Add historical sparklines to host cards

24h of snapshots were already being retained but never read. Adds a
windowed query (last ~40 samples/host, one query total via
ROW_NUMBER() OVER PARTITION BY, not N+1) embedded in the existing
/api/hosts response, rendered as small hand-rolled SVG sparklines
(cpu/mem/disk overlaid) -- no charting library needed at this scale.

Closes #10.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/src/db/index.ts

@@ -101,8 +101,35 @@ export function getLatestSnapshots(db: Database.Database): LatestRow[] {
     .all() as LatestRow[];
 }
 
-// Old snapshots aren't useful yet (no charting in Phase 1) and would grow unbounded
-// on a poll-every-30s cadence, so trim anything older than the retention window.
+export interface HistoryPoint {
+  host_id: string;
+  ts: string;
+  cpu_pct: number | null;
+  mem_pct: number | null;
+  disk_pct: number | null;
+}
+
+// Last N samples per host (not a time window) — at the default 30s poll interval
+// that's ~20 minutes of trend, enough for a sparkline without needing to
+// downsample. A window function keeps this to one query instead of one per host.
+export function getRecentHistory(db: Database.Database, samplesPerHost = 40): HistoryPoint[] {
+  return db
+    .prepare(
+      `
+      SELECT host_id, ts, cpu_pct, mem_pct, disk_pct FROM (
+        SELECT host_id, ts, cpu_pct, mem_pct, disk_pct,
+               ROW_NUMBER() OVER (PARTITION BY host_id ORDER BY id DESC) AS rn
+        FROM metric_snapshots
+      )
+      WHERE rn <= @samplesPerHost
+      ORDER BY host_id, ts ASC
+    `
+    )
+    .all({ samplesPerHost }) as HistoryPoint[];
+}
+
+// Sparklines only ever read the last ~40 samples (see getRecentHistory), so
+// anything older than the retention window is just dead weight — trim it.
 export function pruneOldSnapshots(db: Database.Database, retentionHours: number): void {
   db.prepare(`DELETE FROM metric_snapshots WHERE ts < datetime('now', @cutoff)`).run({
     cutoff: `-${retentionHours} hours`,

apps/api/src/routes/hosts.ts

@@ -1,6 +1,6 @@
 import type { FastifyInstance, FastifyReply, FastifyRequest } from "fastify";
 import type Database from "better-sqlite3";
-import { getLatestSnapshots } from "../db/index.js";
+import { getLatestSnapshots, getRecentHistory } from "../db/index.js";
 
 async function requireAuth(req: FastifyRequest, reply: FastifyReply) {
   if (!req.session.username) {
@@ -11,6 +11,13 @@ async function requireAuth(req: FastifyRequest, reply: FastifyReply) {
 export function registerHostRoutes(app: FastifyInstance, db: Database.Database): void {
   app.get("/api/hosts", { preHandler: requireAuth }, async () => {
     const rows = getLatestSnapshots(db);
+
+    const history = new Map<string, { ts: string; cpuPct: number | null; memPct: number | null; diskPct: number | null }[]>();
+    for (const h of getRecentHistory(db)) {
+      if (!history.has(h.host_id)) history.set(h.host_id, []);
+      history.get(h.host_id)!.push({ ts: h.ts, cpuPct: h.cpu_pct, memPct: h.mem_pct, diskPct: h.disk_pct });
+    }
+
     return {
       hosts: rows.map((r) => ({
         hostId: r.host_id,
@@ -24,6 +31,7 @@ export function registerHostRoutes(app: FastifyInstance, db: Database.Database):
         cpuPressurePct: r.cpu_pressure_pct,
         uptimeSec: r.uptime_sec,
         lastSeen: r.ts,
+        history: history.get(r.host_id) ?? [],
       })),
     };
   });

apps/web/src/api.ts

@@ -1,3 +1,10 @@
+export interface HistoryPoint {
+  ts: string;
+  cpuPct: number | null;
+  memPct: number | null;
+  diskPct: number | null;
+}
+
 export interface HostSummary {
   hostId: string;
   displayName: string;
@@ -10,6 +17,7 @@ export interface HostSummary {
   cpuPressurePct: number | null;
   uptimeSec: number | null;
   lastSeen: string;
+  history: HistoryPoint[];
 }
 
 async function request<T>(path: string, init?: RequestInit): Promise<T> {

apps/web/src/components/HostCard.tsx

@@ -1,4 +1,5 @@
 import type { HostSummary } from "../api";
+import { Sparkline } from "./Sparkline";
 
 function Bar({ label, pct }: { label: string; pct: number | null }) {
   const value = pct ?? 0;
@@ -34,6 +35,7 @@ export function HostCard({ host }: { host: HostSummary }) {
       <Bar label="CPU" pct={host.cpuPct} />
       <Bar label="Mem" pct={host.memPct} />
       <Bar label="Disk" pct={host.diskPct} />
+      <Sparkline history={host.history} />
       {(host.cpuPressurePct !== null || host.memPressurePct !== null) && (
         <div className="pressure-row">
           {host.cpuPressurePct !== null && <span>CPU pressure {host.cpuPressurePct.toFixed(1)}%</span>}

apps/web/src/components/Sparkline.tsx

@@ -0,0 +1,47 @@
+import type { HistoryPoint } from "../api";
+
+const WIDTH = 200;
+const HEIGHT = 32;
+
+interface Series {
+  key: "cpuPct" | "memPct" | "diskPct";
+  color: string;
+}
+
+const SERIES: Series[] = [
+  { key: "cpuPct", color: "#58a6ff" },
+  { key: "memPct", color: "#f5a623" },
+  { key: "diskPct", color: "#3fb950" },
+];
+
+function toPath(points: HistoryPoint[], key: Series["key"]): string {
+  const values = points.map((p) => p[key]).filter((v): v is number => v !== null);
+  if (values.length < 2) return "";
+
+  const step = WIDTH / (points.length - 1);
+  let path = "";
+  let x = 0;
+  for (const p of points) {
+    const v = p[key];
+    if (v !== null) {
+      const y = HEIGHT - (Math.min(Math.max(v, 0), 100) / 100) * HEIGHT;
+      path += (path === "" ? "M" : "L") + x.toFixed(1) + "," + y.toFixed(1);
+    }
+    x += step;
+  }
+  return path;
+}
+
+export function Sparkline({ history }: { history: HistoryPoint[] }) {
+  if (history.length < 2) return null;
+
+  return (
+    <svg className="sparkline" viewBox={`0 0 ${WIDTH} ${HEIGHT}`} preserveAspectRatio="none">
+      {SERIES.map((s) => {
+        const d = toPath(history, s.key);
+        if (!d) return null;
+        return <path key={s.key} d={d} fill="none" stroke={s.color} strokeWidth={1.5} />;
+      })}
+    </svg>
+  );
+}

apps/web/src/index.css

@@ -232,3 +232,10 @@ body {
   background: #4d2a1a;
   color: #f5a623;
 }
+
+.sparkline {
+  width: 100%;
+  height: 24px;
+  margin-top: 0.4rem;
+  display: block;
+}