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/_constants.py

@@ -29,6 +29,12 @@ ACQUIRE_MAX_CHASES: int = 0
 # question: 2× vs ATR-scaled). PROVISIONAL default.
 PROTECTIVE_STOP_MULT_DEFAULT: Decimal = Decimal("2.0")
 
+# Maker-quote lifetime for UNBOUNDED-TTL urgencies (HARVEST/ACQUIRE): how long a resting
+# quote lives before the drive loop sweeps + re-evaluates it. Bounded quote lifetime +
+# cancel/replace is the certified GTX discipline (spec §4-16). PROVISIONAL — calibrate vs
+# L8 GTX fill latencies; measured in injected-clock seconds, never a hardcoded loop literal.
+MAKER_QUOTE_TTL_S: float = 6.0
+
 # Requote hot-window: after an OWN fill, refuse to re-quote for this long because the
 # REST venue reconcile lags the WS fill by seconds — re-quoting inside it double-enters.
 # Provenance: live double-entry, pink_direct.py:1055 / :1323 (2026-06-10). Measured in