docs: add agent inbox check to session protocol

Check get_messages(to_agent="marki-docx") at session start per CUST-WP-0015.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -150,6 +150,12 @@ get_domain_summary("markitect")
 ```
 Note: active workstreams, blocking decisions, recent progress, SBOM status.
 
+**Step 1b — Check the agent inbox**
+```
+get_messages(to_agent="marki-docx", unread_only=True)
+```
+Mark messages read with `mark_message_read(message_id)`. Act on any coordination requests before proceeding.
+
 **Step 2 — Scan local workplans**
 
 ```bash
@@ -315,6 +321,24 @@ Then either:
 
 ---
 
+## Ralph Loop — Workplan-Tied Usage
+
+**Rule: always use `/ralph-workplan` instead of `/ralph-loop` directly.**
+
+```
+/ralph-workplan workplans/<ID>-<slug>.md [--max-iterations 20]
+```
+
+This skill guards against runaway loops:
+1. **Refuses to start** if the workplan `status` is already `done`
+2. **Self-retires** — re-reads the workplan file each iteration; outputs `<promise>HEUREKA</promise>` the moment all tasks are `done`
+3. Always sets `--completion-promise HEUREKA` and a bounded iteration count
+
+**Never** start a ralph loop with a raw static implementation prompt. A static prompt
+has no completion awareness and will loop forever even after the work is done.
+
+---
+
 ## Quick Reference
 
 - MCP tool reference: `~/the-custodian/state-hub/mcp_server/TOOLS.md`