feat(joinir): Phase 70-B - Multihop Relay Passthrough Support (dev-only)

Phase 70-B relaxes runtime guard from "always error" to "unsupported only".
Adds structural detection (is_supported_multihop_pattern) to distinguish:
- Simple passthrough (no self-updates): ACCEPT
- Complex patterns (self-conflict, etc): REJECT with [ownership/relay:runtime_unsupported]

Changes:
- plan_validator.rs: +is_supported_multihop_pattern() method + unit tests
- normalized_joinir_min.rs: +2 integration tests for passthrough/rejection
- phase70-relay-runtime-guard.md: Phase 70 series status table added

Tests: normalized_dev 52/52 PASS, lib 950/950 PASS
Design: Structural detection only (no by-name branching)

🤖 Generated with Claude Code

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

docs/development/current/main/phase70-relay-runtime-guard.md

@@ -74,14 +74,27 @@ Verifies:
 
 ---
 
+## Phase 70 Series
+
+| Phase | Status | Description |
+|-------|--------|-------------|
+| Phase 70-A | ✅ Complete | Runtime guard with standard tag `[ownership/relay:runtime_unsupported]` |
+| Phase 70-B | ✅ Complete | Simple passthrough multihop support (contiguous path, no self-updates) |
+| Phase 70-C | ✅ Complete | Merge relay detection (multiple inner loops → same owner) |
+| Phase 70-D+ | 🚧 Future | Full runtime execution support (exit PHI merge, carrier propagation) |
+
+---
+
 ## Related Documents
 
 - [Phase 65: Multihop Design](phase65-ownership-relay-multihop-design.md)
 - [Phase 66: Multihop Implementation](phase65-ownership-relay-multihop-design.md#phase-66-implementation-status)
+- [Phase 70-C: Merge Relay](phase70c-merge-relay.md)
 - [Phase 56: Ownership-Relay Architecture](phase56-ownership-relay-design.md)
 
 ---
 
 ## Changelog
 
+- **2025-12-13**: Phase 70-C completed - Merge relay detection and validation
 - **2025-12-13**: Phase 70-A created - Fail-Fast tag standardization