We explore the quantum-metrological potential of subwavelength-spaced emitter arrays coupled to a one-dimensional nanophotonic waveguide. In this system, strong dipole-dipole interactions profoundly modify the collective optical response, leading to the emergence of ultranarrow subradiant resonances. Through an eigenmode analysis of the effective non-Hermitian Hamiltonian, we derive the decay rate of the most-subradiant state, which, within the present model and geometry, exhibits an $N^{-3}$ scaling with even-odd oscillatory behavior in the deep-subwavelength regime. This scaling is directly observable in the single-photon scattering spectrum, enabling the detection of minute changes in atomic separation with a figure of merit that scales as $N^3$. The quantum Fisher information scales as $N^6$ and can be closely approached by measuring spectral shifts near the steepest slope of the most-subradiant resonance. These enhancements remain robust under realistic positional disorder, confirming that dipole-dipole-engineered subradiance provides a viable resource for quantum metrology. Our work bridges collective waveguide-QED physics and high-precision sensing, opening a route toward scalable quantum sensors on integrated nanophotonic platforms.

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• Collective effects in quantum optics
• Nanophotonics
• Nonlinear optics
• Quantum Fisher information
• Quantum electrodynamics
• Quantum sensing
• Superradiance & subradiance
• Waveguides