diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8b36f37e8..d51a3da8b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -157,3 +157,43 @@ jobs:
         with:
           setup-script: pnpm run build
           main-script: pnpm run test:npm
+
+  # Repo-owned: every override declares `engines.node: >=24`, but the jobs
+  # above run a newer current-line Node — nothing executes the FLOOR, so a
+  # too-new syntax/API in an override stays green here and only breaks in a
+  # consumer pinned to the floor. This job side-installs the exact floor
+  # release (sha256-verified against nodejs.org's published SHASUMS256 before
+  # extraction) and dynamic-imports every override's node entry under it.
+  floor-node-smoke:
+    name: 🧪 NPM Overrides on Floor Node
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - name: Bootstrap checkout
+        shell: bash
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+          SERVER_URL: ${{ github.server_url }}
+          REPOSITORY: ${{ github.repository }}
+          TRIGGER_REF: ${{ github.ref }}
+        run: |
+          set -euo pipefail
+          git init -q
+          git config --local advice.detachedHead false
+          git remote remove origin 2>/dev/null || true
+          git remote add origin "${SERVER_URL}/${REPOSITORY}"
+          FETCH_ARGS=(--no-tags --prune --depth 1 origin "${TRIGGER_REF}")
+          if [ -n "${GITHUB_TOKEN}" ]; then
+            AUTH_B64="$(printf 'x-access-token:%s' "${GITHUB_TOKEN}" | base64 | tr -d '\n')"
+            git -c "http.${SERVER_URL}/.extraheader=AUTHORIZATION: basic ${AUTH_B64}" fetch "${FETCH_ARGS[@]}"
+          else
+            git fetch "${FETCH_ARGS[@]}"
+          fi
+          git checkout -q --detach FETCH_HEAD
+      - uses: ./.github/actions/fleet/setup-and-install
+        with:
+          node-version: 24
+          socket-api-token: ${{ secrets.SOCKET_API_TOKEN }}
+      - uses: ./.github/actions/fleet/run-script
+        with:
+          main-script: pnpm run test:npm:floor
diff --git a/package.json b/package.json
index 5938732ca..9df4f1faa 100644
--- a/package.json
+++ b/package.json
@@ -48,6 +48,7 @@
     "test": "node scripts/fleet/test.mts",
     "test:fuzz": "node scripts/repo/fuzz.mts",
     "test:npm": "node scripts/npm/run-vitest-npm.mts",
+    "test:npm:floor": "node scripts/npm/floor-node-smoke.mts",
     "type": "node node_modules/typescript/bin/tsc --noEmit -p .config/fleet/tsconfig.check.json",
     "update": "node scripts/fleet/update.mts",
     "update:external-tools": "node scripts/repo/update-external-tools.mts",
diff --git a/scripts/npm/floor-node-smoke.mts b/scripts/npm/floor-node-smoke.mts
new file mode 100644
index 000000000..f703367de
--- /dev/null
+++ b/scripts/npm/floor-node-smoke.mts
@@ -0,0 +1,216 @@
+#!/usr/bin/env node
+/**
+ * @file Prove every npm override runs on the FLOOR Node its engines declare.
+ *   All packages/npm overrides ship `engines.node: >=24`, but regular CI runs
+ *   a newer current-line Node — nothing executes the floor, so an override
+ *   that quietly uses newer-than-floor syntax/APIs stays green here and only
+ *   breaks inside a consumer pinned to the floor. This gate side-installs the
+ *   EXACT floor release (pinned version + sha256, verified before extraction —
+ *   a mismatched download hard-fails) and dynamic-imports every override's
+ *   node entry under that binary.
+ *   The floor binary is a side install: it never touches PATH — the harness
+ *   keeps running on the repo's own Node and spawns the floor binary
+ *   explicitly, so the two runtimes can't be confused.
+ *   Usage: node scripts/npm/floor-node-smoke.mts
+ *   Env: FLOOR_NODE_DIR overrides the install dir (default: RUNNER_TEMP,
+ *   falling back to os.tmpdir()).
+ */
+import { existsSync, mkdirSync, readdirSync, readFileSync } from 'node:fs'
+import os from 'node:os'
+import path from 'node:path'
+import process from 'node:process'
+import { fileURLToPath, pathToFileURL } from 'node:url'
+
+import { safeDeleteSync } from '@socketsecurity/lib-stable/fs/safe'
+import { httpDownload } from '@socketsecurity/lib-stable/http-request/download'
+import { getDefaultLogger } from '@socketsecurity/lib-stable/logger/default'
+import { spawnSync } from '@socketsecurity/lib-stable/process/spawn/child'
+
+const logger = getDefaultLogger()
+
+// The floor is the low edge of packages/npm/*'s `engines.node: >=24` range.
+// Bump BOTH the version and every sha256 together when the engines floor
+// moves — hashes come from https://nodejs.org/dist/v<version>/SHASUMS256.txt.
+// floor-node-pin-matches-engines (check --all) enforces the version half of
+// that lock-step: it fails when any override's engines floor drifts from
+// this pin.
+export const FLOOR_NODE_VERSION = '24.0.0'
+const FLOOR_NODE_PLATFORMS: Record<string, { asset: string; sha256: string }> =
+  {
+    'darwin-arm64': {
+      asset: `node-v${FLOOR_NODE_VERSION}-darwin-arm64.tar.gz`,
+      sha256:
+        '194e2f3dd3ec8c2adcaa713ed40f44c5ca38467880e160974ceac1659be60121',
+    },
+    'darwin-x64': {
+      asset: `node-v${FLOOR_NODE_VERSION}-darwin-x64.tar.gz`,
+      sha256:
+        'f716b3ce14a7e37a6cbf97c9de10d444d7da07ef833cd8da81dd944d111e6a4a',
+    },
+    'linux-x64': {
+      asset: `node-v${FLOOR_NODE_VERSION}-linux-x64.tar.xz`,
+      sha256:
+        '59b8af617dccd7f9f68cc8451b2aee1e86d6bd5cb92cd51dd6216a31b707efd7',
+    },
+    'win-x64': {
+      asset: `node-v${FLOOR_NODE_VERSION}-win-x64.zip`,
+      sha256:
+        '3d0fff80c87bb9a8d7f49f2f27832aa34a1477d137af46f5b14df5498be81304',
+    },
+  }
+
+const repoRoot = path.resolve(
+  path.dirname(fileURLToPath(import.meta.url)),
+  '../..',
+)
+const npmPackagesPath = path.join(repoRoot, 'packages/npm')
+
+/**
+ * Download + verify + extract the floor Node, returning its binary path.
+ * `httpDownload` streams to a temp sibling, checks the pinned sha256, and
+ * atomic-renames on success — a tampered or truncated download never
+ * materializes at the archive path, let alone extracts.
+ */
+async function ensureFloorNode(): Promise<string> {
+  const platKey = `${process.platform}-${process.arch}`
+  const pin = FLOOR_NODE_PLATFORMS[platKey]
+  if (!pin) {
+    throw new Error(
+      `no floor-node pin for ${platKey} — add its asset + sha256 (from ` +
+        `https://nodejs.org/dist/v${FLOOR_NODE_VERSION}/SHASUMS256.txt) to FLOOR_NODE_PLATFORMS`,
+    )
+  }
+  const baseDir =
+    process.env['FLOOR_NODE_DIR'] || process.env['RUNNER_TEMP'] || os.tmpdir()
+  // Strip the archive suffix (.tar.gz / .tar.xz / .zip) to get the top-level
+  // directory name the tarball extracts to (node-v<ver>-<os>-<arch>).
+  const extractDir = path.join(
+    baseDir,
+    pin.asset.replace(/\.(tar\.(gz|xz)|zip)$/, ''),
+  )
+  const binPath =
+    process.platform === 'win32'
+      ? path.join(extractDir, 'node.exe')
+      : path.join(extractDir, 'bin/node')
+  if (existsSync(binPath)) {
+    return binPath
+  }
+  const url = `https://nodejs.org/dist/v${FLOOR_NODE_VERSION}/${pin.asset}`
+  logger.log(`downloading floor node ${FLOOR_NODE_VERSION} (${pin.asset})`)
+  mkdirSync(baseDir, { recursive: true })
+  const archivePath = path.join(baseDir, pin.asset)
+  await httpDownload(url, archivePath, { sha256: pin.sha256 })
+  // `tar -xf` auto-detects gz/xz; bsdtar (macOS + Windows runners) also
+  // extracts zip through the same flag.
+  const tar = spawnSync('tar', ['-xf', archivePath, '-C', baseDir], {
+    stdio: 'inherit',
+  })
+  safeDeleteSync(archivePath, { force: true })
+  if (tar.status !== 0 || !existsSync(binPath)) {
+    safeDeleteSync(extractDir, { force: true, recursive: true })
+    throw new Error(`floor node extract failed (${pin.asset})`)
+  }
+  return binPath
+}
+
+/**
+ * Resolve a package's node-runtime entry from its `exports` map (the
+ * overrides ship no `main`). Condition preference mirrors Node's own
+ * resolution for a `node` consumer; `types` never matches by construction.
+ */
+function resolveNodeEntry(exp: unknown): string | undefined {
+  if (typeof exp === 'string') {
+    return exp
+  }
+  if (!exp || typeof exp !== 'object') {
+    return undefined
+  }
+  const conditions = exp as Record<string, unknown>
+  const conditionOrder = ['node', 'import', 'require', 'default']
+  for (let i = 0, { length } = conditionOrder; i < length; i += 1) {
+    const key = conditionOrder[i]!
+    if (key in conditions) {
+      const resolved = resolveNodeEntry(conditions[key])
+      if (resolved) {
+        return resolved
+      }
+    }
+  }
+  return undefined
+}
+
+async function main(): Promise<void> {
+  const floorNode = await ensureFloorNode()
+  const version = spawnSync(floorNode, ['--version'], { encoding: 'utf8' })
+  logger.log(
+    `floor node ready: ${String(version.stdout).trim()} at ${floorNode}`,
+  )
+
+  const failures: string[] = []
+  let imported = 0
+  let skipped = 0
+  const dirents = readdirSync(npmPackagesPath, { withFileTypes: true })
+  for (let i = 0, { length } = dirents; i < length; i += 1) {
+    const dirent = dirents[i]!
+    if (!dirent.isDirectory()) {
+      continue
+    }
+    const pkgDir = path.join(npmPackagesPath, dirent.name)
+    const pkgJsonPath = path.join(pkgDir, 'package.json')
+    if (!existsSync(pkgJsonPath)) {
+      continue
+    }
+    const pkgJson = JSON.parse(readFileSync(pkgJsonPath, 'utf8'))
+    const entryRel = pkgJson.exports
+      ? resolveNodeEntry(pkgJson.exports['.'] ?? pkgJson.exports)
+      : pkgJson.main
+    if (!entryRel) {
+      skipped += 1
+      logger.log(
+        `skip ${dirent.name}: no node entry (bin-only or asset package)`,
+      )
+      continue
+    }
+    const entryUrl = pathToFileURL(path.join(pkgDir, entryRel)).href
+    // Dynamic import loads every entry kind a floor-pinned ESM consumer can
+    // reach: .cjs, .js/ESM, and .json (which requires the import attribute
+    // on every Node — `date` and `es-iterator-helpers` ship JSON entries).
+    const run = spawnSync(
+      floorNode,
+      [
+        '--input-type=module',
+        '-e',
+        "const s = process.argv[1]; await (s.endsWith('.json') ? import(s, { with: { type: 'json' } }) : import(s))",
+        entryUrl,
+      ],
+      { encoding: 'utf8' },
+    )
+    if (run.status === 0) {
+      imported += 1
+    } else {
+      failures.push(
+        `${dirent.name}: ${String(run.stderr).trim().split('\n')[0]}`,
+      )
+    }
+  }
+
+  logger.log(
+    `floor-node smoke: ${imported} imported, ${skipped} skipped, ${failures.length} failed ` +
+      `(node ${FLOOR_NODE_VERSION})`,
+  )
+  if (failures.length > 0) {
+    for (let i = 0, { length } = failures; i < length; i += 1) {
+      logger.error(`FAIL ${failures[i]}`)
+    }
+    process.exitCode = 1
+  }
+}
+
+// Entrypoint-guarded: floor-node-pin-matches-engines (check --all) imports
+// FLOOR_NODE_VERSION from this module, which must not trigger a download.
+if (process.argv[1] && import.meta.url === `file://${process.argv[1]}`) {
+  main().catch((e: unknown) => {
+    logger.error(e)
+    process.exitCode = 1
+  })
+}
diff --git a/scripts/repo/check/floor-node-pin-matches-engines.mts b/scripts/repo/check/floor-node-pin-matches-engines.mts
new file mode 100644
index 000000000..262e42bfc
--- /dev/null
+++ b/scripts/repo/check/floor-node-pin-matches-engines.mts
@@ -0,0 +1,123 @@
+#!/usr/bin/env node
+/**
+ * @file The floor-node smoke gate tests the Node version the overrides
+ *   actually declare. The gate side-installs FLOOR_NODE_VERSION and imports
+ *   every packages/npm/* entry under it — its whole premise is that the pin
+ *   IS the low edge of every override's `engines.node` range. That
+ *   lock-step used to be a comment ("bump BOTH together"); this law
+ *   enforces the version half: every override must declare `engines.node`,
+ *   and each range's minimum satisfying version must equal the pin. An
+ *   engines bump without a pin bump (or vice versa) would otherwise leave
+ *   the gate green while proving the WRONG floor — the exact silent drift
+ *   it exists to prevent. (The sha256 half of the lock-step is enforced at
+ *   runtime: httpDownload hard-fails on a hash mismatch.)
+ *   Usage: node scripts/repo/check/floor-node-pin-matches-engines.mts.
+ */
+
+import { existsSync, readdirSync, readFileSync } from 'node:fs'
+import path from 'node:path'
+import process from 'node:process'
+// oxlint-disable-next-line socket/prefer-stable-external-semver -- @socketsecurity/lib-stable has no ./external/semver export at the pinned version; semver is a devDependency (scripts/tests only, not bundled).
+import semver from 'semver'
+
+import { getDefaultLogger } from '@socketsecurity/lib-stable/logger/default'
+
+import { FLOOR_NODE_VERSION } from '../../npm/floor-node-smoke.mts'
+
+const logger = getDefaultLogger()
+
+export interface OverrideEngines {
+  name: string
+  enginesNode: string | undefined
+}
+
+/**
+ * Classify each override's declared Node floor against the smoke gate's
+ * pin. Pure: directory reading happens in the caller so this stays
+ * unit-testable on synthetic fixtures.
+ */
+export function findFloorDrift(
+  overrides: OverrideEngines[],
+  floorVersion: string,
+): string[] {
+  const findings: string[] = []
+  for (let i = 0, { length } = overrides; i < length; i += 1) {
+    const { enginesNode, name } = overrides[i]!
+    if (!enginesNode) {
+      findings.push(
+        `${name}: no engines.node — the floor gate's premise (every ` +
+          'override declares its floor) does not hold for it',
+      )
+      continue
+    }
+    let min: semver.SemVer | undefined
+    try {
+      // semver throws on a malformed range instead of returning null.
+      min = semver.minVersion(enginesNode, { loose: true }) ?? undefined
+    } catch {
+      min = undefined
+    }
+    if (!min) {
+      findings.push(
+        `${name}: engines.node ${JSON.stringify(enginesNode)} has no ` +
+          'resolvable minimum version',
+      )
+      continue
+    }
+    if (min.version !== floorVersion) {
+      findings.push(
+        `${name}: engines.node ${JSON.stringify(enginesNode)} floors at ` +
+          `${min.version}, but the smoke gate proves ${floorVersion}`,
+      )
+    }
+  }
+  return findings
+}
+
+function collectOverrideEngines(npmPackagesPath: string): OverrideEngines[] {
+  const out: OverrideEngines[] = []
+  const dirents = readdirSync(npmPackagesPath, { withFileTypes: true })
+  for (let i = 0, { length } = dirents; i < length; i += 1) {
+    const dirent = dirents[i]!
+    if (!dirent.isDirectory()) {
+      continue
+    }
+    const pkgJsonPath = path.join(npmPackagesPath, dirent.name, 'package.json')
+    if (!existsSync(pkgJsonPath)) {
+      continue
+    }
+    const pkgJson = JSON.parse(readFileSync(pkgJsonPath, 'utf8')) as {
+      engines?: { node?: string | undefined } | undefined
+    }
+    out.push({ name: dirent.name, enginesNode: pkgJson.engines?.node })
+  }
+  return out
+}
+
+async function main(): Promise<number> {
+  const repoRoot = path.resolve(import.meta.dirname, '../../..')
+  const overrides = collectOverrideEngines(path.join(repoRoot, 'packages/npm'))
+  const findings = findFloorDrift(overrides, FLOOR_NODE_VERSION)
+  if (findings.length) {
+    logger.fail(
+      [
+        `${findings.length} override(s) out of lock-step with the floor-node pin (${FLOOR_NODE_VERSION}):`,
+        ...findings.map(f => `  ${f}`),
+        'Fix: move engines.node and FLOOR_NODE_VERSION together —',
+        '  scripts/npm/floor-node-smoke.mts (bump the pin + every sha256 from',
+        '  https://nodejs.org/dist/v<version>/SHASUMS256.txt), or correct the',
+        '  drifted engines range.',
+      ].join('\n'),
+    )
+    process.exitCode = 1
+    return 1
+  }
+  logger.success(
+    `all ${overrides.length} overrides floor at ${FLOOR_NODE_VERSION} — the smoke gate proves the declared floor`,
+  )
+  return 0
+}
+
+if (process.argv[1] && import.meta.url === `file://${process.argv[1]}`) {
+  void main()
+}
diff --git a/test/scripts/repo/check/floor-node-pin-matches-engines.test.mts b/test/scripts/repo/check/floor-node-pin-matches-engines.test.mts
new file mode 100644
index 000000000..bd976f387
--- /dev/null
+++ b/test/scripts/repo/check/floor-node-pin-matches-engines.test.mts
@@ -0,0 +1,68 @@
+/**
+ * @file Unit tests for the floor-pin ↔ engines lock-step law's pure core:
+ *   both arms of each classification (in-step, drifted range, missing or
+ *   unresolvable engines). Directory scanning stays in the caller, so the
+ *   suite runs on synthetic fixtures with no repo coupling.
+ */
+
+import { describe, expect, it } from 'vitest'
+
+import { findFloorDrift } from '../../../../scripts/repo/check/floor-node-pin-matches-engines.mts'
+
+const FLOOR = '24.0.0'
+
+describe('scripts/repo/check/floor-node-pin-matches-engines', () => {
+  it('passes when every override floors exactly at the pin', () => {
+    expect(
+      findFloorDrift(
+        [
+          { name: 'a', enginesNode: '>=24' },
+          { name: 'b', enginesNode: '>=24.0.0' },
+          { name: 'c', enginesNode: '^24.0.0 || >=25' },
+        ],
+        FLOOR,
+      ),
+    ).toEqual([])
+  })
+
+  it('flags a range whose floor drifted above or below the pin', () => {
+    const above = findFloorDrift([{ name: 'a', enginesNode: '>=26' }], FLOOR)
+    expect(above).toHaveLength(1)
+    expect(above[0]).toContain('floors at 26.0.0')
+    expect(above[0]).toContain('proves 24.0.0')
+    const below = findFloorDrift([{ name: 'b', enginesNode: '>=18.19' }], FLOOR)
+    expect(below).toHaveLength(1)
+    expect(below[0]).toContain('floors at 18.19.0')
+  })
+
+  it('flags a missing engines.node — the gate premise breaks silently', () => {
+    const findings = findFloorDrift(
+      [{ name: 'a', enginesNode: undefined }],
+      FLOOR,
+    )
+    expect(findings).toHaveLength(1)
+    expect(findings[0]).toContain('no engines.node')
+  })
+
+  it('flags an unresolvable range instead of crashing', () => {
+    const findings = findFloorDrift(
+      [{ name: 'a', enginesNode: 'not-a-range' }],
+      FLOOR,
+    )
+    expect(findings).toHaveLength(1)
+    expect(findings[0]).toContain('no resolvable minimum')
+  })
+
+  it('reports every drifted override, not just the first', () => {
+    expect(
+      findFloorDrift(
+        [
+          { name: 'a', enginesNode: '>=26' },
+          { name: 'b', enginesNode: '>=24' },
+          { name: 'c', enginesNode: undefined },
+        ],
+        FLOOR,
+      ),
+    ).toHaveLength(2)
+  })
+})