ui/phase-27: battle viewer (radial scene, playback, map markers)

Engine wire change: Report.battle switched from []uuid.UUID to
[]BattleSummary{id, planet, shots} so the map can place battle
markers without N extra fetches. FBS schema + generated Go/TS
regenerated; transcoder + report controller updated; openapi
adds the BattleSummary schema with a freeze test.

Backend gateway forwards engine GET /api/v1/battle/:turn/:uuid as
/api/v1/user/games/{game_id}/battles/{turn}/{battle_id} (handler
plus engineclient.FetchBattle, contract test stub, openapi spec).

UI:
- BattleViewer (lib/battle-player/) is a logically isolated SVG
  radial scene that consumes a BattleReport prop. Planet at the
  centre, races on the outer ring at equal angular spacing, race
  clusters by (race, className) with <class>:<numLeft> labels;
  observer groups (inBattle: false) are not drawn; eliminated
  races drop out and survivors re-distribute on the next frame.
- Shot line per frame: red on destroyed, green otherwise; erased
  on the next frame. Playback controls: play/pause + step ± +
  rewind + 1x/2x/4x speed (400/200/100 ms per frame).
- Page wrapper (lib/active-view/battle.svelte) loads BattleReport
  via api/battle-fetch.ts; synthetic-gameId prefix routes to a
  fixture loader, otherwise REST through the gateway. Always-
  visible <ol> text protocol satisfies the accessibility ask.
- section-battles.svelte links every battle UUID into the viewer.
- map/battle-markers.ts: yellow X cross of 2 LinePrim through the
  corners of the planet's circumscribed square (stroke width
  clamps from 1 px at 1 shot to 5 px at 100+ shots); bombing
  marker is a stroke-only ring (yellow when damaged, red when
  wiped). Wired into state-binding.ts; click handler dispatches
  battle clicks to the viewer and bombing clicks to the matching
  Reports row.
- i18n keys for the viewer in en + ru.

Docs: ui/docs/battle-viewer-ux.md, FUNCTIONAL.md §6.5 + ru
mirror, ui/PLAN.md Phase 27 decisions + deferred TODOs (push
event, richer class visuals, animated re-distribution).

Tests: Vitest unit (radial layout + timeline frame builder +
marker stroke formula + marker primitives), Playwright e2e for
the viewer (Reports link → viewer, playback step, not-found),
backend engineclient FetchBattle (200 / 404 / bad input), engine
openapi freezes (BattleReport, BattleReportGroup,
BattleActionReport, BattleSummary, Report.battle items).

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

ui/frontend/src/lib/active-view/battle.svelte

@@ -1,30 +1,134 @@
 <!--
-Phase 10 stub for the battle-log active view. Phase 27 wires the real
-battle viewer.
+Phase 27 — active-view wrapper around the BattleViewer. Loads the
+BattleReport for the supplied `gameId`/`turn`/`battleId` and either
+shows the radial playback (BattleViewer), a loading skeleton, or a
+not-found state. The viewer itself is a logically isolated
+component that takes a `BattleReport` prop — this wrapper owns
+loading and routing concerns.
 -->
 <script lang="ts">
+	import { goto } from "$app/navigation";
+
+	import {
+		BattleFetchError,
+		fetchBattle,
+		type BattleReport,
+	} from "../../api/battle-fetch";
 	import { i18n } from "$lib/i18n/index.svelte";
 
-	type Props = { battleId: string };
-	let { battleId }: Props = $props();
+	import BattleViewer from "../battle-player/battle-viewer.svelte";
+
+	let {
+		gameId,
+		turn,
+		battleId,
+	}: {
+		gameId: string;
+		turn: number;
+		battleId: string;
+	} = $props();
+
+	let state = $state<
+		| { kind: "loading" }
+		| { kind: "ready"; report: BattleReport }
+		| { kind: "not_found" }
+		| { kind: "error"; message: string }
+	>({ kind: "loading" });
+
+	$effect(() => {
+		if (!battleId) {
+			state = { kind: "not_found" };
+			return;
+		}
+		state = { kind: "loading" };
+		fetchBattle(gameId, turn, battleId)
+			.then((report) => {
+				state = { kind: "ready", report };
+			})
+			.catch((err: unknown) => {
+				if (err instanceof BattleFetchError && err.status === 404) {
+					state = { kind: "not_found" };
+				} else {
+					state = {
+						kind: "error",
+						message: err instanceof Error ? err.message : String(err),
+					};
+				}
+			});
+	});
+
+	function backToReport() {
+		goto(`/games/${gameId}/report`);
+	}
+	function backToMap() {
+		goto(`/games/${gameId}/map`);
+	}
 </script>
 
 <section class="active-view" data-testid="active-view-battle" data-battle-id={battleId}>
-	<h2>{i18n.t("game.view.battle")}</h2>
-	<p>{i18n.t("game.shell.coming_soon")}</p>
+	<nav class="back-row">
+		<button
+			type="button"
+			class="back-btn"
+			onclick={backToMap}
+			data-testid="battle-back-to-map"
+		>{i18n.t("game.battle.back_to_map")}</button>
+		<button
+			type="button"
+			class="back-btn"
+			onclick={backToReport}
+			data-testid="battle-back-to-report"
+		>{i18n.t("game.battle.back_to_report")}</button>
+	</nav>
+
+	{#if state.kind === "loading"}
+		<p class="status" data-testid="battle-loading">
+			{i18n.t("game.battle.loading")}
+		</p>
+	{:else if state.kind === "ready"}
+		<BattleViewer report={state.report} />
+	{:else if state.kind === "not_found"}
+		<p class="status" data-testid="battle-not-found">
+			{i18n.t("game.battle.not_found")}
+		</p>
+	{:else}
+		<p class="status error" data-testid="battle-error">{state.message}</p>
+	{/if}
 </section>
 
 <style>
 	.active-view {
-		padding: 1.5rem;
+		padding: 1rem;
 		font-family: system-ui, sans-serif;
+		color: #d6dcf2;
 	}
-	.active-view h2 {
-		margin: 0 0 0.5rem;
-		font-size: 1.1rem;
+	.back-row {
+		display: flex;
+		gap: 0.5rem;
+		max-width: 880px;
+		margin: 0 auto 1rem;
 	}
-	.active-view p {
-		margin: 0;
-		color: #555;
+	.back-btn {
+		appearance: none;
+		background: #1f2748;
+		color: #d6dcf2;
+		border: 1px solid #2c3568;
+		padding: 0.35rem 0.7rem;
+		border-radius: 3px;
+		cursor: pointer;
+		font-size: 0.85rem;
+	}
+	.back-btn:hover {
+		background: #2a3463;
+	}
+	.status {
+		margin: 2rem auto;
+		max-width: 880px;
+		color: #93a0d0;
+		font-size: 0.95rem;
+		text-align: center;
+	}
+	.status.error {
+		color: #e08585;
 	}
 </style>

ui/frontend/src/lib/active-view/map.svelte

@@ -21,6 +21,8 @@ preference the store already manages.
 -->
 <script lang="ts">
 	import { getContext, onDestroy, onMount, untrack } from "svelte";
+	import { goto } from "$app/navigation";
+	import { page } from "$app/state";
 	import { i18n } from "$lib/i18n/index.svelte";
 	import {
 		createRenderer,
@@ -402,13 +404,40 @@ preference the store already manages.
 		if (selection === undefined) return;
 		const hit = handle.hitAt(cursorPx);
 		if (hit === null) return;
-		if (hit.primitive.kind !== "point") return;
 		const target = hitLookup.get(hit.primitive.id);
 		if (target === undefined) return;
-		if (target.kind === "planet") {
-			selection.selectPlanet(target.number);
-		} else {
-			selection.selectShipGroup(target.ref);
+		switch (target.kind) {
+			case "planet":
+				if (hit.primitive.kind !== "point") return;
+				selection.selectPlanet(target.number);
+				break;
+			case "shipGroup":
+				if (hit.primitive.kind !== "point") return;
+				selection.selectShipGroup(target.ref);
+				break;
+			case "battle": {
+				const gameId = page.params.id ?? "";
+				const turn = store?.report?.turn ?? 0;
+				void goto(
+					`/games/${gameId}/battle/${target.battleId}?turn=${turn}`,
+				);
+				break;
+			}
+			case "bombing": {
+				const gameId = page.params.id ?? "";
+				void goto(
+					`/games/${gameId}/report#report-bombings`,
+				).then(() => {
+					if (typeof document === "undefined") return;
+					const row = document.querySelector(
+						`[data-testid="report-bombing-row"][data-planet="${target.planet}"]`,
+					);
+					if (row && row.scrollIntoView) {
+						row.scrollIntoView({ behavior: "smooth", block: "center" });
+					}
+				});
+				break;
+			}
 		}
 	}
 

ui/frontend/src/lib/active-view/report/section-battles.svelte

@@ -1,13 +1,14 @@
 <!--
-Phase 23 Report View — battles section. The wire only carries
-battle UUIDs (the full battle report is fetched lazily by Phase 27),
-so each row is a monospace, non-interactive `<span>` of the battle
-identifier. Phase 27 will turn each row into a link to
-`/games/<id>/battle/<uuid>`; until then dead links are worse than
-plain text.
+Phase 27 Report View — battles section. Each row is a link into the
+Battle Viewer at `/games/<id>/battle/<uuid>?turn=<turn>` where
+`turn` follows the current report's turn so history-mode views land
+on the right battle. Phase 23 rendered the same rows as inactive
+monospace `<span>`; the rewire here is the one-liner the Phase 23
+decision log called out.
 -->
 <script lang="ts">
 	import { getContext } from "svelte";
+	import { page } from "$app/state";
 
 	import { i18n } from "$lib/i18n/index.svelte";
 	import {
@@ -19,7 +20,9 @@ plain text.
 		RENDERED_REPORT_CONTEXT_KEY,
 	);
 	const report = $derived(rendered?.report ?? null);
-	const ids = $derived(report?.battleIds ?? []);
+	const battles = $derived(report?.battles ?? []);
+	const gameId = $derived(page.params.id ?? "");
+	const turn = $derived(report?.turn ?? 0);
 </script>
 
 <section
@@ -31,22 +34,23 @@ plain text.
 
 	{#if report === null}
 		<p class="status">{i18n.t("game.report.loading")}</p>
-	{:else if ids.length === 0}
+	{:else if battles.length === 0}
 		<p class="status" data-testid="battles-empty">
 			{i18n.t("game.report.section.battles.empty")}
 		</p>
 	{:else}
 		<ul class="ids" data-testid="battles-list">
-			{#each ids as id (id)}
+			{#each battles as b (b.id)}
 				<li>
 					<span class="label">
 						{i18n.t("game.report.section.battles.id_label")}
 					</span>
-					<span
+					<a
 						class="uuid"
+						href={`/games/${gameId}/battle/${b.id}?turn=${turn}`}
 						data-testid="report-battle-row"
-						data-id={id}
-					>{id}</span>
+						data-id={b.id}
+					>{b.id}</a>
 				</li>
 			{/each}
 		</ul>
@@ -87,5 +91,10 @@ plain text.
 	.uuid {
 		color: #cfd7ff;
 		font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+		text-decoration: underline;
+		text-underline-offset: 2px;
+	}
+	.uuid:hover {
+		color: #ffffff;
 	}
 </style>

ui/frontend/src/lib/battle-player/battle-scene.svelte

@@ -0,0 +1,223 @@
+<!--
+BattleScene — radial SVG visualisation of one battle frame.
+
+Layout: planet at the centre, race anchors equally spaced on an
+outer ring, each race rendered as a cluster of small class circles
+labelled `<className>:<numLeft>` underneath. The shot line for the
+current frame's `lastAction` is drawn from attacker group to
+defender group; red when the shot destroyed the defender, green
+otherwise. Observer groups (`inBattle === false`) are filtered out
+by `buildFrames`, so they never appear here.
+-->
+<script lang="ts">
+	import type { BattleReport } from "../../api/battle-fetch";
+	import { layoutRaces } from "./radial-layout";
+	import {
+		buildGroupRaceMap,
+		normaliseGroups,
+		type Frame,
+	} from "./timeline";
+
+	let {
+		report,
+		frame,
+	}: {
+		report: BattleReport;
+		frame: Frame;
+	} = $props();
+
+	const VIEW_BOX = 800;
+	const CENTER = { x: VIEW_BOX / 2, y: VIEW_BOX / 2 };
+	const PLANET_RADIUS = 60;
+	const RACE_RING_RADIUS = 280;
+	const CLASS_CIRCLE_RADIUS = 24;
+	const CLASS_SPACING = 64;
+
+	const groupRace = $derived(buildGroupRaceMap(report.protocol));
+	const allGroups = $derived(normaliseGroups(report));
+
+	type ClusterEntry = {
+		key: number;
+		className: string;
+		numLeft: number;
+	};
+
+	const clustersByRace = $derived.by(() => {
+		const out = new Map<number, ClusterEntry[]>();
+		for (const g of allGroups) {
+			const numLeft = frame.remaining.get(g.key) ?? 0;
+			const list = out.get(g.raceId) ?? [];
+			list.push({
+				key: g.key,
+				className: g.group.className,
+				numLeft,
+			});
+			out.set(g.raceId, list);
+		}
+		// Stable cluster order: by classname then key.
+		for (const list of out.values()) {
+			list.sort((a, b) => {
+				const byName = a.className.localeCompare(b.className);
+				if (byName !== 0) return byName;
+				return a.key - b.key;
+			});
+		}
+		return out;
+	});
+
+	const raceLayout = $derived(
+		layoutRaces(frame.activeRaceIds, {
+			center: CENTER,
+			radius: RACE_RING_RADIUS,
+		}),
+	);
+
+	function classCircleX(index: number, count: number): number {
+		const span = (count - 1) * CLASS_SPACING;
+		return -span / 2 + index * CLASS_SPACING;
+	}
+
+	function findClassCircleCenter(groupKey: number) {
+		const raceId = groupRace.get(groupKey);
+		if (raceId === undefined) return null;
+		const anchor = raceLayout.find((a) => a.raceId === raceId);
+		if (!anchor) return null;
+		const cluster = clustersByRace.get(raceId) ?? [];
+		const idx = cluster.findIndex((c) => c.key === groupKey);
+		if (idx === -1) return null;
+		return {
+			x: anchor.x + classCircleX(idx, cluster.length),
+			y: anchor.y,
+		};
+	}
+
+	const shotLine = $derived.by(() => {
+		const action = frame.lastAction;
+		if (!action) return null;
+		const from = findClassCircleCenter(action.sa);
+		const to = findClassCircleCenter(action.sd);
+		if (!from || !to) return null;
+		return { from, to, destroyed: action.x };
+	});
+
+	const raceLabelById = $derived.by(() => {
+		const out = new Map<number, string>();
+		for (const g of allGroups) {
+			out.set(g.raceId, g.group.race);
+		}
+		return out;
+	});
+</script>
+
+<svg
+	class="battle-scene"
+	viewBox="0 0 {VIEW_BOX} {VIEW_BOX}"
+	role="img"
+	aria-label="battle scene"
+	data-testid="battle-scene"
+>
+	<circle
+		cx={CENTER.x}
+		cy={CENTER.y}
+		r={PLANET_RADIUS}
+		class="planet"
+		data-testid="battle-scene-planet"
+	/>
+	<text
+		x={CENTER.x}
+		y={CENTER.y + PLANET_RADIUS + 24}
+		text-anchor="middle"
+		class="planet-label"
+	>{report.planetName} (#{report.planet})</text>
+
+	{#each raceLayout as anchor (anchor.raceId)}
+		{@const cluster = clustersByRace.get(anchor.raceId) ?? []}
+		<g
+			class="race-cluster"
+			data-testid="battle-race-cluster"
+			data-race-id={anchor.raceId}
+		>
+			<text
+				x={anchor.x}
+				y={anchor.y - CLASS_CIRCLE_RADIUS - 12}
+				text-anchor="middle"
+				class="race-label"
+			>{raceLabelById.get(anchor.raceId) ?? `race ${anchor.raceId}`}</text>
+			{#each cluster as entry, i (entry.key)}
+				{@const cx = anchor.x + classCircleX(i, cluster.length)}
+				<g
+					class="class-marker"
+					data-testid="battle-class-marker"
+					data-group-key={entry.key}
+				>
+					<circle
+						cx={cx}
+						cy={anchor.y}
+						r={CLASS_CIRCLE_RADIUS}
+					/>
+					<text
+						x={cx}
+						y={anchor.y + CLASS_CIRCLE_RADIUS + 16}
+						text-anchor="middle"
+						class="class-label"
+					>{entry.className}:{entry.numLeft}</text>
+				</g>
+			{/each}
+		</g>
+	{/each}
+
+	{#if shotLine}
+		<line
+			x1={shotLine.from.x}
+			y1={shotLine.from.y}
+			x2={shotLine.to.x}
+			y2={shotLine.to.y}
+			class="shot"
+			class:destroyed={shotLine.destroyed}
+			data-testid="battle-shot"
+			data-destroyed={shotLine.destroyed ? "true" : "false"}
+		/>
+	{/if}
+</svg>
+
+<style>
+	.battle-scene {
+		width: 100%;
+		height: auto;
+		background: #0a0d1a;
+		display: block;
+	}
+	.planet {
+		fill: #2a345f;
+		stroke: #5b6aa3;
+		stroke-width: 2;
+	}
+	.planet-label {
+		fill: #c4caea;
+		font-size: 18px;
+		font-family: ui-sans-serif, system-ui, sans-serif;
+	}
+	.race-label {
+		fill: #e2e6ff;
+		font-size: 16px;
+		font-weight: 600;
+		font-family: ui-sans-serif, system-ui, sans-serif;
+	}
+	.class-marker circle {
+		fill: #1a2042;
+		stroke: #6d7bb5;
+		stroke-width: 1.5;
+	}
+	.class-label {
+		fill: #b8c0e6;
+		font-size: 12px;
+		font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
+	}
+	.shot {
+		stroke: #44dd66;
+		stroke-width: 2;
+	}
+	.shot.destroyed {
+		stroke: #ee3344;
+	}
+</style>

ui/frontend/src/lib/battle-player/battle-viewer.svelte

@@ -0,0 +1,167 @@
+<!--
+BattleViewer — orchestrates the radial battle scene, the playback
+controls, and the accessibility text log for one BattleReport. Owns
+the playback state (`frameIndex`, `playing`, `speed`). The component
+is logically isolated: feed it any `BattleReport` matching
+`pkg/model/report/battle.go` and it plays back.
+-->
+<script lang="ts">
+	import { onDestroy } from "svelte";
+
+	import { i18n } from "$lib/i18n/index.svelte";
+	import type { BattleReport } from "../../api/battle-fetch";
+
+	import BattleScene from "./battle-scene.svelte";
+	import PlaybackControls from "./playback-controls.svelte";
+	import { buildFrames } from "./timeline";
+
+	let { report }: { report: BattleReport } = $props();
+
+	const frames = $derived(buildFrames(report));
+	let frameIndex = $state(0);
+	let playing = $state(false);
+	let speed = $state<1 | 2 | 4>(1);
+
+	const frame = $derived(frames[Math.min(frameIndex, frames.length - 1)]);
+
+	// 1x = 400 ms per frame, 2x = 200 ms, 4x = 100 ms. The timer is
+	// rescheduled whenever `speed` or `playing` flips.
+	let timer: ReturnType<typeof setInterval> | null = null;
+	$effect(() => {
+		if (timer !== null) {
+			clearInterval(timer);
+			timer = null;
+		}
+		if (!playing) return;
+		const intervalMs = 400 / speed;
+		timer = setInterval(() => {
+			if (frameIndex >= frames.length - 1) {
+				playing = false;
+				return;
+			}
+			frameIndex = frameIndex + 1;
+		}, intervalMs);
+	});
+
+	onDestroy(() => {
+		if (timer !== null) {
+			clearInterval(timer);
+			timer = null;
+		}
+	});
+
+	function describeAction(index: number): string {
+		const action = report.protocol[index];
+		const attackerGroup = report.ships[String(action.sa)];
+		const defenderGroup = report.ships[String(action.sd)];
+		const attackerRace = attackerGroup?.race ?? `race ${action.a}`;
+		const attackerClass = attackerGroup?.className ?? `class ${action.sa}`;
+		const defenderRace = defenderGroup?.race ?? `race ${action.d}`;
+		const defenderClass = defenderGroup?.className ?? `class ${action.sd}`;
+		const key = action.x
+			? "game.battle.log.destroyed"
+			: "game.battle.log.shielded";
+		return i18n.t(key, {
+			attacker_race: attackerRace,
+			attacker_class: attackerClass,
+			defender_race: defenderRace,
+			defender_class: defenderClass,
+		});
+	}
+</script>
+
+<div class="viewer" data-testid="battle-viewer">
+	<header class="header">
+		<h2 data-testid="battle-viewer-title">
+			{i18n.t("game.battle.title")}
+		</h2>
+		<span class="progress" data-testid="battle-frame-index">
+			{frame.shotIndex} / {report.protocol.length}
+		</span>
+	</header>
+
+	<div class="scene">
+		<BattleScene {report} {frame} />
+	</div>
+
+	<PlaybackControls
+		bind:playing
+		bind:frameIndex
+		bind:speed
+		frameCount={frames.length}
+	/>
+
+	<section
+		class="log"
+		aria-label={i18n.t("game.battle.accessibility.protocol_heading")}
+	>
+		<h3>{i18n.t("game.battle.accessibility.protocol_heading")}</h3>
+		<ol data-testid="battle-protocol-log">
+			{#each report.protocol as _action, i (i)}
+				<li
+					data-testid="battle-protocol-log-item"
+					data-current={i + 1 === frame.shotIndex ? "true" : "false"}
+				>{describeAction(i)}</li>
+			{/each}
+		</ol>
+	</section>
+</div>
+
+<style>
+	.viewer {
+		display: flex;
+		flex-direction: column;
+		gap: 0.75rem;
+		max-width: 880px;
+		margin: 0 auto;
+		padding: 1rem;
+		color: #d6dcf2;
+		font-family: inherit;
+	}
+	.header {
+		display: flex;
+		justify-content: space-between;
+		align-items: baseline;
+	}
+	.header h2 {
+		margin: 0;
+		font-size: 1.1rem;
+		text-transform: uppercase;
+		letter-spacing: 0.05em;
+	}
+	.progress {
+		color: #93a0d0;
+		font-variant-numeric: tabular-nums;
+		font-size: 0.9rem;
+	}
+	.scene {
+		background: #0a0d1a;
+		border: 1px solid #1e264a;
+		border-radius: 4px;
+		overflow: hidden;
+	}
+	.log h3 {
+		margin: 0 0 0.4rem;
+		color: #93a0d0;
+		font-size: 0.8rem;
+		text-transform: uppercase;
+		letter-spacing: 0.05em;
+	}
+	.log ol {
+		list-style: decimal inside;
+		margin: 0;
+		padding: 0;
+		font-size: 0.85rem;
+		max-height: 14rem;
+		overflow-y: auto;
+		color: #c6cdf0;
+	}
+	.log li {
+		padding: 0.15rem 0;
+		border-bottom: 1px solid #1c2240;
+	}
+	.log li[data-current="true"] {
+		color: #ffe27a;
+		font-weight: 600;
+	}
+</style>

ui/frontend/src/lib/battle-player/playback-controls.svelte

@@ -0,0 +1,145 @@
+<!--
+PlaybackControls — rewind / step-back / play-pause / step-forward
+plus a 1x/2x/4x speed switch. Owns no playback state; bind `playing`,
+`frameIndex`, and `speed` from the orchestrator. Disables step/rewind
+when there's nowhere to go and disables forward when the timeline is
+already at its end.
+-->
+<script lang="ts">
+	import { i18n } from "$lib/i18n/index.svelte";
+
+	let {
+		playing = $bindable(),
+		frameIndex = $bindable(),
+		speed = $bindable(),
+		frameCount,
+	}: {
+		playing: boolean;
+		frameIndex: number;
+		speed: 1 | 2 | 4;
+		frameCount: number;
+	} = $props();
+
+	function rewind() {
+		playing = false;
+		frameIndex = 0;
+	}
+	function stepBack() {
+		playing = false;
+		if (frameIndex > 0) frameIndex = frameIndex - 1;
+	}
+	function togglePlay() {
+		if (frameIndex >= frameCount - 1) {
+			frameIndex = 0;
+		}
+		playing = !playing;
+	}
+	function stepForward() {
+		playing = false;
+		if (frameIndex < frameCount - 1) frameIndex = frameIndex + 1;
+	}
+	function setSpeed(value: 1 | 2 | 4) {
+		speed = value;
+	}
+</script>
+
+<div class="controls" data-testid="battle-controls">
+	<button
+		type="button"
+		onclick={rewind}
+		disabled={frameIndex === 0}
+		aria-label={i18n.t("game.battle.controls.rewind")}
+		data-testid="battle-control-rewind"
+	>⏮</button>
+	<button
+		type="button"
+		onclick={stepBack}
+		disabled={frameIndex === 0}
+		aria-label={i18n.t("game.battle.controls.step_backward")}
+		data-testid="battle-control-step-back"
+	>◀︎</button>
+	<button
+		type="button"
+		onclick={togglePlay}
+		aria-label={playing
+			? i18n.t("game.battle.controls.pause")
+			: i18n.t("game.battle.controls.play")}
+		data-testid="battle-control-play"
+		data-playing={playing ? "true" : "false"}
+	>{playing ? "⏸" : "▶︎"}</button>
+	<button
+		type="button"
+		onclick={stepForward}
+		disabled={frameIndex >= frameCount - 1}
+		aria-label={i18n.t("game.battle.controls.step_forward")}
+		data-testid="battle-control-step-forward"
+	>▶︎▶︎</button>
+
+	<div class="spacer" aria-hidden="true"></div>
+
+	<span class="speed-label">{i18n.t("game.battle.controls.speed_label")}</span>
+	<button
+		type="button"
+		class:active={speed === 1}
+		onclick={() => setSpeed(1)}
+		data-testid="battle-control-speed-1x"
+	>{i18n.t("game.battle.controls.speed_1x")}</button>
+	<button
+		type="button"
+		class:active={speed === 2}
+		onclick={() => setSpeed(2)}
+		data-testid="battle-control-speed-2x"
+	>{i18n.t("game.battle.controls.speed_2x")}</button>
+	<button
+		type="button"
+		class:active={speed === 4}
+		onclick={() => setSpeed(4)}
+		data-testid="battle-control-speed-4x"
+	>{i18n.t("game.battle.controls.speed_4x")}</button>
+</div>
+
+<style>
+	.controls {
+		display: flex;
+		align-items: center;
+		gap: 0.4rem;
+		padding: 0.5rem 0.75rem;
+		background: #131934;
+		border: 1px solid #1e264a;
+		border-radius: 4px;
+	}
+	.spacer {
+		flex: 1 1 auto;
+	}
+	button {
+		appearance: none;
+		background: #1f2748;
+		color: #d6dcf2;
+		border: 1px solid #2c3568;
+		padding: 0.35rem 0.7rem;
+		border-radius: 3px;
+		cursor: pointer;
+		font-size: 0.9rem;
+		font-family: inherit;
+		min-width: 2.5rem;
+	}
+	button:hover:not(:disabled) {
+		background: #2a3463;
+	}
+	button:disabled {
+		opacity: 0.4;
+		cursor: not-allowed;
+	}
+	button.active {
+		background: #3a4585;
+		border-color: #5d6cb8;
+		color: #ffffff;
+	}
+	.speed-label {
+		color: #93a0d0;
+		font-size: 0.8rem;
+		text-transform: uppercase;
+		letter-spacing: 0.05em;
+		margin-right: 0.2rem;
+	}
+</style>

ui/frontend/src/lib/battle-player/radial-layout.ts

@@ -0,0 +1,50 @@
+// Radial layout for the BattleViewer.
+//
+// Places race anchors on a circle of radius `radius` around `center`
+// at equal angular spacing. The first anchor sits at the top (12
+// o'clock); subsequent anchors march clockwise. When a race is
+// eliminated mid-battle, the caller filters it out of `activeRaceIds`
+// and the survivors are re-spaced on the next frame. The same helper
+// drives both the initial layout and that re-distribution.
+
+export interface RaceAnchor {
+	raceId: number;
+	x: number;
+	y: number;
+	/** Angle in radians measured from the positive Y axis clockwise. */
+	angle: number;
+}
+
+export interface RadialLayoutOptions {
+	center: { x: number; y: number };
+	radius: number;
+}
+
+/**
+ * layoutRaces returns anchor positions for each `activeRaceIds`
+ * entry, placed at equal angular spacing on a circle. The input
+ * order is preserved so consumers get a stable mapping across
+ * frames; eliminated entries should simply be filtered out before
+ * the call.
+ */
+export function layoutRaces(
+	activeRaceIds: number[],
+	options: RadialLayoutOptions,
+): RaceAnchor[] {
+	const count = activeRaceIds.length;
+	if (count === 0) return [];
+	const { center, radius } = options;
+	const out: RaceAnchor[] = [];
+	for (let i = 0; i < count; i++) {
+		// 12 o'clock = -PI/2 in math convention; clockwise → +i*step.
+		const step = (2 * Math.PI) / count;
+		const angle = -Math.PI / 2 + i * step;
+		out.push({
+			raceId: activeRaceIds[i],
+			x: center.x + radius * Math.cos(angle),
+			y: center.y + radius * Math.sin(angle),
+			angle,
+		});
+	}
+	return out;
+}

ui/frontend/src/lib/battle-player/timeline.ts

@@ -0,0 +1,134 @@
+// Timeline builder for the BattleViewer.
+//
+// Given a `BattleReport`, expands the flat `protocol` into a
+// sequence of frames. Frame 0 carries the initial state; frame N
+// (1 ≤ N ≤ protocol.length) reflects the state right after the
+// (N-1)-th action has been applied. Each frame is self-contained so
+// stepping forward and backward is a constant-time index lookup, no
+// rewind logic needed.
+
+import type {
+	BattleActionReport,
+	BattleReport,
+	BattleReportGroup,
+} from "../../api/battle-fetch";
+
+/**
+ * Frame is one tick of the battle playback. `remaining` carries the
+ * surviving ship count for each ship-group key from
+ * `BattleReport.ships`; `activeRaceIds` are the race indices with at
+ * least one surviving in-battle group. `lastAction` is the action
+ * applied to produce this frame, or `null` for the initial frame.
+ */
+export interface Frame {
+	shotIndex: number;
+	remaining: Map<number, number>;
+	activeRaceIds: number[];
+	lastAction: BattleActionReport | null;
+}
+
+export interface NormalisedGroup {
+	key: number;
+	group: BattleReportGroup;
+	raceId: number;
+}
+
+/**
+ * normaliseGroups returns the in-battle ship groups from a
+ * BattleReport indexed by their integer key. Observer groups
+ * (`inBattle === false`) are skipped because they are neither
+ * targeted nor drawn. The race index per group is derived from the
+ * protocol — every in-battle group appears at least once as
+ * attacker or defender, and the engine's pairing (a, sa) / (d, sd)
+ * defines the relationship.
+ */
+export function normaliseGroups(report: BattleReport): NormalisedGroup[] {
+	const raceByKey = buildGroupRaceMap(report.protocol);
+	const out: NormalisedGroup[] = [];
+	for (const [keyRaw, group] of Object.entries(report.ships)) {
+		if (!group.inBattle) continue;
+		const key = Number(keyRaw);
+		if (!Number.isFinite(key)) continue;
+		const raceId = raceByKey.get(key);
+		if (raceId === undefined) continue;
+		out.push({ key, group, raceId });
+	}
+	return out;
+}
+
+/**
+ * buildGroupRaceMap extracts the `ship-group key → race index`
+ * mapping from a battle protocol. Same key appearing twice always
+ * carries the same race index — protocol entries are emitted by the
+ * engine, which never crosses these wires.
+ */
+export function buildGroupRaceMap(
+	protocol: BattleActionReport[],
+): Map<number, number> {
+	const out = new Map<number, number>();
+	for (const action of protocol) {
+		if (!out.has(action.sa)) out.set(action.sa, action.a);
+		if (!out.has(action.sd)) out.set(action.sd, action.d);
+	}
+	return out;
+}
+
+/**
+ * buildFrames walks the protocol once and emits a frame after each
+ * applied action plus the initial frame. The remaining-ships map is
+ * cloned per frame so callers can step backward without manual
+ * bookkeeping. Eliminated races drop out of `activeRaceIds` as soon
+ * as their last in-battle group hits zero.
+ */
+export function buildFrames(report: BattleReport): Frame[] {
+	const groups = normaliseGroups(report);
+	const initialRemaining = new Map<number, number>();
+	const raceTotals = new Map<number, number>();
+	for (const g of groups) {
+		initialRemaining.set(g.key, g.group.num);
+		raceTotals.set(g.raceId, (raceTotals.get(g.raceId) ?? 0) + g.group.num);
+	}
+
+	const frames: Frame[] = [];
+	frames.push({
+		shotIndex: 0,
+		remaining: new Map(initialRemaining),
+		activeRaceIds: collectActiveRaces(raceTotals),
+		lastAction: null,
+	});
+
+	const groupRaceByKey = new Map<number, number>();
+	for (const g of groups) groupRaceByKey.set(g.key, g.raceId);
+
+	const current = new Map(initialRemaining);
+	const runningRaceTotals = new Map(raceTotals);
+	for (let i = 0; i < report.protocol.length; i++) {
+		const action = report.protocol[i];
+		if (action.x) {
+			const left = current.get(action.sd) ?? 0;
+			const next = Math.max(0, left - 1);
+			current.set(action.sd, next);
+			const raceId = groupRaceByKey.get(action.sd);
+			if (raceId !== undefined) {
+				const t = (runningRaceTotals.get(raceId) ?? 0) - 1;
+				runningRaceTotals.set(raceId, Math.max(0, t));
+			}
+		}
+		frames.push({
+			shotIndex: i + 1,
+			remaining: new Map(current),
+			activeRaceIds: collectActiveRaces(runningRaceTotals),
+			lastAction: action,
+		});
+	}
+
+	return frames;
+}
+
+function collectActiveRaces(totals: Map<number, number>): number[] {
+	const out: number[] = [];
+	for (const [raceId, total] of totals.entries()) {
+		if (total > 0) out.push(raceId);
+	}
+	return out.sort((a, b) => a - b);
+}

ui/frontend/src/lib/i18n/locales/en.ts

@@ -483,6 +483,23 @@ const en = {
 	"game.report.section.battles.title": "battles",
 	"game.report.section.battles.empty": "no battles last turn",
 	"game.report.section.battles.id_label": "battle",
+	"game.battle.title": "battle",
+	"game.battle.loading": "loading battle…",
+	"game.battle.not_found": "battle not found",
+	"game.battle.back_to_report": "back to report",
+	"game.battle.back_to_map": "back to map",
+	"game.battle.controls.play": "play",
+	"game.battle.controls.pause": "pause",
+	"game.battle.controls.step_forward": "step forward",
+	"game.battle.controls.step_backward": "step back",
+	"game.battle.controls.rewind": "rewind to start",
+	"game.battle.controls.speed_label": "speed",
+	"game.battle.controls.speed_1x": "1x",
+	"game.battle.controls.speed_2x": "2x",
+	"game.battle.controls.speed_4x": "4x",
+	"game.battle.log.destroyed": "{attacker_race}'s {attacker_class} destroyed {defender_race}'s {defender_class}",
+	"game.battle.log.shielded": "{attacker_race}'s {attacker_class} hit {defender_race}'s {defender_class}, shields held",
+	"game.battle.accessibility.protocol_heading": "battle log",
 	"game.report.section.bombings.title": "bombings",
 	"game.report.section.bombings.empty": "no bombings last turn",
 	"game.report.section.bombings.column.planet": "planet",

ui/frontend/src/lib/i18n/locales/ru.ts

@@ -484,6 +484,23 @@ const ru: Record<keyof typeof en, string> = {
 	"game.report.section.battles.title": "сражения",
 	"game.report.section.battles.empty": "сражений в этом ходу не было",
 	"game.report.section.battles.id_label": "сражение",
+	"game.battle.title": "сражение",
+	"game.battle.loading": "загрузка сражения…",
+	"game.battle.not_found": "сражение не найдено",
+	"game.battle.back_to_report": "к отчёту",
+	"game.battle.back_to_map": "к карте",
+	"game.battle.controls.play": "запустить",
+	"game.battle.controls.pause": "пауза",
+	"game.battle.controls.step_forward": "шаг вперёд",
+	"game.battle.controls.step_backward": "шаг назад",
+	"game.battle.controls.rewind": "к началу",
+	"game.battle.controls.speed_label": "скорость",
+	"game.battle.controls.speed_1x": "1x",
+	"game.battle.controls.speed_2x": "2x",
+	"game.battle.controls.speed_4x": "4x",
+	"game.battle.log.destroyed": "{attacker_class} расы {attacker_race} уничтожает {defender_class} расы {defender_race}",
+	"game.battle.log.shielded": "{attacker_class} расы {attacker_race} попадает в {defender_class} расы {defender_race}, щиты выдержали",
+	"game.battle.accessibility.protocol_heading": "протокол сражения",
 	"game.report.section.bombings.title": "бомбардировки",
 	"game.report.section.bombings.empty": "бомбардировок в этом ходу не было",
 	"game.report.section.bombings.column.planet": "планета",