Document per-node Warp env requirement

shared/long-term/projects/warp-acp-integration.md

@@ -33,6 +33,12 @@ Primary local secret file:
 
 - `~/.openclaw/.env`
 
+Node-local requirement:
+
+- Any machine that may locally execute a Warp-backed ACP harness must have its own local `~/.openclaw/.env`.
+- For the current cluster plan, this means `mac-5`, `mac-6`, and `mac-7` should all be configured.
+- Do not assume secrets from `mac-5` will automatically be available when a harness actually runs on `mac-6` or `mac-7`.
+
 Recommended format:
 
 ```bash