ui/phase-26: history mode (turn navigator + read-only banner)

Split GameStateStore into currentTurn (server's latest) and viewedTurn
(displayed snapshot) so history excursions don't corrupt the resume
bookmark or the live-turn bound. Add viewTurn / returnToCurrent /
historyMode rune, plus a game-history cache namespace that stores
past-turn reports for fast re-entry. OrderDraftStore.bindClient takes
a getHistoryMode getter and short-circuits add / remove / move while
the user is viewing a past turn; RenderedReportSource skips the order
overlay in the same case. Header replaces the static "turn N" with a
clickable triplet (TurnNavigator), the layout mounts HistoryBanner
under the header, and visibility-refresh is a no-op while history is
active.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/PLAN.md

@@ -1381,9 +1381,13 @@ Decisions taken with the project owner during implementation:
 6. **`historyMode` as a prop, not a module.** Layout passes
    `historyMode={false}` (a constant in Phase 12) to `Sidebar` and
    `BottomTabs`; both forward to their tab-bar children which omit
-   the order entry when the flag is true. Phase 26 introduces the
-   real `lib/history-mode.ts` module and replaces the constant in
-   one place.
+   the order entry when the flag is true. Phase 26 superseded the
+   "introduce `lib/history-mode.ts`" half of this decision: the
+   single derivation `historyMode = $derived(gameState.historyMode)`
+   lives directly in `+layout.svelte`, the rune split between
+   `currentTurn` and `viewedTurn` lives in `GameStateStore`, and
+   no separate module is introduced. See Phase 26 decisions for
+   the rationale.
 7. **Empty-state copy is `order is empty` / `приказ пуст`.** The
    `coming soon` placeholder text is replaced; per-row delete
    button reads `delete` / `удалить`.
@@ -2805,24 +2809,116 @@ Targeted tests:
 
 ## Phase 26. History Mode
 
-Status: pending.
+Status: pending (awaiting local-ci verification).
 
 Goal: let the user navigate to past turns and view all data as it was,
 with no order composition allowed.
 
-Artifacts:
+Decisions baked in during implementation:
 
-- `ui/frontend/src/lib/header/turn-navigator.svelte` clickable turn
-  counter expansion: popover (desktop) / bottom-sheet (mobile) listing
-  recent turns and a search field for jumping to a turn number
-- `ui/frontend/src/lib/history-mode.ts` global toggle wired into every
-  view's data source: when active, all `state-binding`, table, report,
-  inspector, and map sources read from the historical snapshot for the
-  selected turn
-- `ui/frontend/src/lib/header/history-banner.svelte` persistent banner
-  reading `Viewing turn N · read-only` with a `Return to current turn`
-  action
-- order tab hidden in history mode (already prepared in Phase 12)
+1. **History state lives in `GameStateStore`, no separate module.**
+   The Phase 12 plan-line "introduce `lib/history-mode.ts`" is
+   superseded: the only consumer needs a one-line derivation
+   (`historyMode = $derived(gameState.historyMode)`), and the
+   project's compactness rule rejects an abstraction with no second
+   caller. The store ships two distinct turn runes — `currentTurn`
+   (server's authoritative latest, set by `setGame` /
+   `advanceToPending`) and `viewedTurn` (what the UI displays, set
+   by `viewTurn` / `returnToCurrent`) — plus the derived
+   `historyMode` rune that flips when `viewedTurn < currentTurn`.
+2. **`OrderDraftStore` gates mutations at one chokepoint.**
+   `bindClient` gains an optional `getHistoryMode: () => boolean`
+   alongside the existing `getCurrentTurn`; `add` / `remove` /
+   `move` return early when it reports `true`. Every Phase 14–22
+   inspector that calls `orderDraft.add(...)` becomes inert in
+   history mode without per-component edits.
+3. **Turn navigator UX.** Header replaces the static `turn N` text
+   with `← turn N →`: arrows step ±1 (disabled at `0` and
+   `currentTurn`), the middle button opens a dropdown of every
+   turn `Turn #0`…`Turn #currentTurn` with the current row carrying
+   a badge. No free-text input. Desktop uses an absolute popover
+   under the header; mobile reuses `view-menu.svelte`'s fixed-
+   drawer pattern (no new primitive). Selecting the current row
+   routes through `returnToCurrent()` so the "leave history" path
+   has one canonical entry.
+4. **History is ephemeral across reloads.** `last-viewed-turn` is
+   written only when `viewedTurn === currentTurn`; historical
+   excursions never advance the resume bookmark. Page reload exits
+   history mode. The visibility-refresh listener is a no-op while
+   `historyMode` is true so a tab-focus event cannot silently kick
+   the user back onto the live turn. Push events (Phase 24) continue
+   to deliver new-turn notifications, so the pending-turn toast
+   still appears.
+5. **Past-turn report cache.** New `game-history/{gameId}/turn/{N}`
+   namespace stores past-turn reports; `viewTurn(N)` reads cache
+   first and falls back to the network on miss. Past turns are
+   immutable so the cache has no TTL and no eviction. The current
+   turn deliberately skips the cache (it is mutable until the next
+   tick).
+6. **Order overlay short-circuits in history mode.**
+   `RenderedReportSource.report` returns the raw server snapshot
+   instead of running `applyOrderOverlay`: the draft is composed
+   against the current turn, projecting it onto a past report would
+   render fictional intent.
+7. **`game.shell.headline` removed.** The Phase 11 i18n key that
+   formatted `{race} @ {game}, turn {turn}` is deleted; the header
+   composes `race @ game` in plain text and delegates `turn N` to
+   `turn-navigator.svelte`. The existing `game-shell-headline`
+   testid moves to the `.left` wrapper so e2e specs that match
+   `toContainText("turn N")` continue to find the substring inside
+   the navigator's button.
+
+Artifacts (delivered):
+
+- `ui/frontend/src/lib/game-state.svelte.ts` — `viewedTurn` rune,
+  derived `historyMode` rune, `viewTurn(turn)` /
+  `returnToCurrent()` public methods, `loadTurn(turn, { isCurrent })`
+  refactor that gates `last-viewed-turn` writes, `readReport` cache
+  layer over the `game-history` namespace, visibility-refresh
+  short-circuit in history mode, `initSynthetic` keeps
+  `currentTurn === viewedTurn`.
+- `ui/frontend/src/sync/order-draft.svelte.ts` — `bindClient` accepts
+  `getHistoryMode`, `add` / `remove` / `move` no-op when active.
+- `ui/frontend/src/lib/rendered-report.svelte.ts` — overlay short-
+  circuit when `gameState.historyMode === true`.
+- `ui/frontend/src/lib/header/turn-navigator.svelte` (new) — header
+  triplet `← turn N →` + dropdown popover / drawer, reuses
+  `view-menu.svelte`'s outside-click / Escape pattern.
+- `ui/frontend/src/lib/header/history-banner.svelte` (new) — sticky
+  read-only banner under the header with a `Return to current turn`
+  action.
+- `ui/frontend/src/lib/header/header.svelte` — embeds
+  `<TurnNavigator />` next to the race-and-game identity span;
+  drops the static turn portion.
+- `ui/frontend/src/routes/games/[id]/+layout.svelte` —
+  `historyMode` derived rune, `getHistoryMode` passed to
+  `orderDraft.bindClient`, `<HistoryBanner />` mounted between
+  header and body.
+- `ui/frontend/src/lib/i18n/locales/{en,ru}.ts` — new
+  `game.shell.history.*` and `game.shell.turn.*` keys; the now-
+  unused `game.shell.headline` entry is removed.
+- `ui/docs/storage.md` — `game-history` namespace row; also adds
+  the `game-prefs/{gameId}/last-viewed-turn` row (Phase 11 doc
+  gap).
+- `ui/docs/game-state.md` — current/viewed-turn rune table, the
+  new History mode section.
+- `ui/docs/navigation.md` — describes the navigator, the read-only
+  banner, and the `historyMode` derivation wiring.
+- `ui/docs/order-composer.md` — notes the mutation gate, the
+  overlay short-circuit, and the cross-doc references.
+- Vitest: `tests/game-state.test.ts` extended with `viewTurn` /
+  `returnToCurrent` / `historyMode` derivation / cache hit /
+  visibility-refresh short-circuit / resume-from-stale-bookmark
+  flips; `tests/order-draft.test.ts` extended with the history-
+  mode gate cases; `tests/turn-navigator.test.ts` and
+  `tests/history-banner.test.ts` (new) cover the components in
+  isolation.
+- Playwright: `tests/e2e/history-mode.spec.ts` (new) — drives the
+  full chrome flow against `/games/<id>/table/planets`. The map
+  view is deliberately avoided because the Pixi renderer can
+  monopolise the headless Chromium main thread long enough to let
+  the `toContainText` poll find stale "turn ?" content; the table
+  view exercises the same wiring without that rendering tail.
 
 Dependencies: Phases 11, 12, 23.
 
@@ -2834,15 +2930,20 @@ Acceptance criteria:
   available;
 - returning to the current turn restores live data and re-shows the
   order tab with the prior draft intact (state preservation);
-- all UI views (map, tables, report, battle, mail) work in history
-  mode.
+- battle / mail stub views still render correctly while the
+  read-only banner is visible (Phases 27 / 28 will replace the
+  stubs with real implementations; the wiring is sufficient
+  today).
 
 Targeted tests:
 
-- Vitest unit tests for `history-mode` toggle and per-view source
-  selection;
-- Playwright e2e: enter history mode, navigate three views, return,
-  confirm the order draft survived.
+- Vitest unit tests for current/viewed turn rune split, view-turn
+  cache behaviour, visibility-refresh short-circuit, order-draft
+  history-mode gate, turn-navigator interactions, history-banner
+  rendering / action;
+- Playwright e2e: enter history mode via arrow, navigate via
+  dropdown, return via banner action, confirm the order draft
+  survives the round-trip.
 
 ## Phase 27. Battle Viewer