  The process how heavy-electron state is established in Kondo-lattice
compounds remains an unsolved issue. Recent angle-resolved photoemission
spectroscopy and ultrafast optical spectroscopy imply an intermediate regime
with hybridization fluctuations prior to the establishment of Kondo coherence,
which appears at odds with traditional transport measurements. Extensive
experimental works are highly demanded to both reconcile this dichotomy and
delineate the intrinsic features in this special regime. Here, on the example
of quasi-one-dimensional Kondo lattice compound CeCo$_2$Ga$_8$, we investigated
angular dependent magnetotransport properties by planar Hall effect and planar
anisotropic magnetoresistance measurements. Upon cooling from $T_K^{on}$ (an
onset of incoherent Kondo scattering ) to below $T^*$ (where coherent $c$-$f$
hybridization comes into play), the two-fold symmetrical pattern of planar Hall
effect changes sign gradually (i.e. $180^\circ$ phase shift); most strikingly,
as a crossover, additional oscillations appear and persist until the
heavy-electron state is stabilized below $T^*$. These results provide new
insights for the regime of hybridization dynamics which might be deemed as a
precursor state of the heavy-electron state.
