docs(agents): document Homebrew resource blocks and --check drift reporting

AGENTS.md

@@ -52,8 +52,13 @@ repo-wide reformat as a side effect of an unrelated change.
 - **`contrib/homebrew/`** — a **git submodule** of the tap at
   `https://tildeforge.dev/beefcarver/homebrew`, not a copy. Formula changes
   belong in the tap repository; commit them there and bump the gitlink here.
-  Never add loose files under that path. The formula still carries a
-  placeholder `sha256`, so it only installs with `--HEAD`.
+  Never add loose files under that path. The formula's Python dependencies are
+  vendored as `resource` blocks: Homebrew installs the sdist with `--no-deps`,
+  so a dependency that has no block (or whose constraint changed in
+  `pyproject.toml`) is simply missing at runtime. Regenerate them in the tap
+  with `brew update-python-resources Formula/b/beefy-player.rb`;
+  `uv run python bump_packaging.py <version> --check` reports a dependency
+  without one.
 
 ## Releases