ci: restrict GitHub Actions cache access with cache-mode

.github/workflows/ci.yml

@@ -8,6 +8,7 @@ on:
   workflow_dispatch:
 
 permissions: {}
+cache-mode: none
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}

.github/workflows/release.yml

@@ -9,6 +9,7 @@ on:
   workflow_dispatch:
 
 permissions: {}
+cache-mode: none
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event_name == 'workflow_dispatch' && 'release' || github.ref }}

.github/workflows/update-material.yml

@@ -10,6 +10,7 @@ on:
   workflow_dispatch:
 
 permissions: {}
+cache-mode: none
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}

AGENTS.md

@@ -38,4 +38,7 @@ This repository publishes dev container features for use with the [Dev Container
   e.g. `uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0`.
 - Set workflow-level permissions to empty (`permissions: {}`) and grant
   the minimum required permissions per job.
+- Set workflow-level cache access to none (`cache-mode: none`) and grant
+  the minimum required mode per job: `read` when a job only restores
+  caches, `write` when it also saves ones later runs restore.
 - Set `persist-credentials: false` on `actions/checkout`.