (spec §10). Mark-based, rides the entry order.
@@ -113,6 +131,8 @@ class ExecutionRequest:
     protective: ProtectiveSpec | None = None
     advice: ExecutionAdvice | None = None
     deadline_ms: int | None = None           # caller's patience budget (ROTATE/ACQUIRE)
+    s_grade: SGrade = SGrade.S0              # size regime (§15.2); default S0 = fits at touch
+    parent_request_id: str | None = None    # slicer family linkage (§15.2 T*.s), telemetry only
 
     def __post_init__(self) -> None:
         if not self.request_id: