docs: guidance audit — refusals up front, version anchors, failure modes, resolution order, drift guards

Apply 7 proposed edits from guidance improver audit:
- CLAUDE.md: refusal rails up front, version anchor, resolution order
- BOOCHAT.md: resolution order section
- BOOCODER.md: tool reliability callouts
- data/AGENTS.md: tool list drift guard, failure modes preamble

CLAUDE.md

@@ -1,5 +1,13 @@
 # CLAUDE.md
 
+<!-- Last meaningful update: 2026-06-08 (v2.8.20-paseo-orchestrator-ph3-5) -->
+
+## You cannot
+- Write, edit, or delete files (BooChat only — use BooCoder for writes)
+- Run shell commands (use booterm terminal panes)
+- Make commits, push, or pull (Sam reviews and commits manually)
+- `git add -A` (stage only files you changed)
+
 This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
 
 **Cursor agents:** start with `docs/ARCHITECTURE.md` (diagram); this file is the deep engineering reference. `data/AGENTS.md` is the agent *registry*, not navigation (the root navigation `AGENTS.md` was removed).
@@ -51,6 +59,9 @@ Detailed engineering notes live in per-app `CLAUDE.md` files, **auto-loaded when
 
 Cross-app contracts (WS-frame & provider-type parity, sentinels) and everything below stay here.
 
+### Guidance resolution order
+When multiple sources conflict: `CLAUDE.md` (repo root) → `BOOCHAT.md` / `BOOCODER.md` (per-surface) → per-app `CLAUDE.md` (auto-loaded by file context) → `data/AGENTS.md` (agent preamble beats per-agent body) → session `system_prompt` → user prompt. Last-encountered wins on samplers; refusals cascade downward (you cannot do what any layer forbids).
+
 ### Data flow for chat
 
 1. User sends message → POST `/api/sessions/:id/messages` creates user + assistant (status=streaming) rows