web: split the rail into fields, overlays and marks with one view state

The layer rail is three sections, one kind of press each. The field
section is a radio: each dataset's core tiles (FORECAST_MODELS[].railCore;
temperature, precipitation, wind and cloud on a forecast model, the solar
radiation in cloud's place on SFLUX, the reflectivity on a radar mosaic),
the tile of the field on screen when it is not a core one, and MORE, which
opens a sheet listing every field the run publishes, grouped by quantity,
with a chip per surface and variant under a family. The overlay section is
switches drawn over the field: the pressure lines (the PRESSURE tile now
toggles them rather than replacing the field), the particles (moved out of
the capsule), the experiment's derived layers. The mark section is the
storm sheet trigger and the two station switches. Switch tiles carry a
ring, sheet triggers a chevron; an empty section hides with its rule; the
dense variant is decided by the visible tile count against the rail's box.
The level row's lines group gains ALONE, the way to the lines-alone view
and back to the field last on screen.

What is on screen is one object, ViewState (viewstate.ts), whose parseView
and searchForView are inverses of each other over every parameter the
shell reads; main.ts holds it as `view` and derives the rail's pressed
states (syncRail) and the address bar (syncUrl) from it, replacing the
composition, particle, derived-layer, storm and station variables.

FamilyInfo.members splits into levels (the same quantity on other
surfaces: the isobaric set, the cloud layers) and variants (related
quantities behind one tile: sea ice cover and thickness, wave height and
period). The level row draws levels only, under a fixed LEVEL caption; a
family tile's gloss follows the member on screen; pressing a pressed
variants family cycles through them.

The web fixture gains a gust bundle, a field outside the core tiles, so
the e2e suite can drive MORE.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016peFTwXxKVuwLqZYYDqr2W

Author: ringsaturn

CLAUDE.md

@@ -710,16 +710,45 @@ to RG8 (u codes in red, v in green, the packing `particles.ts` builds, which
 `main.ts` interleaves once per frame and memoizes) and looks the palette up
 by `magnitude / maxMagnitude`; every vector bundle takes this path with its
 own ceiling from `levels.ts::vectorMaxMagnitude`. `web/src/levels.ts` is the
-family registry: one rail tile per family, the level row on the capsule
-picks the member, and cloud cover lists its members outright in
-`FamilyInfo.members`. Past ten visible rail tiles `main.ts` marks the rail
-dense and the stylesheet drops the tiles to 36px. The rail is a scroll
-column in a fixed box (under the zoom tile down to the capsule on desktop;
-under the round controls on phones, where `main.ts` publishes the capsule's
-measured height as `--capsule-height`), and its tiles are grouped by
-quantity in `index.html`, so a new tile goes into its group. Over a field
-the lines group is on the row whenever the run publishes a pressure surface:
-a pressed member is the overlay, pressing it again takes the lines off.
+family registry: one rail tile per family, and a family's members are
+two kinds. `FamilyInfo.levels` are the same quantity on other surfaces
+(the isobaric set, or the cloud layers listed outright): the level row on
+the capsule picks among them. `FamilyInfo.variants` are related but
+different quantities behind one tile (sea ice cover and thickness, wave
+height and period), never on the level row: the field sheet lists them as
+chips under the family's row, and pressing the pressed tile again cycles
+through them. A family tile's gloss follows the member on screen
+(`syncFamilyGloss`: TEMP 2M, TEMP 850, ICE THICK).
+
+The layer rail is three sections, one kind of press each (`index.html`,
+`.rail-section`): the fields (a radio: the dataset's core tiles,
+`FORECAST_MODELS[].railCore`, the tile of the field on screen when it is
+not a core one, and MORE, which opens `#field-sheet`, every field the run
+publishes grouped by quantity, written by `main.ts::renderFieldSheet` from
+the rail's own tiles and a stopgap group table), the overlays (switches
+drawn over the field and following the playhead: the pressure lines, the
+particles, the experiment's derived layers) and the marks (the storm sheet
+trigger, the soundings and the airports). A switch tile carries
+`data-toggle` and a ring in its corner, a sheet trigger `data-dialog` and a
+chevron. `syncFieldTiles` hides every field tile the run does not ship or
+the screen does not show, and writes a generic tile for a field this build
+has no tile for while it is on screen; the rail is marked dense
+(`syncRailDensity`, tiles at 36px) when its visible tiles would not fit its
+box at full size. The rail is a scroll column in a fixed box (under the
+zoom tile down to the capsule on desktop; under the round controls on
+phones, where `main.ts` publishes the capsule's measured height as
+`--capsule-height`). A new field with an icon is a tile in the field
+section plus a line in `FIELD_GROUP_TILES`; without one it is a row of the
+sheet's last group. What is on screen is one object, `view: ViewState`
+(`web/src/viewstate.ts`: the field and the lines, the particles, the
+experiment's derived layers, the storm and station marks); the rail's
+pressed states (`syncRail`), the level row and the address bar
+(`syncUrl` over `searchForView`, the inverse of `parseView`) are
+projections of it, and nothing else holds a copy. The lines group is on the level row whenever the run
+publishes a pressure surface: a pressed member is the overlay, pressing it
+again takes the lines off, as does the rail's pressure switch, and the
+group's ALONE member drops the field to leave the chart by itself (the
+field last on screen, `lastField`, comes back on the next press).
 
 The pressure family is drawn as contour lines: `web/src/pressure.ts` holds
 the per-level intervals and emphasised lines, `layer.ts::setContours` turns
@@ -740,10 +769,11 @@ once a second; a stop, a step or a pan refreshes at once.
 emphasised lines identical across the three implementations.
 
 `particles.ts` advects GPU particles through the wind field as an overlay in
-one ink, on by default, off from the capsule (`?particles=off`, remembered
-in `localStorage`, off by default under `prefers-reduced-motion`). Wind
-narrows to the viewport while the overlay is off; with it on the session
-takes the whole plane, since the particles respawn across the grid.
+one ink, on by default, off from the rail's overlay section
+(`?particles=off`, remembered in `localStorage`, off by default under
+`prefers-reduced-motion`). Wind narrows to the viewport while the overlay
+is off; with it on the session takes the whole plane, since the particles
+respawn across the grid.
 `playback.ts` holds the frame-rate ladder and the per-frame dwell that keeps
 a mixed-step axis at one apparent speed.
 

README.md

@@ -283,9 +283,13 @@ such as `tmp2m` / `prate` / `wind10m` / `solar` / `radar`, and each isobaric
 field names itself (`pressure`, `hgt500`, `tmp850` / `t850`, `rh700`,
 `wind850`, `qflux850` / `vapor850`; there is no separate `level`
 parameter). Both are case-insensitive, the address bar stays in sync, and
-unrecognized values fall back to defaults. In the page one rail tile stands
-for a whole family and the level row on the transport capsule picks the
-surface.
+unrecognized values fall back to defaults. In the page the rail carries a
+tile for each core field (temperature, precipitation, wind, cloud on a
+forecast model) and a MORE tile opening the list of every field the run
+publishes; one tile stands for a whole family and the level row on the
+transport capsule picks the surface. The pressure lines are a switch in the
+rail's overlay section, and the level row's ALONE member leaves them by
+themselves.
 
 The view is in the fragment, `#map=<zoom>/<lat>/<lon>` (MapLibre's own
 spelling), kept current on every pan and zoom. A link without one opens on