docs(claude): pre-create cache dirs before GOCACHE/GOTMPDIR override

go test fails if GOTMPDIR points at a directory that does not exist
yet. Tell readers to mkdir -p the cache and lint-cache directories
first, then show the full GOCACHE/GOTMPDIR/GOLANGCI_LINT_CACHE
invocations as a runnable block.

https://claude.ai/code/session_01Bwxu5LAwzKLCbx4L4r8QgX

Author: claude

CLAUDE.md

@@ -23,7 +23,13 @@ go test -run TestName ./store/...
 go test -race ./kv/...
 ```
 
-If `$GOCACHE` is sandbox-blocked (macOS), prefix with `GOCACHE=$(pwd)/.cache GOTMPDIR=$(pwd)/.cache/tmp`. The lint cache analog is `GOLANGCI_LINT_CACHE=$(pwd)/.golangci-cache`.
+If `$GOCACHE` is sandbox-blocked (macOS), create the cache dirs first (Go errors out if `GOTMPDIR` does not exist), then prefix the command:
+
+```bash
+mkdir -p "$(pwd)/.cache/tmp" "$(pwd)/.golangci-cache"
+GOCACHE=$(pwd)/.cache GOTMPDIR=$(pwd)/.cache/tmp go test ./...
+GOCACHE=$(pwd)/.cache GOLANGCI_LINT_CACHE=$(pwd)/.golangci-cache golangci-lint run
+```
 
 Single-node server (etcd/raft is the default backend):