# S2S-FM-VN starting design (working hypothesis, NOT locked). Deviate where
# evidence says so and record the evidence in docs/decision_log.md.

architecture:
  pipeline: >
    ECMWF cf coarse LT0-45 -> [local branch, large-scale branch] each
    (variable/level encoder -> spatial encoder) -> cross-scale fusion ->
    temporal/lead encoder over Z0..Z45 -> Z_S2S -> 0.25-deg VN decoder
    (+static/climatology) -> daily & weekly outputs
  spatial_encoder: "small Swin / hierarchical ViT / ConvNeXt+attention (TBC)"
  embeddings: [variable, pressure_level, lead_time, calendar_season]
  do_not_collapse_trajectory: true          # keep Z0..Z45, no single global vector
  backbone: "one shared backbone; optional lead-regime adapters (LT0-10,11-25,26-45) and region adapters"
  no_per_lead_or_per_region_backbones: true

size:
  prototype_params_M: [5, 10]
  base_params_M: [15, 30]                   # only if skill/stability/compute justify
  track: [params, gpu_mem, train_time, infer_time, disk, checkpoint_size]

pretraining:                                # self-supervised, coarse space ONLY
  never_reconstruct_interpolated_025: true
  masks: [variable_level, spatial_patch, lead_time_single, lead_time_interval, combinations]
  loss: "L = l_var*L_var + l_space*L_space + l_time*L_time (add a term only if it helps)"

outputs:
  daily: [Tx_hat, P_EHD]
  weekly_W1_W6: {count_distribution: "P(N=0..7)", optional_direct: [P_EHE_WEEK, P_HW2_WEEK]}
  derived: ["E[N]=sum k P(N=k)", "P(EHE)=1-P(N=0)", "P(HW2)=1-P(N=0)-P(N=1)"]
  W7: "mask classes 5-7 or horizon-aware head"
  consistency_check: "daily P(EHD) head vs weekly count head; report inconsistency"

finetune_loss: [huber_or_mae_Tx, bce_or_focal_daily_EHD, categorical_or_ordinal_counts, brier_calibration, optional_episode_terms]

normalisation: "absolute + lead/calendar-dependent anomalies; fitted on TRAINING years only"

temporal_alignment:
  rule: "valid_date = initialization_date + lead_day; align by actual date, never array index"
  utc_vs_local: "obs Tx is local (UTC+7) day max; ECMWF maxima UTC; LT0 may be partial. Define + unit-test."