feat(intentflow): wire U9–U12 ports and gated OwnerMux

Register dry-run adapters via BuildOwnerMux when independent flags are on;
U9 stub fail-closes on malformed/timeout/out-of-bounds without raising PlanTier.

Co-authored-by: Cursor <cursoragent@cursor.com>

.env.example

@@ -94,4 +94,10 @@ INTENT_V2_DECISION=false
 INTENT_V2_DECISION_TIER=none
 WORKFLOW_INTENTS_ENABLED=true
 MULTI_INTENT_ENABLED=true
+# MULTI_INTENT_PLAN_TIER defaults to legacy; do not raise for U9–U12 scaffolding.
+# MULTI_INTENT_PLAN_TIER=legacy
+MULTI_INTENT_U9_SEGMENT=false
+MULTI_INTENT_U10_MUTATE=false
+MULTI_INTENT_U11_DOCGOV=false
+MULTI_INTENT_U12_RUN_CONTROL=false
 SEMANTIC_FALLBACK_ENABLED=false