[tyffical]

Motivation

• Where a call can't run under Node's permission model, an in-process guard refused writes and subprocesses the Node backend runtime allows, blocking code that runs in production. (APPS-2945, design page)
• Comparable local runners don't build a JavaScript file-system guard: serverless-offline, Netlify dev and Vercel dev run unrestricted; SAM local and wrangler use the real runtime. dev:verify is the parity check.
• Stacked on [APPS-2945 Update: switch the apps plugin's static checks to the Node backend runtime]([APPS-2945] Update: switch the apps plugin's static checks to the Node backend runtime #557).

Architecture

flowchart TD
    E["/__dd/executeAction"] --> Q{"Vite 6.0.4+ with vite/module-runner, no Yarn PnP?"}
    Q -->|"yes"| P{"Node's permission model usable?"}
    P -->|"yes"| C["call's own process under --permission"]
    C --> H["a refusal fails the call with a dev:verify hint"]
    P -->|"no, or --inspect without --allow-inspector"| U1["call's own process, unrestricted"]
    Q -->|"no: Vite 5, Vite 6.0.0 to 6.0.3, Yarn PnP"| U2["dev server's process, unrestricted"]
    U1 --> W["one warning per dev-server start"]
    U2 --> W

Loading

• The permission-model path keeps the limits from [APPS-2961 Add: limit local call processes with Node's permission model]([APPS-2961] Add: limit local call processes with Node's permission model #617).

Changes

7 changes across network-guard.ts, index.ts, local-execution*.ts, package.json, README.md and tests

What changed	File
Delete the in-process guard and its tests.	src/vite/network-guard.ts, src/vite/network-guard.test.ts (deleted)
Stop installing the guard in the dev server and in a call's process.	index.ts, local-execution.ts, local-execution-child.ts
Warn once per dev-server start when calls run unrestricted.	index.ts, local-execution-process.ts
Map Node's refusals to messages with the hint and the refused path.	local-execution-limits.ts
Drop the unused graceful-fs devDependency.	package.json
Document the unrestricted paths and the hint.	README.md
Test the warning, unrestricted calls and hinted refusals.	local-execution-limits.test.ts, local-execution-process.integration.test.ts

QA Instructions

• Test URL: CI run for 0b521ee9 https://github.com/DataDog/build-plugins/actions/runs/39986239888

yarn typecheck:all && yarn lint && yarn cli integrity
# Expected: all exit 0, integrity leaves no file changes ✅ VERIFIED
yarn build:all && yarn test:unit
# Expected: Test Suites: 133 total; Tests: 1 skipped, 3485 total, all passed except 15 manifest-tags and parameters tests on macOS's /var TMPDIR ✅ VERIFIED
TMPDIR=<dir outside /var> yarn test:unit packages/plugins/apps/src/vite/manifest-tags.integration.test.ts packages/plugins/apps/src/vite/parameters.integration.test.ts
# Expected: Test Suites: 2 passed; Tests: 33 passed, 33 total ✅ VERIFIED

• Manual QA uses the helper scripts from [APPS-2945 Update: switch the apps plugin's static checks to the Node backend runtime]([APPS-2945] Update: switch the apps plugin's static checks to the Node backend runtime #557), a Vite 8 scaffold and a Vite 5 app, against a Datadog staging org.
• Both apps live under /tmp, which a call may write; writeRootUncaught shows a refused write.

Fixtures and staging runs: Vite 8 with and without the permission model, Vite 5, dev:verify

• src/guardRefusal.backend.ts:

import { execFileSync } from 'child_process';
import fs from 'fs';
import path from 'path';
import { fileURLToPath } from 'url';

// Each lets its refusal reach the response instead of catching it.
const projectDir = path.dirname(path.dirname(fileURLToPath(import.meta.url)));

export async function spawnUncaught() {
    return execFileSync(process.execPath, ['-e', "process.stdout.write('spawned')"]).toString();
}

export async function writeProjectUncaught() {
    fs.writeFileSync(path.join(projectDir, 'qa-guard-probe.txt'), 'probe');
    return 'written';
}

export async function writeOutsideUncaught() {
    const outsideDir = path.join(path.dirname(projectDir), 'qa-outside-probe');
    fs.mkdirSync(outsideDir, { recursive: true });
    fs.writeFileSync(path.join(outsideDir, 'probe.txt'), 'probe');
    return 'written';
}

export async function writeRootUncaught() {
    fs.writeFileSync('/qa-limits-probe.txt', 'probe');
    return 'written';
}

• guardRun, useLogger, cacheWrite and useFetch are unchanged; the Vite 5 app pins vite@5.4.21.

cd "$QA_DIR" && QA_APP=<vite 8 scaffold> ./install-plugin.sh 563 <build-plugins checkout of this branch>
QA_APP=<vite 8 scaffold> ./qa-run.sh development guardRefusal useFetch
# spawnUncaught and writeRootUncaught: HTTP 500 "Spawning a subprocess is blocked..." / "Writing outside the call's temp dirs is blocked... run `dev:verify`"
# writeProjectUncaught, writeOutsideUncaught: written (the scaffold sits under /tmp); getStatus 200; no unrestricted warning ✅ VERIFIED
QA_APP=<vite 8 scaffold> QA_NODE=<node 22.23.3> QA_NODE_OPTIONS=--inspect=127.0.0.1:0 ./qa-run.sh development guardRefusal
# spawnUncaught "spawned", both writes written, writeRootUncaught fails with the OS's EROFS;
# one "Backend functions run locally without Node's permission model..." warning ✅ VERIFIED
QA_APP=<vite 5 app> ./qa-run.sh development guardRun useLogger useLogger cacheWrite useFetch
# writeAndSpawn {"project":"written","tmp":"written","outside":"written","subprocess":"spawned"}; the logger gains a line each run;
# cache, package.json and node_modules/vite appends written; one unrestricted warning ✅ VERIFIED
QA_APP=<vite 8 scaffold> ./qa-run.sh dev-verify guardRun
# writeAndSpawn {"outside":"written","project":"written","subprocess":"spawned","tmp":"written"} on the real runtime ✅ VERIFIED

Blast Radius

• Local execution only; cloud execution, dev:verify and builds are untouched.
• On the fallback paths, calls the guard refused now run, with one warning per dev-server start.
• Under the permission model, limits are unchanged; refusals gain the hint.
• No feature flag.
• Low risk: local only, and it removes refusals production doesn't make.

Out of Scope / Follow-ups

3 items deferred

Item	Status	Next step
The 2026-10-17 decision to keep blocking subprocesses locally is superseded	Doc follow-up	Update the design page's local execution section
A refusal the function catches, raises in a callback or wraps in another error shows Node's raw text	Accepted	None
A project under /tmp is writable from a call's own process, since the permission model grants /tmp	Accepted	None

Documentation

• Design page
• Jira: APPS-2945
• Node.js permission model

🤖 Generated with Claude Code

[datadog-datadog-prod-us1-2]

 

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 0b521ee | Docs | View more details | Give us feedback!}

[github-actions]

Live Debugger Runtime Benchmark

SDK-loaded dormant-probe runtime overhead, measured against an uninstrumented bundle in the same browser session.

Browser	Workload	Quality	Per-call overhead upper
chrome	Hot	clean	<= 2.55 ns
chrome	Tiny	clean	<= 0.02 ns
firefox	Hot	clean	<= 9.78 ns
firefox	Tiny	clean	<= 0.00 ns
safari	Hot	clean	<= 5.86 ns
safari	Tiny	clean	<= 0.44 ns

What do the Tiny and Hot workloads represent?

Browser Debugger SDK: 7.16.1 · built 2026-10-21 · S3 ETag 1426183a

Full diagnostics

browser  workload  quality  per-call overhead upper  overhead upper           95% CI        A/A diag         block CI  acf(1)   baseline  instrumented                         samples
-------  --------  -------  -----------------------  --------------  ---------------  --------------  ---------------  ------  ---------  ------------  ------------------------------
chrome   Hot       clean                 <= 2.55 ns        <= 5.13%    2.51..2.55 ns  -0.01..0.01 ns    2.51..2.55 ns    0.03  52.655 ms     55.335 ms   102 (trim 20%, outliers 6.9%)
chrome   Tiny      clean                 <= 0.02 ns        <= 0.20%   -0.01..0.02 ns  -0.01..0.00 ns   -0.01..0.02 ns    0.08  43.300 ms     43.327 ms  102 (trim 20%, outliers 15.7%)
firefox  Hot       clean                 <= 9.78 ns       <= 38.86%    9.76..9.78 ns  -0.01..0.00 ns    9.76..9.78 ns   -0.11  39.900 ms     55.400 ms   102 (trim 20%, outliers 9.8%)
firefox  Tiny      clean                 <= 0.00 ns        <= 0.00%  -0.30..-0.29 ns  -0.00..0.01 ns  -0.30..-0.29 ns   -0.22  53.680 ms     52.620 ms   102 (trim 20%, outliers 8.8%)
safari   Hot       clean                 <= 5.86 ns       <= 23.44%    5.81..5.83 ns  -0.01..0.00 ns    5.81..5.86 ns    0.36  44.960 ms     55.420 ms  102 (trim 20%, outliers 11.8%)
safari   Tiny      clean                 <= 0.44 ns       <= 11.76%    0.42..0.44 ns  -0.00..0.00 ns    0.42..0.44 ns    0.00  51.360 ms     57.310 ms   102 (trim 20%, outliers 2.0%)

Raw samples are in the live-debugger-runtime-bench-results artifact.