  Heat and charge transport were used to probe the magnetic field-tuned quantum
critical point in the heavy-fermion metal CeCoIn$_5$. A comparison of
electrical and thermal resistivities reveals three characteristic energy
scales. A Fermi-liquid regime is observed below $T_{FL}$, with both transport
coefficients diverging in parallel and $T_{FL}\to 0$ as $H\to H_c$, the
critical field. The characteristic temperature of antiferromagnetic spin
fluctuations, $T_{SF}$, is tuned to a minimum but {\it finite} value at $H_c$,
which coincides with the end of the $T$-linear regime in the electrical
resistivity. A third temperature scale, $T_{QP}$, signals the formation of
quasiparticles, as fermions of charge $e$ obeying the Wiedemann-Franz law.
Unlike $T_{FL}$, it remains finite at $H_c$, so that the integrity of
quasiparticles is preserved, even though the standard signature of Fermi-liquid
theory fails.
