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/allocation-profile.ts

@@ -0,0 +1,55 @@
+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 AllocationSiteResult {
+	readonly site: string;
+	readonly bytes: number;
+}
+
+interface AllocationProfileResult {
+	readonly target: string;
+	readonly dataset: string;
+	readonly entryCount: number;
+	readonly allocatedBytes: number;
+	readonly topSites: readonly AllocationSiteResult[];
+}
+
+const execFileAsync = promisify(execFile);
+const packageRoot = fileURLToPath(new URL("../..", import.meta.url));
+const workerPath = fileURLToPath(new URL("./allocation-profile-worker.ts", import.meta.url));
+const tsconfigPath = fileURLToPath(new URL("../tsconfig.json", import.meta.url));
+const results: AllocationProfileResult[] = [];
+
+for (const target of storageBenchmarkTargets) {
+	for (const dataset of STORAGE_BENCHMARK_DATASETS) {
+		const { stdout } = await execFileAsync(
+			process.execPath,
+			["--import", "tsx", workerPath, target.name, dataset.name],
+			{ cwd: packageRoot, env: { ...process.env, TSX_TSCONFIG_PATH: tsconfigPath } },
+		);
+		results.push(JSON.parse(stdout) as AllocationProfileResult);
+	}
+}
+
+const mebibytes = (bytes: number): string => (bytes / 1024 / 1024).toFixed(2);
+console.log("Storage allocation sampling (inputs generated before sampling):");
+console.table(
+	results.map((result) => ({
+		backend: result.target,
+		dataset: result.dataset,
+		"allocated MiB": mebibytes(result.allocatedBytes),
+		"allocated bytes/entry": Math.round(result.allocatedBytes / result.entryCount),
+	})),
+);
+for (const result of results) {
+	console.log(`\n${result.target}, ${result.dataset}, top sampled allocation sites:`);
+	console.table(
+		result.topSites.map(({ site, bytes }) => ({
+			site,
+			"sampled MiB": mebibytes(bytes),
+		})),
+	);
+}