diff --git a/ui/frontend/src/map/render.ts b/ui/frontend/src/map/render.ts
index b94138d..7fb721d 100644
--- a/ui/frontend/src/map/render.ts
+++ b/ui/frontend/src/map/render.ts
@@ -584,6 +584,7 @@ export async function createRenderer(opts: RendererOptions): Promise<RendererHan
 	let currentLabels: ReadonlyArray<PlanetLabelData> = [];
 	let currentLabelsFingerprint: string | null = null;
 	let currentLabelsSelectedId: number | null = null;
+	let currentPlanetSetFingerprint: string | null = null;
 	const fingerprintPlanetLabels = (
 		labels: ReadonlyArray<PlanetLabelData>,
 	): string => {
@@ -593,6 +594,14 @@ export async function createRenderer(opts: RendererOptions): Promise<RendererHan
 		}
 		return parts.join("|");
 	};
+	const fingerprintPlanetSet = (
+		labels: ReadonlyArray<PlanetLabelData>,
+	): string => {
+		const ids: number[] = [];
+		for (const l of labels) ids.push(l.planetNumber);
+		ids.sort((a, b) => a - b);
+		return ids.join(",");
+	};
 	const LABEL_FONT_SIZE_PX = 11;
 	const LABEL_LINE_GAP_PX = 0;
 	const LABEL_FRAME_PADDING_PX = 3;
@@ -638,31 +647,34 @@ export async function createRenderer(opts: RendererOptions): Promise<RendererHan
 		planetLabelInstances.clear();
 		currentLabelsFingerprint = null;
 		currentLabelsSelectedId = null;
+		currentPlanetSetFingerprint = null;
 	};
 
 	const paintLabelEntry = (entry: LabelGfx, isSelected: boolean): void => {
 		// Text colours flip on selection so the legend reads on the
 		// inverse-fill frame.
+		const nameVisible =
+			entry.nameText !== null && entry.nameText.visible;
 		const nameFill = isSelected ? theme.labelInverseText : theme.labelText;
 		const numberFill = isSelected
 			? theme.labelInverseText
-			: entry.nameText !== null
+			: nameVisible
 				? theme.labelMuted
 				: theme.labelText;
 		if (entry.nameText !== null) {
 			entry.nameText.style.fill = nameFill;
 		}
 		entry.numberText.style.fill = numberFill;
-		const nameHeight = entry.nameText?.height ?? 0;
+		const nameHeight = nameVisible ? entry.nameText!.height : 0;
 		const numberHeight = entry.numberText.height;
 		const totalTextHeight =
-			nameHeight + (entry.nameText !== null ? LABEL_LINE_GAP_PX : 0) + numberHeight;
-		entry.numberText.y = entry.nameText !== null ? nameHeight + LABEL_LINE_GAP_PX : 0;
+			nameHeight + (nameVisible ? LABEL_LINE_GAP_PX : 0) + numberHeight;
+		entry.numberText.y = nameVisible ? nameHeight + LABEL_LINE_GAP_PX : 0;
 		// Refresh the click hit area to match the label's bounding box
 		// plus the padding from the selection frame (so the player can
 		// click anywhere inside the visible legend, not just the glyphs).
 		const widestText = Math.max(
-			entry.nameText?.width ?? 0,
+			nameVisible ? entry.nameText!.width : 0,
 			entry.numberText.width,
 		);
 		const hitWidth = widestText + LABEL_FRAME_PADDING_PX * 2;
@@ -846,10 +858,33 @@ export async function createRenderer(opts: RendererOptions): Promise<RendererHan
 			requestRender();
 			return;
 		}
+		const planetSetFp = fingerprintPlanetSet(labels);
+		if (planetSetFp === currentPlanetSetFingerprint) {
+			// Same planet set, only the per-row text changed (almost
+			// always the F8-12 / #29 `planetNames` toggle flipping name
+			// strings on / off). Rebuilding 9-copies × N labels here
+			// dwarfed everything else on a 500-planet map — instead, walk
+			// the live entries and just update text content / visibility.
+			currentLabels = labels.slice();
+			for (const data of labels) {
+				const list = planetLabelInstances.get(data.planetNumber);
+				if (list === undefined) continue;
+				for (const entry of list) {
+					applyLabelContent(entry, data);
+					paintLabelEntry(entry, data.planetNumber === selectedPlanetId);
+				}
+			}
+			currentLabelsFingerprint = fp;
+			currentLabelsSelectedId = selectedPlanetId;
+			updateLabelTransforms();
+			requestRender();
+			return;
+		}
 		clearAllLabels();
 		currentLabels = labels.slice();
 		currentLabelsFingerprint = fp;
 		currentLabelsSelectedId = selectedPlanetId;
+		currentPlanetSetFingerprint = planetSetFp;
 		for (const data of labels) {
 			const targetPlanet = data.planetNumber;
 			const list: LabelGfx[] = [];
@@ -858,11 +893,12 @@ export async function createRenderer(opts: RendererOptions): Promise<RendererHan
 				const frame = new Graphics();
 				frame.visible = false;
 				container.addChild(frame);
-				const nameText =
-					data.name === null
-						? null
-						: buildLabelText(data.name, theme.labelText);
-				if (nameText !== null) container.addChild(nameText);
+				// We always build both lines and toggle visibility for
+				// the name line, so the `planetNames` flip can swap
+				// content without destroying Pixi.Text instances.
+				const nameText = buildLabelText(data.name ?? "", theme.labelText);
+				nameText.visible = data.name !== null;
+				container.addChild(nameText);
 				const numberText = buildLabelText(data.numberLabel, theme.labelMuted);
 				container.addChild(numberText);
 				layer.addChild(container);
@@ -890,6 +926,19 @@ export async function createRenderer(opts: RendererOptions): Promise<RendererHan
 		requestRender();
 	};
 
+	const applyLabelContent = (entry: LabelGfx, data: PlanetLabelData): void => {
+		if (entry.nameText !== null) {
+			const desired = data.name ?? "";
+			if (entry.nameText.text !== desired) {
+				entry.nameText.text = desired;
+			}
+			entry.nameText.visible = data.name !== null;
+		}
+		if (entry.numberText.text !== data.numberLabel) {
+			entry.numberText.text = data.numberLabel;
+		}
+	};
+
 	const simulatePlanetClick = (planetNumber: number): void => {
 		const prim = pointPrimitivesById.get(planetNumber);
 		if (prim === undefined) return;
@@ -959,15 +1008,24 @@ export async function createRenderer(opts: RendererOptions): Promise<RendererHan
 			{ widthPx: viewport.screenWidth, heightPx: viewport.screenHeight },
 			opts.world,
 		);
+		const maxScale = maxScaleForViewport(
+			viewport.screenWidth,
+			viewport.screenHeight,
+		);
 		currentScaleRef = minScale;
 		// Both modes enforce minScale on zoom-out: the world (origin
 		// copy) always fills at least the viewport. Without this, in
 		// torus mode the user would zoom out far enough to see the
 		// 3×3 grid of wrap copies at once; the copies are there to
 		// fill the partial slack near a panned edge, not to be
-		// visible simultaneously.
-		viewport.clampZoom({ minScale });
+		// visible simultaneously. The matching maxScale cap (F8-12
+		// follow-up) keeps the longest viewport axis showing at least
+		// `MIN_VISIBLE_WORLD_AT_MAX_ZOOM` world units of map, so the
+		// player can never zoom past the point where individual
+		// glyphs become uselessly large.
+		viewport.clampZoom({ minScale, maxScale });
 		if (viewport.scaled < minScale) viewport.setZoom(minScale, true);
+		if (viewport.scaled > maxScale) viewport.setZoom(maxScale, true);
 		if (newMode === "no-wrap") {
 			viewport.clamp({ direction: "all" });
 			viewport.on("moved", enforceCentreWhenLarger);
@@ -1451,10 +1509,12 @@ export async function createRenderer(opts: RendererOptions): Promise<RendererHan
 			app.renderer.resize(w, h);
 			viewport.resize(w, h, opts.world.width, opts.world.height);
 			const minScale = minScaleNoWrap({ widthPx: w, heightPx: h }, opts.world);
+			const maxScale = maxScaleForViewport(w, h);
 			currentScaleRef = minScale;
 			viewport.plugins.remove("clamp-zoom");
-			viewport.clampZoom({ minScale });
+			viewport.clampZoom({ minScale, maxScale });
 			if (viewport.scaled < minScale) viewport.setZoom(minScale, true);
+			if (viewport.scaled > maxScale) viewport.setZoom(maxScale, true);
 			if (mode === "no-wrap") {
 				enforceCentreWhenLarger();
 			}
@@ -1534,6 +1594,23 @@ function rendererBackendName(r: Renderer): "webgl" | "webgpu" | "canvas" {
  */
 const SMOOTH_CIRCLE_SEGMENTS = 32;
 
+/**
+ * MIN_VISIBLE_WORLD_AT_MAX_ZOOM caps zoom-in so the longest viewport
+ * axis never covers fewer than this many world units. Tuned on the
+ * F8-12 owner-feedback round: 5 keeps individual planet glyphs from
+ * filling half the screen on either mobile (longest ≈ 412 px → max
+ * scale ≈ 82) or desktop (longest ≈ 1200 px → max scale ≈ 240) — the
+ * "useful detail" budget at full zoom is still a 5×5-world tile in
+ * the centre of the viewport.
+ */
+const MIN_VISIBLE_WORLD_AT_MAX_ZOOM = 5;
+
+function maxScaleForViewport(widthPx: number, heightPx: number): number {
+	const longest = Math.max(widthPx, heightPx);
+	if (longest <= 0) return Number.POSITIVE_INFINITY;
+	return longest / MIN_VISIBLE_WORLD_AT_MAX_ZOOM;
+}
+
 function traceSmoothCircle(
 	g: Graphics,
 	x: number,