Close Phase C5

Author: iamfurydammit

PHASE-C5-CLOSED.md

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+# Phase C5 — Closed
+
+Phase C5 (Extended Formal Verification) is complete.
+
+All declared safety invariants for the frozen XSTRP protocol
+(Phases C1–C4) were formally verified using TLA+ and TLC within
+the stated scope.
+
+No protocol changes were required.
+
+Phase C5 is now closed.