  Context: Accretion onto galactic and supermassive black holes occurs in
different modes, which are documented in hard and soft spectral states,
commonly attributed to an advection-dominated flow (ADAF) inside a truncated
disk and standard disk accretion, respectively.
  At the times of spectral transition an intermediate state is observed, for
which the accretion flow pattern is still unclear.
  Aims: We analyze the geometry of the accretion flow when the mass flow rate
in the disk decreases (soft/hard transition) and evaporation of gas into the
coronal flow leads to disk truncation.
  Methods: We evaluate the physics of an advection-dominated flow affected by
thermal conduction to a cool accretion disk underneath.
  We find re-condensation of gas from the ADAF into the underlying inner disk
at distances from the black hole and at rates, that depend on the properties of
the hot ADAF and vary with the mass accretion rate. This sustains an inner disk
for longer than a viscous decay time after the spectral transition occurred, in
accordance with the spectra that indicate cool gas in the neighborhood of the
accreting black hole. The model allows us to understand why Cyg X-1 does not
show hysteresis in the spectral state transition luminosity that is commonly
observed for X-ray transient sources.
  Conclusions: Our results shed new light on the complex mass flow pattern
during spectral state transition.
