Add Phase C6 charter construction rules

Author: iamfurydammit

phase-c6/PHASE-C6-CHARTER-RULES.md

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+# Phase C6 Charter Construction Rules — XSTRP
+
+## Status
+ACTIVE — GOVERNING
+
+## Purpose
+
+This document defines mandatory constraints on the construction of any
+Phase C6 charter.
+
+No Phase C6 charter may be proposed unless it conforms to these rules.
+
+## Rule 1 — No Core Mutation
+
+A Phase C6 charter must not propose, imply, or allow changes to any
+artifacts, semantics, or guarantees defined in Phases C1–C5.
+
+## Rule 2 — Additive Only
+
+All Phase C6 work must be strictly additive.
+
+Removal, replacement, reinterpretation, or shadowing of core behavior
+is prohibited.
+
+## Rule 3 — Authority Preservation
+
+A Phase C6 charter must explicitly preserve authority separation:
+
+- XSTRP Core: intent semantics only
+- Wallets: keys and signing
+- Ledgers: settlement
+- Extensions: non-authoritative
+
+## Rule 4 — Deterministic Failure Preservation
+
+Any extension described under Phase C6 must fail closed and preserve
+deterministic refund or non-completion behavior.
+
+No extension may introduce stranded or ambiguous outcomes.
+
+## Rule 5 — Optionality
+
+All Phase C6 outputs must be optional.
+
+The XSTRP core must remain correct, complete, and usable without any
+Phase C6 extensions present.
+
+## Rule 6 — Explicit Scope Declaration
+
+Every Phase C6 charter must explicitly list:
+
+- What it does
+- What it does not do
+- What it intentionally leaves unresolved
+
+## Rule 7 — Single-Concern Charters
+
+A Phase C6 charter must address exactly one concern domain.
+
+Multi-domain charters are prohibited.
+
+## Rule 8 — No Implicit Authorization
+
+A Phase C6 charter does not authorize implementation, deployment, or
+integration unless explicitly stated.
+
+## Enforcement
+
+Any charter violating these rules is invalid by definition.