diff --git a/.gitignore b/.gitignore
index 00b7d046..6557b985 100644
--- a/.gitignore
+++ b/.gitignore
@@ -72,3 +72,9 @@ tests/e2e/test-results/
 # were still tracked candidates.
 /playwright-report/
 /test-results/
+
+# Agent/test scratch and tool caches — generated, never source.
+# Added by the 2026-08-25 fleet hygiene sweep (ADR-100 Decision 2).
+.stale/
+/.e2e-state/
+.phpunit.cache