Add Phase C5 TLA+ module skeleton

Author: iamfurydammit

formal/XSTRP_C5.tla

@@ -0,0 +1,50 @@
+----------------------------- MODULE XSTRP_C5 -----------------------------
+
+EXTENDS Naturals, TLC
+
+(*
+Phase C5 formal model for XSTRP.
+
+This module models only the protocol logic defined in Phases C1–C4.
+It does not model XRPL behavior, cryptography, wallets, networking,
+or persistence.
+
+This is a safety-only model.
+*)
+
+VARIABLES
+    intent_state,
+    authorization_valid,
+    proof_present,
+    is_expired
+
+(*
+The set of all valid protocol states.
+*)
+States ==
+{
+    "Created",
+    "Committed",
+    "Completed",
+    "Expired",
+    "Refunded",
+    "Invalid"
+}
+
+(*
+Initial conditions.
+*)
+Init ==
+    /\ intent_state = "Created"
+    /\ authorization_valid = FALSE
+    /\ proof_present = FALSE
+    /\ is_expired = FALSE
+
+(*
+Placeholder for the transition relation.
+This will be fully defined in the next step.
+*)
+Next ==
+    FALSE
+
+=============================================================================