Eval: 2-round policy + sync-start gate + no auto-advance

- Sample 2 rounds per (match, map) instead of 4: one endpoint (round 1
or last, picked deterministically) plus one PRNG-chosen middle round.
- Eval mode no longer auto-advances when the round ends — reviewers
drive navigation explicitly via the eval bar's Prev/Next.
- New sync-start gate in eval mode: the round starts paused and only
auto-plays once every POV tile has emitted `loadeddata` (first frame
decoded), so the comparison view never starts mid-buffer with some
panes blank. A small "Loading N / 10 POVs…" indicator overlays the
grid while we wait; touching play or leaving eval mode releases the
gate immediately. preloadAllPlayers is force-on in eval mode so the
HTTP-level prefetch runs alongside the MSE attach.

src/lib/components/grid-tile.svelte

@@ -23,6 +23,7 @@
 		onLeaderTime?: (t: number) => void;
 		onLeaderEnded?: () => void;
 		onBufferedChange?: (player: number, ranges: BufferedRange[]) => void;
+		onReady?: (player: number) => void;
 	}
 
 	let {
@@ -40,7 +41,8 @@
 		onSelect,
 		onLeaderTime,
 		onLeaderEnded,
-		onBufferedChange
+		onBufferedChange,
+		onReady
 	}: Props = $props();
 
 	let videoEl = $state<HTMLVideoElement | undefined>();
@@ -127,6 +129,11 @@
 		onBufferedChange(player, out);
 	}
 
+	function onLoadedData() {
+		// First decoded frame available — the tile is now safe to play.
+		onReady?.(player);
+	}
+
 	function onKeyDown(e: KeyboardEvent) {
 		if (!available) return;
 		if (e.key === 'Enter' || e.key === ' ') {
@@ -177,6 +184,7 @@
 		ontimeupdate={onTimeUpdate}
 		onended={onEnded}
 		onprogress={onProgress}
+		onloadeddata={onLoadedData}
 		class="size-full object-cover"
 	></video>
 

src/lib/components/perspective-grid.svelte

@@ -19,6 +19,7 @@
 		onTimeUpdate?: (t: number) => void;
 		onLeaderEnded?: () => void;
 		onBufferedChange?: (ranges: BufferedRange[]) => void;
+		onReady?: (player: number) => void;
 	}
 
 	let {
@@ -33,7 +34,8 @@
 		onSelect,
 		onTimeUpdate,
 		onLeaderEnded,
-		onBufferedChange
+		onBufferedChange,
+		onReady
 	}: Props = $props();
 
 	type PerPlayer = {
@@ -152,6 +154,7 @@
 								{onLeaderTime}
 								onLeaderEnded={() => onLeaderEnded?.()}
 								onBufferedChange={handleTileBuffered}
+								{onReady}
 							/>
 							<div class="flex items-center gap-1.5 px-0.5 text-xs">
 								<span
@@ -192,6 +195,7 @@
 								{onLeaderTime}
 								onLeaderEnded={() => onLeaderEnded?.()}
 								onBufferedChange={handleTileBuffered}
+								{onReady}
 							/>
 							<div class="flex items-center gap-1.5 px-0.5 text-xs">
 								<span

src/lib/eval.ts

@@ -218,13 +218,13 @@ function prng(seed: number): number {
 }
 
 /**
- * Evaluation policy: per (match, map), sample 4 rounds — first, last, and
- * two deterministic random rounds in the middle. Sorted by match_id then
+ * Evaluation policy: per (match, map), sample 2 rounds — one endpoint
+ * (deterministically either the first or the last round) plus one
+ * deterministic random round in the middle. Sorted by match_id then
  * map_index to match the rest of the app's canonical order.
  *
- * Validating ALL 4 candidates of a (match, map) without flagging implies the
- * whole match-map is good; flagging any one of the 4 marks the match-map as
- * having issues.
+ * Validating BOTH candidates of a (match, map) without flagging implies the
+ * whole match-map is good; flagging either one marks it as having issues.
  */
 export function buildEvalQueue(matches: Match[]): EvalCandidate[] {
 	const sorted = matches
@@ -236,19 +236,26 @@ export function buildEvalQueue(matches: Match[]): EvalCandidate[] {
 		const total = m.rounds_played;
 		if (!total || total < 1) continue;
 
-		const picks = new Set<number>([1, total]);
-		// Two PRNG-picked middle rounds when there's room for them.
-		if (total >= 4) {
-			const seedBase = m.match_id * 31 + m.map_name.length * 17 + (m.map_index ?? 0);
+		const seedBase = m.match_id * 31 + m.map_name.length * 17 + (m.map_index ?? 0);
+
+		const picks = new Set<number>();
+		// Endpoint: either round 1 or the last round, picked deterministically.
+		const endpoint = prng(seedBase) < 0.5 || total === 1 ? 1 : total;
+		picks.add(endpoint);
+
+		// One PRNG-picked middle round when there's room. For tiny matches
+		// (≤ 2 rounds) the second pick falls back to the other endpoint so
+		// every match-map still contributes 2 candidates when possible.
+		if (total >= 3) {
 			const span = total - 2; // pick from [2, total - 1]
 			let attempts = 0;
-			while (picks.size < 4 && attempts < 16) {
-				const r = 2 + Math.floor(prng(seedBase + attempts) * span);
+			while (picks.size < 2 && attempts < 16) {
+				const r = 2 + Math.floor(prng(seedBase + 100 + attempts) * span);
 				picks.add(r);
 				attempts++;
 			}
-		} else if (total === 3) {
-			picks.add(2);
+		} else if (total === 2) {
+			picks.add(endpoint === 1 ? 2 : 1);
 		}
 
 		for (const round of [...picks].sort((a, b) => a - b)) {

src/routes/match/[matchId]/[mapName]/+page.svelte

@@ -81,6 +81,14 @@
 	let preloadAllPlayers = $state(false);
 	let preloadedPlayers = $state(new Set<number>());
 
+	// Players whose first decoded frame is on screen — populated by GridTile
+	// `loadeddata` events. Used in eval mode to gate auto-play until every
+	// POV is showing.
+	let readyPlayers = $state(new Set<number>());
+	// True between (round change) and (all 10 tiles ready) while in eval
+	// mode. Auto-clears once all tiles report ready, which auto-resumes play.
+	let awaitingAllReady = $state(false);
+
 	let viewMode = $state<'single' | 'grid'>(readViewFromUrl());
 
 	// Evaluation mode driven by ?eval=1&i=N. Queue is deterministic from the
@@ -146,6 +154,15 @@
 		activeVideoEnded = false;
 		bufferedRanges = [];
 		preloadedPlayers = new Set();
+		readyPlayers = new Set();
+		// In eval mode every round starts paused and only auto-plays once
+		// every POV tile has its first frame decoded — so reviewers always
+		// see all 10 perspectives in sync from t=0.
+		if (inEvalMode) {
+			masterPaused = true;
+			awaitingAllReady = true;
+			preloadAllPlayers = true;
+		}
 		try {
 			const rows = await listRoundPreviews(data.match.match_id, data.match.map_name, round, {
 				signal: ctrl.signal
@@ -173,6 +190,39 @@
 		preloadedPlayers = next;
 	}
 
+	function markPlayerVisible(p: number) {
+		if (readyPlayers.has(p)) return;
+		const next = new Set(readyPlayers);
+		next.add(p);
+		readyPlayers = next;
+	}
+
+	// Eval-mode auto-play gate: once every POV present in the round has
+	// reported its first frame, drop the awaiting flag and resume playback
+	// (unless the user has already pressed play, in which case master remains
+	// unpaused and this is a no-op).
+	$effect(() => {
+		if (!awaitingAllReady) return;
+		const expected = playerDurations.size;
+		if (!expected) return;
+		if (readyPlayers.size < expected) return;
+		untrack(() => {
+			awaitingAllReady = false;
+			masterPaused = false;
+		});
+	});
+
+	// Leaving eval mode shouldn't strand the player paused with a half-active
+	// gate — release both immediately.
+	$effect(() => {
+		if (inEvalMode) return;
+		if (!awaitingAllReady) return;
+		untrack(() => {
+			awaitingAllReady = false;
+			masterPaused = false;
+		});
+	});
+
 	// When preloadAllPlayers is on, fetch every (other) player's chunks so
 	// they're hot in the HTTP cache. The active player's chunks are already
 	// being fetched by the video player itself.
@@ -253,6 +303,12 @@
 	}
 
 	function handlePlaybackEnded() {
+		// In eval mode, never auto-advance to the next round — the reviewer
+		// drives navigation with the eval bar's Prev/Next buttons.
+		if (inEvalMode) {
+			masterPaused = true;
+			return;
+		}
 		const ri = data.rounds.findIndex((r) => r.round === currentRoundNum);
 		if (ri >= 0 && ri < data.rounds.length - 1) {
 			selectRound(data.rounds[ri + 1].round);
@@ -273,6 +329,9 @@
 			virtualTime = 0;
 			activeVideoEnded = false;
 		}
+		// User overrides the eval-mode auto-resume gate as soon as they
+		// touch the play button.
+		awaitingAllReady = false;
 		masterPaused = !masterPaused;
 	}
 
@@ -516,25 +575,35 @@
 					{initialVirtualTime}
 				/>
 			{:else}
-				<PerspectiveGrid
-					{previews}
-					{currentPlayer}
-					{availablePlayers}
-					{playerDurations}
-					{virtualTime}
-					paused={masterPaused}
-					muted={masterMuted}
-					playbackRate={masterPlaybackRate}
-					onPausedChange={(p) => (masterPaused = p)}
-					onSelect={(p) => {
-						selectPlayer(p);
-						// Stay in grid mode after selecting; the new
-						// current player just becomes the audio leader.
-					}}
-					onTimeUpdate={handleTimeUpdate}
-					onLeaderEnded={handleVideoEnded}
-					onBufferedChange={(r) => (bufferedRanges = r)}
-				/>
+				<div class="relative">
+					<PerspectiveGrid
+						{previews}
+						{currentPlayer}
+						{availablePlayers}
+						{playerDurations}
+						{virtualTime}
+						paused={masterPaused}
+						muted={masterMuted}
+						playbackRate={masterPlaybackRate}
+						onPausedChange={(p) => (masterPaused = p)}
+						onSelect={(p) => {
+							selectPlayer(p);
+							// Stay in grid mode after selecting; the new
+							// current player just becomes the audio leader.
+						}}
+						onTimeUpdate={handleTimeUpdate}
+						onLeaderEnded={handleVideoEnded}
+						onBufferedChange={(r) => (bufferedRanges = r)}
+						onReady={markPlayerVisible}
+					/>
+					{#if awaitingAllReady && playerDurations.size > 0}
+						<div
+							class="pointer-events-none absolute top-3 right-3 z-30 rounded-md border border-amber-500/40 bg-amber-500/15 px-2.5 py-1 font-mono text-[11px] text-amber-700 tabular-nums shadow-sm backdrop-blur-sm dark:text-amber-200"
+						>
+							Loading {readyPlayers.size} / {playerDurations.size} POVs…
+						</div>
+					{/if}
+				</div>
 			{/if}
 
 			{#if previews.length}