diff --git a/docker/plugin-setup/Dockerfile b/docker/plugin-setup/Dockerfile
new file mode 100644
index 000000000..bb8a6501a
--- /dev/null
+++ b/docker/plugin-setup/Dockerfile
@@ -0,0 +1,44 @@
+ARG NODE_IMAGE=node:22-bookworm-slim@sha256:6c74791e557ce11fc957704f6d4fe134a7bc8d6f5ca4403205b2966bd488f6b3
+ARG OS_IMAGE=node:22-bookworm-slim@sha256:6c74791e557ce11fc957704f6d4fe134a7bc8d6f5ca4403205b2966bd488f6b3
+
+FROM ${NODE_IMAGE} AS node-runtime
+FROM ${OS_IMAGE}
+
+ARG DISTRO=debian
+ARG CLAUDE_CODE_VERSION=2.1.220
+
+RUN apt-get update \
+    && apt-get install --yes --no-install-recommends \
+      bash \
+      ca-certificates \
+      git \
+      libatomic1 \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=node-runtime /usr/local/ /usr/local/
+
+RUN getent passwd 1000 >/dev/null \
+    && getent group 1000 >/dev/null
+
+RUN npm install --global --include=optional --ignore-scripts \
+      "@anthropic-ai/claude-code@${CLAUDE_CODE_VERSION}" \
+      "@iarna/toml@2.2.5" \
+      "ajv@8.20.0" \
+      "sql.js@1.14.1" \
+    && global_node_modules="$(npm root --global)" \
+    && node "${global_node_modules}/@anthropic-ai/claude-code/install.cjs" \
+    && npm cache clean --force \
+    && claude --version
+
+RUN mkdir -p /workspace \
+    && chown 1000:1000 /workspace
+
+ENV CLAUDE_CONFIG_DIR=/tmp/ecc-claude-config
+ENV DISABLE_AUTOUPDATER=1
+ENV HOME=/tmp/ecc-home
+ENV NODE_PATH=/usr/local/lib/node_modules
+
+WORKDIR /workspace
+USER 1000:1000
+
+LABEL org.opencontainers.image.title="ECC plugin setup test (${DISTRO})"
diff --git a/docker/plugin-setup/compose.yaml b/docker/plugin-setup/compose.yaml
new file mode 100644
index 000000000..ef19064e5
--- /dev/null
+++ b/docker/plugin-setup/compose.yaml
@@ -0,0 +1,91 @@
+name: ecc-plugin-setup-test
+
+x-node-image: &node-image node:22-bookworm-slim@sha256:6c74791e557ce11fc957704f6d4fe134a7bc8d6f5ca4403205b2966bd488f6b3
+
+x-real-cli: &real-cli
+  working_dir: /workspace
+  network_mode: none
+  read_only: true
+  pids_limit: 256
+  cap_drop:
+    - ALL
+  security_opt:
+    - no-new-privileges:true
+  tmpfs:
+    - /tmp:rw,nosuid,nodev,exec,size=${ECC_TMPFS_SIZE:-2g},uid=1000,gid=1000,mode=0700
+    - /workspace:rw,nosuid,nodev,noexec,size=${ECC_WORKSPACE_SIZE:-1g},uid=1000,gid=1000,mode=0700
+  environment:
+    CLAUDE_CONFIG_DIR: /tmp/ecc-claude-config
+    DISABLE_AUTOUPDATER: "1"
+    HOME: /tmp/ecc-home
+    NPM_CONFIG_CACHE: /tmp/npm-cache
+  volumes:
+    - type: bind
+      source: ../..
+      target: /ecc
+      read_only: true
+    - type: bind
+      source: "${TEST_PROJECT:-../../tests/fixtures/docker-plugin-project}"
+      target: /source-project
+      read_only: true
+  stdin_open: true
+  tty: true
+  entrypoint:
+    - /bin/bash
+    - /ecc/docker/plugin-setup/run-real-cli.sh
+  command:
+    - dry-run
+
+services:
+  fixture-tests:
+    image: *node-image
+    working_dir: /ecc
+    user: "1000:1000"
+    network_mode: none
+    read_only: true
+    pids_limit: 256
+    cap_drop:
+      - ALL
+    security_opt:
+      - no-new-privileges:true
+    tmpfs:
+      - /tmp:rw,nosuid,nodev,exec,size=256m
+    volumes:
+      - type: bind
+        source: ../..
+        target: /ecc
+        read_only: true
+    entrypoint:
+      - /bin/bash
+      - /ecc/docker/plugin-setup/run-fixture-tests.sh
+
+  real-cli:
+    <<: *real-cli
+    image: ecc-plugin-setup:debian
+    build:
+      context: .
+      dockerfile: Dockerfile
+      args:
+        NODE_IMAGE: *node-image
+        OS_IMAGE: *node-image
+        DISTRO: debian
+        CLAUDE_CODE_VERSION: 2.1.220
+
+  real-cli-networked:
+    <<: *real-cli
+    profiles:
+      - networked
+    network_mode: default
+    image: ecc-plugin-setup:debian
+
+  real-cli-ubuntu:
+    <<: *real-cli
+    image: ecc-plugin-setup:ubuntu
+    build:
+      context: .
+      dockerfile: Dockerfile
+      args:
+        NODE_IMAGE: *node-image
+        OS_IMAGE: ubuntu:24.04@sha256:4fbb8e6a8395de5a7550b33509421a2bafbc0aab6c06ba2cef9ebffbc7092d90
+        DISTRO: ubuntu
+        CLAUDE_CODE_VERSION: 2.1.220
diff --git a/docker/plugin-setup/interactive-plan.js b/docker/plugin-setup/interactive-plan.js
new file mode 100644
index 000000000..27470016f
--- /dev/null
+++ b/docker/plugin-setup/interactive-plan.js
@@ -0,0 +1,118 @@
+#!/usr/bin/env node
+
+'use strict';
+
+const path = require('path');
+
+const usage = `Usage: node docker/plugin-setup/interactive-plan.js [options] [-- command ...]
+
+Emit the Docker side of the terminal-opener executable-plus-argv contract.
+
+Options:
+  --container <name>  Named running container (default: ecc-plugin-shell).
+  --workdir <path>    Absolute container working directory (default: /workspace/project).
+  --json              Emit compact JSON.
+  --help, -h          Show this help.
+  -- command ...      Interactive command (default: bash).
+`;
+
+function fail(message) {
+  const error = new Error(message);
+  error.exitCode = 2;
+  throw error;
+}
+
+function readValue(argv, index, option) {
+  const value = argv[index + 1];
+  if (!value || value === '--') {
+    fail(`Invalid ${option}: expected a value.`);
+  }
+  return value;
+}
+
+function parseArgs(argv) {
+  let container = 'ecc-plugin-shell';
+  let workdir = '/workspace/project';
+  let json = false;
+  let command = ['bash'];
+
+  for (let index = 0; index < argv.length; index += 1) {
+    const argument = argv[index];
+    if (argument === '--') {
+      command = argv.slice(index + 1);
+      if (command.length === 0) {
+        fail('Invalid command: expected at least one argv entry after --.');
+      }
+      break;
+    }
+    if (argument === '--container') {
+      container = readValue(argv, index, '--container');
+      index += 1;
+    } else if (argument === '--workdir') {
+      workdir = readValue(argv, index, '--workdir');
+      index += 1;
+    } else if (argument === '--json') {
+      json = true;
+    } else if (argument === '--help' || argument === '-h') {
+      return { help: true };
+    } else {
+      fail(`Invalid option: ${argument}`);
+    }
+  }
+
+  if (container.length > 128 || !/^[A-Za-z0-9][A-Za-z0-9_.-]*$/.test(container)) {
+    fail('Invalid container name. Use Docker name characters only.');
+  }
+  const normalizedWorkdir = path.posix.normalize(workdir);
+  if (
+    !path.posix.isAbsolute(workdir)
+    || /[\r\n\0]/.test(workdir)
+    || (
+      normalizedWorkdir !== '/workspace'
+      && !normalizedWorkdir.startsWith('/workspace/')
+    )
+  ) {
+    fail('Invalid workdir. Use an absolute path within /workspace.');
+  }
+  if (command.some((entry) => entry.length === 0 || /\0/.test(entry))) {
+    fail('Invalid command argv entry.');
+  }
+
+  return { command, container, help: false, json, workdir };
+}
+
+function buildPlan(options) {
+  return {
+    contractVersion: 1,
+    executable: 'docker',
+    argv: [
+      'exec',
+      '-it',
+      '-w',
+      options.workdir,
+      options.container,
+      ...options.command,
+    ],
+  };
+}
+
+function main() {
+  try {
+    const options = parseArgs(process.argv.slice(2));
+    if (options.help) {
+      process.stdout.write(usage);
+      return;
+    }
+    const spacing = options.json ? 0 : 2;
+    process.stdout.write(`${JSON.stringify(buildPlan(options), null, spacing)}\n`);
+  } catch (error) {
+    process.stderr.write(`Error: ${error.message}\n`);
+    process.exitCode = error.exitCode || 1;
+  }
+}
+
+if (require.main === module) {
+  main();
+}
+
+module.exports = { buildPlan, parseArgs };
diff --git a/docker/plugin-setup/prepare-packed-cli.js b/docker/plugin-setup/prepare-packed-cli.js
new file mode 100644
index 000000000..4af1c0053
--- /dev/null
+++ b/docker/plugin-setup/prepare-packed-cli.js
@@ -0,0 +1,167 @@
+#!/usr/bin/env node
+
+'use strict';
+
+const { spawnSync } = require('child_process');
+const fs = require('fs');
+const path = require('path');
+
+const EXPECTED_NAME = 'ecc-universal';
+const EXPECTED_BIN = 'scripts/ecc.js';
+const CHILD_PROCESS_TIMEOUT_MS = 5 * 60 * 1000;
+const REQUIRED_FILES = Object.freeze([
+  'scripts/ecc.js',
+  'manifests/install-components.json',
+  'manifests/install-modules.json',
+  'manifests/install-profiles.json',
+]);
+
+function fail(message) {
+  throw new Error(message);
+}
+
+function isWithin(root, candidate) {
+  const relative = path.relative(root, candidate);
+  return relative === '' || (
+    relative !== '..'
+    && !relative.startsWith(`..${path.sep}`)
+    && !path.isAbsolute(relative)
+  );
+}
+
+function requireRegularFile(packageRoot, relativePath) {
+  const resolvedPath = path.resolve(packageRoot, relativePath);
+  if (!isWithin(packageRoot, resolvedPath)) {
+    fail(`Package path escapes the extracted root: ${relativePath}`);
+  }
+  let file;
+  try {
+    file = fs.lstatSync(resolvedPath);
+  } catch {
+    fail(`Packed package is missing ${relativePath}.`);
+  }
+  if (!file.isFile() || file.isSymbolicLink()) {
+    fail(`Packed package path is not a regular file: ${relativePath}`);
+  }
+  return resolvedPath;
+}
+
+function validatePackedPackage(packageRoot) {
+  const resolvedRoot = path.resolve(packageRoot);
+  const packageJsonPath = requireRegularFile(resolvedRoot, 'package.json');
+  const manifest = JSON.parse(fs.readFileSync(packageJsonPath, 'utf8'));
+
+  if (manifest.name !== EXPECTED_NAME) {
+    fail(`Unexpected packed package name: ${manifest.name || '<missing>'}.`);
+  }
+  if (typeof manifest.version !== 'string' || manifest.version.length === 0) {
+    fail('Packed package version is missing.');
+  }
+  if (!manifest.bin || manifest.bin.ecc !== EXPECTED_BIN) {
+    fail(`Packed package bin.ecc must map to ${EXPECTED_BIN}.`);
+  }
+
+  for (const requiredFile of REQUIRED_FILES) {
+    requireRegularFile(resolvedRoot, requiredFile);
+  }
+
+  const binTarget = path.resolve(resolvedRoot, manifest.bin.ecc);
+  if (!isWithin(resolvedRoot, binTarget)) {
+    fail('Packed package bin.ecc escapes the extracted package root.');
+  }
+  if (process.platform !== 'win32') {
+    fs.accessSync(binTarget, fs.constants.X_OK);
+  }
+  return binTarget;
+}
+
+function run(executable, argv, options = {}) {
+  const result = spawnSync(executable, argv, {
+    ...options,
+    encoding: 'utf8',
+    shell: false,
+    timeout: CHILD_PROCESS_TIMEOUT_MS,
+  });
+  if (result.error) {
+    fail(`Unable to run ${executable}: ${result.error.message}`);
+  }
+  if (result.status !== 0) {
+    const detail = (result.stderr || result.stdout || '').trim();
+    fail(`${executable} exited with status ${result.status}${detail ? `: ${detail}` : ''}`);
+  }
+  return result;
+}
+
+function preparePackedCli(sourceRoot, outputRoot) {
+  const resolvedSource = path.resolve(sourceRoot);
+  const resolvedOutput = path.resolve(outputRoot);
+  if (resolvedSource !== '/ecc') {
+    fail('Package source must be the read-only /ecc checkout.');
+  }
+  if (resolvedOutput !== '/tmp' && !resolvedOutput.startsWith('/tmp/')) {
+    fail('Packed CLI output must remain under /tmp.');
+  }
+
+  fs.mkdirSync(resolvedOutput, { recursive: true, mode: 0o700 });
+  const workRoot = fs.mkdtempSync(path.join(resolvedOutput, 'artifact-'));
+  const childEnv = {
+    ...process.env,
+    NPM_CONFIG_CACHE: '/tmp/npm-cache',
+    npm_config_audit: 'false',
+    npm_config_fund: 'false',
+    npm_config_ignore_scripts: 'true',
+    npm_config_offline: 'true',
+  };
+  const packed = run('npm', [
+    'pack',
+    resolvedSource,
+    '--ignore-scripts',
+    '--pack-destination',
+    workRoot,
+    '--json',
+  ], { env: childEnv });
+
+  let metadata;
+  try {
+    metadata = JSON.parse(packed.stdout);
+  } catch (error) {
+    fail(`npm pack returned invalid JSON: ${error.message}`);
+  }
+  const filename = metadata?.[0]?.filename;
+  if (
+    typeof filename !== 'string'
+    || path.basename(filename) !== filename
+    || !filename.endsWith('.tgz')
+  ) {
+    fail('npm pack did not return a confined tarball filename.');
+  }
+
+  const archivePath = path.resolve(workRoot, filename);
+  if (!isWithin(workRoot, archivePath)) {
+    fail('npm pack tarball escaped the artifact directory.');
+  }
+  const extractRoot = path.join(workRoot, 'extracted');
+  fs.mkdirSync(extractRoot, { mode: 0o700 });
+  run('tar', ['-xzf', archivePath, '-C', extractRoot]);
+
+  const binTarget = validatePackedPackage(path.join(extractRoot, 'package'));
+  const binRoot = path.join(workRoot, 'bin');
+  fs.mkdirSync(binRoot, { mode: 0o700 });
+  const publicBin = path.join(binRoot, 'ecc');
+  fs.symlinkSync(binTarget, publicBin);
+  return publicBin;
+}
+
+function main() {
+  try {
+    const publicBin = preparePackedCli(process.argv[2], process.argv[3]);
+    process.stdout.write(`${publicBin}\n`);
+  } catch (error) {
+    process.stderr.write(`Error: ${error.message}\n`);
+    process.exitCode = 1;
+  }
+}
+
+if (require.main === module) main();
+
+module.exports = { isWithin, preparePackedCli, validatePackedPackage };
diff --git a/docker/plugin-setup/resolve-project-dir.js b/docker/plugin-setup/resolve-project-dir.js
new file mode 100644
index 000000000..96ea412cd
--- /dev/null
+++ b/docker/plugin-setup/resolve-project-dir.js
@@ -0,0 +1,36 @@
+#!/usr/bin/env node
+
+'use strict';
+
+const path = require('path');
+
+const WORKSPACE_ROOT = '/workspace';
+
+function resolveProjectDir(candidate) {
+  if (
+    typeof candidate !== 'string'
+    || !path.posix.isAbsolute(candidate)
+    || /[\0\r\n]/.test(candidate)
+  ) {
+    throw new Error('ECC_PROJECT_DIR must be an absolute path within /workspace.');
+  }
+
+  const resolved = path.posix.resolve(candidate);
+  if (resolved === WORKSPACE_ROOT || !resolved.startsWith(`${WORKSPACE_ROOT}/`)) {
+    throw new Error('ECC_PROJECT_DIR must be a child path within /workspace.');
+  }
+  return resolved;
+}
+
+function main() {
+  try {
+    process.stdout.write(`${resolveProjectDir(process.argv[2])}\n`);
+  } catch (error) {
+    process.stderr.write(`Error: ${error.message}\n`);
+    process.exitCode = 2;
+  }
+}
+
+if (require.main === module) main();
+
+module.exports = { resolveProjectDir };
diff --git a/docker/plugin-setup/run-fixture-tests.sh b/docker/plugin-setup/run-fixture-tests.sh
new file mode 100755
index 000000000..4031abd86
--- /dev/null
+++ b/docker/plugin-setup/run-fixture-tests.sh
@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+readonly ECC_ROOT=/ecc
+
+fixture_uid="$(id -u)"
+readonly fixture_uid
+fixture_gid="$(id -g)"
+readonly fixture_gid
+if [[ "$fixture_uid" != 1000 || "$fixture_gid" != 1000 ]]; then
+  printf 'Fixture tests must run as uid/gid 1000:1000 (got %s:%s)\n' \
+    "$fixture_uid" "$fixture_gid" >&2
+  exit 1
+fi
+
+cd "$ECC_ROOT"
+
+exec node docker/plugin-setup/run-platform-tests.js
diff --git a/docker/plugin-setup/run-platform-tests.js b/docker/plugin-setup/run-platform-tests.js
new file mode 100755
index 000000000..530683c54
--- /dev/null
+++ b/docker/plugin-setup/run-platform-tests.js
@@ -0,0 +1,46 @@
+#!/usr/bin/env node
+
+'use strict';
+
+const path = require('path');
+const { spawnSync } = require('child_process');
+
+const repoRoot = path.resolve(__dirname, '..', '..');
+const CHILD_PROCESS_TIMEOUT_MS = 5 * 60 * 1000;
+const testFiles = [
+  'tests/lib/install-manifests.test.js',
+  'tests/lib/install-targets.test.js',
+  'tests/lib/install-executor.test.js',
+];
+const excludedGitEnvKeys = new Set([
+  'GIT_DIR',
+  'GIT_WORK_TREE',
+  'GIT_INDEX_FILE',
+  'GIT_COMMON_DIR',
+  'GIT_PREFIX',
+]);
+const childEnv = Object.fromEntries(
+  Object.entries(process.env).filter(([key]) => !excludedGitEnvKeys.has(key))
+);
+
+console.log(`Running ECC install tests on ${process.platform}/${process.arch}`);
+
+for (const testFile of testFiles) {
+  const result = spawnSync(process.execPath, [path.join(repoRoot, testFile)], {
+    cwd: repoRoot,
+    env: childEnv,
+    shell: false,
+    stdio: 'inherit',
+    timeout: CHILD_PROCESS_TIMEOUT_MS,
+  });
+
+  if (result.error) {
+    console.error(`Unable to run ${testFile}: ${result.error.message}`);
+    process.exit(1);
+  }
+
+  if (result.status !== 0) {
+    console.error(`${testFile} exited with status ${result.status}`);
+    process.exit(result.status ?? 1);
+  }
+}
diff --git a/docker/plugin-setup/run-real-cli.sh b/docker/plugin-setup/run-real-cli.sh
new file mode 100755
index 000000000..e1291836e
--- /dev/null
+++ b/docker/plugin-setup/run-real-cli.sh
@@ -0,0 +1,126 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+readonly ECC_ROOT=/ecc
+readonly SOURCE_PROJECT=/source-project
+readonly MODE="${1:-dry-run}"
+readonly requested_project_dir="${ECC_PROJECT_DIR:-/workspace/project}"
+
+NPM_CONFIG_CACHE=/tmp/npm-cache
+export NPM_CONFIG_CACHE
+readonly NPM_CONFIG_CACHE
+
+usage() {
+  printf '%s\n' \
+    'Usage: docker compose run --rm real-cli <mode>' \
+    '' \
+    'Modes:' \
+    '  dry-run  Inspect a project-local ECC install without mutation (default).' \
+    '  install  Install ECC into the isolated project copy.' \
+    '  plugin   Launch Claude with the local ECC checkout via --plugin-dir.' \
+    '  shell    Open a shell in the isolated project copy.'
+}
+
+case "$MODE" in
+  dry-run|install|plugin|shell)
+    ;;
+  help|--help|-h)
+    usage
+    exit 0
+    ;;
+  *)
+    printf 'Unknown mode: %s\n\n' "$MODE" >&2
+    usage >&2
+    exit 2
+    ;;
+esac
+
+if [[ ! -f "$ECC_ROOT/package.json" ]]; then
+  printf 'ECC checkout is not mounted at %s\n' "$ECC_ROOT" >&2
+  exit 2
+fi
+if [[ ! -d "$SOURCE_PROJECT" ]]; then
+  printf 'Source project is not mounted at %s\n' "$SOURCE_PROJECT" >&2
+  exit 2
+fi
+project_dir="$(
+  node "$ECC_ROOT/docker/plugin-setup/resolve-project-dir.js" \
+    "$requested_project_dir"
+)"
+readonly project_dir
+
+mkdir -p "$HOME" "$CLAUDE_CONFIG_DIR" "$NPM_CONFIG_CACHE"
+chmod 0700 "$HOME" "$CLAUDE_CONFIG_DIR" "$NPM_CONFIG_CACHE"
+
+if [[ ! -e "$project_dir" ]]; then
+  mkdir -m 0700 "$project_dir"
+  cp -a "$SOURCE_PROJECT/." "$project_dir/"
+elif [[ ! -d "$project_dir" ]]; then
+  printf 'ECC project path is not a directory: %s\n' "$project_dir" >&2
+  exit 2
+fi
+cd "$project_dir"
+
+if [[ ! -d .git ]]; then
+  git init --quiet
+fi
+
+packed_cli=''
+if [[ "$MODE" == dry-run || "$MODE" == install ]]; then
+  packed_cli="$(
+    node "$ECC_ROOT/docker/plugin-setup/prepare-packed-cli.js" \
+      "$ECC_ROOT" \
+      /tmp/ecc-packed-cli
+  )"
+fi
+readonly packed_cli
+
+run_ecc() {
+  if [[ ! -x "$packed_cli" ]]; then
+    printf 'Packed ECC public executable is unavailable\n' >&2
+    return 1
+  fi
+  "$packed_cli" "$@"
+}
+
+run_install() {
+  run_ecc install \
+    --profile core \
+    --target claude-project \
+    "$@"
+}
+
+claude --version
+printf 'Isolated project: %s\n' "$project_dir"
+
+case "$MODE" in
+  dry-run)
+    plan_file="$(mktemp /tmp/ecc-install-plan.XXXXXX.json)"
+    run_install \
+      --dry-run \
+      --json > "$plan_file"
+    if [[ -e "$project_dir/.claude" ]]; then
+      printf 'Dry run unexpectedly mutated %s/.claude\n' "$project_dir" >&2
+      exit 1
+    fi
+    node "$ECC_ROOT/docker/plugin-setup/verify-install-plan.js" "$project_dir" --dry-run < "$plan_file"
+    cat "$plan_file"
+    ;;
+  install)
+    run_install --json
+    if [[ ! -f "$project_dir/.claude/ecc/install-state.json" ]]; then
+      printf 'Install did not create confined install state\n' >&2
+      exit 1
+    fi
+    run_install --json
+    run_ecc list-installed --json
+    run_ecc doctor --target claude-project
+    ;;
+  plugin)
+    exec claude --plugin-dir "$ECC_ROOT"
+    ;;
+  shell)
+    exec /bin/bash
+    ;;
+esac
diff --git a/docker/plugin-setup/verify-install-plan.js b/docker/plugin-setup/verify-install-plan.js
new file mode 100644
index 000000000..f66558ded
--- /dev/null
+++ b/docker/plugin-setup/verify-install-plan.js
@@ -0,0 +1,71 @@
+#!/usr/bin/env node
+
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+
+function fail(message) {
+  throw new Error(message);
+}
+
+function isWithin(root, candidate) {
+  const relative = path.relative(root, candidate);
+  return relative === '' || (
+    relative !== '..'
+    && !relative.startsWith(`..${path.sep}`)
+    && !path.isAbsolute(relative)
+  );
+}
+
+function validatePlan(payload, projectDir, requireDryRun) {
+  const expectedRoot = path.resolve(projectDir, '.claude');
+  if (!payload || typeof payload !== 'object' || !payload.plan) {
+    fail('Install output is missing a plan.');
+  }
+  if (requireDryRun && payload.dryRun !== true) {
+    fail('Install plan did not report dryRun=true.');
+  }
+  if (payload.plan.target !== 'claude-project') {
+    fail('Install plan target is not claude-project.');
+  }
+  if (
+    typeof payload.plan.installRoot !== 'string'
+    || path.resolve(payload.plan.installRoot) !== expectedRoot
+  ) {
+    fail('Install root is not confined to the isolated project.');
+  }
+  if (!Array.isArray(payload.plan.operations) || payload.plan.operations.length === 0) {
+    fail('Install plan has no operations.');
+  }
+  for (const operation of payload.plan.operations) {
+    if (
+      !operation
+      || typeof operation.destinationPath !== 'string'
+      || !isWithin(expectedRoot, path.resolve(operation.destinationPath))
+    ) {
+      fail('Install plan contains an operation outside the isolated project root.');
+    }
+  }
+}
+
+function main() {
+  try {
+    const projectDir = process.argv[2];
+    if (!projectDir || !path.isAbsolute(projectDir)) {
+      fail('Expected an absolute isolated project path.');
+    }
+    const requireDryRun = process.argv.includes('--dry-run');
+    const payload = JSON.parse(fs.readFileSync(0, 'utf8'));
+    validatePlan(payload, projectDir, requireDryRun);
+  } catch (error) {
+    process.stderr.write(`Error: ${error.message}\n`);
+    process.exitCode = 1;
+  }
+}
+
+if (require.main === module) {
+  main();
+}
+
+module.exports = { isWithin, validatePlan };
diff --git a/package.json b/package.json
index 5470d60f1..f12f080c9 100644
--- a/package.json
+++ b/package.json
@@ -450,6 +450,7 @@
     "discussion:audit": "node scripts/discussion-audit.js",
     "security:ioc-scan": "node scripts/ci/scan-supply-chain-iocs.js",
     "security:advisory-sources": "node scripts/ci/supply-chain-advisory-sources.js",
+    "test:plugin-setup-platform": "node docker/plugin-setup/run-platform-tests.js",
     "claw": "node scripts/claw.js",
     "orchestrate:status": "node scripts/orchestration-status.js",
     "orchestrate:worker": "bash scripts/orchestrate-codex-worker.sh",
diff --git a/skills/docker-patterns/SKILL.md b/skills/docker-patterns/SKILL.md
index 00bf3fd5b..e60c1d20f 100644
--- a/skills/docker-patterns/SKILL.md
+++ b/skills/docker-patterns/SKILL.md
@@ -1,22 +1,12 @@
 ---
 name: docker-patterns
-description: Docker and Docker Compose patterns for local development, container security, networking, volume strategies, and multi-service orchestration.
-metadata:
-  origin: ECC
+description: Docker and Docker Compose patterns for local development, hardened CLI installer harnesses, container security, networking, volumes, and multi-service orchestration. Use when creating or reviewing Dockerfiles and Compose services, testing installers across Linux distributions, or planning accurate native macOS and Windows validation.
 ---
 
 # Docker Patterns
 
 Docker and Docker Compose best practices for containerized development.
 
-## When to Activate
-
-- Setting up Docker Compose for local development
-- Designing multi-container architectures
-- Troubleshooting container networking or volume issues
-- Reviewing Dockerfiles for security and size
-- Migrating from local dev to containerized workflow
-
 ## Docker Compose for Local Development
 
 ### Standard Web App Stack
@@ -282,6 +272,171 @@ services:
 # ENV API_KEY=sk-proj-xxxxx      # NEVER DO THIS
 ```
 
+## Hardened CLI Installer Harnesses
+
+Use containers to test installer behavior against disposable project copies without allowing the test to mutate the source checkout.
+
+### Respect the Platform Boundary
+
+- Run real containers for Linux distributions such as Debian and Ubuntu.
+- macOS cannot run as a Docker container because Docker shares a Linux kernel. Run the same shell-free test entry point natively on macOS.
+- Windows containers require a Windows Docker engine. Run platform-independent logic on a native Windows CI runner and reserve Windows containers for a Windows host.
+- Keep a native Ubuntu/macOS/Windows CI matrix for host-specific paths, command shims, quoting, and filesystem behavior.
+
+Do not claim that a Linux container validates macOS or Windows behavior.
+
+### Enforce the Isolation Contract
+
+- Pin base images by immutable digest and pin installed CLI versions.
+- Run as a non-root numeric UID/GID when distro account names differ.
+- Mount the repository and source project read-only.
+- Copy the source project into a writable `tmpfs` workspace before any mutation.
+- Mount `/workspace` with `noexec`, UID/GID 1000, and `mode=0700` so only the
+  container user can inspect project data.
+- Keep npm and npx's executable cache at `NPM_CONFIG_CACHE=/tmp/npm-cache` on
+  the executable `/tmp` mount. Its default size is 2 GiB and can be adjusted
+  with `ECC_TMPFS_SIZE`; `ECC_WORKSPACE_SIZE` separately controls the private
+  workspace mount.
+- Set `read_only: true`, `no-new-privileges:true`, `cap_drop: [ALL]`, and a finite `pids_limit`.
+- Keep the default real-CLI services on `network_mode: none`. Add network access
+  only through a visibly named opt-in service for an authenticated provider
+  session; never make it an accidental environment-driven default.
+- Create only the writable temporary paths the tool needs.
+- Do not pass host credentials into the container by default.
+- Default to a dry run and whitelist only the explicit `dry-run`, `install`,
+  `plugin`, and `shell` modes.
+- Use argument arrays or `spawnSync(..., { shell: false })` for cross-platform runners. Never interpolate project paths into a shell command.
+
+### Exercise the ECC Plugin Setup Harness
+
+Use `docker/plugin-setup/compose.yaml` as the reference implementation. It provides:
+
+- `fixture-tests` for the focused install manifest, target, and executor suite.
+- `real-cli` for the pinned Debian-based generic Linux image.
+- `real-cli-ubuntu` for the pinned Ubuntu image.
+
+Validate the Compose model before building:
+
+```bash
+docker compose -f docker/plugin-setup/compose.yaml config --quiet
+```
+
+Build both real Linux images:
+
+```bash
+docker compose -f docker/plugin-setup/compose.yaml \
+  build real-cli real-cli-ubuntu
+```
+
+Run the safe default flow in each image:
+
+```bash
+docker compose -p ecc-plugin-debian-test \
+  -f docker/plugin-setup/compose.yaml \
+  run --rm -T real-cli dry-run
+
+docker compose -p ecc-plugin-ubuntu-test \
+  -f docker/plugin-setup/compose.yaml \
+  run --rm -T real-cli-ubuntu dry-run
+```
+
+The dry run executes the current public command contract:
+
+```bash
+ecc install --profile core --target claude-project --dry-run --json
+```
+
+Before that command runs, the container creates a locally packed npm artifact
+from the read-only checkout with `npm pack --ignore-scripts`. It extracts the
+self-created tarball under `/tmp`, validates the `ecc-universal` package name,
+required install manifests, and the confined `package.json` `bin.ecc` mapping,
+then invokes the extracted `ecc` executable. The runtime stays on
+`network_mode: none`, does not execute package lifecycle scripts, and does not
+rely on host `node_modules`; its exact pinned production dependencies are
+already present in the image.
+
+The harness rejects an empty plan, a non-`claude-project` target, any operation
+outside `/workspace/project/.claude`, or any dry run that creates the target
+directory. `install` performs the isolated apply twice, checks its managed
+install state, lists the installed target, and runs `doctor`.
+
+### Start, Open, Reconnect, and Clean Up a Named Session
+
+Start a detached container without `--rm` so leaving a terminal does not remove
+the session:
+
+```bash
+docker compose -p ecc-plugin-session \
+  -f docker/plugin-setup/compose.yaml \
+  run --detach --name ecc-plugin-shell real-cli shell
+```
+
+The container copies the read-only fixture to the stable private directory
+`/workspace/project`. Confirm it is running, then emit the Docker side of the
+terminal-opener v1 data contract:
+
+```bash
+docker inspect --format '{{.State.Running}}' ecc-plugin-shell
+node docker/plugin-setup/interactive-plan.js \
+  --container ecc-plugin-shell \
+  --workdir /workspace/project \
+  --json \
+  -- bash
+```
+
+The JSON result has exactly an `executable` and `argv` boundary (plus
+`contractVersion: 1`): the executable is `docker`, and argv begins with
+`exec`, `-it`, and `-w`. Pass that data to the separate terminal-opener skill
+when it is installed. This Docker harness deliberately does not import a
+terminal adapter, interpolate a shell command, or manage a host GUI process.
+Until then, open the same PTY in the current host terminal directly:
+
+```bash
+docker exec -it -w /workspace/project ecc-plugin-shell bash
+```
+
+Exit the shell without stopping the detached container. Reconnect with the
+same `docker exec -it` command. When finished, remove the exact named container
+and its Compose project resources:
+
+```bash
+docker rm --force ecc-plugin-shell
+docker compose -p ecc-plugin-session \
+  -f docker/plugin-setup/compose.yaml \
+  down --remove-orphans
+```
+
+Host credentials are absent by default and credential directories are never
+mounted. The default service also has no network access. When an authenticated
+provider session genuinely needs a network, build `real-cli` first and then opt
+in visibly with `docker compose --profile networked run real-cli-networked
+shell`. Prefer authenticating inside that disposable session. If a CI run must
+inherit a host environment credential, make that opt-in at invocation with an
+explicit Compose `--env NAME` flag, understand that the value is inspectable
+and can be exfiltrated for the container lifetime, and remove the exact named
+container immediately after.
+
+Run the same focused suite natively on the host:
+
+```bash
+npm run test:plugin-setup-platform
+```
+
+Inspect the produced identity and environment before trusting the image:
+
+```bash
+docker image inspect ecc-plugin-setup:debian ecc-plugin-setup:ubuntu
+```
+
+Clean each named test project without deleting unrelated volumes or images:
+
+```bash
+docker compose -p ecc-plugin-debian-test \
+  -f docker/plugin-setup/compose.yaml down --remove-orphans
+docker compose -p ecc-plugin-ubuntu-test \
+  -f docker/plugin-setup/compose.yaml down --remove-orphans
+```
+
 ## .dockerignore
 
 ```
diff --git a/tests/docker/plugin-setup-harness.test.js b/tests/docker/plugin-setup-harness.test.js
new file mode 100644
index 000000000..3e7ee7221
--- /dev/null
+++ b/tests/docker/plugin-setup-harness.test.js
@@ -0,0 +1,420 @@
+'use strict';
+
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+
+const repoRoot = path.join(__dirname, '..', '..');
+const harnessRoot = path.join(repoRoot, 'docker', 'plugin-setup');
+const SUBPROCESS_TIMEOUT_MS = 30_000;
+const files = {
+  ci: path.join(repoRoot, '.github', 'workflows', 'ci.yml'),
+  compose: path.join(harnessRoot, 'compose.yaml'),
+  dockerfile: path.join(harnessRoot, 'Dockerfile'),
+  fixtureProject: path.join(
+    repoRoot,
+    'tests',
+    'fixtures',
+    'docker-plugin-project',
+    'package.json'
+  ),
+  fixtureRunner: path.join(harnessRoot, 'run-fixture-tests.sh'),
+  interactivePlan: path.join(harnessRoot, 'interactive-plan.js'),
+  packageJson: path.join(repoRoot, 'package.json'),
+  packedCliPreparer: path.join(harnessRoot, 'prepare-packed-cli.js'),
+  platformRunner: path.join(harnessRoot, 'run-platform-tests.js'),
+  planValidator: path.join(harnessRoot, 'verify-install-plan.js'),
+  projectDirResolver: path.join(harnessRoot, 'resolve-project-dir.js'),
+  realRunner: path.join(harnessRoot, 'run-real-cli.sh'),
+};
+
+let passed = 0;
+let failed = 0;
+
+function test(name, fn) {
+  try {
+    fn();
+    console.log(`  ✓ ${name}`);
+    passed += 1;
+  } catch (error) {
+    console.log(`  ✗ ${name}`);
+    console.log(`    Error: ${error.message}`);
+    failed += 1;
+  }
+}
+
+function read(filePath) {
+  return fs.readFileSync(filePath, 'utf8');
+}
+
+function runNode(argv, options = {}) {
+  const result = spawnSync(process.execPath, argv, {
+    ...options,
+    shell: false,
+    timeout: SUBPROCESS_TIMEOUT_MS,
+  });
+  assert.ifError(result.error);
+  return result;
+}
+
+console.log('\n=== Docker plugin setup harness tests ===\n');
+
+test('ships the focused Docker harness and default fixture project', () => {
+  for (const filePath of Object.values(files)) {
+    assert.ok(
+      fs.existsSync(filePath),
+      `Missing ${path.relative(repoRoot, filePath)}`
+    );
+  }
+});
+
+test('builds pinned Debian and Ubuntu images as a non-root user', () => {
+  const dockerfile = read(files.dockerfile);
+  const compose = read(files.compose);
+  assert.match(dockerfile, /node:22-bookworm-slim@sha256:[a-f0-9]{64}/);
+  assert.match(dockerfile, /ARG OS_IMAGE=/);
+  assert.match(dockerfile, /FROM \$\{NODE_IMAGE\} AS node-runtime/);
+  assert.match(dockerfile, /FROM \$\{OS_IMAGE\}/);
+  assert.match(dockerfile, /COPY --from=node-runtime \/usr\/local\/ \/usr\/local\//);
+  assert.match(dockerfile, /ARG CLAUDE_CODE_VERSION=\d+\.\d+\.\d+/);
+  assert.match(dockerfile, /@anthropic-ai\/claude-code@\$\{CLAUDE_CODE_VERSION\}/);
+  assert.match(dockerfile, /@iarna\/toml@2\.2\.5/);
+  assert.match(dockerfile, /ajv@8\.20\.0/);
+  assert.match(dockerfile, /sql\.js@1\.14\.1/);
+  assert.match(dockerfile, /--ignore-scripts/);
+  assert.match(
+    dockerfile,
+    /@anthropic-ai\/claude-code\/install\.cjs/
+  );
+  assert.match(dockerfile, /ENV DISABLE_AUTOUPDATER=1/);
+  assert.match(dockerfile, /ENV HOME=\/tmp\/ecc-home/);
+  assert.match(dockerfile, /ENV NODE_PATH=\/usr\/local\/lib\/node_modules/);
+  assert.match(dockerfile, /chown 1000:1000 \/workspace/);
+  assert.match(dockerfile, /USER 1000:1000/);
+  assert.doesNotMatch(dockerfile, /:latest/);
+  assert.match(compose, /image:\s*ecc-plugin-setup:debian/);
+  assert.match(compose, /image:\s*ecc-plugin-setup:ubuntu/);
+  assert.match(compose, /ubuntu:24\.04@sha256:[a-f0-9]{64}/);
+  assert.match(compose, /real-cli-ubuntu:/);
+  assert.match(
+    compose,
+    /fixture-tests:[\s\S]*?user:\s*["']1000:1000["']/
+  );
+  assert.strictEqual(
+    (compose.match(/node:22-bookworm-slim@sha256:[a-f0-9]{64}/g) || []).length,
+    1,
+    'The pinned Node image must have one source of truth in Compose'
+  );
+  assert.match(compose, /x-node-image:\s*&node-image/);
+  assert.match(compose, /image:\s*\*node-image/);
+  assert.match(compose, /NODE_IMAGE:\s*\*node-image/);
+  assert.match(compose, /OS_IMAGE:\s*\*node-image/);
+});
+
+test('keeps checkout and source project read-only with hardened defaults', () => {
+  const compose = read(files.compose);
+  assert.match(compose, /network_mode:\s*none/);
+  assert.match(compose, /x-real-cli:[\s\S]*?network_mode:\s*none[\s\S]*?services:/);
+  assert.match(
+    compose,
+    /real-cli-networked:[\s\S]*?profiles:[\s\S]*?-\s*networked[\s\S]*?network_mode:\s*default/
+  );
+  assert.match(compose, /read_only:\s*true/);
+  assert.match(compose, /no-new-privileges:true/);
+  assert.match(compose, /cap_drop:\s*\n\s*-\s*ALL/);
+  assert.match(compose, /pids_limit:\s*256/);
+  assert.match(compose, /target:\s*\/ecc\s*\n\s*read_only:\s*true/);
+  assert.match(compose, /target:\s*\/source-project\s*\n\s*read_only:\s*true/);
+  assert.match(compose, /CLAUDE_CONFIG_DIR:\s*\/tmp\/ecc-claude-config/);
+  assert.match(
+    compose,
+    /\/tmp:rw,nosuid,nodev,exec,size=\$\{ECC_TMPFS_SIZE:-2g\},uid=1000,gid=1000,mode=0700/
+  );
+  assert.match(
+    compose,
+    /\/workspace:rw,nosuid,nodev,noexec,size=\$\{ECC_WORKSPACE_SIZE:-1g\},uid=1000,gid=1000,mode=0700/
+  );
+  assert.match(compose, /NPM_CONFIG_CACHE:\s*\/tmp\/npm-cache/);
+  assert.doesNotMatch(
+    compose,
+    /ANTHROPIC_API_KEY|CLAUDE_CODE_OAUTH_TOKEN|env_file:/
+  );
+});
+
+test('real runner copies into tmpfs and exposes only explicit safe modes', () => {
+  const runner = read(files.realRunner);
+  assert.match(runner, /ECC_PROJECT_DIR:-\/workspace\/project/);
+  assert.match(runner, /mkdir -p "\$HOME" "\$CLAUDE_CONFIG_DIR" "\$NPM_CONFIG_CACHE"/);
+  assert.match(runner, /dry-run\|install\|plugin\|shell/);
+  assert.match(runner, /--target claude-project/);
+  assert.match(runner, /--dry-run/);
+  assert.match(runner, /verify-install-plan\.js.*--dry-run/);
+  assert.match(runner, /resolve-project-dir\.js/);
+  assert.match(
+    runner,
+    /project_dir="\$\([\s\S]*?resolve-project-dir\.js[\s\S]*?\)"\s*\nreadonly project_dir/
+  );
+  assert.doesNotMatch(runner, /readonly project_dir="\$\(/);
+  assert.match(runner, /prepare-packed-cli\.js/);
+  assert.match(runner, /run_ecc install/);
+  assert.match(runner, /run_ecc list-installed --json/);
+  assert.match(runner, /run_ecc doctor --target claude-project/);
+  assert.match(runner, /\[\[ -e "\$project_dir\/\.claude" \]\]/);
+  assert.doesNotMatch(
+    runner,
+    /scripts\/ecc\.js" setup|--move-scope|\bmigrate\b/
+  );
+  assert.doesNotMatch(runner, /scripts\/ecc\.js" install/);
+  assert.doesNotMatch(runner, /\beval\b|rm\s+-rf/);
+});
+
+test('prepares a local npm artifact through the confined public bin contract', () => {
+  const preparer = read(files.packedCliPreparer);
+  assert.match(preparer, /spawnSync\(executable, argv/);
+  assert.match(preparer, /run\(['"]npm['"]/);
+  assert.match(preparer, /['"]pack['"]/);
+  assert.match(preparer, /['"]--ignore-scripts['"]/);
+  assert.match(preparer, /npm_config_offline:\s*['"]true['"]/);
+  assert.match(preparer, /run\(['"]tar['"]/);
+  assert.match(preparer, /shell:\s*false/g);
+  assert.match(
+    preparer,
+    /const CHILD_PROCESS_TIMEOUT_MS\s*=\s*5 \* 60 \* 1000;/
+  );
+  assert.match(preparer, /timeout:\s*CHILD_PROCESS_TIMEOUT_MS/);
+  assert.doesNotMatch(preparer, /execSync\(|\beval\b/);
+
+  const { validatePackedPackage } = require(files.packedCliPreparer);
+  const fixtureRoot = fs.mkdtempSync(path.join(os.tmpdir(), 'ecc-packed-cli-'));
+
+  function createFixture(name, options = {}) {
+    const packageRoot = path.join(fixtureRoot, name);
+    fs.mkdirSync(path.join(packageRoot, 'scripts'), { recursive: true });
+    fs.mkdirSync(path.join(packageRoot, 'manifests'), { recursive: true });
+    fs.writeFileSync(
+      path.join(packageRoot, 'package.json'),
+      JSON.stringify({
+        name: options.packageName || 'ecc-universal',
+        version: '2.1.0',
+        bin: options.bin === undefined ? { ecc: 'scripts/ecc.js' } : options.bin,
+      })
+    );
+    fs.writeFileSync(path.join(packageRoot, 'scripts', 'ecc.js'), '#!/usr/bin/env node\n');
+    fs.chmodSync(path.join(packageRoot, 'scripts', 'ecc.js'), 0o755);
+    for (const manifest of [
+      'install-components.json',
+      'install-modules.json',
+      'install-profiles.json',
+    ]) {
+      if (manifest !== options.omitManifest) {
+        fs.writeFileSync(path.join(packageRoot, 'manifests', manifest), '{}\n');
+      }
+    }
+    return packageRoot;
+  }
+
+  try {
+    const validRoot = createFixture('valid');
+    assert.strictEqual(
+      validatePackedPackage(validRoot),
+      path.join(validRoot, 'scripts', 'ecc.js')
+    );
+
+    for (const [name, options, pattern] of [
+      ['wrong-name', { packageName: 'not-ecc' }, /package name/i],
+      ['missing-bin', { bin: {} }, /bin\.ecc/i],
+      ['escaping-bin', { bin: { ecc: '../escape.js' } }, /bin\.ecc/i],
+      ['missing-manifest', { omitManifest: 'install-profiles.json' }, /missing/i],
+    ]) {
+      assert.throws(() => validatePackedPackage(createFixture(name, options)), pattern);
+    }
+  } finally {
+    fs.rmSync(fixtureRoot, { recursive: true, force: true });
+  }
+});
+
+test('normalizes the isolated project path before enforcing workspace containment', () => {
+  const valid = runNode([
+    files.projectDirResolver,
+    '/workspace/nested/../project',
+  ], { encoding: 'utf8' });
+  assert.strictEqual(valid.status, 0, valid.stderr);
+  assert.strictEqual(valid.stdout.trim(), '/workspace/project');
+
+  for (const candidate of [
+    '/workspace',
+    '/workspace/../tmp/project',
+    '/tmp/project',
+    'workspace/project',
+  ]) {
+    const invalid = runNode([
+      files.projectDirResolver,
+      candidate,
+    ], { encoding: 'utf8' });
+    assert.strictEqual(invalid.status, 2, `${candidate}: ${invalid.stderr}`);
+    assert.match(invalid.stderr, /within \/workspace/i);
+  }
+});
+
+test('fixture runner delegates to the cross-platform test entry point', () => {
+  const runner = read(files.fixtureRunner);
+  assert.match(runner, /id -u/);
+  assert.match(runner, /id -g/);
+  assert.match(runner, /must run as uid\/gid 1000:1000/i);
+  assert.match(
+    runner,
+    /exec node docker\/plugin-setup\/run-platform-tests\.js/
+  );
+});
+
+test('uses one shell-free focused runner across Linux, macOS, and Windows', () => {
+  const ci = read(files.ci);
+  const packageJson = read(files.packageJson);
+  const platformRunner = read(files.platformRunner);
+
+  assert.match(
+    ci,
+    /os:\s*\[ubuntu-latest,\s*windows-latest,\s*macos-latest\]/
+  );
+  assert.match(
+    packageJson,
+    /"test:plugin-setup-platform":\s*"node docker\/plugin-setup\/run-platform-tests\.js"/
+  );
+  assert.match(platformRunner, /spawnSync\(/);
+  assert.match(platformRunner, /shell:\s*false/);
+  assert.match(
+    platformRunner,
+    /const CHILD_PROCESS_TIMEOUT_MS\s*=\s*5 \* 60 \* 1000;/
+  );
+  assert.match(platformRunner, /timeout:\s*CHILD_PROCESS_TIMEOUT_MS/);
+  assert.match(platformRunner, /Object\.fromEntries\(/);
+  assert.match(platformRunner, /Object\.entries\(process\.env\)\.filter/);
+  assert.doesNotMatch(platformRunner, /delete childEnv\[/);
+  assert.match(platformRunner, /tests\/lib\/install-manifests\.test\.js/);
+  assert.match(platformRunner, /tests\/lib\/install-targets\.test\.js/);
+  assert.match(platformRunner, /tests\/lib\/install-executor\.test\.js/);
+  assert.doesNotMatch(platformRunner, /\beval\b|execSync\(/);
+});
+
+test('emits docker exec as an executable plus argv integration contract', () => {
+  const result = runNode([
+    files.interactivePlan,
+    '--container', 'ecc-plugin-shell',
+    '--workdir', '/workspace/project',
+    '--json',
+    '--',
+    'node',
+    '-p',
+    'process.stdin.isTTY',
+  ], {
+    cwd: repoRoot,
+    encoding: 'utf8',
+  });
+  assert.strictEqual(result.status, 0, result.stderr);
+  assert.deepStrictEqual(JSON.parse(result.stdout), {
+    contractVersion: 1,
+    executable: 'docker',
+    argv: [
+      'exec',
+      '-it',
+      '-w',
+      '/workspace/project',
+      'ecc-plugin-shell',
+      'node',
+      '-p',
+      'process.stdin.isTTY',
+    ],
+  });
+});
+
+test('keeps Docker session values as argv entries and validates boundaries', () => {
+  const literalArgument = '$(touch should-not-run)';
+  const result = runNode([
+    files.interactivePlan,
+    '--container', 'ecc.plugin-shell_1',
+    '--workdir', '/workspace/project with spaces',
+    '--json',
+    '--',
+    'printf',
+    '%s',
+    literalArgument,
+  ], {
+    cwd: repoRoot,
+    encoding: 'utf8',
+  });
+  assert.strictEqual(result.status, 0, result.stderr);
+  assert.deepStrictEqual(JSON.parse(result.stdout).argv.slice(-3), [
+    'printf',
+    '%s',
+    literalArgument,
+  ]);
+
+  for (const args of [
+    ['--container', '../escape', '--json'],
+    ['--container', 'valid-name', '--workdir', 'relative/path', '--json'],
+    ['--container', 'valid-name', '--workdir', '/workspace/../tmp', '--json'],
+  ]) {
+    const invalid = runNode([files.interactivePlan, ...args], {
+      cwd: repoRoot,
+      encoding: 'utf8',
+    });
+    assert.strictEqual(invalid.status, 2);
+    assert.match(invalid.stderr, /invalid/i);
+  }
+});
+
+test('validates dry-run target confinement and nonempty operations', () => {
+  const projectDir = path.join(repoRoot, 'workspace-project');
+  const installRoot = path.join(projectDir, '.claude');
+  const safePlan = {
+    dryRun: true,
+    plan: {
+      target: 'claude-project',
+      installRoot,
+      operations: [
+        { destinationPath: path.join(installRoot, 'rules', 'ecc', 'base.md') },
+      ],
+    },
+  };
+  const safe = runNode(
+    [files.planValidator, projectDir, '--dry-run'],
+    { encoding: 'utf8', input: JSON.stringify(safePlan) }
+  );
+  assert.strictEqual(safe.status, 0, safe.stderr);
+
+  const unsafePlan = {
+    ...safePlan,
+    plan: {
+      ...safePlan.plan,
+      operations: [{ destinationPath: '/tmp/escape.md' }],
+    },
+  };
+  const unsafe = runNode(
+    [files.planValidator, projectDir, '--dry-run'],
+    { encoding: 'utf8', input: JSON.stringify(unsafePlan) }
+  );
+  assert.strictEqual(unsafe.status, 1);
+  assert.match(unsafe.stderr, /outside/i);
+
+  for (const installRootValue of [undefined, 42, { path: installRoot }]) {
+    const invalidRootPlan = {
+      ...safePlan,
+      plan: {
+        ...safePlan.plan,
+        installRoot: installRootValue,
+      },
+    };
+    const invalidRoot = runNode(
+      [files.planValidator, projectDir, '--dry-run'],
+      { encoding: 'utf8', input: JSON.stringify(invalidRootPlan) }
+    );
+    assert.strictEqual(invalidRoot.status, 1);
+    assert.match(invalidRoot.stderr, /install root is not confined/i);
+    assert.doesNotMatch(invalidRoot.stderr, /ERR_INVALID_ARG_TYPE|TypeError/);
+  }
+});
+
+console.log(`\nResults: Passed: ${passed}, Failed: ${failed}`);
+process.exit(failed > 0 ? 1 : 0);
diff --git a/tests/fixtures/docker-plugin-project/package.json b/tests/fixtures/docker-plugin-project/package.json
new file mode 100644
index 000000000..aa71ff72d
--- /dev/null
+++ b/tests/fixtures/docker-plugin-project/package.json
@@ -0,0 +1,5 @@
+{
+  "name": "ecc-docker-plugin-test-project",
+  "version": "0.0.0",
+  "private": true
+}
diff --git a/tests/skills/docker-patterns.test.js b/tests/skills/docker-patterns.test.js
new file mode 100644
index 000000000..870af65f9
--- /dev/null
+++ b/tests/skills/docker-patterns.test.js
@@ -0,0 +1,97 @@
+'use strict';
+
+const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
+
+const repoRoot = path.resolve(__dirname, '..', '..');
+const skillPath = path.join(repoRoot, 'skills', 'docker-patterns', 'SKILL.md');
+
+let passed = 0;
+let failed = 0;
+
+function test(name, fn) {
+  try {
+    fn();
+    console.log(`  ✓ ${name}`);
+    passed += 1;
+  } catch (error) {
+    console.log(`  ✗ ${name}`);
+    console.log(`    Error: ${error.message}`);
+    failed += 1;
+  }
+}
+
+const skill = fs.readFileSync(skillPath, 'utf8');
+
+console.log('\n=== Docker patterns skill tests ===\n');
+
+test('triggers for hardened installer and cross-platform harness work', () => {
+  const frontmatter = skill.match(/^---\n([\s\S]*?)\n---/);
+  assert.ok(frontmatter, 'SKILL.md frontmatter is missing');
+  assert.match(frontmatter[1], /description:.*installer/i);
+  assert.match(frontmatter[1], /description:.*macOS.*Windows/i);
+});
+
+test('documents the ECC plugin setup harness and safe operating modes', () => {
+  assert.match(skill, /docker\/plugin-setup\/compose\.yaml/);
+  assert.match(skill, /\breal-cli\b/);
+  assert.match(skill, /\breal-cli-ubuntu\b/);
+  assert.match(skill, /\bfixture-tests\b/);
+  assert.match(skill, /dry-run.*install.*plugin.*shell/is);
+  assert.doesNotMatch(skill, /explicit modes such as.*migrate/i);
+});
+
+test('requires hardened ephemeral installer execution', () => {
+  for (const pattern of [
+    /read[_ -]only/i,
+    /tmpfs/i,
+    /no-new-privileges/i,
+    /cap_drop/i,
+    /pids_limit/i,
+    /non-root/i,
+    /digest/i,
+    /credential/i,
+  ]) {
+    assert.match(skill, pattern);
+  }
+});
+
+test('states the honest macOS and Windows validation boundary', () => {
+  assert.match(skill, /macOS cannot run as a Docker container/i);
+  assert.match(skill, /Windows containers require a Windows Docker engine/i);
+  assert.match(skill, /native.*ubuntu.*macOS.*Windows.*CI/is);
+  assert.doesNotMatch(skill, /macOS container image|simulate Windows/i);
+});
+
+test('provides a repeatable build, run, inspect, and cleanup sequence', () => {
+  assert.match(skill, /docker compose.*build.*real-cli.*real-cli-ubuntu/is);
+  assert.match(skill, /docker compose.*run.*real-cli.*dry-run/is);
+  assert.match(skill, /docker image inspect/is);
+  assert.match(skill, /down --remove-orphans/);
+});
+
+test('documents the private named-container lifecycle and terminal boundary', () => {
+  assert.match(skill, /ECC_TMPFS_SIZE/);
+  assert.match(skill, /\/workspace.*mode=0700/is);
+  assert.match(skill, /NPM_CONFIG_CACHE.*\/tmp\/npm-cache/is);
+  assert.match(skill, /docker compose.*run.*--detach.*--name/is);
+  assert.match(skill, /interactive-plan\.js/);
+  assert.match(skill, /executable.*argv/is);
+  assert.match(skill, /docker exec -it/);
+  assert.match(skill, /reconnect/i);
+  assert.match(skill, /docker rm.*ecc-plugin-shell/is);
+  assert.match(skill, /host credentials.*opt-in/is);
+  assert.doesNotMatch(skill, /skills\/docker-patterns\/scripts\/open-interactive\.js/);
+});
+
+test('requires the offline smoke to execute the locally packed public bin', () => {
+  assert.match(skill, /npm pack.*--ignore-scripts/is);
+  assert.match(skill, /package\.json.*bin\.ecc/is);
+  assert.match(skill, /locally packed/i);
+  assert.match(skill, /network_mode:\s*none/);
+  assert.match(skill, /does not\s+rely on.*host `node_modules`/is);
+});
+
+console.log(`\nResults: Passed: ${passed}, Failed: ${failed}`);
+process.exit(failed > 0 ? 1 : 0);