fix(host): bound host-environment cleanup and reclaim leaked scratch dirs (#1024)

Fixes #1023.

## Problem
In Windows host mode, a single stalled delete syscall (AV/EDR filter driver, unresponsive mount, dying disk) wedged the job forever at `Cleaning up container`. `HostEnvironment.Remove()` bounds every teardown phase (`terminateRunningProcesses`, both `removePathWithRetry` calls) except the `CleanUp` callback — an unbounded `os.RemoveAll(miscpath)` assigned in `startHostEnvironment`. The runner then held its capacity slot indefinitely, the task was reaped as a zombie, and there were no diagnostics.

## Fix
- **Bound the cleanup (availability):** `Remove()` now runs `CleanUp` under `hostCleanupTimeout` (30s) via `runWithTimeout`; on timeout it logs a warning and continues job completion. The stuck goroutine is left to finish (a delete syscall can't be interrupted). Added debug logs around the phase.
- **Reclaim the leak (disk hygiene):** a timed-out cleanup can leave a scratch dir behind, so the existing idle stale-dir sweep is extended to also remove orphaned host-mode scratch dirs (16-hex names) under `Host.WorkdirParent`, leaving the shared `tool_cache` and operator data untouched. The `bind_workdir` gate is dropped from `shouldRunIdleCleanup` so host-mode runners run the sweep.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1024
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>

internal/app/run/runner_idle_cleanup_test.go

@@ -52,6 +52,55 @@ func TestRunnerCleanupStaleTaskDirs(t *testing.T) {
 	assert.DirExists(t, alphaNumericTask)
 }
 
+// TestRunnerOnIdleCleansStaleHostScratchDirs covers the host-mode leak path:
+// a per-job scratch dir (16 hex chars) left behind by a timed-out cleanup must
+// be reclaimed, while the shared tool_cache and operator data are preserved.
+func TestRunnerOnIdleCleansStaleHostScratchDirs(t *testing.T) {
+	now := time.Date(2026, time.April, 29, 20, 0, 0, 0, time.UTC)
+	hostRoot := filepath.Join(t.TempDir(), "act")
+	require.NoError(t, os.MkdirAll(hostRoot, 0o700))
+
+	staleScratch := filepath.Join(hostRoot, "0123456789abcdef") // 16 hex
+	freshScratch := filepath.Join(hostRoot, "fedcba9876543210")
+	toolCache := filepath.Join(hostRoot, "tool_cache")
+	operatorData := filepath.Join(hostRoot, "keep-me")
+	for _, path := range []string{staleScratch, freshScratch, toolCache, operatorData} {
+		require.NoError(t, os.MkdirAll(path, 0o700))
+	}
+	require.NoError(t, os.Chtimes(staleScratch, now.Add(-48*time.Hour), now.Add(-48*time.Hour)))
+	require.NoError(t, os.Chtimes(freshScratch, now.Add(-10*time.Minute), now.Add(-10*time.Minute)))
+	require.NoError(t, os.Chtimes(toolCache, now.Add(-72*time.Hour), now.Add(-72*time.Hour)))
+	require.NoError(t, os.Chtimes(operatorData, now.Add(-72*time.Hour), now.Add(-72*time.Hour)))
+
+	r := &Runner{
+		cfg: &config.Config{
+			Host: config.Host{WorkdirParent: hostRoot},
+			Runner: config.Runner{
+				WorkdirCleanupAge:   24 * time.Hour,
+				IdleCleanupInterval: time.Minute,
+			},
+		},
+		now: func() time.Time { return now },
+	}
+
+	r.OnIdle(context.Background())
+
+	assert.NoDirExists(t, staleScratch) // stale scratch reclaimed
+	assert.DirExists(t, freshScratch)   // within cleanup age, kept
+	assert.DirExists(t, toolCache)      // shared cache, never a scratch match
+	assert.DirExists(t, operatorData)   // non-hex name, untouched
+}
+
+func TestIsHostScratchDir(t *testing.T) {
+	assert.True(t, isHostScratchDir("0123456789abcdef"))
+	assert.True(t, isHostScratchDir("ffffffffffffffff"))
+	assert.False(t, isHostScratchDir("tool_cache"))
+	assert.False(t, isHostScratchDir("0123456789ABCDEF"))  // hex.EncodeToString is lowercase
+	assert.False(t, isHostScratchDir("0123456789abcde"))   // 15 chars
+	assert.False(t, isHostScratchDir("0123456789abcdef0")) // 17 chars
+	assert.False(t, isHostScratchDir("123"))
+}
+
 func TestRunnerCleanupStaleTaskDirsMissingRoot(t *testing.T) {
 	r := &Runner{
 		cfg: &config.Config{
@@ -135,7 +184,10 @@ func TestRunnerShouldRunIdleCleanupSkipsWhenJobRunning(t *testing.T) {
 	assert.False(t, r.shouldRunIdleCleanup())
 }
 
-func TestRunnerShouldRunIdleCleanupSkipsWhenBindWorkdirDisabled(t *testing.T) {
+// Idle cleanup runs regardless of bind_workdir: host mode (bind_workdir off)
+// still leaves per-job scratch dirs that the sweep must reclaim.
+func TestRunnerShouldRunIdleCleanupRunsWithoutBindWorkdir(t *testing.T) {
+	now := time.Date(2026, time.April, 29, 20, 0, 0, 0, time.UTC)
 	r := &Runner{
 		cfg: &config.Config{
 			Runner: config.Runner{
@@ -143,10 +195,10 @@ func TestRunnerShouldRunIdleCleanupSkipsWhenBindWorkdirDisabled(t *testing.T) {
 				IdleCleanupInterval: time.Minute,
 			},
 		},
-		now: time.Now,
+		now: func() time.Time { return now },
 	}
 
-	assert.False(t, r.shouldRunIdleCleanup())
+	assert.True(t, r.shouldRunIdleCleanup())
 }
 
 func TestRunnerShouldRunIdleCleanupSkipsWhenDisabled(t *testing.T) {