diff --git a/README.md b/README.md
index f159e44b..975bc28e 100644
--- a/README.md
+++ b/README.md
@@ -132,6 +132,12 @@ Besides `GITEA_INSTANCE_URL` and `GITEA_RUNNER_REGISTRATION_TOKEN`, the image en
 
 For a fuller container-oriented walkthrough, see [examples/docker](examples/docker/README.md).
 
+When `container.bind_workdir` is enabled, stale task workspace directories can be cleaned while the runner is idle:
+- directories older than `runner.workdir_cleanup_age` are removed (default: `24h`; set `0` to disable)
+- cleanup runs every `runner.idle_cleanup_interval` (default: `10m`; set `0` to disable)
+- only purely numeric subdirectories under `container.workdir_parent` are treated as task workspaces and may be removed
+- cleanup assumes `container.workdir_parent` is not shared across multiple runners
+
 ### Example Deployments
 
 Check out the [examples](examples) directory for sample deployment types.
diff --git a/internal/app/poll/poller.go b/internal/app/poll/poller.go
index 37ab7b28..9e3ea61a 100644
--- a/internal/app/poll/poller.go
+++ b/internal/app/poll/poller.go
@@ -27,6 +27,11 @@ type TaskRunner interface {
 	Run(ctx context.Context, task *runnerv1.Task) error
 }
 
+// IdleRunner can run maintenance while the poller is idle.
+type IdleRunner interface {
+	OnIdle(ctx context.Context)
+}
+
 type Poller struct {
 	client       client.Client
 	runner       TaskRunner
@@ -95,6 +100,7 @@ func (p *Poller) Poll() {
 
 		task, ok := p.fetchTask(p.pollingCtx, s)
 		if !ok {
+			p.runIdleMaintenance()
 			<-sem
 			if !p.waitBackoff(s) {
 				return
@@ -119,6 +125,7 @@ func (p *Poller) PollOnce() {
 	for {
 		task, ok := p.fetchTask(p.pollingCtx, s)
 		if !ok {
+			p.runIdleMaintenance()
 			if !p.waitBackoff(s) {
 				return
 			}
@@ -130,6 +137,12 @@ func (p *Poller) PollOnce() {
 	}
 }
 
+func (p *Poller) runIdleMaintenance() {
+	if idleRunner, ok := p.runner.(IdleRunner); ok {
+		idleRunner.OnIdle(p.jobsCtx)
+	}
+}
+
 func (p *Poller) Shutdown(ctx context.Context) error {
 	p.shutdownPolling()
 
diff --git a/internal/app/poll/poller_test.go b/internal/app/poll/poller_test.go
index e9d10d12..61e43c05 100644
--- a/internal/app/poll/poller_test.go
+++ b/internal/app/poll/poller_test.go
@@ -125,6 +125,11 @@ type mockRunner struct {
 	totalCompleted atomic.Int64
 }
 
+type idleAwareRunner struct {
+	mockRunner
+	idleCalls atomic.Int64
+}
+
 func (m *mockRunner) Run(ctx context.Context, _ *runnerv1.Task) error {
 	atomicMax(&m.maxConcurrent, m.running.Add(1))
 	select {
@@ -136,6 +141,78 @@ func (m *mockRunner) Run(ctx context.Context, _ *runnerv1.Task) error {
 	return nil
 }
 
+func TestPollerRunIdleMaintenance(t *testing.T) {
+	runner := &idleAwareRunner{}
+	p := &Poller{runner: runner, jobsCtx: context.Background()}
+
+	p.runIdleMaintenance()
+
+	assert.Equal(t, int64(1), runner.idleCalls.Load())
+}
+
+func (m *idleAwareRunner) OnIdle(_ context.Context) {
+	m.idleCalls.Add(1)
+}
+
+func TestPollerPollCallsOnIdle(t *testing.T) {
+	cli := mocks.NewClient(t)
+	cli.On("FetchTask", mock.Anything, mock.Anything).Return(
+		func(_ context.Context, _ *connect_go.Request[runnerv1.FetchTaskRequest]) (*connect_go.Response[runnerv1.FetchTaskResponse], error) {
+			return connect_go.NewResponse(&runnerv1.FetchTaskResponse{}), nil
+		},
+	)
+
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.Runner.Capacity = 1
+	cfg.Runner.FetchInterval = 10 * time.Millisecond
+	cfg.Runner.FetchIntervalMax = 10 * time.Millisecond
+
+	runner := &idleAwareRunner{}
+	poller := New(cfg, cli, runner)
+
+	var wg sync.WaitGroup
+	wg.Go(poller.Poll)
+
+	require.Eventually(t, func() bool {
+		return runner.idleCalls.Load() > 0
+	}, time.Second, 10*time.Millisecond)
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	require.NoError(t, poller.Shutdown(ctx))
+	wg.Wait()
+}
+
+func TestPollerPollOnceCallsOnIdle(t *testing.T) {
+	cli := mocks.NewClient(t)
+	cli.On("FetchTask", mock.Anything, mock.Anything).Return(
+		func(_ context.Context, _ *connect_go.Request[runnerv1.FetchTaskRequest]) (*connect_go.Response[runnerv1.FetchTaskResponse], error) {
+			return connect_go.NewResponse(&runnerv1.FetchTaskResponse{}), nil
+		},
+	)
+
+	cfg, err := config.LoadDefault("")
+	require.NoError(t, err)
+	cfg.Runner.FetchInterval = 10 * time.Millisecond
+	cfg.Runner.FetchIntervalMax = 10 * time.Millisecond
+
+	runner := &idleAwareRunner{}
+	poller := New(cfg, cli, runner)
+
+	var wg sync.WaitGroup
+	wg.Go(poller.PollOnce)
+
+	require.Eventually(t, func() bool {
+		return runner.idleCalls.Load() > 0
+	}, time.Second, 10*time.Millisecond)
+
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	require.NoError(t, poller.Shutdown(ctx))
+	wg.Wait()
+}
+
 // TestPoller_ConcurrencyLimitedByCapacity verifies that with capacity=3 and
 // 6 available tasks, at most 3 tasks run concurrently, and FetchTask is
 // never called concurrently (single poller).
diff --git a/internal/app/run/runner.go b/internal/app/run/runner.go
index c10e87c3..bb67ef9d 100644
--- a/internal/app/run/runner.go
+++ b/internal/app/run/runner.go
@@ -7,12 +7,14 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"maps"
 	"net/http"
 	"os"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -46,8 +48,10 @@ type Runner struct {
 	envs         map[string]string
 	cacheHandler *artifactcache.Handler
 
-	runningTasks sync.Map
-	runningCount atomic.Int64
+	runningTasks            sync.Map
+	runningCount            atomic.Int64
+	lastIdleCleanupUnixNano atomic.Int64
+	now                     func() time.Time
 }
 
 func NewRunner(cfg *config.Config, reg *config.Registration, cli client.Client) *Runner {
@@ -90,13 +94,94 @@ func NewRunner(cfg *config.Config, reg *config.Registration, cli client.Client)
 	envs["GITEA_ACTIONS"] = "true"
 	envs["GITEA_ACTIONS_RUNNER_VERSION"] = ver.Version()
 
-	return &Runner{
+	runner := &Runner{
 		name:         reg.Name,
 		cfg:          cfg,
 		client:       cli,
 		labels:       ls,
 		envs:         envs,
 		cacheHandler: cacheHandler,
+		now:          time.Now,
+	}
+	return runner
+}
+
+// OnIdle performs lightweight maintenance during polling idle windows.
+// It runs synchronously on the poller goroutine; shouldRunIdleCleanup
+// throttles invocations to runner.idle_cleanup_interval so the impact on
+// poll cadence is bounded even when the workdir root is large.
+func (r *Runner) OnIdle(ctx context.Context) {
+	if !r.shouldRunIdleCleanup() {
+		return
+	}
+	workdirParent := strings.TrimLeft(r.cfg.Container.WorkdirParent, "/")
+	workdirRoot := filepath.FromSlash("/" + workdirParent)
+	r.cleanupStaleTaskDirs(ctx, workdirRoot)
+}
+
+func (r *Runner) shouldRunIdleCleanup() bool {
+	if !r.cfg.Container.BindWorkdir {
+		return false
+	}
+	if r.cfg.Runner.WorkdirCleanupAge <= 0 || r.cfg.Runner.IdleCleanupInterval <= 0 {
+		return false
+	}
+	if r.RunningCount() != 0 {
+		return false
+	}
+	now := r.now()
+	interval := r.cfg.Runner.IdleCleanupInterval
+	for {
+		last := r.lastIdleCleanupUnixNano.Load()
+		if last != 0 && now.Sub(time.Unix(0, last)) < interval {
+			return false
+		}
+		if r.lastIdleCleanupUnixNano.CompareAndSwap(last, now.UnixNano()) {
+			return true
+		}
+	}
+}
+
+func (r *Runner) cleanupStaleTaskDirs(ctx context.Context, workdirRoot string) {
+	entries, err := os.ReadDir(workdirRoot)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return
+		}
+		log.Warnf("failed to list task workspace root %s for stale cleanup: %v", workdirRoot, err)
+		return
+	}
+
+	// A task may begin between shouldRunIdleCleanup's running-count check and
+	// the loop below. That is safe because new task dirs are created with the
+	// current mtime and therefore fall on the keep side of cutoff.
+	cutoff := r.now().Add(-r.cfg.Runner.WorkdirCleanupAge)
+	for _, entry := range entries {
+		if err := ctx.Err(); err != nil {
+			return
+		}
+		if !entry.IsDir() {
+			continue
+		}
+		// Task workspaces are indexed by numeric task IDs; skip any other
+		// directories to avoid deleting operator-managed data under workdir_root.
+		if _, err := strconv.ParseUint(entry.Name(), 10, 64); err != nil {
+			continue
+		}
+		info, err := entry.Info()
+		if err != nil {
+			log.Warnf("failed to stat task workspace %s: %v", filepath.Join(workdirRoot, entry.Name()), err)
+			continue
+		}
+		if info.ModTime().After(cutoff) {
+			continue
+		}
+		taskDir := filepath.Join(workdirRoot, entry.Name())
+		if err := os.RemoveAll(taskDir); err != nil {
+			log.Warnf("failed to clean stale task workspace %s: %v", taskDir, err)
+			continue
+		}
+		log.Infof("cleaned stale task workspace %s", taskDir)
 	}
 }
 
diff --git a/internal/app/run/runner_idle_cleanup_test.go b/internal/app/run/runner_idle_cleanup_test.go
new file mode 100644
index 00000000..8f1dce47
--- /dev/null
+++ b/internal/app/run/runner_idle_cleanup_test.go
@@ -0,0 +1,247 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package run
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strconv"
+	"testing"
+	"time"
+
+	"gitea.com/gitea/runner/internal/pkg/config"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRunnerCleanupStaleTaskDirs(t *testing.T) {
+	now := time.Date(2026, time.April, 29, 20, 0, 0, 0, time.UTC)
+	workdirRoot := filepath.Join(t.TempDir(), "workspace")
+	require.NoError(t, os.MkdirAll(workdirRoot, 0o700))
+
+	oldTask := filepath.Join(workdirRoot, "1001")
+	freshTask := filepath.Join(workdirRoot, "1002")
+	nonTask := filepath.Join(workdirRoot, "shared")
+	alphaNumericTask := filepath.Join(workdirRoot, "123abc")
+	for _, path := range []string{oldTask, freshTask, nonTask, alphaNumericTask} {
+		require.NoError(t, os.MkdirAll(path, 0o700))
+	}
+
+	require.NoError(t, os.Chtimes(oldTask, now.Add(-3*time.Hour), now.Add(-3*time.Hour)))
+	require.NoError(t, os.Chtimes(freshTask, now.Add(-30*time.Minute), now.Add(-30*time.Minute)))
+	require.NoError(t, os.Chtimes(nonTask, now.Add(-5*time.Hour), now.Add(-5*time.Hour)))
+	require.NoError(t, os.Chtimes(alphaNumericTask, now.Add(-5*time.Hour), now.Add(-5*time.Hour)))
+
+	r := &Runner{
+		cfg: &config.Config{
+			Runner: config.Runner{
+				WorkdirCleanupAge: 2 * time.Hour,
+			},
+		},
+		now: func() time.Time { return now },
+	}
+
+	r.cleanupStaleTaskDirs(context.Background(), workdirRoot)
+
+	assert.NoDirExists(t, oldTask)
+	assert.DirExists(t, freshTask)
+	assert.DirExists(t, nonTask)
+	assert.DirExists(t, alphaNumericTask)
+}
+
+func TestRunnerCleanupStaleTaskDirsMissingRoot(t *testing.T) {
+	r := &Runner{
+		cfg: &config.Config{
+			Runner: config.Runner{WorkdirCleanupAge: time.Hour},
+		},
+		now: time.Now,
+	}
+
+	// Must be a silent no-op rather than a warning or panic when the root
+	// has not yet been created (e.g. the runner has never executed a task).
+	r.cleanupStaleTaskDirs(context.Background(), filepath.Join(t.TempDir(), "missing"))
+}
+
+func TestRunnerCleanupStaleTaskDirsHonorsContext(t *testing.T) {
+	now := time.Date(2026, time.April, 29, 20, 0, 0, 0, time.UTC)
+	workdirRoot := filepath.Join(t.TempDir(), "workspace")
+	require.NoError(t, os.MkdirAll(workdirRoot, 0o700))
+
+	for i := 1001; i <= 1003; i++ {
+		dir := filepath.Join(workdirRoot, strconv.Itoa(i))
+		require.NoError(t, os.MkdirAll(dir, 0o700))
+		require.NoError(t, os.Chtimes(dir, now.Add(-3*time.Hour), now.Add(-3*time.Hour)))
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	r := &Runner{
+		cfg: &config.Config{
+			Runner: config.Runner{WorkdirCleanupAge: time.Hour},
+		},
+		now: func() time.Time { return now },
+	}
+
+	r.cleanupStaleTaskDirs(ctx, workdirRoot)
+
+	for i := 1001; i <= 1003; i++ {
+		assert.DirExists(t, filepath.Join(workdirRoot, strconv.Itoa(i)))
+	}
+}
+
+func TestRunnerShouldRunIdleCleanupThrottles(t *testing.T) {
+	now := time.Date(2026, time.April, 29, 20, 0, 0, 0, time.UTC)
+	r := &Runner{
+		cfg: &config.Config{
+			Container: config.Container{
+				BindWorkdir: true,
+			},
+			Runner: config.Runner{
+				WorkdirCleanupAge:   24 * time.Hour,
+				IdleCleanupInterval: time.Hour,
+			},
+		},
+		now: func() time.Time { return now },
+	}
+
+	assert.True(t, r.shouldRunIdleCleanup())
+
+	now = now.Add(30 * time.Minute)
+	assert.False(t, r.shouldRunIdleCleanup())
+
+	now = now.Add(31 * time.Minute)
+	assert.True(t, r.shouldRunIdleCleanup())
+}
+
+func TestRunnerShouldRunIdleCleanupSkipsWhenJobRunning(t *testing.T) {
+	r := &Runner{
+		cfg: &config.Config{
+			Container: config.Container{
+				BindWorkdir: true,
+			},
+			Runner: config.Runner{
+				WorkdirCleanupAge:   24 * time.Hour,
+				IdleCleanupInterval: time.Minute,
+			},
+		},
+		now: time.Now,
+	}
+	r.runningCount.Store(1)
+
+	assert.False(t, r.shouldRunIdleCleanup())
+}
+
+func TestRunnerShouldRunIdleCleanupSkipsWhenBindWorkdirDisabled(t *testing.T) {
+	r := &Runner{
+		cfg: &config.Config{
+			Runner: config.Runner{
+				WorkdirCleanupAge:   24 * time.Hour,
+				IdleCleanupInterval: time.Minute,
+			},
+		},
+		now: time.Now,
+	}
+
+	assert.False(t, r.shouldRunIdleCleanup())
+}
+
+func TestRunnerShouldRunIdleCleanupSkipsWhenDisabled(t *testing.T) {
+	now := time.Date(2026, time.April, 29, 20, 0, 0, 0, time.UTC)
+
+	t.Run("cleanup age disabled", func(t *testing.T) {
+		r := &Runner{
+			cfg: &config.Config{
+				Container: config.Container{
+					BindWorkdir: true,
+				},
+				Runner: config.Runner{
+					WorkdirCleanupAge:   -1,
+					IdleCleanupInterval: time.Minute,
+				},
+			},
+			now: func() time.Time { return now },
+		}
+
+		assert.False(t, r.shouldRunIdleCleanup())
+	})
+
+	t.Run("idle interval disabled", func(t *testing.T) {
+		r := &Runner{
+			cfg: &config.Config{
+				Container: config.Container{
+					BindWorkdir: true,
+				},
+				Runner: config.Runner{
+					WorkdirCleanupAge:   24 * time.Hour,
+					IdleCleanupInterval: -1,
+				},
+			},
+			now: func() time.Time { return now },
+		}
+
+		assert.False(t, r.shouldRunIdleCleanup())
+	})
+}
+
+// TestRunnerOnIdleIntegratesCleanup wires the full OnIdle entry point and
+// confirms it walks workdir_parent (after the leading-slash trim that
+// matches the production path construction) and removes stale numeric dirs.
+func TestRunnerOnIdleIntegratesCleanup(t *testing.T) {
+	now := time.Date(2026, time.April, 29, 20, 0, 0, 0, time.UTC)
+	root := t.TempDir()
+	stale := filepath.Join(root, "1234")
+	require.NoError(t, os.MkdirAll(stale, 0o700))
+	require.NoError(t, os.Chtimes(stale, now.Add(-48*time.Hour), now.Add(-48*time.Hour)))
+
+	r := &Runner{
+		cfg: &config.Config{
+			Container: config.Container{
+				BindWorkdir:   true,
+				WorkdirParent: root, // leading slash absent, OnIdle reattaches it
+			},
+			Runner: config.Runner{
+				WorkdirCleanupAge:   24 * time.Hour,
+				IdleCleanupInterval: time.Minute,
+			},
+		},
+		now: func() time.Time { return now },
+	}
+
+	r.OnIdle(context.Background())
+
+	assert.NoDirExists(t, stale)
+}
+
+// TestRunnerOnIdleSkipsWhenAlreadyCancelled verifies a pre-cancelled ctx
+// short-circuits cleanup before any directory entry is touched.
+func TestRunnerOnIdleSkipsWhenAlreadyCancelled(t *testing.T) {
+	now := time.Date(2026, time.April, 29, 20, 0, 0, 0, time.UTC)
+	root := t.TempDir()
+	stale := filepath.Join(root, "1234")
+	require.NoError(t, os.MkdirAll(stale, 0o700))
+	require.NoError(t, os.Chtimes(stale, now.Add(-48*time.Hour), now.Add(-48*time.Hour)))
+
+	r := &Runner{
+		cfg: &config.Config{
+			Container: config.Container{
+				BindWorkdir:   true,
+				WorkdirParent: root,
+			},
+			Runner: config.Runner{
+				WorkdirCleanupAge:   24 * time.Hour,
+				IdleCleanupInterval: time.Minute,
+			},
+		},
+		now: func() time.Time { return now },
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	r.OnIdle(ctx)
+
+	assert.DirExists(t, stale)
+}
diff --git a/internal/pkg/config/config.example.yaml b/internal/pkg/config/config.example.yaml
index d1551d5b..eded51c3 100644
--- a/internal/pkg/config/config.example.yaml
+++ b/internal/pkg/config/config.example.yaml
@@ -40,6 +40,12 @@ runner:
   # The runner uses exponential backoff when idle, increasing the interval up to this maximum.
   # Set to 0 or same as fetch_interval to disable backoff.
   fetch_interval_max: 5s
+  # While idle, remove stale bind-workdir task directories older than this duration.
+  # Setting either workdir_cleanup_age or idle_cleanup_interval to 0 (or any
+  # non-positive value) disables workdir cleanup entirely.
+  workdir_cleanup_age: 24h
+  # Cadence for the idle stale bind-workdir cleanup pass.
+  idle_cleanup_interval: 10m
   # The base interval for periodic log flush to the Gitea instance.
   # Logs may be sent earlier if the buffer reaches log_report_batch_size
   # or if log_report_max_latency expires after the first buffered row.
@@ -107,6 +113,7 @@ container:
   # If the path starts with '/', the '/' will be trimmed.
   # For example, if the parent directory is /path/to/my/dir, workdir_parent should be path/to/my/dir
   # If it's empty, /workspace will be used.
+  # Purely numeric subdirectories under this path are reserved for task workspaces and may be removed by idle cleanup.
   workdir_parent:
   # Volumes (including bind mounts) can be mounted to containers. Glob syntax is supported, see https://github.com/gobwas/glob
   # You can specify multiple volumes. If the sequence is empty, no volumes can be mounted.
diff --git a/internal/pkg/config/config.go b/internal/pkg/config/config.go
index 48aa9dab..a257a9dd 100644
--- a/internal/pkg/config/config.go
+++ b/internal/pkg/config/config.go
@@ -33,6 +33,8 @@ type Runner struct {
 	FetchTimeout        time.Duration     `yaml:"fetch_timeout"`          // FetchTimeout specifies the timeout duration for fetching resources.
 	FetchInterval       time.Duration     `yaml:"fetch_interval"`         // FetchInterval specifies the interval duration for fetching resources.
 	FetchIntervalMax    time.Duration     `yaml:"fetch_interval_max"`     // FetchIntervalMax specifies the maximum backoff interval when idle.
+	WorkdirCleanupAge   time.Duration     `yaml:"workdir_cleanup_age"`    // WorkdirCleanupAge removes stale bind-workdir task directories older than this duration during idle cleanup.
+	IdleCleanupInterval time.Duration     `yaml:"idle_cleanup_interval"`  // IdleCleanupInterval runs stale bind-workdir cleanup periodically while the runner is idle. Set to 0 to disable cleanup cadence.
 	LogReportInterval   time.Duration     `yaml:"log_report_interval"`    // LogReportInterval specifies the base interval for periodic log flush.
 	LogReportMaxLatency time.Duration     `yaml:"log_report_max_latency"` // LogReportMaxLatency specifies the max time a log row can wait before being sent.
 	LogReportBatchSize  int               `yaml:"log_report_batch_size"`  // LogReportBatchSize triggers immediate log flush when buffer reaches this size.
@@ -92,6 +94,7 @@ type Config struct {
 // If file is not empty, it will be used to load the configuration.
 func LoadDefault(file string) (*Config, error) {
 	cfg := &Config{}
+	definedRunnerKeys := map[string]bool{}
 	if file != "" {
 		content, err := os.ReadFile(file)
 		if err != nil {
@@ -100,6 +103,10 @@ func LoadDefault(file string) (*Config, error) {
 		if err := yaml.Unmarshal(content, cfg); err != nil {
 			return nil, fmt.Errorf("parse config file %q: %w", file, err)
 		}
+		definedRunnerKeys, err = definedRunnerConfigKeys(content)
+		if err != nil {
+			return nil, fmt.Errorf("parse config file %q for defaults metadata: %w", file, err)
+		}
 	}
 	compatibleWithOldEnvs(file != "", cfg)
 
@@ -157,6 +164,12 @@ func LoadDefault(file string) (*Config, error) {
 	if cfg.Runner.FetchIntervalMax <= 0 {
 		cfg.Runner.FetchIntervalMax = 5 * time.Second
 	}
+	if cfg.Runner.WorkdirCleanupAge == 0 && !definedRunnerKeys["workdir_cleanup_age"] {
+		cfg.Runner.WorkdirCleanupAge = 24 * time.Hour
+	}
+	if cfg.Runner.IdleCleanupInterval == 0 && !definedRunnerKeys["idle_cleanup_interval"] {
+		cfg.Runner.IdleCleanupInterval = 10 * time.Minute
+	}
 	if cfg.Runner.LogReportInterval <= 0 {
 		cfg.Runner.LogReportInterval = 5 * time.Second
 	}
@@ -199,3 +212,30 @@ func LoadDefault(file string) (*Config, error) {
 
 	return cfg, nil
 }
+
+func definedRunnerConfigKeys(content []byte) (map[string]bool, error) {
+	var root yaml.Node
+	if err := yaml.Unmarshal(content, &root); err != nil {
+		return nil, err
+	}
+
+	defined := map[string]bool{}
+	if len(root.Content) == 0 {
+		return defined, nil
+	}
+
+	doc := root.Content[0]
+	for i := 0; i+1 < len(doc.Content); i += 2 {
+		key := doc.Content[i]
+		value := doc.Content[i+1]
+		if key.Value != "runner" || value.Kind != yaml.MappingNode {
+			continue
+		}
+		for j := 0; j+1 < len(value.Content); j += 2 {
+			defined[value.Content[j].Value] = true
+		}
+		break
+	}
+
+	return defined, nil
+}
diff --git a/internal/pkg/config/config_test.go b/internal/pkg/config/config_test.go
index da0e414b..4986ee94 100644
--- a/internal/pkg/config/config_test.go
+++ b/internal/pkg/config/config_test.go
@@ -7,6 +7,7 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -39,3 +40,80 @@ cache:
 	_, err := LoadDefault(path)
 	require.NoError(t, err)
 }
+
+func TestLoadDefault_DefaultsWorkdirCleanupAge(t *testing.T) {
+	cfg, err := LoadDefault("")
+	require.NoError(t, err)
+	assert.Equal(t, 24*time.Hour, cfg.Runner.WorkdirCleanupAge)
+	assert.Equal(t, 10*time.Minute, cfg.Runner.IdleCleanupInterval)
+}
+
+func TestLoadDefault_UsesConfiguredWorkdirCleanupAge(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.yaml")
+	require.NoError(t, os.WriteFile(path, []byte(`
+runner:
+  workdir_cleanup_age: 2h30m
+`), 0o600))
+
+	cfg, err := LoadDefault(path)
+	require.NoError(t, err)
+	assert.Equal(t, 150*time.Minute, cfg.Runner.WorkdirCleanupAge)
+}
+
+func TestLoadDefault_UsesConfiguredIdleCleanupInterval(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.yaml")
+	require.NoError(t, os.WriteFile(path, []byte(`
+runner:
+  idle_cleanup_interval: 45m
+`), 0o600))
+
+	cfg, err := LoadDefault(path)
+	require.NoError(t, err)
+	assert.Equal(t, 45*time.Minute, cfg.Runner.IdleCleanupInterval)
+}
+
+func TestLoadDefault_AllowsDisablingWorkdirCleanup(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.yaml")
+	require.NoError(t, os.WriteFile(path, []byte(`
+runner:
+  workdir_cleanup_age: 0s
+  idle_cleanup_interval: 0s
+`), 0o600))
+
+	cfg, err := LoadDefault(path)
+	require.NoError(t, err)
+	assert.Equal(t, time.Duration(0), cfg.Runner.WorkdirCleanupAge)
+	assert.Equal(t, time.Duration(0), cfg.Runner.IdleCleanupInterval)
+}
+
+func TestLoadDefault_AllowsNegativeWorkdirCleanupValues(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.yaml")
+	require.NoError(t, os.WriteFile(path, []byte(`
+runner:
+  workdir_cleanup_age: -1s
+  idle_cleanup_interval: -1s
+`), 0o600))
+
+	cfg, err := LoadDefault(path)
+	require.NoError(t, err)
+	assert.Equal(t, -1*time.Second, cfg.Runner.WorkdirCleanupAge)
+	assert.Equal(t, -1*time.Second, cfg.Runner.IdleCleanupInterval)
+}
+
+// TestLoadDefault_MalformedYAMLReturnsParseError pins the error surfaced for
+// invalid YAML to the canonical "parse config file" message rather than the
+// "for defaults metadata" variant — i.e. the main yaml.Unmarshal runs first.
+func TestLoadDefault_MalformedYAMLReturnsParseError(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "config.yaml")
+	require.NoError(t, os.WriteFile(path, []byte("runner:\n  capacity: [unterminated\n"), 0o600))
+
+	_, err := LoadDefault(path)
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "parse config file")
+	assert.NotContains(t, err.Error(), "defaults metadata")
+}