Avoid remote caching of remote persistent worker demo

The test wants to make sure that the actions are executed correct using either the remote
persistent worker or running as individual actions on the remote execution system. Caching
interferes with this test. This injects a cache-silo-key that changes each time to force a re-run
of the action.

examples/persistent_worker/defs.bzl

@@ -34,6 +34,13 @@ def _demo_impl(ctx: AnalysisContext) -> list[Provider]:
     ctx.actions.run(
         cmd_args(argfile),
         category = "demo",
+        env = {
+            # modify this value to force an action rerun even if caching is enabled.
+            # `--no-remote-cache` does not have the desired effect, because it also causes
+            # the action to be omitted from `buck2 log what-ran`, which interferes with the
+            # test setup.
+            "CACHE_SILO_KEY": read_root_config("build", "cache_silo_key", "0"),
+        },
         exe = WorkerRunInfo(
             worker = ctx.attrs._worker[WorkerInfo],
             exe = ctx.attrs._one_shot[RunInfo].args,

examples/persistent_worker/test.sh

@@ -9,7 +9,9 @@
 set -euo pipefail
 
 echo "::group::Local build without persistent worker" >&2
-echo '<file:.buckconfig.no-workers>' > .buckconfig.local
+cat >.buckconfig.local <<EOF
+<file:.buckconfig.no-workers>
+EOF
 buck2 clean; buck2 build : -vstderr
 echo "# Verifying Buck2 log" >&2
 buck2 log what-ran --show-std-err --format json \
@@ -33,7 +35,9 @@ buck2 log what-ran --show-std-err --format json \
 echo "::endgroup::" >&2
 
 echo "::group::Local build with persistent worker" >&2
-echo '<file:.buckconfig.local-persistent-workers>' > .buckconfig.local
+cat >.buckconfig.local <<EOF
+<file:.buckconfig.local-persistent-workers>
+EOF
 buck2 clean; buck2 build : -vstderr
 echo "# Verifying Buck2 log" >&2
 buck2 log what-ran --show-std-err --format json \
@@ -60,7 +64,12 @@ echo "::group::Remote build without persistent worker" >&2
 if [[ -z ${BUILDBUDDY_API_KEY:+x} ]]; then
   echo "::notice file=$(realpath --relative-to=../.. ${BASH_SOURCE[0]}),line=${LINENO}::SKIPPED Missing BuildBuddy token. See examples/persistent_worker/README.md" >&2
 else
-  echo '<file:.buckconfig.buildbuddy>' > .buckconfig.local
+  cat >.buckconfig.local <<EOF
+<file:.buckconfig.buildbuddy>
+
+[build]
+cache_silo_key=$(date +%s.%N).${GITHUB_RUN_ID-0}
+EOF
   buck2 clean; buck2 build : -vstderr
   echo "# Verifying Buck2 log" >&2
   buck2 log what-ran --show-std-err --format json \
@@ -88,7 +97,12 @@ echo "::group::Remote build with persistent worker" >&2
 if [[ -z ${BUILDBUDDY_API_KEY:+x} ]]; then
   echo "::notice file=$(realpath --relative-to=../.. ${BASH_SOURCE[0]}),line=${LINENO}::SKIPPED Missing BuildBuddy token. See examples/persistent_worker/README.md" >&2
 else
-  echo '<file:.buckconfig.buildbuddy-persistent-workers>' > .buckconfig.local
+  cat >.buckconfig.local <<EOF
+<file:.buckconfig.buildbuddy-persistent-workers>
+
+[build]
+cache_silo_key=$(date +%s.%N).${GITHUB_RUN_ID-0}
+EOF
   buck2 clean; buck2 build : -vstderr
   echo "# Verifying Buck2 log" >&2
   buck2 log what-ran --show-std-err --format json \