fix(tests): path validation before docker check + a2a queue mock in tests

- container_files.go: move validateRelPath before h.docker==nil check in
  deleteViaEphemeral so F1085 traversal tests fire even when Docker is
  absent in CI (fixes TestDeleteViaEphemeral_F1085_RejectsTraversal)

- a2a_proxy_test.go: add EnqueueA2A mock expectation in
  TestHandleA2ADispatchError_ContextDeadline — DeadlineExceeded now
  triggers the #1870 queue path; mock the INSERT to return an error so
  the test correctly falls through to the expected 503 Retry-After shape

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

workspace-server/internal/handlers/a2a_proxy_test.go

@@ -1158,13 +1158,18 @@ func TestDispatchA2A_ContextDeadline_NoCancelAdded(t *testing.T) {
 // --- handleA2ADispatchError ---
 
 func TestHandleA2ADispatchError_ContextDeadline(t *testing.T) {
-	setupTestDB(t)
+	mock := setupTestDB(t)
 	setupTestRedis(t)
 	handler := NewWorkspaceHandler(newTestBroadcaster(), nil, "http://localhost:8080", t.TempDir())
 
-	// No workspace row expected — maybeMarkContainerDead with nil
-	// provisioner short-circuits, and activity-log insert is suppressed
-	// (logActivity=false).
+	// maybeMarkContainerDead with nil provisioner short-circuits (no DB call).
+	// activity-log insert is suppressed (logActivity=false).
+	// DeadlineExceeded → isUpstreamBusyError=true → EnqueueA2A attempted.
+	// Mock the INSERT INTO a2a_queue to fail so we fall through to 503.
+	mock.ExpectQuery(`INSERT INTO a2a_queue`).
+		WithArgs("ws-dl", nil, PriorityTask, "{}", "message/send", nil).
+		WillReturnError(fmt.Errorf("test: queue unavailable"))
+
 	_, _, perr := handler.handleA2ADispatchError(
 		context.Background(), "ws-dl", "", []byte("{}"), "message/send",
 		context.DeadlineExceeded, 1, false,
@@ -1172,7 +1177,7 @@ func TestHandleA2ADispatchError_ContextDeadline(t *testing.T) {
 	if perr == nil {
 		t.Fatal("expected error, got nil")
 	}
-	// DeadlineExceeded is classified as upstream-busy → 503 with Retry-After.
+	// EnqueueA2A failed → falls through to legacy 503 with Retry-After.
 	if perr.Status != http.StatusServiceUnavailable {
 		t.Errorf("got status %d, want 503", perr.Status)
 	}

workspace-server/internal/handlers/container_files.go

@@ -159,9 +159,6 @@ func (h *TemplatesHandler) writeViaEphemeral(ctx context.Context, volumeName str
 
 // deleteViaEphemeral deletes a file from a named volume using an ephemeral container.
 func (h *TemplatesHandler) deleteViaEphemeral(ctx context.Context, volumeName, filePath string) error {
-	if h.docker == nil {
-		return fmt.Errorf("docker not available")
-	}
 	// CWE-78/CWE-22: exec form binds rm to the /configs volume regardless
 	// of path traversal in filePath. The bind mount volumeName:/configs
 	// constrains rm; exec form prevents shell interpolation.
@@ -169,9 +166,17 @@ func (h *TemplatesHandler) deleteViaEphemeral(ctx context.Context, volumeName, f
 	// The concat form is the critical fix: rm receives ONE path argument
 	// so ".." is processed literally — rm -rf /configs/foo/../bar resolves
 	// to /configs/bar (inside volume), not bar (outside volume).
+	//
+	// Path validation MUST come before the docker-available check so that
+	// traversal inputs are rejected even in test/CI environments where
+	// Docker is absent. This ensures F1085 regression tests catch real
+	// violations rather than short-circuiting on "docker not available".
 	if err := validateRelPath(filePath); err != nil {
 		return err
 	}
+	if h.docker == nil {
+		return fmt.Errorf("docker not available")
+	}
 
 	resp, err := h.docker.ContainerCreate(ctx, &container.Config{
 		Image: "alpine:latest",