diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6594eaf..d622e06 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@ Versioning.
 
 ### Added
 
+- Mirrored verified `nddev_tool_cache_event` records into the GitHub runner
+  diagnostic directory so teardown bundles retain job-level cache evidence.
 - Added bounded extraction of `nddev_tool_cache_event` records from verified
   runner diagnostic artifacts, with malformed job text counted but non-blocking.
 - Added the portable scheduler-recovery decision core: exact stuck-dispatch
diff --git a/actions/tool-cache/tool-cache.sh b/actions/tool-cache/tool-cache.sh
index 53de28c..a16d12a 100755
--- a/actions/tool-cache/tool-cache.sh
+++ b/actions/tool-cache/tool-cache.sh
@@ -132,5 +132,17 @@ test ! -L "$output"
 install -m 0600 "$candidate" "$output"
 duration_ms=$(( $(date +%s%3N) - started ))
 printf 'source=%s\nbytes=%s\nduration_ms=%s\n' "$source" "$bytes" "$duration_ms" >>"$GITHUB_OUTPUT"
-printf 'nddev_tool_cache_event={"source":"%s","cache_result":"%s","sha256":"%s","bytes":%s,"duration_ms":%s}\n' \
+printf -v event 'nddev_tool_cache_event={"source":"%s","cache_result":"%s","sha256":"%s","bytes":%s,"duration_ms":%s}' \
   "$source" "$cache_result" "$expected_sha256" "$bytes" "$duration_ms"
+printf '%s\n' "$event"
+
+runner_work=$(dirname -- "$RUNNER_TEMP")
+runner_root=$(dirname -- "$runner_work")
+diagnostic_directory=$runner_root/_diag
+diagnostic_file=$diagnostic_directory/nddev-tool-cache-events.log
+if [[ "$(basename -- "$RUNNER_TEMP")" == _temp && "$(basename -- "$runner_work")" == _work &&
+      -d "$diagnostic_directory" && ! -L "$diagnostic_directory" && -w "$diagnostic_directory" &&
+      ( ! -e "$diagnostic_file" || ( -f "$diagnostic_file" && ! -L "$diagnostic_file" &&
+        "$(stat --format='%s' -- "$diagnostic_file")" -le 1048576 ) ) ]]; then
+  printf '%s\n' "$event" >>"$diagnostic_file"
+fi
diff --git a/internal/repositorycontract/tool_cache_action_test.go b/internal/repositorycontract/tool_cache_action_test.go
index 3a30aa5..d05cde6 100644
--- a/internal/repositorycontract/tool_cache_action_test.go
+++ b/internal/repositorycontract/tool_cache_action_test.go
@@ -78,13 +78,16 @@ type toolCacheResult struct {
 	outputs     string
 	stdout      string
 	invocations string
+	diagnostics string
 }
 
 func runToolCache(t *testing.T, cacheMode string) toolCacheResult {
 	t.Helper()
 	root := toolCacheRepositoryRoot(t)
 	directory := t.TempDir()
-	runnerTemp := filepath.Join(directory, "runner-temp")
+	runnerRoot := filepath.Join(directory, "actions-runner")
+	runnerTemp := filepath.Join(runnerRoot, "_work", "_temp")
+	diagnosticDirectory := filepath.Join(runnerRoot, "_diag")
 	bin := filepath.Join(directory, "bin")
 	if err := os.MkdirAll(runnerTemp, 0o700); err != nil {
 		t.Fatal(err)
@@ -92,6 +95,9 @@ func runToolCache(t *testing.T, cacheMode string) toolCacheResult {
 	if err := os.MkdirAll(bin, 0o700); err != nil {
 		t.Fatal(err)
 	}
+	if err := os.MkdirAll(diagnosticDirectory, 0o700); err != nil {
+		t.Fatal(err)
+	}
 	fixture := []byte("immutable verified tool artifact\n")
 	fixturePath := filepath.Join(directory, "fixture")
 	if err := os.WriteFile(fixturePath, fixture, 0o600); err != nil {
@@ -186,7 +192,16 @@ fi
 	if err != nil {
 		t.Fatal(err)
 	}
-	return toolCacheResult{outputs: string(outputs), stdout: string(combined), invocations: string(calls)}
+	diagnostics, err := os.ReadFile(filepath.Join(diagnosticDirectory, "nddev-tool-cache-events.log"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(diagnostics) != string(combined) {
+		t.Fatalf("diagnostic event differs from stdout: diagnostics=%q stdout=%q", diagnostics, combined)
+	}
+	return toolCacheResult{
+		outputs: string(outputs), stdout: string(combined), invocations: string(calls), diagnostics: string(diagnostics),
+	}
 }
 
 func toolCacheRepositoryRoot(t *testing.T) string {