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diff --git a/src/zen/frontend/html/counters.js b/src/zen/frontend/html/counters.js
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+++ b/src/zen/frontend/html/counters.js
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+// Copyright Epic Games, Inc. All Rights Reserved.
+// Counters viewer — list registered TRACE_INT_VALUE / TRACE_FLOAT_VALUE
+// counters and chart selected ones.
+//
+// Mirrors csvstats.js layout (tree on the left, line chart on the right),
+// adapted to the simpler counter-id keyed series model.
+
+import { getCounters, getCounterSeries } from "./api.js";
+import { escapeHtml } from "./util.js";
+
+function formatTime(us) {
+	if (us < 1000) return `${us} µs`;
+	if (us < 1_000_000) return `${(us / 1000).toFixed(2)} ms`;
+	return `${(us / 1_000_000).toFixed(2)} s`;
+}
+
+const BYTE_UNITS = ["B", "KiB", "MiB", "GiB", "TiB"];
+function formatBytes(value) {
+	let v = value;
+	let i = 0;
+	while (Math.abs(v) >= 1024 && i + 1 < BYTE_UNITS.length) {
+		v /= 1024;
+		++i;
+	}
+	return `${v.toFixed(i === 0 ? 0 : 2)} ${BYTE_UNITS[i]}`;
+}
+
+function formatCounterValue(value, def) {
+	if (def && def.display_hint === 1) {
+		return formatBytes(value);
+	}
+	if (def && def.type === 0) {
+		// Integer — render without fractional digits.
+		return Number(value).toLocaleString();
+	}
+	return value.toFixed(3);
+}
+
+const LINE_COLORS = [
+	"#4fc3f7", "#81c784", "#ffb74d", "#e57373", "#ba68c8",
+	"#4db6ac", "#fff176", "#f06292", "#7986cb", "#a1887f",
+];
+
+export class CountersView {
+	constructor(model, containerEl) {
+		this.model = model;
+		this.container = containerEl;
+		this.loaded = false;
+		this.defs = [];
+		this.defById = new Map();
+
+		this.selected = new Set();
+		this.seriesData = new Map();
+		this.colorIndex = 0;
+		this.colorById = new Map();
+
+		this.viewStartUs = 0;
+		this.viewEndUs = (model.session && model.session.trace_end_us) || 1;
+
+		this.buildLayout();
+	}
+
+	buildLayout() {
+		this.container.innerHTML =
+			`<div class="csv-layout">` +
+			`<div class="csv-tree-panel">` +
+			`<div class="sidebar-label">Counters</div>` +
+			`<div class="csv-tree counters-tree"></div>` +
+			`</div>` +
+			`<div class="csv-chart-panel">` +
+			`<canvas class="csv-chart-canvas"></canvas>` +
+			`<div class="csv-chart-tooltip" hidden></div>` +
+			`</div>` +
+			`</div>`;
+
+		this.treeEl = this.container.querySelector(".counters-tree");
+		this.canvas = this.container.querySelector(".csv-chart-canvas");
+		this.tooltipEl = this.container.querySelector(".csv-chart-tooltip");
+		this.ctx = this.canvas.getContext("2d");
+		this.dpr = Math.max(1, window.devicePixelRatio || 1);
+
+		this.resizeObserver = new ResizeObserver(() => this.drawChart());
+		this.resizeObserver.observe(this.canvas);
+		this.canvas.addEventListener("mousemove", (e) => this.onChartHover(e));
+		this.canvas.addEventListener("mouseleave", () => { this.tooltipEl.hidden = true; });
+
+		this.panning = false;
+		this.canvas.addEventListener("mousedown", (e) => this.onPanStart(e));
+		window.addEventListener("mousemove", (e) => this.onPanMove(e));
+		window.addEventListener("mouseup", () => this.onPanEnd());
+		this.canvas.addEventListener("wheel", (e) => this.onWheel(e), { passive: false });
+	}
+
+	async ensureLoaded() {
+		if (this.loaded) {
+			this.drawChart();
+			return;
+		}
+		try {
+			this.defs = await getCounters();
+			for (const d of this.defs) {
+				this.defById.set(d.id, d);
+			}
+			this.renderTree();
+		} catch (e) {
+			this.treeEl.innerHTML = `<div class="csv-empty">Failed to load counters: ${escapeHtml(e.message)}</div>`;
+			console.error(e);
+		}
+		this.loaded = true;
+		this.drawChart();
+	}
+
+	renderTree() {
+		// Group by leading path component (everything before the first "/").
+		const groups = new Map();
+		for (const d of this.defs) {
+			if (!d.sample_count) continue;
+			const slash = d.name.indexOf("/");
+			const group = slash > 0 ? d.name.substring(0, slash) : "";
+			if (!groups.has(group)) groups.set(group, []);
+			groups.get(group).push(d);
+		}
+
+		if (groups.size === 0) {
+			this.treeEl.innerHTML = `<div class="csv-empty">No counters in this trace.</div>`;
+			return;
+		}
+
+		const groupNames = Array.from(groups.keys()).sort((a, b) => a.localeCompare(b));
+		const parts = [];
+		for (const g of groupNames) {
+			const list = groups.get(g);
+			parts.push(`<div class="csv-cat-header">${escapeHtml(g || "(ungrouped)")}</div>`);
+			for (const d of list) {
+				parts.push(
+					`<label class="csv-stat-row">` +
+					`<input type="checkbox" data-counter-id="${d.id}">` +
+					`<span class="csv-stat-name"></span>` +
+					`<span class="thread-count">${Number(d.sample_count).toLocaleString()}</span>` +
+					`</label>`
+				);
+			}
+		}
+		this.treeEl.innerHTML = parts.join("");
+
+		// Set names via DOM (XSS safe).
+		const rows = this.treeEl.querySelectorAll(".csv-stat-row");
+		let idx = 0;
+		for (const g of groupNames) {
+			for (const d of groups.get(g)) {
+				if (idx < rows.length) {
+					const slash = d.name.indexOf("/");
+					const display = slash > 0 ? d.name.substring(slash + 1) : d.name;
+					rows[idx].querySelector(".csv-stat-name").textContent = display;
+					rows[idx].title = d.name;
+				}
+				++idx;
+			}
+		}
+
+		// Wire checkboxes.
+		for (const cb of this.treeEl.querySelectorAll("input[type=checkbox]")) {
+			cb.addEventListener("change", () => {
+				const id = Number(cb.dataset.counterId);
+				if (cb.checked) {
+					this.selected.add(id);
+					if (!this.colorById.has(id)) {
+						this.colorById.set(id, LINE_COLORS[this.colorIndex++ % LINE_COLORS.length]);
+					}
+					this.fetchSeries(id);
+				} else {
+					this.selected.delete(id);
+					this.drawChart();
+				}
+			});
+		}
+	}
+
+	async fetchSeries(id) {
+		if (this.seriesData.has(id)) {
+			this.drawChart();
+			return;
+		}
+		try {
+			const result = await getCounterSeries(id);
+			const samples = (result.samples || []).map(([t, v]) => ({ timeUs: t, value: v }));
+			this.seriesData.set(id, samples);
+			this.drawChart();
+		} catch (e) {
+			console.error(`Failed to fetch counter series for ${id}: ${e.message}`);
+		}
+	}
+
+	resizeCanvas() {
+		const rect = this.canvas.getBoundingClientRect();
+		this.width = Math.floor(rect.width);
+		this.height = Math.floor(rect.height);
+		const bw = Math.floor(rect.width * this.dpr);
+		const bh = Math.floor(rect.height * this.dpr);
+		if (this.canvas.width !== bw || this.canvas.height !== bh) {
+			this.canvas.width = bw;
+			this.canvas.height = bh;
+		}
+		this.ctx.setTransform(this.dpr, 0, 0, this.dpr, 0, 0);
+	}
+
+	drawChart() {
+		this.resizeCanvas();
+		const ctx = this.ctx;
+		const W = this.width;
+		const H = this.height;
+
+		const bg = getComputedStyle(document.body).getPropertyValue("--bg0") || "#0d1117";
+		const fg2 = getComputedStyle(document.body).getPropertyValue("--fg2") || "#8b949e";
+		const border = getComputedStyle(document.body).getPropertyValue("--border") || "#30363d";
+		ctx.fillStyle = bg;
+		ctx.fillRect(0, 0, W, H);
+
+		if (this.selected.size === 0) {
+			ctx.fillStyle = fg2;
+			ctx.font = "12px -apple-system, Segoe UI, sans-serif";
+			ctx.textAlign = "center";
+			ctx.textBaseline = "middle";
+			ctx.fillText("Select counters from the tree to chart them", W / 2, H / 2);
+			return;
+		}
+
+		const PAD_L = 70, PAD_R = 12, PAD_T = 12, PAD_B = 28;
+		const chartW = W - PAD_L - PAD_R;
+		const chartH = H - PAD_T - PAD_B;
+		if (chartW <= 0 || chartH <= 0) return;
+
+		const startUs = this.viewStartUs;
+		const endUs = this.viewEndUs;
+		const rangeUs = Math.max(1, endUs - startUs);
+
+		let minVal = Infinity, maxVal = -Infinity;
+		for (const id of this.selected) {
+			const samples = this.seriesData.get(id);
+			if (!samples) continue;
+			for (const s of samples) {
+				if (s.timeUs < startUs || s.timeUs > endUs) continue;
+				if (s.value < minVal) minVal = s.value;
+				if (s.value > maxVal) maxVal = s.value;
+			}
+		}
+		if (!isFinite(minVal)) { minVal = 0; maxVal = 1; }
+		if (minVal === maxVal) { minVal -= 0.5; maxVal += 0.5; }
+		const valRange = maxVal - minVal;
+		const valPad = valRange * 0.05;
+		minVal -= valPad;
+		maxVal += valPad;
+
+		const xAt = (us) => PAD_L + (us - startUs) / rangeUs * chartW;
+		const yAt = (v) => PAD_T + (1 - (v - minVal) / (maxVal - minVal)) * chartH;
+
+		ctx.strokeStyle = border;
+		ctx.lineWidth = 0.5;
+		for (let i = 0; i <= 4; i++) {
+			const y = PAD_T + chartH * i / 4;
+			ctx.beginPath(); ctx.moveTo(PAD_L, y); ctx.lineTo(PAD_L + chartW, y); ctx.stroke();
+		}
+
+		// Format Y-axis labels using the display hint of the first selected counter.
+		const firstSelected = this.selected.values().next().value;
+		const firstDef = this.defById.get(firstSelected);
+
+		ctx.fillStyle = fg2;
+		ctx.font = "10px -apple-system, Segoe UI, sans-serif";
+		ctx.textAlign = "right";
+		ctx.textBaseline = "middle";
+		for (let i = 0; i <= 4; i++) {
+			const v = minVal + (maxVal - minVal) * (1 - i / 4);
+			const y = PAD_T + chartH * i / 4;
+			ctx.fillText(formatCounterValue(v, firstDef), PAD_L - 4, y);
+		}
+
+		ctx.textAlign = "center";
+		ctx.textBaseline = "top";
+		const tickCount = Math.max(2, Math.min(8, Math.floor(chartW / 80)));
+		for (let i = 0; i <= tickCount; i++) {
+			const us = startUs + rangeUs * i / tickCount;
+			const x = xAt(us);
+			ctx.fillText(formatTime(us), x, PAD_T + chartH + 4);
+		}
+
+		// Draw step-style lines (counters change at discrete events).
+		for (const id of this.selected) {
+			const samples = this.seriesData.get(id);
+			if (!samples || samples.length === 0) continue;
+			const color = this.colorById.get(id) || "#fff";
+
+			ctx.strokeStyle = color;
+			ctx.lineWidth = 1.5;
+			ctx.beginPath();
+			let started = false;
+			let prevY = 0;
+			for (const s of samples) {
+				if (s.timeUs < startUs || s.timeUs > endUs) continue;
+				const x = xAt(s.timeUs);
+				const y = yAt(s.value);
+				if (!started) { ctx.moveTo(x, y); started = true; }
+				else { ctx.lineTo(x, prevY); ctx.lineTo(x, y); }
+				prevY = y;
+			}
+			ctx.stroke();
+		}
+
+		ctx.strokeStyle = border;
+		ctx.lineWidth = 1;
+		ctx.strokeRect(PAD_L, PAD_T, chartW, chartH);
+
+		ctx.font = "10px -apple-system, Segoe UI, sans-serif";
+		ctx.textAlign = "left";
+		ctx.textBaseline = "top";
+		let legendX = PAD_L + 6;
+		for (const id of this.selected) {
+			const def = this.defById.get(id);
+			const name = def ? def.name : `counter ${id}`;
+			const color = this.colorById.get(id) || "#fff";
+			ctx.fillStyle = color;
+			ctx.fillRect(legendX, PAD_T + 4, 10, 10);
+			ctx.fillStyle = "#ccc";
+			ctx.fillText(name, legendX + 14, PAD_T + 4);
+			legendX += ctx.measureText(name).width + 24;
+		}
+
+		this._chartLayout = { PAD_L, PAD_R, PAD_T, PAD_B, chartW, chartH, startUs, endUs, rangeUs, minVal, maxVal, xAt, yAt, firstDef };
+	}
+
+	onChartHover(e) {
+		if (!this._chartLayout || this.selected.size === 0) {
+			this.tooltipEl.hidden = true;
+			return;
+		}
+		const rect = this.canvas.getBoundingClientRect();
+		const mx = e.clientX - rect.left;
+		const my = e.clientY - rect.top;
+		const { PAD_L, PAD_T, chartW, chartH, startUs, rangeUs } = this._chartLayout;
+
+		if (mx < PAD_L || mx > PAD_L + chartW || my < PAD_T || my > PAD_T + chartH) {
+			this.tooltipEl.hidden = true;
+			return;
+		}
+
+		const cursorUs = startUs + (mx - PAD_L) / chartW * rangeUs;
+		const lines = [];
+		for (const id of this.selected) {
+			const samples = this.seriesData.get(id);
+			if (!samples || samples.length === 0) continue;
+			let best = null, bestDist = Infinity;
+			for (const s of samples) {
+				const d = Math.abs(s.timeUs - cursorUs);
+				if (d < bestDist) { bestDist = d; best = s; }
+			}
+			if (best) {
+				const def = this.defById.get(id);
+				const name = def ? def.name : `counter ${id}`;
+				const color = this.colorById.get(id) || "#fff";
+				lines.push(`<span style="color:${color}">${escapeHtml(name)}</span>: ${formatCounterValue(best.value, def)}`);
+			}
+		}
+		if (lines.length === 0) { this.tooltipEl.hidden = true; return; }
+		this.tooltipEl.innerHTML = `<div style="margin-bottom:2px">${formatTime(cursorUs)}</div>` + lines.join("<br>");
+		this.tooltipEl.style.left = `${mx + 12}px`;
+		this.tooltipEl.style.top = `${my + 12}px`;
+		this.tooltipEl.hidden = false;
+	}
+
+	onPanStart(e) {
+		if (e.button !== 0) return;
+		this.panning = true;
+		this.panStartX = e.clientX;
+		this.panStartViewStart = this.viewStartUs;
+		this.panStartViewEnd = this.viewEndUs;
+	}
+
+	onPanMove(e) {
+		if (!this.panning || !this._chartLayout) return;
+		const dx = e.clientX - this.panStartX;
+		const usPerPx = (this.panStartViewEnd - this.panStartViewStart) / this._chartLayout.chartW;
+		const shift = -dx * usPerPx;
+		this.viewStartUs = this.panStartViewStart + shift;
+		this.viewEndUs = this.panStartViewEnd + shift;
+		this.drawChart();
+	}
+
+	onPanEnd() { this.panning = false; }
+
+	onWheel(e) {
+		e.preventDefault();
+		if (!this._chartLayout) return;
+		const rect = this.canvas.getBoundingClientRect();
+		const mx = e.clientX - rect.left;
+		const { PAD_L, chartW, startUs, rangeUs } = this._chartLayout;
+		const cursorUs = startUs + (mx - PAD_L) / chartW * rangeUs;
+		const factor = e.deltaY > 0 ? 1.25 : 0.8;
+		const newRange = Math.max(10, (this.viewEndUs - this.viewStartUs) * factor);
+		const ratio = (mx - PAD_L) / chartW;
+		this.viewStartUs = cursorUs - ratio * newRange;
+		this.viewEndUs = this.viewStartUs + newRange;
+		this.drawChart();
+	}
+}