LOFAR Detects Multiple Steep-Spectrum Synchrotron Threads in Abell 2199's 3C 338

LOFAR observations at 144 MHz combined with archival Chandra X-ray data and non-detections at 1.5 GHz VLA frequencies isolated three narrow threads east, west and north of the AGN. These features lie outside detected X-ray cavities and exhibit spectral indices steeper than α_1500^144 < -3.0, indicating they are physically distinct from the lobes themselves. The lobes display nearly constant spectral index across their volumes, contradicting standard spectral ageing gradients. The uniform lobe spectra are best explained by a homogeneous cosmic-ray electron population whose observed variations arise solely from local magnetic-field strength differences rather than electron ageing. This pattern connects directly to emerging models of magnetic threads that trap relativistic plasma, offering a mechanism that could operate across many cool-core clusters where optical and X-ray studies have overlooked low-frequency structures. Future wide-field LOFAR and SKA-low surveys will test whether such threads are ubiquitous in merging and relaxed clusters, constraining the volume-filling factor of strong magnetic filaments and their role in particle re-acceleration. Higher-resolution polarisation maps at 50-80 MHz are required to measure field ordering within the threads and distinguish between reconnection and draping scenarios.