diff --git a/.github/workflows/ssh-relay-runtime-artifacts.yml b/.github/workflows/ssh-relay-runtime-artifacts.yml
index f0d4dc9aee2..21e36216a16 100644
--- a/.github/workflows/ssh-relay-runtime-artifacts.yml
+++ b/.github/workflows/ssh-relay-runtime-artifacts.yml
@@ -110,6 +110,7 @@ jobs:
             config/scripts/ssh-relay-node-zip-inspection.test.mjs \
             config/scripts/ssh-relay-runtime-artifact.test.mjs \
             config/scripts/ssh-relay-runtime-pty-smoke.test.mjs \
+            config/scripts/ssh-relay-runtime-reproducibility.test.mjs \
             config/scripts/ssh-relay-runtime-resource-diagnostics.test.mjs \
             config/scripts/ssh-relay-runtime-windows-tree.test.mjs \
             config/scripts/ssh-relay-runtime-zip.test.mjs \
@@ -129,34 +130,44 @@ jobs:
           done
           printf 'NODE_INPUTS=%s\n' "$inputs" >> "$GITHUB_ENV"
 
-      - name: Build, inspect, and smoke exact runtime
+      - name: Build twice, inspect, smoke, and compare exact runtime
         shell: bash
         run: |
           set -euo pipefail
-          output="$RUNNER_TEMP/ssh-relay-runtime/${{ matrix.tuple }}"
-          mkdir -p "$(dirname "$output")"
+          output_root="$RUNNER_TEMP/ssh-relay-runtime/${{ matrix.tuple }}"
+          mkdir -p "$output_root"
+          first_output="$output_root/first"
+          second_output="$output_root/second"
           source_commit=$(git rev-parse HEAD)
           source_date_epoch=$(git show -s --format=%ct "$source_commit")
-          /usr/bin/time -p node config/scripts/build-ssh-relay-runtime.mjs \
+          for output in "$first_output" "$second_output"; do
+            printf 'clean_build_output=%s\n' "$output"
+            /usr/bin/time -p node config/scripts/build-ssh-relay-runtime.mjs \
+              --tuple '${{ matrix.tuple }}' \
+              --inputs-directory "$NODE_INPUTS" \
+              --output-directory "$output" \
+              --source-date-epoch "$source_date_epoch" \
+              --git-commit "$source_commit"
+            identity="$output/orca-ssh-relay-runtime-${{ matrix.tuple }}.identity.json"
+            archive=$(find "$output" -maxdepth 1 -name '*.tar.xz' -print -quit)
+            test -n "$archive"
+            /usr/bin/time -p node config/scripts/verify-ssh-relay-runtime.mjs \
+              --runtime-directory "$output/runtime" \
+              --identity "$identity" \
+              --archive "$archive"
+            if find "$output/runtime" -type f \( -name npm -o -name npx -o -name corepack -o -name '*.map' \) -print -quit | grep -q .; then
+              echo 'Runtime contains a prohibited package manager or source map.' >&2
+              exit 1
+            fi
+            parcel_packages=$(find "$output/runtime/node_modules/@parcel" -mindepth 1 -maxdepth 1 -type d | wc -l | tr -d ' ')
+            test "$parcel_packages" = 2
+          done
+          node config/scripts/ssh-relay-runtime-reproducibility.mjs \
             --tuple '${{ matrix.tuple }}' \
-            --inputs-directory "$NODE_INPUTS" \
-            --output-directory "$output" \
-            --source-date-epoch "$source_date_epoch" \
-            --git-commit "$source_commit"
-          identity="$output/orca-ssh-relay-runtime-${{ matrix.tuple }}.identity.json"
-          archive=$(find "$output" -maxdepth 1 -name '*.tar.xz' -print -quit)
-          /usr/bin/time -p node config/scripts/verify-ssh-relay-runtime.mjs \
-            --runtime-directory "$output/runtime" \
-            --identity "$identity" \
-            --archive "$archive"
-          if find "$output/runtime" -type f \( -name npm -o -name npx -o -name corepack -o -name '*.map' \) -print -quit | grep -q .; then
-            echo 'Runtime contains a prohibited package manager or source map.' >&2
-            exit 1
-          fi
-          parcel_packages=$(find "$output/runtime/node_modules/@parcel" -mindepth 1 -maxdepth 1 -type d | wc -l | tr -d ' ')
-          test "$parcel_packages" = 2
+            --first-output-directory "$first_output" \
+            --second-output-directory "$second_output"
           mkdir -p "$GITHUB_WORKSPACE/runtime-evidence/${{ matrix.tuple }}"
-          cp "$output"/*.tar.xz "$output"/*.spdx.json "$output"/*.provenance.json "$output"/*.identity.json \
+          cp "$first_output"/*.tar.xz "$first_output"/*.spdx.json "$first_output"/*.provenance.json "$first_output"/*.identity.json \
             "$GITHUB_WORKSPACE/runtime-evidence/${{ matrix.tuple }}/"
 
       - name: Upload unpublished artifact evidence
@@ -254,6 +265,7 @@ jobs:
             config/scripts/ssh-relay-node-zip-inspection.test.mjs `
             config/scripts/ssh-relay-runtime-artifact.test.mjs `
             config/scripts/ssh-relay-runtime-pty-smoke.test.mjs `
+            config/scripts/ssh-relay-runtime-reproducibility.test.mjs `
             config/scripts/ssh-relay-runtime-resource-diagnostics.test.mjs `
             config/scripts/ssh-relay-runtime-windows-tree.test.mjs `
             config/scripts/ssh-relay-runtime-zip.test.mjs `
@@ -284,41 +296,52 @@ jobs:
           }
           "NODE_INPUTS=$inputs" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
 
-      - name: Build, inspect, and smoke exact runtime
+      - name: Build twice, inspect, smoke, and compare exact runtime
         shell: pwsh
         run: |
           $ErrorActionPreference = 'Stop'
-          $output = Join-Path $env:RUNNER_TEMP 'ssh-relay-runtime/${{ matrix.tuple }}'
-          New-Item -ItemType Directory -Path (Split-Path -Parent $output) -Force | Out-Null
+          $outputRoot = Join-Path $env:RUNNER_TEMP 'ssh-relay-runtime/${{ matrix.tuple }}'
+          New-Item -ItemType Directory -Path $outputRoot -Force | Out-Null
+          $firstOutput = Join-Path $outputRoot 'first'
+          $secondOutput = Join-Path $outputRoot 'second'
           $sourceCommit = git rev-parse HEAD
           $sourceDateEpoch = git show -s --format=%ct $sourceCommit
-          node config/scripts/build-ssh-relay-runtime.mjs `
-            --tuple '${{ matrix.tuple }}' `
-            --inputs-directory $env:NODE_INPUTS `
-            --output-directory $output `
-            --source-date-epoch $sourceDateEpoch `
-            --git-commit $sourceCommit
-          if ($LASTEXITCODE -ne 0) { throw 'runtime build failed' }
-          $identity = Join-Path $output 'orca-ssh-relay-runtime-${{ matrix.tuple }}.identity.json'
-          $archive = Get-ChildItem -LiteralPath $output -Filter '*.zip' -File | Select-Object -First 1
-          if (-not $archive) { throw 'runtime ZIP is missing' }
-          node config/scripts/verify-ssh-relay-runtime.mjs `
-            --runtime-directory (Join-Path $output 'runtime') `
-            --identity $identity `
-            --archive $archive.FullName
-          if ($LASTEXITCODE -ne 0) { throw 'runtime verification failed' }
-          $prohibited = Get-ChildItem -LiteralPath (Join-Path $output 'runtime') -Recurse -File |
-            Where-Object { $_.Name -in @('npm', 'npm.cmd', 'npx', 'npx.cmd', 'corepack', 'corepack.cmd') -or $_.Name.EndsWith('.map') } |
-            Select-Object -First 1
-          if ($prohibited) { throw "Runtime contains a prohibited file: $($prohibited.FullName)" }
-          $parcelRoot = Join-Path $output 'runtime/node_modules/@parcel'
-          if (@(Get-ChildItem -LiteralPath $parcelRoot -Directory).Count -ne 2) {
-            throw 'Runtime must contain exactly the watcher wrapper and one native package'
+          foreach ($output in @($firstOutput, $secondOutput)) {
+            "clean_build_output=$output"
+            node config/scripts/build-ssh-relay-runtime.mjs `
+              --tuple '${{ matrix.tuple }}' `
+              --inputs-directory $env:NODE_INPUTS `
+              --output-directory $output `
+              --source-date-epoch $sourceDateEpoch `
+              --git-commit $sourceCommit
+            if ($LASTEXITCODE -ne 0) { throw 'runtime build failed' }
+            $identity = Join-Path $output 'orca-ssh-relay-runtime-${{ matrix.tuple }}.identity.json'
+            $archive = Get-ChildItem -LiteralPath $output -Filter '*.zip' -File | Select-Object -First 1
+            if (-not $archive) { throw 'runtime ZIP is missing' }
+            node config/scripts/verify-ssh-relay-runtime.mjs `
+              --runtime-directory (Join-Path $output 'runtime') `
+              --identity $identity `
+              --archive $archive.FullName
+            if ($LASTEXITCODE -ne 0) { throw 'runtime verification failed' }
+            $prohibited = Get-ChildItem -LiteralPath (Join-Path $output 'runtime') -Recurse -File |
+              Where-Object { $_.Name -in @('npm', 'npm.cmd', 'npx', 'npx.cmd', 'corepack', 'corepack.cmd') -or $_.Name.EndsWith('.map') } |
+              Select-Object -First 1
+            if ($prohibited) { throw "Runtime contains a prohibited file: $($prohibited.FullName)" }
+            $parcelRoot = Join-Path $output 'runtime/node_modules/@parcel'
+            if (@(Get-ChildItem -LiteralPath $parcelRoot -Directory).Count -ne 2) {
+              throw 'Runtime must contain exactly the watcher wrapper and one native package'
+            }
           }
+          node config/scripts/ssh-relay-runtime-reproducibility.mjs `
+            --tuple '${{ matrix.tuple }}' `
+            --first-output-directory $firstOutput `
+            --second-output-directory $secondOutput
+          if ($LASTEXITCODE -ne 0) { throw 'runtime reproducibility verification failed' }
           $evidence = Join-Path $env:GITHUB_WORKSPACE 'runtime-evidence/${{ matrix.tuple }}'
           New-Item -ItemType Directory -Path $evidence -Force | Out-Null
-          Copy-Item -LiteralPath $archive.FullName -Destination $evidence
-          Get-ChildItem -LiteralPath $output -File |
+          $firstArchive = Get-ChildItem -LiteralPath $firstOutput -Filter '*.zip' -File | Select-Object -First 1
+          Copy-Item -LiteralPath $firstArchive.FullName -Destination $evidence
+          Get-ChildItem -LiteralPath $firstOutput -File |
             Where-Object { $_.Name -match '\.(?:spdx|provenance|identity)\.json$' } |
             Copy-Item -Destination $evidence
 
diff --git a/config/scripts/ssh-relay-runtime-reproducibility.mjs b/config/scripts/ssh-relay-runtime-reproducibility.mjs
new file mode 100644
index 00000000000..febadab9db0
--- /dev/null
+++ b/config/scripts/ssh-relay-runtime-reproducibility.mjs
@@ -0,0 +1,268 @@
+#!/usr/bin/env node
+
+import { createHash } from 'node:crypto'
+import { createReadStream } from 'node:fs'
+import { lstat, opendir, readFile, realpath } from 'node:fs/promises'
+import { join, resolve } from 'node:path'
+
+// The bounded output adds four release assets around a runtime tree capped at 5,000 entries.
+const MAX_ENTRIES = 6_000
+const MAX_FILE_BYTES = 250 * 1024 * 1024
+const MAX_TOTAL_BYTES = 500 * 1024 * 1024
+const MAX_PATH_BYTES = 512
+const MAX_PATH_DEPTH = 40
+const MAX_IDENTITY_BYTES = 1024 * 1024
+const COMPARISON_TIMEOUT_MS = 5 * 60 * 1000
+const SUPPORTED_TUPLES = new Set([
+  'linux-x64-glibc',
+  'linux-arm64-glibc',
+  'darwin-x64',
+  'darwin-arm64',
+  'win32-x64',
+  'win32-arm64'
+])
+
+async function sha256File(path, signal) {
+  const digest = createHash('sha256')
+  for await (const chunk of createReadStream(path, { signal })) {
+    signal.throwIfAborted()
+    digest.update(chunk)
+  }
+  return `sha256:${digest.digest('hex')}`
+}
+
+function validateRelativePath(path) {
+  if (
+    Buffer.byteLength(path) > MAX_PATH_BYTES ||
+    path.split('/').length > MAX_PATH_DEPTH ||
+    path.includes('\\')
+  ) {
+    throw new Error(`reproducibility output path exceeds limits: ${path}`)
+  }
+}
+
+async function snapshotOutput(directory, label, signal) {
+  const entries = new Map()
+  let files = 0
+  let bytes = 0
+
+  async function visit(absoluteDirectory, relativeDirectory = '') {
+    const children = []
+    const handle = await opendir(absoluteDirectory)
+    for await (const child of handle) {
+      children.push(child.name)
+    }
+    children.sort()
+    for (const name of children) {
+      signal.throwIfAborted()
+      const path = relativeDirectory ? `${relativeDirectory}/${name}` : name
+      validateRelativePath(path)
+      const absolutePath = join(absoluteDirectory, name)
+      const metadata = await lstat(absolutePath)
+      if (metadata.isSymbolicLink() || (!metadata.isDirectory() && !metadata.isFile())) {
+        throw new Error(`${label} contains a prohibited special entry: ${path}`)
+      }
+      if (entries.size >= MAX_ENTRIES) {
+        throw new Error(`${label} exceeds the reproducibility entry-count limit`)
+      }
+      if (metadata.isDirectory()) {
+        entries.set(path, { path, type: 'directory', mode: metadata.mode & 0o777 })
+        await visit(absolutePath, path)
+        continue
+      }
+      if (metadata.size > MAX_FILE_BYTES) {
+        throw new Error(`${label} file exceeds the reproducibility size limit: ${path}`)
+      }
+      files += 1
+      bytes += metadata.size
+      if (bytes > MAX_TOTAL_BYTES) {
+        throw new Error(`${label} exceeds the reproducibility total-size limit`)
+      }
+      entries.set(path, {
+        path,
+        type: 'file',
+        mode: metadata.mode & 0o777,
+        size: metadata.size,
+        sha256: await sha256File(absolutePath, signal)
+      })
+    }
+  }
+
+  const root = await lstat(directory)
+  if (!root.isDirectory() || root.isSymbolicLink()) {
+    throw new Error(`${label} must be a real directory`)
+  }
+  await visit(directory)
+  return { bytes, entries, files }
+}
+
+async function validateCompleteOutput(directory, label, tuple, snapshot) {
+  const identityName = `orca-ssh-relay-runtime-${tuple}.identity.json`
+  const required = [
+    'runtime',
+    'runtime/relay.js',
+    'runtime/relay-watcher.js',
+    'runtime/runtime-metadata.json',
+    identityName,
+    `orca-ssh-relay-runtime-${tuple}.spdx.json`,
+    `orca-ssh-relay-runtime-${tuple}.provenance.json`
+  ]
+  for (const path of required) {
+    if (!snapshot.entries.has(path)) {
+      throw new Error(`${label} is missing required asset: ${path}`)
+    }
+  }
+  const identityEntry = snapshot.entries.get(identityName)
+  if (identityEntry.type !== 'file' || identityEntry.size > MAX_IDENTITY_BYTES) {
+    throw new Error(`${label} identity exceeds its size or type contract`)
+  }
+  let identity
+  try {
+    identity = JSON.parse(await readFile(join(directory, identityName), 'utf8'))
+  } catch {
+    throw new Error(`${label} identity is not valid JSON`)
+  }
+  if (
+    identity.tupleId !== tuple ||
+    !/^sha256:[0-9a-f]{64}$/.test(identity.contentId) ||
+    typeof identity.archive?.name !== 'string' ||
+    !/^sha256:[0-9a-f]{64}$/.test(identity.archive.sha256)
+  ) {
+    throw new Error(`${label} identity does not match the requested tuple or digest contract`)
+  }
+  if (!snapshot.entries.has(identity.archive.name)) {
+    throw new Error(`${label} is missing required asset: ${identity.archive.name}`)
+  }
+  const archiveEntry = snapshot.entries.get(identity.archive.name)
+  if (archiveEntry.type !== 'file' || archiveEntry.sha256 !== identity.archive.sha256) {
+    throw new Error(`${label} archive digest does not match its identity`)
+  }
+  const expectedTopLevel = new Set([...required.slice(4), identity.archive.name, 'runtime'])
+  const unexpected = [...snapshot.entries.keys()].find(
+    (path) => !path.includes('/') && !expectedTopLevel.has(path)
+  )
+  if (unexpected) {
+    throw new Error(`${label} contains an unexpected top-level asset: ${unexpected}`)
+  }
+  return identity
+}
+
+function compareSnapshots(first, second) {
+  const paths = [...new Set([...first.entries.keys(), ...second.entries.keys()])].sort()
+  for (const path of paths) {
+    const left = first.entries.get(path)
+    const right = second.entries.get(path)
+    if (!left) {
+      throw new Error(`first output is missing reproducibility entry: ${path}`)
+    }
+    if (!right) {
+      throw new Error(`second output is missing reproducibility entry: ${path}`)
+    }
+    for (const field of ['type', 'mode', 'size', 'sha256']) {
+      if (left[field] !== right[field]) {
+        throw new Error(`reproducibility mismatch for ${path}: ${field}`)
+      }
+    }
+  }
+}
+
+export async function verifySshRelayRuntimeReproducibility({
+  firstOutputDirectory,
+  secondOutputDirectory,
+  tuple,
+  signal = AbortSignal.timeout(COMPARISON_TIMEOUT_MS)
+}) {
+  const started = process.hrtime.bigint()
+  if (!SUPPORTED_TUPLES.has(tuple)) {
+    throw new Error(`unsupported runtime reproducibility tuple: ${tuple}`)
+  }
+  const firstDirectory = resolve(firstOutputDirectory)
+  const secondDirectory = resolve(secondOutputDirectory)
+  if (firstDirectory === secondDirectory) {
+    throw new Error('clean-build outputs must be distinct directories')
+  }
+  signal.throwIfAborted()
+  const [firstRealPath, secondRealPath] = await Promise.all([
+    realpath(firstDirectory),
+    realpath(secondDirectory)
+  ])
+  if (firstRealPath === secondRealPath) {
+    throw new Error('clean-build outputs must resolve to distinct directories')
+  }
+
+  // Walk sequentially so the clean-build gate cannot double file and read pressure on CI runners.
+  const first = await snapshotOutput(firstDirectory, 'first output', signal)
+  const second = await snapshotOutput(secondDirectory, 'second output', signal)
+  const firstIdentity = await validateCompleteOutput(firstDirectory, 'first output', tuple, first)
+  const secondIdentity = await validateCompleteOutput(
+    secondDirectory,
+    'second output',
+    tuple,
+    second
+  )
+  compareSnapshots(first, second)
+  if (
+    firstIdentity.contentId !== secondIdentity.contentId ||
+    firstIdentity.archive.sha256 !== secondIdentity.archive.sha256
+  ) {
+    throw new Error('reproducibility identity or archive digest mismatch')
+  }
+
+  return {
+    tuple,
+    contentId: firstIdentity.contentId,
+    archiveSha256: firstIdentity.archive.sha256,
+    entries: first.entries.size,
+    files: first.files,
+    bytes: first.bytes,
+    durationMs: Number(process.hrtime.bigint() - started) / 1e6
+  }
+}
+
+function valueAfter(argv, index, flag) {
+  const value = argv[index + 1]
+  if (!value || value.startsWith('--')) {
+    throw new Error(`${flag} requires a value`)
+  }
+  return value
+}
+
+export function parseReproducibilityArguments(argv) {
+  const result = {}
+  for (let index = 0; index < argv.length; index += 1) {
+    const flag = argv[index]
+    const value = valueAfter(argv, index, flag)
+    if (flag === '--tuple') {
+      result.tuple = value
+    } else if (flag === '--first-output-directory') {
+      result.firstOutputDirectory = resolve(value)
+    } else if (flag === '--second-output-directory') {
+      result.secondOutputDirectory = resolve(value)
+    } else {
+      throw new Error(`Unknown argument: ${flag}`)
+    }
+    index += 1
+  }
+  for (const field of ['tuple', 'firstOutputDirectory', 'secondOutputDirectory']) {
+    if (!result[field]) {
+      throw new Error(`Missing required reproducibility argument: ${field}`)
+    }
+  }
+  return result
+}
+
+async function main() {
+  const result = await verifySshRelayRuntimeReproducibility(
+    parseReproducibilityArguments(process.argv.slice(2))
+  )
+  process.stdout.write(`${JSON.stringify(result, null, 2)}\n`)
+}
+
+if (process.argv[1] && resolve(process.argv[1]) === import.meta.filename) {
+  main().catch((error) => {
+    process.stderr.write(
+      `SSH relay runtime reproducibility verification failed: ${error.message}\n`
+    )
+    process.exitCode = 1
+  })
+}
diff --git a/config/scripts/ssh-relay-runtime-reproducibility.test.mjs b/config/scripts/ssh-relay-runtime-reproducibility.test.mjs
new file mode 100644
index 00000000000..0a346a6f6c9
--- /dev/null
+++ b/config/scripts/ssh-relay-runtime-reproducibility.test.mjs
@@ -0,0 +1,145 @@
+import { createHash } from 'node:crypto'
+import { chmod, cp, mkdir, mkdtemp, rm, symlink, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+
+import { afterEach, describe, expect, it } from 'vitest'
+
+import { verifySshRelayRuntimeReproducibility } from './ssh-relay-runtime-reproducibility.mjs'
+
+const temporaryDirectories = []
+const tuple = 'linux-x64-glibc'
+const contentId = `sha256:${'a'.repeat(64)}`
+const archiveBytes = 'archive bytes'
+const archiveSha256 = `sha256:${createHash('sha256').update(archiveBytes).digest('hex')}`
+const archiveName = `orca-ssh-relay-runtime-v1-${tuple}-${contentId.slice('sha256:'.length)}.tar.xz`
+
+afterEach(async () => {
+  await Promise.all(temporaryDirectories.splice(0).map((path) => rm(path, { recursive: true })))
+})
+
+async function writeOutput(directory) {
+  await mkdir(join(directory, 'runtime'), { recursive: true })
+  await Promise.all([
+    writeFile(join(directory, 'runtime', 'relay.js'), 'relay bytes'),
+    writeFile(join(directory, 'runtime', 'relay-watcher.js'), 'watcher bytes'),
+    writeFile(join(directory, 'runtime', 'runtime-metadata.json'), '{"schemaVersion":1}\n'),
+    writeFile(join(directory, archiveName), archiveBytes),
+    writeFile(
+      join(directory, `orca-ssh-relay-runtime-${tuple}.identity.json`),
+      `${JSON.stringify({ tupleId: tuple, contentId, archive: { name: archiveName, sha256: archiveSha256 } })}\n`
+    ),
+    writeFile(
+      join(directory, `orca-ssh-relay-runtime-${tuple}.spdx.json`),
+      '{"spdxVersion":"SPDX-2.3"}\n'
+    ),
+    writeFile(
+      join(directory, `orca-ssh-relay-runtime-${tuple}.provenance.json`),
+      '{"predicateType":"https://slsa.dev/provenance/v1"}\n'
+    )
+  ])
+}
+
+async function createOutputs() {
+  const directory = await mkdtemp(join(tmpdir(), 'orca-runtime-reproducibility-'))
+  temporaryDirectories.push(directory)
+  const firstOutputDirectory = join(directory, 'first')
+  const secondOutputDirectory = join(directory, 'second')
+  await writeOutput(firstOutputDirectory)
+  await cp(firstOutputDirectory, secondOutputDirectory, { recursive: true })
+  return { directory, firstOutputDirectory, secondOutputDirectory }
+}
+
+describe('SSH relay runtime clean-build reproducibility', () => {
+  it('accepts byte-and-mode-identical complete outputs', async () => {
+    const fixture = await createOutputs()
+
+    await expect(
+      verifySshRelayRuntimeReproducibility({
+        ...fixture,
+        tuple
+      })
+    ).resolves.toEqual(expect.objectContaining({ tuple, contentId, archiveSha256, files: 7 }))
+  })
+
+  it('rejects runtime-tree byte drift', async () => {
+    const fixture = await createOutputs()
+    await writeFile(join(fixture.secondOutputDirectory, 'runtime', 'relay.js'), 'other bytes')
+
+    await expect(verifySshRelayRuntimeReproducibility({ ...fixture, tuple })).rejects.toThrow(
+      'reproducibility mismatch for runtime/relay.js: sha256'
+    )
+  })
+
+  it('rejects SBOM byte drift', async () => {
+    const fixture = await createOutputs()
+    await writeFile(
+      join(fixture.secondOutputDirectory, `orca-ssh-relay-runtime-${tuple}.spdx.json`),
+      '{"spdxVersion":"SPDX-2.2"}\n'
+    )
+
+    await expect(verifySshRelayRuntimeReproducibility({ ...fixture, tuple })).rejects.toThrow(
+      `reproducibility mismatch for orca-ssh-relay-runtime-${tuple}.spdx.json: sha256`
+    )
+  })
+
+  it('rejects an archive that disagrees with its identity', async () => {
+    const fixture = await createOutputs()
+    await writeFile(join(fixture.secondOutputDirectory, archiveName), 'other archive bytes')
+
+    await expect(verifySshRelayRuntimeReproducibility({ ...fixture, tuple })).rejects.toThrow(
+      'second output archive digest does not match its identity'
+    )
+  })
+
+  it('rejects a missing published metadata asset', async () => {
+    const fixture = await createOutputs()
+    await rm(join(fixture.secondOutputDirectory, `orca-ssh-relay-runtime-${tuple}.spdx.json`))
+
+    await expect(verifySshRelayRuntimeReproducibility({ ...fixture, tuple })).rejects.toThrow(
+      `second output is missing required asset: orca-ssh-relay-runtime-${tuple}.spdx.json`
+    )
+  })
+
+  it.skipIf(process.platform === 'win32')('rejects mode drift', async () => {
+    const fixture = await createOutputs()
+    await chmod(join(fixture.secondOutputDirectory, 'runtime', 'relay.js'), 0o755)
+
+    await expect(verifySshRelayRuntimeReproducibility({ ...fixture, tuple })).rejects.toThrow(
+      'reproducibility mismatch for runtime/relay.js: mode'
+    )
+  })
+
+  it.skipIf(process.platform === 'win32')(
+    'rejects links before reading their targets',
+    async () => {
+      const fixture = await createOutputs()
+      await symlink(
+        join(fixture.directory, 'outside'),
+        join(fixture.firstOutputDirectory, 'runtime', 'escape')
+      )
+
+      await expect(verifySshRelayRuntimeReproducibility({ ...fixture, tuple })).rejects.toThrow(
+        'first output contains a prohibited special entry: runtime/escape'
+      )
+    }
+  )
+
+  it('rejects the same directory and a pre-aborted comparison', async () => {
+    const fixture = await createOutputs()
+    await expect(
+      verifySshRelayRuntimeReproducibility({
+        firstOutputDirectory: fixture.firstOutputDirectory,
+        secondOutputDirectory: fixture.firstOutputDirectory,
+        tuple
+      })
+    ).rejects.toThrow('clean-build outputs must be distinct directories')
+    await expect(
+      verifySshRelayRuntimeReproducibility({
+        ...fixture,
+        tuple,
+        signal: AbortSignal.abort()
+      })
+    ).rejects.toThrow('aborted')
+  })
+})
diff --git a/config/scripts/ssh-relay-runtime-workflow.test.mjs b/config/scripts/ssh-relay-runtime-workflow.test.mjs
index 3fc07e0ff8d..e505f7887f1 100644
--- a/config/scripts/ssh-relay-runtime-workflow.test.mjs
+++ b/config/scripts/ssh-relay-runtime-workflow.test.mjs
@@ -35,12 +35,13 @@ describe('SSH relay runtime artifact workflow', () => {
     }
   })
 
-  it('uploads only archive and metadata evidence after executable verification', async () => {
+  it('uploads only the first output after two clean builds verify and compare', async () => {
     const source = await readFile(workflowUrl, 'utf8')
     const workflow = parse(source)
     const steps = workflow.jobs['build-posix-runtime'].steps
+    const windowsSteps = workflow.jobs['build-windows-runtime'].steps
     const buildIndex = steps.findIndex(
-      (step) => step.name === 'Build, inspect, and smoke exact runtime'
+      (step) => step.name === 'Build twice, inspect, smoke, and compare exact runtime'
     )
     const uploadIndex = steps.findIndex(
       (step) => step.name === 'Upload unpublished artifact evidence'
@@ -52,12 +53,16 @@ describe('SSH relay runtime artifact workflow', () => {
     expect(source).toContain('ssh-relay-runtime-workflow.test.mjs')
     expect(source).toContain('pnpm install --frozen-lockfile --ignore-scripts')
     expect(source).toContain('--connect-timeout 20 --max-time 300 --retry 2')
-    expect(source).toContain('mkdir -p "$(dirname "$output")"')
+    expect(source).toContain('mkdir -p "$output_root"')
     expect(source).toContain('source_commit=$(git rev-parse HEAD)')
     expect(source).toContain('--git-commit "$source_commit"')
     expect(source).not.toContain('--git-commit "$GITHUB_SHA"')
-    expect(source).toContain('cp "$output"/*.tar.xz')
-    expect(source).toContain("Get-ChildItem -LiteralPath $output -Filter '*.zip'")
+    expect(source).toContain('for output in "$first_output" "$second_output"')
+    expect(source).toContain('foreach ($output in @($firstOutput, $secondOutput))')
+    expect(source).toContain('ssh-relay-runtime-reproducibility.mjs')
+    expect(source).toContain('ssh-relay-runtime-reproducibility.test.mjs')
+    expect(source).toContain('cp "$first_output"/*.tar.xz')
+    expect(source).toContain("Get-ChildItem -LiteralPath $firstOutput -Filter '*.zip'")
     expect(source).toContain('ssh-relay-node-zip-inspection.test.mjs')
     expect(source).toContain('ssh-relay-runtime-pty-smoke.test.mjs')
     expect(source).toContain('ssh-relay-runtime-resource-diagnostics.test.mjs')
@@ -65,6 +70,17 @@ describe('SSH relay runtime artifact workflow', () => {
     expect(source).toContain('node-v24.18.0-headers.tar.gz')
     expect(source).toContain('node_library: win-x64/node.lib')
     expect(source).toContain("@('gpg.exe', 'gpgv.exe')")
+    for (const jobSteps of [steps, windowsSteps]) {
+      const run = jobSteps.find(
+        (step) => step.name === 'Build twice, inspect, smoke, and compare exact runtime'
+      ).run
+      expect(run.indexOf('ssh-relay-runtime-reproducibility.mjs')).toBeGreaterThan(
+        run.indexOf('verify-ssh-relay-runtime.mjs')
+      )
+      expect(run.indexOf('runtime-evidence/${{ matrix.tuple }}')).toBeGreaterThan(
+        run.indexOf('ssh-relay-runtime-reproducibility.mjs')
+      )
+    }
     expect(steps[uploadIndex].with.path).toBe('runtime-evidence/${{ matrix.tuple }}/')
     expect(source).not.toMatch(/releases\/|gh release|contents:\s*write/i)
   })
diff --git a/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist.md b/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist.md
index 776ae307de6..72dd4cd7ae6 100644
--- a/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist.md
+++ b/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist.md
@@ -2,7 +2,7 @@
 
 Date created: 2026-07-14<br>
 Last updated: 2026-07-14<br>
-Current phase: Milestone 3 / Work Package 2 target-native runtime assembly — add and prove a same-head, same-runner two-clean-build identity oracle now that all six glibc/macOS/Windows target-native artifact and executable cells are green; oldest-baseline, native-trust, cross-family remote, and measured-baseline gates remain open; no bundled-runtime path is enabled<br>
+Current phase: Milestone 3 / Work Package 2 target-native runtime assembly — the bounded same-head, same-runner two-clean-build identity oracle is locally green and awaits exact-head execution on all six glibc/macOS/Windows native runners; oldest-baseline, native-trust, cross-family remote, and measured-baseline gates remain open; no bundled-runtime path is enabled<br>
 Primary design: [SSH relay GitHub Release plan](./2026-07-14-ssh-relay-github-release-plan.html)<br>
 Motivating issues: [#8450](https://github.com/stablyai/orca/issues/8450), [#1693](https://github.com/stablyai/orca/issues/1693)
 
@@ -87,8 +87,10 @@ same change as the work it records.
   diff gates. The first exact-head native run exposed a macOS `/var` versus `/private/var` watcher
   oracle mismatch under E-M3-CI-RED-001. The corrected exact-head run passed target-native build,
   archive/tree verification, bundled Node, patched PTY, and watcher smoke for Linux x64/arm64 and
-  macOS x64/arm64 under E-M3-CI-001. Same-runner clean-rebuild identity, oldest-baseline,
-  native-trust, SSH, Windows, and musl cells remain open.
+  macOS x64/arm64 under E-M3-CI-001. A bounded comparator now rejects incomplete outputs and any
+  runtime-tree, archive, identity, SPDX, provenance, type, mode, size, or digest drift after two
+  independently verified clean builds; its focused contract is locally green, but exact-head native
+  execution remains pending. Oldest-baseline, native-trust, SSH, and musl cells remain open.
 - Windows input correction: E-M3-WINDOWS-INPUT-GAP-001 proved the official Windows ZIP lacks headers
   and `node.lib`. Both artifacts now require the exact signed headers archive and tuple import
   library as explicit inputs. The schema, signed-checksum verifier, bounded ZIP/header extraction,
@@ -125,11 +127,12 @@ same change as the work it records.
 - Rollout control: existing per-SSH-target configuration; legacy is the default and the bundled
   runtime is an explicit per-target Beta opt-in under E-M1-ROLLOUT-DECISION-001.
 - Legacy fallback removal: not authorized.
-- Next required action: add a same-head/same-runner two-clean-build identity comparison that fails
-  closed on any tree, archive, SBOM, provenance, or identity drift, then run it for every target-
-  native candidate. Keep oldest-baseline, cross-family remote infrastructure, signing/trust, and
-  measured legacy baseline gates open; do not introduce publication, resolver, transfer, rollout,
-  tuple enablement, or default behavior.
+- Next required action: finish the exact implementation-commit local gates, push the bounded
+  two-clean-build comparator/workflow package to draft PR #8741, and require every target-native job
+  to compare complete runtime-tree, archive, identity, SPDX, and provenance outputs before upload.
+  Record every native drift instead of weakening the oracle. Keep oldest-baseline, cross-family
+  remote infrastructure, signing/trust, and measured legacy baseline gates open; do not introduce
+  publication, resolver, transfer, rollout, tuple enablement, or default behavior.
 
 ## Non-Negotiable Invariants
 
@@ -597,8 +600,11 @@ transfer, install, fallback, rollout setting, or tuple enablement belongs in thi
 
 **Active sub-gate — 2026-07-14, Codex implementation owner:** exact-head run 29345126283 proves all
 six target-native artifact/executable jobs, including normal Windows x64/arm64 settlement and
-unpublished upload. Add a bounded same-head/same-runner two-clean-build comparison without changing
-artifact consumers, publication, the repository-wide node-pty patch, or the legacy/default path.
+unpublished upload. The locally green bounded comparator now requires two independently verified
+clean outputs and exact type/mode/size/SHA-256 equality for the runtime tree, archive, identity,
+SPDX, and provenance before uploading only the first output. Exact-head native execution remains
+open; artifact consumers, publication, the repository-wide node-pty patch, and the legacy/default
+path remain unchanged.
 
 Each runtime must contain only the executable closure required by the relay.
 
@@ -1258,6 +1264,7 @@ focused commands as their scripts/tests are introduced.
 - [x] `pnpm exec vitest run --config config/vitest.config.ts config/scripts/ssh-relay-runtime-pty-smoke.test.mjs` (E-M3-WINDOWS-SMOKE-SETTLEMENT-LOCAL-RED-001, E-M3-WINDOWS-SMOKE-SETTLEMENT-LOCAL-001; native evidence remains pending)
 - [x] `pnpm exec vitest run --config config/vitest.config.ts config/scripts/ssh-relay-runtime-resource-diagnostics.test.mjs` (E-M3-WINDOWS-RESOURCE-DIAGNOSTIC-LOCAL-001; native classification pending)
 - [x] `pnpm exec vitest run --config config/vitest.config.ts config/scripts/ssh-relay-node-pty-windows-settlement.test.mjs` (E-M3-WINDOWS-CONPTY-WORKER-LOCAL-RED-001, E-M3-WINDOWS-CONPTY-WORKER-LOCAL-001; native settlement pending)
+- [ ] `pnpm exec vitest run --config config/vitest.config.ts config/scripts/ssh-relay-runtime-reproducibility.test.mjs config/scripts/ssh-relay-runtime-workflow.test.mjs` (locally green on the uncommitted implementation tree; rerun on the exact implementation commit before checking)
 - [x] `node config/scripts/verify-ssh-relay-node-release-inputs.mjs --inputs-directory <verified-windows-input-directory> --archive win32-x64` (E-M3-WINDOWS-INPUT-001; signed real Node ZIP, headers, and import library; no Windows execution)
 - [x] `node config/scripts/build-ssh-relay-runtime.mjs --tuple linux-arm64-glibc --inputs-directory <verified-input-directory> --output-directory <exclusive-output> --source-date-epoch <epoch> --git-commit <full-sha>` (E-M3-RUNTIME-LOCAL-001; local native Linux arm64 only)
 - [x] `node config/scripts/verify-ssh-relay-runtime.mjs --runtime-directory <runtime-tree> --identity <identity.json> --archive <runtime.tar.xz>` (E-M3-RUNTIME-LOCAL-001; local native Linux arm64 only)
@@ -3599,10 +3606,12 @@ The project is not complete until every applicable item below is checked with ev
 
 ## Next Required Action
 
-Commit and push the bounded post-smoke resource diagnostic, then capture both native Windows
-resource snapshots through the existing parent timeout without making another cleanup change. Use
-that evidence to isolate the owning subsystem before requiring exact-head normal exit and artifact
-upload. The separate clean-build identity gate, cross-family Layer B target pool, protected
-manifest-signing environment, and paired legacy performance baseline remain release/default-path
-blockers; no publication, desktop resolver, SSH transfer/install, per-target Beta, fallback, tuple
-enablement, or default behavior may be connected by this package.
+Complete the exact implementation-commit local gates, push the bounded two-clean-build
+reproducibility package to draft PR #8741, and run all six target-native jobs. Each job must build,
+verify, and smoke two exclusive outputs, compare every runtime-tree/archive/identity/SPDX/provenance
+entry, and upload only after equality. Record exact differing paths and fields for every native red
+result and correct the producer without weakening the oracle. Cross-family Layer B targets, the
+protected manifest-signing environment, oldest-baseline/native-trust cells, and the paired legacy
+performance baseline remain release/default-path blockers; no publication, desktop resolver, SSH
+transfer/install, per-target Beta, fallback, tuple enablement, or default behavior may be connected
+by this package.