fix: harden ACP secret handling and exec preflight boundaries

docs/tools/exec.md

@@ -41,6 +41,9 @@ Notes:
 - Important: sandboxing is **off by default**. If sandboxing is off, `host=sandbox` runs directly on
   the gateway host (no container) and **does not require approvals**. To require approvals, run with
   `host=gateway` and configure exec approvals (or enable sandboxing).
+- Script preflight checks (for common Python/Node shell-syntax mistakes) only inspect files inside the
+  effective `workdir` boundary. If a script path resolves outside `workdir`, preflight is skipped for
+  that file.
 
 ## Config