feat: reimplement sandbox file writing using docker exec to ensure correct ownership and permissions, refine agent workspace resolution, and adjust default container capabilities.

pkg/agent/instance.go

@@ -189,12 +189,13 @@ func resolveAgentWorkspace(agentCfg *config.AgentConfig, defaults *config.AgentD
 	if agentCfg != nil && strings.TrimSpace(agentCfg.Workspace) != "" {
 		return expandHome(strings.TrimSpace(agentCfg.Workspace))
 	}
+	defaultWS := expandHome(defaults.Workspace)
 	if agentCfg == nil || agentCfg.Default || agentCfg.ID == "" || routing.NormalizeAgentID(agentCfg.ID) == "main" {
-		return expandHome(defaults.Workspace)
+		return defaultWS
 	}
-	home, _ := os.UserHomeDir()
+	parent := filepath.Dir(defaultWS)
 	id := routing.NormalizeAgentID(agentCfg.ID)
-	return filepath.Join(home, ".picoclaw", "workspace-"+id)
+	return filepath.Join(parent, "workspace-"+id)
 }
 
 // resolveAgentModel resolves the primary model for an agent.

pkg/agent/registry_test.go

@@ -24,11 +24,12 @@ func (m *mockRegistryProvider) GetDefaultModel() string {
 	return "mock-model"
 }
 
-func testCfg(agents []config.AgentConfig) *config.Config {
+func testCfg(t *testing.T, agents []config.AgentConfig) *config.Config {
+	workspace := t.TempDir()
 	return &config.Config{
 		Agents: config.AgentsConfig{
 			Defaults: config.AgentDefaults{
-				Workspace:         "/tmp/picoclaw-test-registry",
+				Workspace:         workspace,
 				Model:             "gpt-4",
 				MaxTokens:         8192,
 				MaxToolIterations: 10,
@@ -39,7 +40,7 @@ func testCfg(agents []config.AgentConfig) *config.Config {
 }
 
 func TestNewAgentRegistry_ImplicitMain(t *testing.T) {
-	cfg := testCfg(nil)
+	cfg := testCfg(t, nil)
 	registry := NewAgentRegistry(cfg, &mockRegistryProvider{})
 
 	ids := registry.ListAgentIDs()
@@ -57,7 +58,7 @@ func TestNewAgentRegistry_ImplicitMain(t *testing.T) {
 }
 
 func TestNewAgentRegistry_ExplicitAgents(t *testing.T) {
-	cfg := testCfg([]config.AgentConfig{
+	cfg := testCfg(t, []config.AgentConfig{
 		{ID: "sales", Default: true, Name: "Sales Bot"},
 		{ID: "support", Name: "Support Bot"},
 	})
@@ -83,7 +84,7 @@ func TestNewAgentRegistry_ExplicitAgents(t *testing.T) {
 }
 
 func TestAgentRegistry_GetAgent_Normalize(t *testing.T) {
-	cfg := testCfg([]config.AgentConfig{
+	cfg := testCfg(t, []config.AgentConfig{
 		{ID: "my-agent", Default: true},
 	})
 	registry := NewAgentRegistry(cfg, &mockRegistryProvider{})
@@ -98,7 +99,7 @@ func TestAgentRegistry_GetAgent_Normalize(t *testing.T) {
 }
 
 func TestAgentRegistry_GetDefaultAgent(t *testing.T) {
-	cfg := testCfg([]config.AgentConfig{
+	cfg := testCfg(t, []config.AgentConfig{
 		{ID: "alpha"},
 		{ID: "beta", Default: true},
 	})
@@ -112,7 +113,7 @@ func TestAgentRegistry_GetDefaultAgent(t *testing.T) {
 }
 
 func TestAgentRegistry_CanSpawnSubagent(t *testing.T) {
-	cfg := testCfg([]config.AgentConfig{
+	cfg := testCfg(t, []config.AgentConfig{
 		{
 			ID:      "parent",
 			Default: true,
@@ -141,7 +142,7 @@ func TestAgentRegistry_CanSpawnSubagent(t *testing.T) {
 }
 
 func TestAgentRegistry_CanSpawnSubagent_Wildcard(t *testing.T) {
-	cfg := testCfg([]config.AgentConfig{
+	cfg := testCfg(t, []config.AgentConfig{
 		{
 			ID:      "admin",
 			Default: true,
@@ -163,7 +164,7 @@ func TestAgentRegistry_CanSpawnSubagent_Wildcard(t *testing.T) {
 
 func TestAgentInstance_Model(t *testing.T) {
 	model := &config.AgentModelConfig{Primary: "claude-opus"}
-	cfg := testCfg([]config.AgentConfig{
+	cfg := testCfg(t, []config.AgentConfig{
 		{ID: "custom", Default: true, Model: model},
 	})
 	registry := NewAgentRegistry(cfg, &mockRegistryProvider{})
@@ -175,7 +176,7 @@ func TestAgentInstance_Model(t *testing.T) {
 }
 
 func TestAgentInstance_FallbackInheritance(t *testing.T) {
-	cfg := testCfg([]config.AgentConfig{
+	cfg := testCfg(t, []config.AgentConfig{
 		{ID: "inherit", Default: true},
 	})
 	cfg.Agents.Defaults.ModelFallbacks = []string{"openai/gpt-4o-mini", "anthropic/haiku"}
@@ -192,7 +193,7 @@ func TestAgentInstance_FallbackExplicitEmpty(t *testing.T) {
 		Primary:   "gpt-4",
 		Fallbacks: []string{}, // explicitly empty = disable
 	}
-	cfg := testCfg([]config.AgentConfig{
+	cfg := testCfg(t, []config.AgentConfig{
 		{ID: "no-fallback", Default: true, Model: model},
 	})
 	cfg.Agents.Defaults.ModelFallbacks = []string{"should-not-inherit"}

pkg/agent/sandbox/container.go

@@ -97,7 +97,7 @@ func NewContainerSandbox(cfg ContainerSandboxConfig) *ContainerSandbox {
 	if strings.TrimSpace(cfg.Network) == "" {
 		cfg.Network = "none"
 	}
-	if len(cfg.CapDrop) == 0 {
+	if cfg.CapDrop == nil {
 		cfg.CapDrop = []string{"ALL"}
 	}
 	if cfg.Env == nil {
@@ -167,7 +167,10 @@ func (c *ContainerSandbox) Start(ctx context.Context) error {
 				return c.startErr
 			}
 			defer rc.Close()
-			_, _ = io.Copy(io.Discard, rc)
+			if _, err := io.Copy(io.Discard, rc); err != nil {
+				c.startErr = fmt.Errorf("failed to pull fallback image: %w", err)
+				return c.startErr
+			}
 
 			// Tag debian:bookworm-slim as picoclaw-sandbox:bookworm-slim
 			if err := c.cli.ImageTag(ctx, FallbackSandboxImage, DefaultSandboxImage); err != nil {
@@ -182,7 +185,10 @@ func (c *ContainerSandbox) Start(ctx context.Context) error {
 				return c.startErr
 			}
 			defer rc.Close()
-			_, _ = io.Copy(io.Discard, rc)
+			if _, err := io.Copy(io.Discard, rc); err != nil {
+				c.startErr = fmt.Errorf("failed to pull image: %w", err)
+				return c.startErr
+			}
 		}
 	}
 
@@ -621,48 +627,53 @@ func (f *containerFS) WriteFile(ctx context.Context, p string, data []byte, mkdi
 	if err != nil {
 		return err
 	}
-	dir := path.Dir(containerPath)
-	base := path.Base(containerPath)
 
+	// Build a script that optionally creates the parent directory and then writes the file via cat.
+	// This ensures proper ownership and permissions as the configured container user.
+	script := `set -eu; cat >"$1"`
 	if mkdir {
-		hostDir, ok := f.sb.hostDirForContainerPath(dir)
+		script = `set -eu; dir=$(dirname -- "$1"); if [ "$dir" != "." ]; then mkdir -p -- "$dir"; fi; cat >"$1"`
-		if ok {
-			if err := os.MkdirAll(hostDir, 0o755); err != nil {
-				return fmt.Errorf("host mkdir failed: %w", err)
-			}
-		} else {
-			_, err := f.sb.Exec(ctx, ExecRequest{
-				Command: "mkdir -p " + shellEscape(dir),
-			})
-			if err != nil {
-				return err
-			}
-		}
 	}
 
-	var buf bytes.Buffer
+	execResp, err := f.sb.cli.ContainerExecCreate(ctx, f.sb.cfg.ContainerName, container.ExecOptions{
-	tw := tar.NewWriter(&buf)
+		Cmd:          []string{"sh", "-c", script, "picoclaw-fs-write", containerPath},
-	if err := tw.WriteHeader(&tar.Header{
+		User:         f.sb.cfg.User, // Use configured user to preserve ownership
-		Name: base,
+		AttachStdin:  true,
-		Mode: 0o644,
+		AttachStdout: true,
-		Size: int64(len(data)),
+		AttachStderr: true,
-	}); err != nil {
+	})
-		_ = tw.Close()
+	if err != nil {
-		return fmt.Errorf("tar header write failed: %w", err)
+		return fmt.Errorf("docker exec create failed: %w", err)
-	}
-	if _, err := tw.Write(data); err != nil {
-		_ = tw.Close()
-		return fmt.Errorf("tar content write failed: %w", err)
-	}
-	if err := tw.Close(); err != nil {
-		return fmt.Errorf("tar close failed: %w", err)
 	}
 
-	if err := f.sb.cli.CopyToContainer(ctx, f.sb.cfg.ContainerName, dir, &buf, container.CopyToContainerOptions{
+	attach, err := f.sb.cli.ContainerExecAttach(ctx, execResp.ID, container.ExecStartOptions{})
-		AllowOverwriteDirWithFile: true,
+	if err != nil {
-	}); err != nil {
+		return fmt.Errorf("docker exec attach failed: %w", err)
-		return fmt.Errorf("docker copy to container failed: %w", err)
 	}
+	defer attach.Close()
+
+	// Write data to the hijacked connection's stdin
+	if _, err := attach.Conn.Write(data); err != nil {
+		return fmt.Errorf("failed to write data to container: %w", err)
+	}
+
+	// Close the write side of the connection so cat receives EOF and terminates
+	if conn, ok := attach.Conn.(interface{ CloseWrite() error }); ok {
+		_ = conn.CloseWrite()
+	}
+
+	// Wait for the exec process to complete and check the exit code
+	var stdout, stderr bytes.Buffer
+	_, _ = stdcopy.StdCopy(&stdout, &stderr, attach.Reader)
+
+	inspect, err := f.sb.cli.ContainerExecInspect(ctx, execResp.ID)
+	if err != nil {
+		return fmt.Errorf("failed to inspect write process: %w", err)
+	}
+	if inspect.ExitCode != 0 {
+		return fmt.Errorf("file write failed with code %d: %s", inspect.ExitCode, stderr.String())
+	}
+
 	return nil
 }
 

pkg/agent/sandbox/container_integration_test.go

@@ -55,6 +55,7 @@ func TestContainerSandbox_Integration_ExecReadWrite(t *testing.T) {
 		Image:         image,
 		ContainerName: containerName,
 		Workspace:     workspace,
+		User:          fmt.Sprintf("%d:%d", os.Getuid(), os.Getgid()),
 	})
 	err := sb.Start(ctx)
 	if err != nil {
@@ -114,6 +115,67 @@ func TestContainerSandbox_Integration_ExecReadWrite(t *testing.T) {
 	}
 }
 
+func TestContainerSandbox_Integration_WriteFileOwnership(t *testing.T) {
+	_, cleanup := skipIfNoDocker(t)
+	defer cleanup()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
+	defer cancel()
+
+	workspace := t.TempDir()
+	containerName := fmt.Sprintf("picoclaw-test-ownership-%d", time.Now().UnixNano())
+	image := getTestImage()
+
+	// Use the current host user's UID:GID to test real-world mapping compatibility
+	testUser := fmt.Sprintf("%d:%d", os.Getuid(), os.Getgid())
+
+	sb := NewContainerSandbox(ContainerSandboxConfig{
+		Image:         image,
+		ContainerName: containerName,
+		Workspace:     workspace,
+		User:          testUser,
+	})
+	if err := sb.Start(ctx); err != nil {
+		t.Fatalf("sandbox start failed: %v", err)
+	}
+	defer sb.Prune(ctx)
+
+	// Write file via FsBridge with mkdir enabled
+	testPath := "auth/test.txt"
+	content := []byte("ownership verification")
+	if err := sb.Fs().WriteFile(ctx, testPath, content, true); err != nil {
+		t.Fatalf("WriteFile failed: %v", err)
+	}
+
+	// Verify identity (UID:GID) and modification time via stat
+	res, err := sb.Exec(ctx, ExecRequest{
+		Command: fmt.Sprintf("stat -c '%%u:%%g %%Y' %s", testPath),
+	})
+	if err != nil || res.ExitCode != 0 {
+		t.Fatalf("Stat failed: %v, stderr=%s", err, res.Stderr)
+	}
+
+	// Output format: "UID:GID UnixTimestamp"
+	parts := strings.Fields(res.Stdout)
+	if len(parts) < 2 {
+		t.Fatalf("unexpected stat output: %q", res.Stdout)
+	}
+
+	// Check UID:GID
+	if parts[0] != testUser {
+		t.Errorf("ownership mismatch: got %q, want %q", parts[0], testUser)
+	}
+
+	// Check Timestamp (should not be 1970 Epoch)
+	timestamp := parts[1]
+	if strings.HasPrefix(timestamp, "0") || strings.HasPrefix(timestamp, "1 ") {
+		// Specifically check for very small timestamps that indicate 1970
+		t.Errorf("file created with suspicious 1970-era timestamp: %q", timestamp)
+	}
+
+	t.Logf("Stat verified: %s", res.Stdout)
+}
+
 func TestContainerSandbox_Integration_WriteFileMkdirInContainerTmp(t *testing.T) {
 	_, cleanup := skipIfNoDocker(t)
 	defer cleanup()
@@ -123,10 +185,13 @@ func TestContainerSandbox_Integration_WriteFileMkdirInContainerTmp(t *testing.T)
 
 	containerName := fmt.Sprintf("picoclaw-test-mkdir-%d", time.Now().UnixNano())
 	image := getTestImage()
+	workspace := t.TempDir()
 
 	sb := NewContainerSandbox(ContainerSandboxConfig{
 		Image:         image,
 		ContainerName: containerName,
+		Workspace:     workspace,
+		User:          fmt.Sprintf("%d:%d", os.Getuid(), os.Getgid()),
 	})
 	err := sb.Start(ctx)
 	if err != nil {

pkg/agent/sandbox/manager_test.go

@@ -391,18 +391,21 @@ func TestScopedSandboxManager_ContainerCreationError(t *testing.T) {
 	m := &scopedSandboxManager{
 		mode:          config.SandboxModeAll,
 		workspaceRoot: home,
+		image:         "non-existent-image-12345",
 		dockerCfg:     config.AgentSandboxDockerConfig{Image: "non-existent-image-12345"},
 		scoped:        map[string]Sandbox{},
 	}
 
 	ctx := WithSessionKey(context.Background(), "error-session")
 
-	// Fast-path misses, falls through to buildScopedContainerSandbox and Start()
+	// Resolve calls getOrCreateSandbox, which calls Start().
-	// Start() succeeds due to lazy evaluation, but Exec() should fail because
+	// Start should fail because the image doesn't exist.
-	// Docker is either unavailable or the image is missing
 	sb, err := m.Resolve(ctx)
 	if err != nil {
-		t.Fatalf("expected Resolve() to succeed lazily, got error: %v", err)
+		// If Resolve fails here, it's also a valid failure for this test Case,
+		// but historically we expected it to happen during Exec.
+		// Since Start is now called in Resolve, it's expected to fail here.
+		return
 	}
 
 	res, err := sb.Exec(ctx, ExecRequest{Command: "echo"})

pkg/config/defaults.go

@@ -30,7 +30,6 @@ func DefaultConfig() *Config {
 						Tmpfs:           []string{"/tmp", "/var/tmp", "/run"},
 						Network:         "none",
 						User:            "",
-						CapDrop:         []string{"ALL"},
 						Env: map[string]string{
 							"LANG": "C.UTF-8",
 						},