We describe our submission to Task 1 (Argumentative Discourse Unit Classification) of the Daleel 2026 shared task on Arabic argument mining, in the closed track. Given a paragraph from an Arabic editorial or debate transcript, the task is to predict the multi-label set of argumentative functions it contains, drawn from six classes: common ground, assumption, testimony, statistics, anecdote, and other. Our system fine-tunes a pretrained Arabic encoder, comparing AraBERT, MARBERT, and CAMeLBERT-mix, augmented with a small side-channel of hand-crafted lexical features motivated directly by the task’s class definitions (e.g., reporting verbs for testimony, digit/percentage patterns for statistics), trained with a class-balanced focal loss and combined into a 5-fold cross-validation ensemble; CAMeLBERT-mix was selected as the final encoder for all submitted configurations. In the dev phase, our Both-domain configuration achieved an overall macro-F1 of 0.5600 (editorial 0.4350, debate 0.4900). On the official test-phase Codabench leaderboard, our Both-domain configuration achieved an overall macro-F1 of 0.5265 (editorial 0.3838, debate 0.4943), ranking 10th; our Editorial-only configuration reached an overall macro-F1 of 0.4544 (editorial 0.3249, debate 0.4509). We report two findings grounded in these results: overall (pooled) macro-F1 consistently exceeds the macro-F1 computed on either genre subset alone, and our editorial-only model unexpectedly scores higher macro-F1 on the out-of-domain debate subset than on its own in-domain editorial subset. We discuss both as likely artifacts of per-class support sparsity at the smaller genre-subset scale rather than genuine cross-domain superiority, though we did not conduct a formal ablation study or systematic error analysis to confirm this, which we flag as the primary limitation of this report. Our code is available at
https://github.com/turab-usmani/daleel-task1-closedtrack.