galaxy-game/ui/docs/game-state.md

# Per-game state store

This document describes the per-game state owned by the in-game shell
layout. The store serves the header turn counter, the map view,
inspector tabs, the order composer, and the calculator.

## Lifecycle

The in-game shell (`lib/game/game-shell.svelte`) instantiates one
`GameStateStore` per game. The shell is mounted by the single-route
dispatcher only while `appScreen.screen === "game"`, and remounts when
`appScreen.gameId` changes, so each game gets a fresh store. The shell
exposes the instance through Svelte context under
`GAME_STATE_CONTEXT_KEY`; descendants read it via
`getContext(GAME_STATE_CONTEXT_KEY)`.

The shell's boot effect builds the `GalaxyClient`, loads `Cache`
through `loadStore()`, then calls `gameState.init({ client, cache,
gameId })`. `init`:

1. installs a `visibilitychange` listener on `document` so the report
   is refreshed when the tab regains focus;
2. calls `setGame(gameId)`, which:
   - reads the per-game wrap-mode preference from `Cache`
     (`game-prefs / <gameId>/wrap-mode`, default `torus`);
   - calls `lobby.my.games.list` (`findGame`) and finds the game
     record (`GameSummary` carries `current_turn`); if the game is not
     in the player's list, the store sets the `notFound` flag (see
     below);
   - calls `user.games.report` for the discovered turn and decodes
     the FlatBuffers response into a TS-friendly `GameReport` shape.

The store exposes:

| field         | type                          | meaning                                              |
| ------------- | ----------------------------- | ---------------------------------------------------- |
| `gameId`      | `string`                      | active game id                                       |
| `status`      | `idle / loading / ready / error` | current lifecycle state                            |
| `report`      | `GameReport \| null`          | latest decoded report, `null` until first fetch      |
| `currentTurn` | `number`                      | server's authoritative current turn (live snapshot)  |
| `viewedTurn`  | `number`                      | turn whose snapshot is in `report`; equals `currentTurn` in live mode |
| `historyMode` | `boolean` (derived)           | true while `status === "ready"` and `viewedTurn < currentTurn` |
| `pendingTurn` | `number \| null`              | latest server turn the user has not yet opened       |
| `wrapMode`    | `torus / no-wrap`             | per-game preference, persisted via `Cache`           |
| `error`       | `string \| null`              | localised error message when `status === "error"`    |
| `notFound`    | `boolean`                     | true when the game is not in the player's list (cancelled / removed / access revoked); the shell drops to the lobby |

## Missing or inaccessible game

A restored or stale game id (a `sessionStorage` snapshot pointing at a
game that was cancelled, removed, or whose access was revoked) is a
distinct case from a transient failure. When `findGame` returns no
matching record, `setGame` sets the boolean `notFound` flag rather
than synthesising an error message. After `init` resolves, the in-game
shell reads `gameState.notFound` and, when true, calls
`appScreen.go("lobby")` and shows a `game.events.unavailable` toast —
the player lands back in the lobby instead of on an in-game error
screen. A transient network failure takes the catch path instead,
leaving `notFound` false and flipping `status` to `error` so the
in-game error state offers a retry. `notFound` resets to false at the
start of every `setGame` / `advanceToPending`. See
[`navigation.md`](navigation.md) for the restore-and-validate flow.

## Store extensions

`GameReport` and `decodeReport` are extended as each slice of the
wire lands (ships, fleets, sciences, routes, battles, mail).
`currentTurn` is split from `viewedTurn`, and `viewTurn(turn)` /
`returnToCurrent()` handle history navigation. The derived
`historyMode` rune flips automatically when `viewedTurn <
currentTurn`; the shell passes it to the sidebar / bottom-tabs
wiring (which hides the order tab) and to
`OrderDraftStore.bindClient` (which gates `add` / `remove` / `move`).
See "History mode" below for the cache and refresh rules.
Tab-focus refreshes are supplemented by push-event-driven refreshes;
the visibility listener stays as a fallback for background tabs that
miss a push. The wrap-mode toggle UI is wired on top of
`setWrapMode`.

## Why `current_turn` lives on `GameSummary`

The user-facing surface needs the current turn number to know which
report to fetch. Two alternatives were rejected:

- a brand-new `user.games.state` message — adds a full wire-flow
  (fbs schema, transcoder, gateway routing, backend handler) for a
  one-field response;
- hard-coding `turn=0` for all games — works for a synthetic report
  loaded at turn zero but mis-renders the initial state for any real
  game past turn zero.

Extending `GameSummary` reuses the existing lobby pipeline; the
backend already tracks `current_turn` in its runtime projection
(`backend/internal/server/handlers_user_lobby_helpers.go`
`gameSummaryToWire` reads it from `g.RuntimeSnapshot.CurrentTurn`).
The `current_turn` field defaults to zero on the FB side, so existing
tests and the synthetic-report flow continue to work unchanged.

## State binding

`map/state-binding.ts::reportToWorld(report)` translates a
`GameReport` into a renderer-ready `World`. It emits one Point
primitive per planet across all four kinds (local / other /
uninhabited / unidentified). Each kind gets a distinct fill colour,
fill alpha, and point radius so the four classes are
visually-distinguishable at a glance; colour-palette refinement is
deferred to the finalization plan
([../PLAN-finalize.md](../PLAN-finalize.md)).

The planet engine number is reused as the primitive id so a hit-test
result can resolve back to a planet without an extra lookup table.

## Refresh discipline

`refresh()` re-fetches the current-turn snapshot. It is called by
the `visibilitychange` handler when `document.visibilityState ===
"visible"` and the store is already in `ready` state. The map
view's mount effect skips a re-render when the new snapshot's turn
matches the previously-mounted turn (and the wrap mode is
unchanged), so a no-op refresh does not flicker the canvas.

In history mode `refresh()` is a no-op — forcing a reload would
silently bump the user back onto the current turn while they are
intentionally viewing a past one. Push events still deliver
new-turn notifications asynchronously while the user explores
history, so the pending-turn toast continues to work.

`setWrapMode(mode)` writes to `Cache` and updates the rune; the
map view's effect picks the change up and re-mounts the renderer
with the new mode.

## Map visibility toggles

A `mapToggles: MapToggles` rune drives the gear popover in the map
view. Every flag defaults to `true` — including `unreachablePlanets`
(showing every planet by default) and `visibleHyperspace` (the fog
overlay on by default). The exhaustive shape lives in
`src/lib/game-state.svelte.ts`; the gear popover
(`src/lib/active-view/map-toggles.svelte`) is a thin view of the
rune.

`setMapToggle(key, value)` flips one entry in place and persists
the whole blob to `Cache` under the `game-map-toggles/{gameId}` key.
The blob carries a companion `lastResetTurn` number — the turn at
which the toggles were last reset to defaults — so the new-turn reset
path (below) can detect a stale blob even across a cross-session gap.

### New-turn reset

A new server-side turn force-resets every toggle to defaults so a
hidden category never makes the player miss what changed:

- `setGame` reads the persisted `{toggles, lastResetTurn}` blob.
  If `lastResetTurn < currentTurn`, the rune is overwritten with
  `DEFAULT_MAP_TOGGLES` and the blob is rewritten with
  `lastResetTurn = currentTurn` before the report load. Otherwise
  the persisted overrides are restored.
- `advanceToPending` (the user's explicit jump onto the new turn)
  calls the same reset path after `loadTurn(currentTurn, …)`
  succeeds, updating `lastResetTurn` to the freshly-loaded
  current turn.
- `viewTurn` (history mode) does NOT reset — toggles are a
  single shared state per game, not per turn.
- `refresh()` does not advance turns, so it does not reset.

The cache namespace and blob shape are documented in
`storage.md`.

## History mode

The store lets the user step backward through the report timeline
without losing the live snapshot. The store keeps two turn runes:

- `currentTurn` — the server's authoritative latest. Only
  `setGame` and `advanceToPending` write to it.
- `viewedTurn` — the turn currently rendered. `viewTurn(N)` flips
  this rune and the underlying `report` to `N` without touching
  `currentTurn`. `returnToCurrent()` is a one-line wrapper that
  navigates back to live.

The derived `historyMode` rune (`status === "ready" && viewedTurn
< currentTurn`) drives every history-aware consumer:

- the shell passes it to `Sidebar` / `BottomTabs` so the order
  tab vanishes;
- the shell passes a `getHistoryMode` getter to
  `OrderDraftStore.bindClient` so `add` / `remove` / `move` are
  no-ops while the user is looking at a past turn;
- `RenderedReportSource` returns the raw report (no order overlay)
  because the draft is composed against the current turn;
- the new `HistoryBanner` component renders the sticky "Viewing
  turn N · read-only" strip when the flag is true.

`last-viewed-turn` means "the latest turn the user was caught up
on". `loadTurn` only writes the cache row when called with
`isCurrent === true` (i.e. when the load matches `currentTurn`).
Historical excursions are therefore ephemeral: closing the tab and
reopening the game resumes on the last caught-up turn, not on the
last clicked one.

Past-turn reports are cached in the `game-history` namespace
(`{gameId}/turn/{N}` → `GameReport`). The cache is written by
`loadTurn` on every successful historical fetch and read first by
`viewTurn(N)` before falling back to the network. Past turns are
immutable, so the cache has no TTL and no eviction. The current-turn
snapshot is deliberately *not* cached — it is mutable until the next
engine tick.