fix(e2e): stream docker stats resource scans

scripts/e2e/lib/docker-stats/assert-resource-ceiling.mjs

@@ -1,4 +1,5 @@
 import fs from "node:fs";
+import { createInterface } from "node:readline";
 
 const [statsFile, maxMemoryRaw, maxCpuRaw, label = "docker"] = process.argv.slice(2);
 const maxMemoryMiB = Number(maxMemoryRaw);
@@ -55,9 +56,19 @@ function assertSampleValue(value, raw, name, labelLocal) {
   }
 }
 
-const lines = fs.existsSync(statsFile)
-  ? fs.readFileSync(statsFile, "utf8").split(/\r?\n/u).filter(Boolean)
-  : [];
+async function scanStatsFileLines(file, onLine) {
+  if (!fs.existsSync(file)) {
+    return;
+  }
+  const input = fs.createReadStream(file, { encoding: "utf8" });
+  const lines = createInterface({ crlfDelay: Infinity, input });
+  for await (const line of lines) {
+    if (line) {
+      onLine(line);
+    }
+  }
+}
+
 let maxObservedMemoryMiB = 0;
 let maxObservedCpuPercent = 0;
 let parsedSamples = 0;
@@ -65,7 +76,7 @@ let parsedSamples = 0;
 assertFiniteLimit(maxMemoryMiB, maxMemoryRaw, "max memory MiB");
 assertFiniteLimit(maxCpuPercent, maxCpuRaw, "max CPU percent");
 
-for (const line of lines) {
+await scanStatsFileLines(statsFile, (line) => {
   let parsed;
   try {
     parsed = JSON.parse(line);
@@ -79,7 +90,7 @@ for (const line of lines) {
   parsedSamples += 1;
   maxObservedMemoryMiB = Math.max(maxObservedMemoryMiB, observedMemoryMiB);
   maxObservedCpuPercent = Math.max(maxObservedCpuPercent, observedCpuPercent);
-}
+});
 
 console.log(
   `${label} resource peak: memory=${maxObservedMemoryMiB.toFixed(1)}MiB cpu=${maxObservedCpuPercent.toFixed(1)}% samples=${parsedSamples}`,

test/scripts/docker-stats-resource-ceiling.test.ts

@@ -1,5 +1,5 @@
 import { spawnSync } from "node:child_process";
-import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, describe, expect, it } from "vitest";
@@ -16,9 +16,13 @@ function writeStats(contents: string): string {
 }
 
 function runAssert(statsFile: string, maxMemoryMiB = "512", maxCpuPercent = "100") {
-  return spawnSync(process.execPath, [SCRIPT_PATH, statsFile, maxMemoryMiB, maxCpuPercent, "test"], {
-    encoding: "utf8",
-  });
+  return spawnSync(
+    process.execPath,
+    [SCRIPT_PATH, statsFile, maxMemoryMiB, maxCpuPercent, "test"],
+    {
+      encoding: "utf8",
+    },
+  );
 }
 
 afterEach(() => {
@@ -36,7 +40,10 @@ describe("scripts/e2e/lib/docker-stats/assert-resource-ceiling.mjs", () => {
   });
 
   it("rejects invalid resource limits instead of disabling the ceiling", () => {
-    const result = runAssert(writeStats('{"MemUsage":"128MiB / 2GiB","CPUPerc":"25.0%"}\n'), "nope");
+    const result = runAssert(
+      writeStats('{"MemUsage":"128MiB / 2GiB","CPUPerc":"25.0%"}\n'),
+      "nope",
+    );
 
     expect(result.status).not.toBe(0);
     expect(result.stderr).toContain("max memory MiB must be a finite non-negative number");
@@ -67,6 +74,14 @@ describe("scripts/e2e/lib/docker-stats/assert-resource-ceiling.mjs", () => {
     expect(result.stdout).toContain("samples=1");
   });
 
+  it("streams stats logs instead of slurping them into memory", () => {
+    const source = readFileSync(SCRIPT_PATH, "utf8");
+
+    expect(source).toContain("createReadStream");
+    expect(source).not.toContain("readFileSync(statsFile");
+    expect(source).not.toContain("split(/\\r?\\n/u)");
+  });
+
   it("accepts byte-unit Docker memory samples", () => {
     const result = runAssert(writeStats('{"MemUsage":"512B / 2GiB","CPUPerc":"0.5%"}\n'));