diff --git a/agents/AGENTS.md b/agents/AGENTS.md
index 0677925..457b689 100644
--- a/agents/AGENTS.md
+++ b/agents/AGENTS.md
@@ -14,6 +14,12 @@
   project's `AGENTS.md` / `CLAUDE.md` specifies a different directory,
   that wins.
 
+## Temporary Files
+
+- **Use `$TMPDIR` or `.tmp/` (project-local) for temporary files.** Never use `/tmp` directly or paths like `/Library/Application Support` — those are not in the sandbox allowlist and trigger permission prompts.
+- `$TMPDIR` is set by the sandbox to a writable path. `.tmp/` inside the project directory is always writable without prompts.
+- Ensure `.tmp/` is listed in `.gitignore` when creating temp files in a tracked repo.
+
 ## Tooling
 
 - **`ccc` for semantic code search.** Repos containing a