Stage 3 (Elixir foundation) of the HRDPS plan. Lands the scaffolding
that lets the Rust prop-grid-rs HRDPS branch be wired up cleanly when
it ships, without further DB or Elixir-side changes.
What ships:
- `grid_tasks.source` column (default 'hrrr', backfill is a no-op).
Replaces the (run_time, forecast_hour, kind) unique index with a
4-column key (..., source) so HRRR and HRDPS analysis/forecast rows
for the same cycle coexist.
- `Grid.hrdps_only_points/0` — Canadian cells inside HRDPS bbox
(49-60°N, -141 to -52°W) but outside HRRR's CONUS bbox. Disjoint
from `conus_points/0` by construction so the two grids never
double-write the same (lat, lon).
- `Grid.point_source/1` — `:hrrr | :hrdps | :neither` classification
for a (lat, lon) pair. Routes per-QSO enrichment to the right NWP
source.
- `GridTaskEnqueuer.seed_with_analysis/2` and `seed/2` accept a
`:source` option; defaults to "hrrr" so existing callers are
unchanged.
- `HrdpsGridWorker` cycle seeder mirroring PropagationGridWorker's
shape but for HRDPS's 4×/day cadence. `:hrdps` queue added to base
Oban config.
What's deferred:
- The Rust `prop-grid-rs` worker doesn't yet branch on
`task.source`. Until that ships, `HrdpsGridWorker` stays out of
runtime.exs cron — it would just produce rows that the Rust worker
mishandles as HRRR. Module doc explicitly notes the dormant state.
- Map overlay extension and FreshnessMonitor HRDPS staleness deferred
to follow-up sessions once real data flows.
Activation path documented in the updated plan file.
Coverage cap recorded as Stage 8 decision: 60°N for v1 (SRTM stops
there). Arctic CDEM deferred to a follow-up plan.