Merge pull request 'docs(agents): one workspace per agent run — the shared checkout is off-limits' (#56) from docs/agents-work-in-their-own-workspace into main

Reviewed-on: #56
Reviewed-by: Keith Jackson <[email protected]>

README.md

@@ -11,6 +11,9 @@ specification** at [`../home-network-k3s`](../home-network-k3s).
 - **Done = a green, reproducible, requirement-tagged conformance test** — never "merged," never a
   manual demo (spec `docs/14`, `agents/definition-of-done.md`).
 - **No work on `main`.** Every change is a feature branch merged into `main` (spec `CONTRIBUTING.md`).
+- **No work in a shared checkout.** Every agent run gets its own git worktree, outside the repo
+  root, branched from `origin/main`. This checkout is shared mutable state — see
+  [`CLAUDE.md` §0](CLAUDE.md).
 - **No plaintext secrets** — SOPS-encrypted only (spec `docs/07`).
 - **Phase discipline** — only build what the active roadmap phase authorizes (spec `roadmap/phases.md`).
 
@@ -95,6 +98,20 @@ The running narrative — decisions, root causes, incidents, follow-ups — is
 
 ## Working on this repo
 
+**First, get out of this checkout.** It is the operator's working copy and several agents
+share it; concurrent runs here have overwritten each other's branches and left each other's
+uncommitted files behind. One workspace per change:
+
+```bash
+git fetch origin main
+git worktree add -b <type>/<slug> /path/outside/the/repo/wt-<slug> origin/main
+cd /path/outside/the/repo/wt-<slug>
+```
+
+Outside the repo root specifically — a worktree under `.claude/worktrees/` is a second full
+copy that tree-walking gate checks then count twice. The rule, the measurements behind it, and
+the three gate workarounds a worktree needs are in [`CLAUDE.md` §0](CLAUDE.md) and §3.
+
 Everything the gate needs is baked into the pinned dev container — **do not install the
 toolchain on the host**: