docs(claude): add cross-repo mesh guidelines

Author: pratikbin

CLAUDE.md

@@ -1,5 +1,52 @@
 # CreateOS CLI — Development Guide
 
+## Cross-repo mesh — CreateOS Sandbox
+
+**You are in `createos-cli` — the public Go CLI.** The `fc` control plane
+defines the API this calls; `createos-plugin` wraps this CLI; the website
+mirrors these commands. On any command / flag change, run the protocol below —
+the concrete website-regen steps live in "Keeping the Website Docs in Sync" near
+the end of this file. This repo is one of five in the product mesh.
+
+### Repo map
+
+| repo | path | role | public? | changes that ripple across the mesh |
+|---|---|---|---|---|
+| **fc** | `../fc` | control-plane — **source of truth** | 🔒 private | HTTP API, wire/JSON fields, error shapes, lifecycle/state, limits/quotas, behavior |
+| **fc-sdk** | `../fc-sdk` | TypeScript SDK **+ `examples/`** | 🌐 public | public SDK methods, wire types, example apps |
+| **createos-cli** | `../createos-cli` | Go CLI | 🌐 public | commands, flags, help/UX text |
+| **website-04** | `../website-04` (`content/docs/Sandbox`) | public docs | 🌐 public | REST / SDK / CLI reference + concept pages |
+| **createos-plugin** | `../createos-plugin` | Claude Code plugin over the `createos` CLI | 🌐 public | skills, slash commands, hooks |
+
+### What counts as a shared surface
+
+HTTP endpoint or method · wire or JSON field · error shape · sandbox
+lifecycle/state · limit or quota · CLI command or flag · public SDK method ·
+documented behavior. A change confined to internals — refactor, comment,
+private helper, test-only — is **not** a shared surface, so skip the mesh for it.
+
+### Protocol — run before finalizing a shared-surface change
+
+1. **Classify origin.** `fc` is the source of truth; SDK / CLI / docs / plugin
+   are downstream consumers. A downstream change that implies a backend change
+   (new field, new endpoint) → surface it to the user; never invent server
+   behavior inside a client.
+2. **Search every sibling** for the touched symbol / endpoint / flag —
+   `semble search` first, then `rg`.
+3. **Build a status matrix** per sibling: `already-present` ·
+   `missing-needs-update` · `n/a`. **Flag the already-present ones to the user**
+   ("already exists in fc-sdk + docs"). Never silently duplicate a change that is
+   already there — that is the whole point of this check.
+4. **`fc` → any public repo is a leak-guard boundary (security).** Strip private
+   implementation, security internals, infra, threat-model notes, and
+   internal-only tooling (`fcctl`, host filesystem paths, mTLS/CA internals)
+   before anything lands in a public repo. Respect each public repo's own wording
+   rules (e.g. `fc-sdk/AGENTS.md` forbids the word "VM"). Report the proposed diff
+   and **ask for approval before landing any public edit** — never auto-write
+   across the boundary.
+5. **Use the `sync-docs` skill** to execute SDK / CLI / website reconciliation
+   against upstream `fc` where it applies.
+
 ## Project Structure
 
 ```