chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

third_party/pi/packages/agent/benchmark/session/loaded-footprint.ts

@@ -0,0 +1,51 @@
+import { execFile } from "node:child_process";
+import { fileURLToPath } from "node:url";
+import { promisify } from "node:util";
+import { STORAGE_BENCHMARK_DATASETS } from "../../src/harness/session/testing/index.ts";
+import { storageBenchmarkTargets } from "./storage-targets.ts";
+
+interface LoadedFootprintResult {
+	readonly target: string;
+	readonly dataset: string;
+	readonly entryCount: number;
+	readonly heapUsedBytes: number;
+	readonly rssBytes: number;
+	readonly externalBytes: number;
+}
+
+const execFileAsync = promisify(execFile);
+const packageRoot = fileURLToPath(new URL("../..", import.meta.url));
+const workerPath = fileURLToPath(new URL("./loaded-footprint-worker.ts", import.meta.url));
+const tsconfigPath = fileURLToPath(new URL("../tsconfig.json", import.meta.url));
+const results: LoadedFootprintResult[] = [];
+
+for (const target of storageBenchmarkTargets) {
+	for (const dataset of STORAGE_BENCHMARK_DATASETS) {
+		const { stdout } = await execFileAsync(
+			process.execPath,
+			[
+				"--expose-gc",
+				"--import",
+				"tsx",
+				workerPath,
+				target.name,
+				dataset.name,
+			],
+			{ cwd: packageRoot, env: { ...process.env, TSX_TSCONFIG_PATH: tsconfigPath } },
+		);
+		results.push(JSON.parse(stdout) as LoadedFootprintResult);
+	}
+}
+
+const mebibytes = (bytes: number): string => (bytes / 1024 / 1024).toFixed(2);
+console.log("Loaded footprint (synthetic payloads generated and ingested after the baseline):");
+console.table(
+	results.map((result) => ({
+		backend: result.target,
+		dataset: result.dataset,
+		"heap MiB": mebibytes(result.heapUsedBytes),
+		"heap bytes/entry": Math.round(result.heapUsedBytes / result.entryCount),
+		"RSS MiB": mebibytes(result.rssBytes),
+		"external MiB": mebibytes(result.externalBytes),
+	})),
+);