diff --git a/infra/deploy-runner/build-engine-auth-redirect-recovery-artifact.mjs b/infra/deploy-runner/build-engine-auth-redirect-recovery-artifact.mjs
new file mode 100644
index 0000000..f7692d0
--- /dev/null
+++ b/infra/deploy-runner/build-engine-auth-redirect-recovery-artifact.mjs
@@ -0,0 +1,154 @@
+#!/usr/bin/env node
+import { createHash } from 'node:crypto'
+import { spawnSync } from 'node:child_process'
+import { copyFile, lstat, mkdir, mkdtemp, readFile, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { dirname, join, resolve } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const here = dirname(fileURLToPath(import.meta.url))
+const platformRoot = resolve(here, '../..')
+const workspaceRoot = resolve(platformRoot, '..')
+const engineRoot = resolve(workspaceRoot, 'NODEDC_ENGINE_INFRA')
+const artifactRoot = resolve(process.env.NODEDC_DEPLOY_ARTIFACT_DIR || join(workspaceRoot, 'deploy-artifacts'))
+const predecessorArtifact = resolve(
+  process.env.NODEDC_ENGINE_AUTH_RECOVERY_PREDECESSOR
+    || '/Volumes/docker/nodedc-deploy/applied/nodedc-engine-restart-safe-auth-20260719-001.tgz',
+)
+const [patchId = '', ...extra] = process.argv.slice(2)
+
+if (extra.length || !/^engine-auth-redirect-recovery-\d{8}-\d{3}$/.test(patchId)) {
+  throw new Error('usage: build-engine-auth-redirect-recovery-artifact.mjs engine-auth-redirect-recovery-YYYYMMDD-NNN')
+}
+
+const predecessorArtifactSha256 = 'f6830046d7bd2bc32c1dbda8dce7ddf68d15c1e728f594c0f64ee8feec3911b8'
+const predecessorManifest = 'id=engine-restart-safe-auth-20260719-001\ncomponent=engine\ntype=app-overlay\n'
+const predecessorSha256 = Object.freeze({
+  'nodedc-source/src/platform/auth/access.ts': '9610dc1622a1c9b383eb3a1569347098002aa058dbbcbb23f096f2622d452222',
+  'nodedc-source/src/platform/auth/sessionRecovery.ts': 'f931cbb45d64d5d6a2868194e8c73879a408dffca1fdd7e41acfa262441c50d7',
+  'nodedc-source/dist/index.html': 'b031f6720683f6fb5ccfa59a01414ff2a3efcdf548b1c6aab33e1748ee3f003d',
+})
+const entries = Object.freeze([
+  'nodedc-source/src/platform/auth/access.ts',
+  'nodedc-source/src/platform/auth/sessionRecovery.ts',
+  'nodedc-source/dist/index.html',
+  'nodedc-source/dist/assets/index-DJ1CMfu4.js',
+])
+const candidateSha256 = Object.freeze({
+  'nodedc-source/src/platform/auth/access.ts': 'c686db2568912a093ea8934e34889254ddd659594f7084025c280732ef627002',
+  'nodedc-source/src/platform/auth/sessionRecovery.ts': '63f3e2379628dea3b119c4283bc0c3bb10e94199c673b9d9c579bac3c54be98f',
+  'nodedc-source/dist/index.html': '8894f62ad590168862e81266bc4602410279634b666af72cb14ad80aeb71ea74',
+  'nodedc-source/dist/assets/index-DJ1CMfu4.js': 'a0aaf72d2ed390142ff2ea03dbcfdd534637e5faefd80d8aa7d705a804abe065',
+})
+
+const predecessorInfo = await lstat(predecessorArtifact)
+if (predecessorInfo.isSymbolicLink() || !predecessorInfo.isFile()) {
+  throw new Error('engine_auth_recovery_predecessor_unsafe')
+}
+if (digest(await readFile(predecessorArtifact)) !== predecessorArtifactSha256) {
+  throw new Error('engine_auth_recovery_predecessor_archive_mismatch')
+}
+run('python3', [
+  '-c', verifyPredecessorScript(), predecessorArtifact,
+  predecessorArtifactSha256, predecessorManifest, JSON.stringify(predecessorSha256),
+])
+
+for (const rel of entries) {
+  const source = resolve(engineRoot, rel)
+  const info = await lstat(source)
+  if (info.isSymbolicLink() || !info.isFile()) throw new Error(`engine_auth_recovery_candidate_unsafe:${rel}`)
+  if (digest(await readFile(source)) !== candidateSha256[rel]) {
+    throw new Error(`engine_auth_recovery_candidate_sha256_mismatch:${rel}`)
+  }
+}
+const indexHtml = await readFile(resolve(engineRoot, 'nodedc-source/dist/index.html'), 'utf8')
+if (!indexHtml.includes('/assets/index-DJ1CMfu4.js') || !indexHtml.includes('/assets/index-Bim2pv1P.css')) {
+  throw new Error('engine_auth_recovery_dist_entrypoint_mismatch')
+}
+
+await mkdir(artifactRoot, { recursive: true })
+const artifact = join(artifactRoot, `nodedc-${patchId}.tgz`)
+await assertArtifactTargetFresh(artifact)
+const stage = await mkdtemp(join(tmpdir(), 'nodedc-engine-auth-redirect-recovery-'))
+
+try {
+  await writeFile(
+    join(stage, 'manifest.env'),
+    `id=${patchId}\ncomponent=engine\ntype=app-overlay\n`,
+    'utf8',
+  )
+  await writeFile(join(stage, 'files.txt'), `${entries.join('\n')}\n`, 'utf8')
+  for (const rel of entries) {
+    const target = join(stage, 'payload', rel)
+    await mkdir(dirname(target), { recursive: true })
+    await copyFile(resolve(engineRoot, rel), target)
+  }
+  run('python3', ['-c', canonicalTarScript(), artifact, stage])
+  console.log(JSON.stringify({
+    ok: true,
+    patchId,
+    artifact,
+    sha256: digest(await readFile(artifact)),
+    predecessorArtifact,
+    predecessorArtifactSha256,
+    predecessorSha256,
+    candidateSha256,
+    entries,
+    runtimeServices: ['nodedc-backend', 'app'],
+  }, null, 2))
+} finally {
+  await rm(stage, { recursive: true, force: true })
+}
+
+function verifyPredecessorScript() {
+  return [
+    'import hashlib,json,pathlib,sys,tarfile',
+    'source=pathlib.Path(sys.argv[1]); expected_archive=sys.argv[2]',
+    'expected_manifest=sys.argv[3].encode(); hashes=json.loads(sys.argv[4])',
+    "assert hashlib.sha256(source.read_bytes()).hexdigest()==expected_archive, 'archive-sha256'",
+    "with tarfile.open(source,'r:gz') as tar:",
+    "  assert tar.extractfile('manifest.env').read()==expected_manifest, 'manifest'",
+    '  for rel,wanted in hashes.items():',
+    "    data=tar.extractfile('payload/'+rel).read()",
+    "    assert hashlib.sha256(data).hexdigest()==wanted, 'payload:'+rel",
+  ].join('\n')
+}
+
+async function assertArtifactTargetFresh(target) {
+  try {
+    await lstat(target)
+  } catch (error) {
+    if (error?.code === 'ENOENT') return
+    throw error
+  }
+  throw new Error('engine_auth_recovery_artifact_already_exists')
+}
+
+function canonicalTarScript() {
+  return [
+    'import gzip,io,pathlib,sys,tarfile',
+    'root=pathlib.Path(sys.argv[2])',
+    "with open(sys.argv[1],'wb') as out:",
+    "  with gzip.GzipFile(filename='',mode='wb',fileobj=out,compresslevel=9,mtime=0) as gz:",
+    "    with tarfile.open(fileobj=gz,mode='w',format=tarfile.PAX_FORMAT) as tar:",
+    "      for top in ('manifest.env','files.txt','payload'):",
+    "        p=root/top; paths=[p]+(sorted(p.rglob('*')) if p.is_dir() else [])",
+    '        for x in paths:',
+    "          info=tar.gettarinfo(str(x),arcname=x.relative_to(root).as_posix())",
+    "          info.uid=info.gid=0; info.uname=info.gname='root'; info.mtime=0; info.mode=0o755 if info.isdir() else 0o644",
+    "          with (open(x,'rb') if info.isfile() else io.BytesIO()) as src: tar.addfile(info,src if info.isfile() else None)",
+  ].join('\n')
+}
+
+function run(command, args) {
+  const result = spawnSync(command, args, {
+    encoding: 'utf8',
+    stdio: ['ignore', 'pipe', 'pipe'],
+    maxBuffer: 128 * 1024 * 1024,
+  })
+  if (result.status !== 0) throw new Error(`${command}_failed:${result.stderr || result.stdout}`)
+}
+
+function digest(bytes) {
+  return createHash('sha256').update(bytes).digest('hex')
+}
diff --git a/infra/deploy-runner/build-engine-restart-safe-auth-artifact.mjs b/infra/deploy-runner/build-engine-restart-safe-auth-artifact.mjs
new file mode 100644
index 0000000..fc4964e
--- /dev/null
+++ b/infra/deploy-runner/build-engine-restart-safe-auth-artifact.mjs
@@ -0,0 +1,148 @@
+#!/usr/bin/env node
+import { createHash } from 'node:crypto'
+import { spawnSync } from 'node:child_process'
+import { copyFile, lstat, mkdir, mkdtemp, readFile, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { dirname, join, resolve } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const here = dirname(fileURLToPath(import.meta.url))
+const platformRoot = resolve(here, '../..')
+const workspaceRoot = resolve(platformRoot, '..')
+const engineRoot = resolve(workspaceRoot, 'NODEDC_ENGINE_INFRA')
+const artifactRoot = resolve(process.env.NODEDC_DEPLOY_ARTIFACT_DIR || join(workspaceRoot, 'deploy-artifacts'))
+const [patchId = '', ...extra] = process.argv.slice(2)
+
+if (extra.length || !/^engine-restart-safe-auth-\d{8}-\d{3}$/.test(patchId)) {
+  throw new Error('usage: build-engine-restart-safe-auth-artifact.mjs engine-restart-safe-auth-YYYYMMDD-NNN')
+}
+
+const entries = Object.freeze([
+  'nodedc-source/server/auth/engineHandoffSession.js',
+  'nodedc-source/server/index.js',
+  'nodedc-source/src/App.tsx',
+  'nodedc-source/src/platform/auth/access.ts',
+  'nodedc-source/src/platform/auth/sessionRecovery.ts',
+  'nodedc-source/dist/index.html',
+  'nodedc-source/dist/assets/index-Bim2pv1P.css',
+  'nodedc-source/dist/assets/index-4TenBzkg.js',
+])
+
+const candidateSha256 = Object.freeze({
+  'nodedc-source/server/auth/engineHandoffSession.js': '0cc5bf02b11cd5fc8cc8cad018091ca93efb13bc72616348ada61105af15bd8e',
+  'nodedc-source/server/index.js': '0ac408e0e9a7bc5c8e13a00afc957b982b065e2bc414919839e0b0a11aa05ba4',
+  'nodedc-source/src/App.tsx': 'd9bc0f23ceaaf4f5534ac9a9b1f97d84fd8eee4679c59b5999b5a75b8c77bb32',
+  'nodedc-source/src/platform/auth/access.ts': '9610dc1622a1c9b383eb3a1569347098002aa058dbbcbb23f096f2622d452222',
+  'nodedc-source/src/platform/auth/sessionRecovery.ts': 'f931cbb45d64d5d6a2868194e8c73879a408dffca1fdd7e41acfa262441c50d7',
+  'nodedc-source/dist/index.html': 'b031f6720683f6fb5ccfa59a01414ff2a3efcdf548b1c6aab33e1748ee3f003d',
+  'nodedc-source/dist/assets/index-Bim2pv1P.css': '18322addd45c126a7b8396f36b005f3085fddba3e9b346dd2c910f6fa6987ebf',
+  'nodedc-source/dist/assets/index-4TenBzkg.js': 'a48fcacf3348c20a432cd6da2627b89c0c3e54bc989c727b620125dd3412538a',
+})
+
+const predecessorSha256 = Object.freeze({
+  'nodedc-source/server/index.js': 'b2b790b02839570d967a2ca68b00e2724485a99389ac9b3a589a1b22302a36b8',
+  'nodedc-source/src/App.tsx': '2ea264a59c3e82f763be74f0312cb1aa6bce856644ba0bc7024d77e238e7eb41',
+  'nodedc-source/src/platform/auth/access.ts': '4fb9c4d524765dff8a5360efa1c0acf1d203da1cc2c7fd3b98e1456261d43d41',
+  'nodedc-source/src/platform/auth/sessionRecovery.ts': '997d3a18e439308d4650e3c7324710a8b17dea29976001c4275c84d96b18ccfe',
+})
+
+for (const [rel, expected] of Object.entries(predecessorSha256)) {
+  const result = spawnSync('git', ['-C', engineRoot, 'show', `HEAD:${rel}`], {
+    stdio: ['ignore', 'pipe', 'pipe'],
+    maxBuffer: 128 * 1024 * 1024,
+  })
+  if (result.status !== 0 || digest(result.stdout) !== expected) {
+    throw new Error(`engine_auth_predecessor_mismatch:${rel}`)
+  }
+}
+
+const newModulePath = 'nodedc-source/server/auth/engineHandoffSession.js'
+const newModuleProbe = spawnSync('git', ['-C', engineRoot, 'cat-file', '-e', `HEAD:${newModulePath}`], {
+  stdio: 'ignore',
+})
+if (newModuleProbe.status === 0) throw new Error('engine_auth_new_module_predecessor_unexpected')
+
+for (const rel of entries) {
+  const source = resolve(engineRoot, rel)
+  const info = await lstat(source)
+  if (info.isSymbolicLink() || !info.isFile()) throw new Error(`engine_auth_candidate_unsafe:${rel}`)
+  if (digest(await readFile(source)) !== candidateSha256[rel]) {
+    throw new Error(`engine_auth_candidate_sha256_mismatch:${rel}`)
+  }
+}
+
+const indexHtml = await readFile(resolve(engineRoot, 'nodedc-source/dist/index.html'), 'utf8')
+if (!indexHtml.includes('/assets/index-4TenBzkg.js') || !indexHtml.includes('/assets/index-Bim2pv1P.css')) {
+  throw new Error('engine_auth_dist_entrypoint_mismatch')
+}
+
+await mkdir(artifactRoot, { recursive: true })
+const artifact = join(artifactRoot, `nodedc-${patchId}.tgz`)
+await assertArtifactTargetFresh(artifact)
+const stage = await mkdtemp(join(tmpdir(), 'nodedc-engine-restart-safe-auth-'))
+
+try {
+  await writeFile(
+    join(stage, 'manifest.env'),
+    `id=${patchId}\ncomponent=engine\ntype=app-overlay\n`,
+    'utf8',
+  )
+  await writeFile(join(stage, 'files.txt'), `${entries.join('\n')}\n`, 'utf8')
+  for (const rel of entries) {
+    const target = join(stage, 'payload', rel)
+    await mkdir(dirname(target), { recursive: true })
+    await copyFile(resolve(engineRoot, rel), target)
+  }
+  run('python3', ['-c', canonicalTarScript(), artifact, stage])
+  console.log(JSON.stringify({
+    ok: true,
+    patchId,
+    artifact,
+    sha256: digest(await readFile(artifact)),
+    entries,
+    predecessorSha256,
+    candidateSha256,
+    runtimeServices: ['nodedc-backend', 'app'],
+  }, null, 2))
+} finally {
+  await rm(stage, { recursive: true, force: true })
+}
+
+async function assertArtifactTargetFresh(target) {
+  try {
+    await lstat(target)
+  } catch (error) {
+    if (error?.code === 'ENOENT') return
+    throw error
+  }
+  throw new Error('engine_auth_artifact_already_exists')
+}
+
+function canonicalTarScript() {
+  return [
+    'import gzip,io,pathlib,sys,tarfile',
+    'root=pathlib.Path(sys.argv[2])',
+    "with open(sys.argv[1],'wb') as out:",
+    "  with gzip.GzipFile(filename='',mode='wb',fileobj=out,compresslevel=9,mtime=0) as gz:",
+    "    with tarfile.open(fileobj=gz,mode='w',format=tarfile.PAX_FORMAT) as tar:",
+    "      for top in ('manifest.env','files.txt','payload'):",
+    "        p=root/top; paths=[p]+(sorted(p.rglob('*')) if p.is_dir() else [])",
+    '        for x in paths:',
+    "          info=tar.gettarinfo(str(x),arcname=x.relative_to(root).as_posix())",
+    "          info.uid=info.gid=0; info.uname=info.gname='root'; info.mtime=0; info.mode=0o755 if info.isdir() else 0o644",
+    "          with (open(x,'rb') if info.isfile() else io.BytesIO()) as src: tar.addfile(info,src if info.isfile() else None)",
+  ].join('\n')
+}
+
+function run(command, args) {
+  const result = spawnSync(command, args, {
+    encoding: 'utf8',
+    stdio: ['ignore', 'pipe', 'pipe'],
+    maxBuffer: 128 * 1024 * 1024,
+  })
+  if (result.status !== 0) throw new Error(`${command}_failed:${result.stderr || result.stdout}`)
+}
+
+function digest(bytes) {
+  return createHash('sha256').update(bytes).digest('hex')
+}