Improvements needed to messages from filter/pmo move_ahead for model obs time mismatches

Discussing today (7/3/25) at standup, quick notes on this issues:

Error messages & info messages from filter/pmo & move_ahead are tripping up users

When you have an obs_seq longer than the assimilation window:

ERROR FROM:
source : filter_mod.f90
routine: filter:
message: advancing the model inside filter and multiple file output not curren
tly supported
message: ... support will be added in subsequent releases
message: ... set "single_file_out=.true" for filter to advance the model, or a
dvance the model outside filter

Q. Is it ok to assimilate only some of the obs in a sequence if the obs_seq is long?

When the model time is too early, no info about the obs time:

 PE 0: perfect_model_obs: Main evaluation loop, starting iteration    0
 PE 0: move_ahead Next assimilation window starts    at:  day=  149748 sec= 4320
 2
 PE 0: move_ahead Next assimilation window ends      at:  day=  149749 sec= 4320
 1
 PE 0: perfect_model_obs: Ready to run model to advance data ahead in time
 ERROR FROM:
  source : perfect_model_obs.f90
  routine: filter:
  message: advancing the model inside PMO and multiple file output not currently
  supported
  message: ... support will be added in subsequent releases
  message: ... set "single_file_out=.true" for PMO to advance the model, or adva
 nce the model outside PMO

You have to set trace_execution = .true. to get the obs time
Days seconds given, but typically people have their obs sequence files organized by year-month-day-hour,
e.g. obs_seq2016122106, obs_seq.0Z.20020828

Q. What is better output? Window center and width? In the calendar being used as well as dart time?
Start and end of obs sequence?

PE 0: move_ahead Current model data time            is:  day=  149748 sec=     
 0
 PE 0: move_ahead Current assimilation window starts at:  day=  149747 sec= 4320
 1
 PE 0: move_ahead Next available observation time    is:  day=  149748 sec= 4327
 5
 PE 0: move_ahead Current assimilation window ends   at:  day=  149748 sec= 4320
 0
 PE 0: move_ahead Next data time should be           at:  day=  149749 sec=     
 1
 PE 0: move_ahead Not within current window, model will be called to advance sta
 te.
 PE 0: move_ahead Next assimilation window starts    at:  day=  149748 sec= 4320
 2
 PE 0: move_ahead Next assimilation window ends      at:  day=  149749 sec= 4320
 1
 PE 0: move_ahead Next assimilation window contains up to    49953 observations
 PE 0: p_m_o trace: After  move_ahead checks time of data and next obs
 PE 0: perfect_model_obs: Ready to run model to advance data ahead in time
 p_m_o trace: Ensemble data time before advance day=149748, sec=0
 ERROR FROM:
  source : perfect_model_obs.f90
  routine: filter:
  message: advancing the model inside PMO and multiple file output not currently
  supported
  message: ... support will be added in subsequent releases
  message: ... set "single_file_out=.true" for PMO to advance the model, or adva
 nce the model outside PMO

Review filter_mod.f90 and perfect_model_obs.f90, especially the filter and move_ahead paths that emit the reported messages; compare their behavior with trace_execution enabled. Clarify the desired observation-time and assimilation-window information, including calendar and DART time, and ensure the messages explain the relevant obs_seq and single_file_out choices.