feat: add loco support

[nils3er]

feat: follow live datasets that stream one timestep at a time

Summary

Adds support for live datasets — a Zarr store whose time axis is fully declared up front, but where only the currently-available timestep can be fetched at any moment. This lets Gridlook follow a running simulation or a rolling forecast, jumping to and re-rendering each new timestep as the model produces it.

Enable it by appending ::live=true to the dataset URL:

https://gridlook.pages.dev/#<ZARR_URI>::live=true

How it works

When live mode is active, Gridlook:

1. Seeds the initial time index from a current-timestep endpoint, so the very first render requests a chunk that actually exists (bounded by a 10s timeout; best-effort — the follow loop recovers on its own if it fails).
2. Long-polls a next-timestep endpoint and, whenever a newer timestep is reported, writes it into the time slider — which the existing grid loader already watches — triggering a refetch and re-render.
3. Locks the time slider (only one timestep is fetchable at a time) and swaps the playback controls for a LIVE badge with a pause/resume button. Pausing freezes the current frame; resuming jumps back to the newest timestep.
4. Reconnects with exponential backoff (1s → 30s cap) on network drops or 5xx, showing a subtle "Reconnecting…" indicator until the connection recovers.

Live mode is HTTP-only (Zarr FetchStore); Icechunk stores are not supported. The live time index is deliberately kept out of the shareable URL, since it's re-seeded from the server on load.

Server contract

The data server must expose two endpoints as siblings of the store root, each returning { "timestep": <index> }:

Endpoint	Behaviour
current-timestep	Responds immediately with the index available right now
next-timestep	Long-polls; responds only once a newer timestep is ready

Full details in docs/live-datasets.md.

Changes

• New src/lib/data/liveTimestep.ts — endpoint helpers plus LiveTimestepController, which drives the fetch-current-then-long-poll loop with backoff and abort handling.
• New src/store/useLiveTimestep.ts — Vue composable wiring the controller into the store, starting/stopping it as live/pause state and the datasource change.
• Store — new live / livePaused / liveConnected / liveTimestep state and actions; live URL param plumbed through paramStore and urlParams.
• UI — DimensionControl.vue shows the LIVE badge + pause/resume and disables manual time scrubbing; useTimeAnimation.ts disables playback for live datasets; GlobeView.vue seeds the initial timestep on load.
• Tests — tests/unit/lib/data/liveTimestep.test.ts covers URL joining, payload parsing/validation, HTTP-only detection, and the controller's emit-current-then-follow / stop-before-start behaviour.
• Docs — new docs/live-datasets.md; README pointer.

Incidental: more robust HEALPix nside detection

Healpix.vue's getNside() was refactored into a clear fallback chain — healpix_nside on the CRS variable → dggs.refinement_level on the group → inferring from a global grid's cell count (ncells = 12 · nside²) — with a descriptive error when none apply. This makes grid rendering more resilient for stores that don't carry an explicit healpix_nside.

Notes

• package-lock.json churn is metadata only (devOptional → dev reclassification of platform-specific optional deps).

[cloudflare-workers-and-pages]

Deploying gridlook with    Cloudflare Pages

Latest commit:	460d9fc
Status:	✅  Deploy successful!
Preview URL:	https://af1a44f0.gridlook.pages.dev
Branch Preview URL:	https://loco.gridlook.pages.dev

View logs