Whether an antiferromagnet can host direction-robust spin-polarized transport without a conventional spin-selective band gap remains a central challenge in antiferromagnetic spintronics. Here we establish a gapless, direction-robust spin-filtering mechanism in a compensated two-dimensional altermagnetic Weyl semimetal that requires neither a spin-selective band gap nor a large velocity contrast between spin projections. Using Janus monolayer Ta${}_2$TeSeO as a realistic platform, we combine symmetry analysis with first-principles calculations, full-Brillouin-zone Wannier interpolation, and semiclassical transport. Rotating the N'eel vector removes a unitary-mirror constraint and shifts one Weyl-cone pair away from its parent high-symmetry line. For an in-plane N'eel vector, the residual $C_{2z}𝒯$ symmetry forbids the independent ${\sigma }_y$ mass that would open a local gap, allowing the reconstructed cones to shift in momentum while remaining gapless. Breaking unitary $C_{2z}$ simultaneously lifts the energy equivalence of the remaining mirror-pinned Weyl cones. The resulting coexistence of a metallic spin-projected manifold and a low-DOS Weyl-derived manifold produces a predominantly DOS-driven conductance imbalance. At charge neutrality and 20~K, the longitudinal conductivity polarization for $𝐧\parallel x$ remains positive for every in-plane current direction and ranges from $76.4\%$ to $82.0\%$. The symmetry-related in-plane N'eel orientations provide two distinct spin-filtering states. This N'eel-vector-driven symmetry mechanism provides a general route to direction-robust gapless spin filtering in compensated altermagnets.