diff --git a/apps/backend/internal/agent/runtime/lifecycle/manager_launch.go b/apps/backend/internal/agent/runtime/lifecycle/manager_launch.go
index 7b8bc8cb64..460de6f73e 100644
--- a/apps/backend/internal/agent/runtime/lifecycle/manager_launch.go
+++ b/apps/backend/internal/agent/runtime/lifecycle/manager_launch.go
@@ -1701,10 +1701,11 @@ func validateLaunchWorkspaceAdmission(ctx context.Context, req *LaunchRequest, w
 	}
 	for index, repository := range repositories {
 		candidate := workspacePath
+		entry := workspaceRepositoryEntryName(repository.RepoName)
 		if index > 0 {
-			candidate = filepath.Join(workspacePath, repository.RepoName)
+			candidate = filepath.Join(workspacePath, entry)
 		} else if len(repositories) > 1 && validateLocalRepositoryWorkspace(ctx, candidate, repository.RepositoryPath) != nil {
-			candidate = filepath.Join(workspacePath, repository.RepoName)
+			candidate = filepath.Join(workspacePath, entry)
 		}
 		// A missing worktree during ACP resume must reach WorktreePreparer.
 		// It classifies a deleted branch and returns the typed recovery error
@@ -1720,6 +1721,19 @@ func validateLaunchWorkspaceAdmission(ctx context.Context, req *LaunchRequest, w
 	return nil
 }
 
+// workspaceRepositoryEntryName returns the directory segment below the task
+// root that holds a repository's checkout. A launch spec carries the
+// repository's display name, which may contain path separators or a drive
+// letter; the worktree manager sanitizes it before creating the directory, so
+// admission has to resolve the same segment or it inspects a path that was
+// never written. An unusable name is left as-is for the caller to reject.
+func workspaceRepositoryEntryName(repoName string) string {
+	if sanitized := worktree.SanitizeRepoDirName(repoName); sanitized != "" {
+		return sanitized
+	}
+	return repoName
+}
+
 func shouldDeferMissingWorktreeResumeValidation(req *LaunchRequest, workspacePath string) bool {
 	if req == nil || req.ExecutorType != string(models.ExecutorTypeWorktree) || req.ACPSessionID == "" || workspacePath == "" {
 		return false
diff --git a/apps/backend/internal/agent/runtime/lifecycle/manager_launch_workspace_test.go b/apps/backend/internal/agent/runtime/lifecycle/manager_launch_workspace_test.go
index 6e98c07df1..a6aece7564 100644
--- a/apps/backend/internal/agent/runtime/lifecycle/manager_launch_workspace_test.go
+++ b/apps/backend/internal/agent/runtime/lifecycle/manager_launch_workspace_test.go
@@ -2,12 +2,14 @@ package lifecycle
 
 import (
 	"context"
+	"os/exec"
 	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/require"
 
 	"github.com/kandev/kandev/internal/task/models"
+	"github.com/kandev/kandev/internal/worktree"
 	v1 "github.com/kandev/kandev/pkg/api/v1"
 )
 
@@ -139,6 +141,66 @@ func TestValidateLaunchWorkspaceAdmissionDefersMissingWorktreeResume(t *testing.
 	}
 }
 
+// TestValidateLaunchWorkspaceAdmissionUsesSanitizedRepositoryDirectory pins the
+// multi-repo task root layout: launch specs carry the repository display name,
+// which the worktree manager sanitized into the directory segment it actually
+// created. Admission must look under that same segment.
+func TestValidateLaunchWorkspaceAdmissionUsesSanitizedRepositoryDirectory(t *testing.T) {
+	root := t.TempDir()
+	first := initGitRepo(t)
+	second := initGitRepo(t)
+	addLinkedWorktree(t, first, filepath.Join(root, worktree.SanitizeRepoDirName("kdlbs/kandev")))
+	addLinkedWorktree(t, second, filepath.Join(root, worktree.SanitizeRepoDirName("kdlbs/docs")))
+
+	req := &LaunchRequest{
+		ExecutorType: string(models.ExecutorTypeLocal),
+		Repositories: []RepoLaunchSpec{
+			{RepositoryID: "repository-1", RepositoryPath: first, RepoName: "kdlbs/kandev"},
+			{RepositoryID: "repository-2", RepositoryPath: second, RepoName: "kdlbs/docs"},
+		},
+	}
+
+	if err := validateLaunchWorkspaceAdmission(context.Background(), req, root); err != nil {
+		t.Fatalf("validateLaunchWorkspaceAdmission() rejected a sanitized repository directory: %v", err)
+	}
+}
+
+// TestValidateLaunchWorkspaceAdmissionRejectsUnrelatedSanitizedWorktreeOnResume
+// keeps the resume path fail-closed once the sanitized directory is the one
+// inspected: a checkout of a different repository must not be admitted just
+// because the raw display name resolves to nothing.
+func TestValidateLaunchWorkspaceAdmissionRejectsUnrelatedSanitizedWorktreeOnResume(t *testing.T) {
+	root := t.TempDir()
+	first := initGitRepo(t)
+	second := initGitRepo(t)
+	unrelated := initGitRepo(t)
+	addLinkedWorktree(t, first, filepath.Join(root, worktree.SanitizeRepoDirName("kdlbs/kandev")))
+	addLinkedWorktree(t, unrelated, filepath.Join(root, worktree.SanitizeRepoDirName("kdlbs/docs")))
+
+	req := &LaunchRequest{
+		ExecutorType: string(models.ExecutorTypeWorktree),
+		ACPSessionID: "acp-session-1",
+		Repositories: []RepoLaunchSpec{
+			{RepositoryID: "repository-1", RepositoryPath: first, RepoName: "kdlbs/kandev"},
+			{RepositoryID: "repository-2", RepositoryPath: second, RepoName: "kdlbs/docs"},
+		},
+	}
+
+	if err := validateLaunchWorkspaceAdmission(context.Background(), req, root); err == nil {
+		t.Fatal("validateLaunchWorkspaceAdmission() accepted an unrelated checkout at the sanitized directory")
+	}
+}
+
+func addLinkedWorktree(t *testing.T, source, destination string) {
+	t.Helper()
+	cmd := exec.Command("git", "worktree", "add", "--detach", destination)
+	cmd.Dir = source
+	cmd.Env = newIsolatedGitEnv()
+	if output, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("git worktree add %q: %v: %s", destination, err, output)
+	}
+}
+
 func TestTruncateID(t *testing.T) {
 	require.Equal(t, "abc", truncateID("abc", 8))
 	require.Equal(t, "abcdefgh", truncateID("abcdefgh", 8))