@@ -3,24 +3,35 @@
 set -euo pipefail
 phase="${1:?usage: ecosystem-cn.sh release VERSION}"
 version="${2:?mcpp version under test required}"
-base="${XLINGS_HOME:?explicit isolated XLINGS_HOME required}"
+controller="${XLINGS_HOME:?explicit isolated XLINGS_HOME required}"
+probes="${CN_PROBE_ROOT:?instance-owned probe root required}"
+[[ "$probes" == "$controller/subos/cn-arm64-published/probes" ]] || exit 1
+base="$probes/client-home"
+[[ ! -e "$base" ]] || { echo 'consumer client home must be cold'; exit 1; }
 [[ "$(uname -m)" == aarch64 ]] || { echo "native ARM64 required"; exit 1; }
 [[ "$phase" == release ]] || { echo "published release only"; exit 1; }
 [[ ! -d "${CN_HOST_CHECKOUT:?host checkout path required}" ]] || {
     echo 'host checkout must not be visible in the SubOS'; exit 1;
 }
 xl="${CN_PUBLISHED_XLINGS:?published client path required}"
-work="${CN_PROBE_RUN_DIR:-$base/probes/runs/$phase-$version-$(date +%Y%m%dT%H%M%S)}"
-[[ "$work" == "$base/probes/runs/"* ]] || exit 1
+work="${CN_PROBE_RUN_DIR:-$probes/runs/$phase-$version-$(date +%Y%m%dT%H%M%S)}"
+[[ "$work" == "$probes/runs/"* ]] || exit 1
 mkdir -p "$work"
 exec > >(tee -a "$work/probe.log") 2>&1
+export XLINGS_HOME="$base"
+# A fresh client inside the namespace must not inherit its controller's
+# project, active instance, or shim dispatch context. Filesystem isolation
+# remains enforced by the already-entered SubOS, including the check above.
+unset XLINGS_PROJECT_DIR XLINGS_ACTIVE_SUBOS XLINGS_ROOT_INSTANCE XLINGS_ROOT_LOGIN
+unset XLINGS_SHIM_DEPTH XLINGS_SUBOS_LIB XLINGS_BIN
 printf 'phase=%s version=%s XLINGS_HOME=%s sandbox_HOME=%s\n' "$phase" "$version" "$base" "$HOME"
 cat /proc/self/mountinfo > "$work/subos-mountinfo.txt"
 export MCPP_HOME="$work/mcpp-home"
 export MCPP_VENDORED_XLINGS="$xl"
 export MCPP_E2E_MIRROR=CN MCPP_E2E_LLVM_VERSION=23.1.3 MCPP_E2E_EXPECT_ARCH=aarch64
 unset LD_LIBRARY_PATH LD_PRELOAD MCPP_TOOLCHAIN
 "$xl" config --mirror CN
+"$xl" update
 "$xl" install "mcpp@$version" -g -y -u
 MCPP="$base/data/xpkgs/xim-x-mcpp/$version/bin/mcpp"
 [[ -x "$MCPP" ]] || { echo "mcpp not executable: $MCPP"; exit 1; }
@@ -43,8 +54,20 @@ project="${CN_PROBE_PROJECT:-hello}"
 "$MCPP" new "$project"
 cd "$work/$project"
 "$MCPP" build 2>&1 | tee "$work/native-default-build.log"
-grep -q 'Resolved llvm@23.1.3' "$work/native-default-build.log"
-grep -Eq 'aarch64-(unknown-)?linux-gnu' "$work/native-default-build.log"
+# Cold automatic provisioning and warm resolution have different progress
+# messages. Assert the documented build facts instead of a human log banner.
+"$MCPP" emit build-database --format json > "$work/native-build-database.json"
+python3 - "$work/native-build-database.json" "$project" "$MCPP_HOME" <<'PYDEFAULT'
+import json,pathlib,sys
+envelope=json.load(open(sys.argv[1]))
+assert envelope['kind']=='mcpp.build-database',envelope
+database=envelope['data']['database']
+selected=next(s for s in database['sets'] if s['name']==sys.argv[2])
+toolchain=database['ide']['toolchains'][selected['ide']['toolchain']]
+assert toolchain['family']=='clang' and toolchain['version']=='23.1.3',toolchain
+assert toolchain['target'] in ('aarch64-linux-gnu','aarch64-unknown-linux-gnu'),toolchain
+pathlib.Path(toolchain['driver']).resolve().relative_to(pathlib.Path(sys.argv[3]).resolve())
+PYDEFAULT
 mapfile -t native_bins < <(find target -type f -path "*/bin/$project")
 [[ "${#native_bins[@]}" == 1 ]] || exit 1
 readelf -hW "${native_bins[0]}" | tee "$work/native-header.txt"
@@ -157,5 +180,5 @@ for target in x86_64-linux-gnu aarch64-macos x86_64-windows-gnu; do
 done
 echo 'RELEASE BUILD PASS: CN install/default/new/build/run/pack, native openkal, four consumers and three target artifacts.'
 cp "$work/openkal-source-sha.txt" "$work/cross/source-sha.txt"
-printf '%s\n' "$work" > "$base/probes/last-run.txt"
+printf '%s\n' "$work" > "$probes/last-run.txt"
 echo 'Foreign target execution is pending the three target-system jobs.'
@@ -123,7 +123,7 @@ done
 # literal:
 if grep -qE "MCPP_PIN:[[:space:]]*['\"]?[0-9]" .github/workflows/ci-fresh-install.yml; then
   bad "ci-fresh-install.yml hardcodes MCPP_PIN again — it must stay derived from
-       wait-index's releases-API lookup, or the index guard and the install jobs
+       resolve-version's releases-API lookup, or the index guard and the install jobs
        can once more disagree about which version is under test (#265)"
 fi
 
 
@@ -3,13 +3,13 @@
 set -euo pipefail
 version=${1:?exact published mcpp version}
 repo=${2:?checkout holding these tools and the canonical client pin}
-backend=${3:-proot}
+backend=${3:-bwrap}
 [[ "$version" =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]] || exit 2
 [[ "$(uname -m)" == aarch64 ]] || exit 2
 [[ "$backend" == proot || "$backend" == bwrap ]] || exit 2
 base=${XLINGS_HOME:?cold isolated home required}
 [[ ! -e "$base" ]] || { echo 'home must be cold'; exit 1; }
-mkdir -p "$base/bootstrap" "$base/probes" "$base/reports"
+mkdir -p "$base/bootstrap" "$base/reports"
 cd "$base"
 # Derive the client version from the repository's existing single pin.
 xl_version=$(python3 - "$repo/src/provider/xlings/xlings.cppm" <<'PY'
@@ -43,17 +43,17 @@ xl="$base/bootstrap/xlings-$xl_version-linux-aarch64/bin/xlings"
 "$xl" update
 cp "$base/data/xim-pkgindex/.xlings-index-cache.json" "$base/reports/outer-published-index.json"
 # Native backend is provided by distro infrastructure, never labeled an xim
-# ARM package. The published bwrap package is x86-only. The client locates the
-# system proot directly; bwrap's current locator needs this explicit private
-# system-backend directory. Record the symlink and actual distro version.
+# ARM package. Record its distro version and use the published client's
+# documented isolation setup, which prepares a root-owned bwrap and a narrow
+# AppArmor profile when needed, without disabling the host's restriction.
 backend_package="$backend"
 [[ "$backend" != bwrap ]] || backend_package=bubblewrap
 dpkg-query -W "$backend_package" | tee "$base/reports/backend-version.txt"
 command -v "$backend" | tee "$base/reports/backend-path.txt"
 sha256sum "$(command -v "$backend")" > "$base/reports/backend.sha256"
 if [[ "$backend" == bwrap ]]; then
-    mkdir -p "$base/data/xpkgs/xim-x-bwrap/ci-system-backend/bin"
-    ln -s /usr/bin/bwrap "$base/data/xpkgs/xim-x-bwrap/ci-system-backend/bin/bwrap"
+    "$xl" self doctor --isolation --fix -y | tee "$base/reports/isolation-doctor.txt"
+    "$xl" self doctor --isolation --json > "$base/reports/isolation-doctor.json"
 fi
 # Independently prove the exact mcpp archive is available through public CN.
 mcpp_archive="mcpp-$version-linux-aarch64.tar.gz"
@@ -69,15 +69,20 @@ mcpp_binary_sha=$(sha256sum "${archive_binaries[0]}" | cut -d ' ' -f 1)
 printf '%s\n' "$mcpp_binary_sha" > "$base/reports/mcpp-cn-binary.sha256"
 "$xl" subos new cn-arm64-published
 "$xl" subos runtime glibc@2.44.3 cn-arm64-published
-cp "$repo/.github/tools/check_published_arm64_cn_ecosystem.sh" "$base/probes/ecosystem.sh"
-printf -v command 'CN_HOST_CHECKOUT=%q CN_EXPECTED_BINARY_SHA=%q CN_PUBLISHED_XLINGS=%q bash %q release %q' "$repo" "$mcpp_binary_sha" "$xl" "$base/probes/ecosystem.sh" "$version"
+# The controller home is read-only inside a real SubOS. The selected instance
+# owns its writable workspace; its consumer uses a separate cold client home.
+probes="$base/subos/cn-arm64-published/probes"
+mkdir -p "$probes"
+cp "$repo/.github/tools/check_published_arm64_cn_ecosystem.sh" "$probes/ecosystem.sh"
+printf -v command 'CN_HOST_CHECKOUT=%q CN_EXPECTED_BINARY_SHA=%q CN_PUBLISHED_XLINGS=%q CN_PROBE_ROOT=%q bash %q release %q' "$repo" "$mcpp_binary_sha" "$xl" "$probes" "$probes/ecosystem.sh" "$version"
 "$xl" subos use cn-arm64-published --sandbox "$backend" --cmd "$command"
-work=$(cat "$base/probes/last-run.txt")
-[[ "$work" == "$base/probes/runs/"* ]] || exit 1
+work=$(cat "$probes/last-run.txt")
+[[ "$work" == "$probes/runs/"* ]] || exit 1
 cmp "$base/reports/release-tag-sha.txt" "$work/mcpp-source-sha.txt"
 cp "$base/reports/release-tag-sha.txt" "$work/cross/engine-release-sha.txt"
 cp "$work/mcpp-home/registry/data/xim-pkgindex/.xlings-index-cache.json" "$base/reports/inner-published-index.json"
 cp "$work/mcpp-home/registry/.xlings.json" "$base/reports/inner-config.json"
+cp "$probes/client-home/.xlings.json" "$base/reports/consumer-client-config.json"
 cp "$base/.xlings.json" "$base/reports/outer-config.json"
 echo "CN_REPORT=$base/reports" >> "$GITHUB_ENV"
 echo "CN_CONSUMER_REPORT=$work" >> "$GITHUB_ENV"
 
@@ -10,8 +10,8 @@ on:
         description: Native distro backend used only as CI isolation infrastructure
         required: true
         type: choice
-        default: proot
-        options: [proot, bwrap]
+        default: bwrap
+        options: [bwrap, proot]
 permissions:
   contents: read
 concurrency:
@@ -56,11 +56,12 @@ jobs:
             ${{ env.XLINGS_HOME }}/reports/*.json
             ${{ env.XLINGS_HOME }}/reports/*.txt
             ${{ env.XLINGS_HOME }}/reports/*.sha256
-            ${{ env.XLINGS_HOME }}/probes/runs/*/probe.log
-            ${{ env.XLINGS_HOME }}/probes/runs/*/*.txt
-            ${{ env.XLINGS_HOME }}/probes/runs/*/*.sha256
-            ${{ env.XLINGS_HOME }}/probes/runs/*/*.log
-            ${{ env.XLINGS_HOME }}/probes/runs/*/members.tsv
+            ${{ env.XLINGS_HOME }}/subos/cn-arm64-published/probes/runs/*/probe.log
+            ${{ env.XLINGS_HOME }}/subos/cn-arm64-published/probes/runs/*/*.txt
+            ${{ env.XLINGS_HOME }}/subos/cn-arm64-published/probes/runs/*/*.json
+            ${{ env.XLINGS_HOME }}/subos/cn-arm64-published/probes/runs/*/*.sha256
+            ${{ env.XLINGS_HOME }}/subos/cn-arm64-published/probes/runs/*/*.log
+            ${{ env.XLINGS_HOME }}/subos/cn-arm64-published/probes/runs/*/members.tsv
           if-no-files-found: warn
   target-run:
     needs: consume
@@ -90,7 +91,11 @@ jobs:
         run: |
           set -euo pipefail
           cd art
-          sha256sum -c SHA256SUMS
+          if [ "$TARGET_SYSTEM" = macos ]; then
+            shasum -a 256 -c SHA256SUMS
+          else
+            sha256sum -c SHA256SUMS
+          fi
           grep -Eq '^[0-9a-f]{40}$' source-sha.txt
           grep -Eq '^[0-9a-f]{40}$' engine-release-sha.txt
           grep -Eq '^[0-9a-f]{40}$' index-source-sha.txt
 
@@ -67,10 +67,10 @@ jobs:
   # Convert the race into a bounded wait: poll the index's mcpp.lua until
   # it carries the released version (<=15 min), then let every job run.
   # Non-workflow_run triggers (manual, cron, PR) skip the wait.
-  wait-index:
+  resolve-version:
     runs-on: ubuntu-latest
     if: ${{ github.event_name != 'workflow_run' || github.event.workflow_run.conclusion == 'success' }}
-    timeout-minutes: 20
+    timeout-minutes: 5
     outputs:
       version: ${{ steps.resolve.outputs.version }}
     steps:
@@ -91,10 +91,19 @@ jobs:
           esac
           echo "version=$VER" >> "$GITHUB_OUTPUT"
           echo "version under test: $VER"
+
+  wait-index:
+    needs: resolve-version
+    runs-on: ubuntu-latest
+    if: ${{ github.event_name != 'workflow_run' || github.event.workflow_run.conclusion == 'success' }}
+    timeout-minutes: 20
+    outputs:
+      version: ${{ needs.resolve-version.outputs.version }}
+    steps:
       - name: Wait for the PUBLISHED index artifact to track the released mcpp
         if: ${{ github.event_name == 'workflow_run' }}
         env:
-          VER: ${{ steps.resolve.outputs.version }}
+          VER: ${{ needs.resolve-version.outputs.version }}
         run: |
           # Poll the ARTIFACT, not the git file.
           #
@@ -537,7 +546,10 @@ jobs:
   #   from BOTH sides: refused before `brew trust`, accepted after.
   macos-brew-fresh:
     name: macOS fresh install (Homebrew, ${{ matrix.image }})
+    needs: resolve-version
     if: ${{ github.event_name != 'workflow_run' || github.event.workflow_run.conclusion == 'success' }}
+    env:
+      MCPP_PIN: ${{ needs.resolve-version.outputs.version }}
     # Same two images as macos-fresh: the formula declares `depends_on macos:
     # :sonoma` + arm64, macos-14 is the oldest image satisfying it, and
     # xcode-27 is macOS 27, the newest release.
@@ -561,6 +573,27 @@ jobs:
             [ "$(sw_vers -productVersion | cut -d. -f1)" = 27 ] || { echo "::error::xcode-27 delivered macOS $(sw_vers -productVersion), not 27"; exit 1; }
           fi
 
+      # The tap's update is asynchronous, independently of the xlings index.
+      # Read its published formula without tapping, so the one-liner below
+      # still exercises a machine that has never added this tap.
+      - name: Wait for the tap to carry the version under test
+        run: |
+          set -euo pipefail
+          deadline=$((SECONDS + 600))
+          ready=false
+          while (( SECONDS < deadline )); do
+            formula=$(curl -fsSL --retry 2 --retry-all-errors --max-time 30 \
+              https://raw.githubusercontent.com/mcpp-community/homebrew-mcpp/main/Formula/mcpp-m.rb 2>/dev/null || true)
+            version=$(printf '%s\n' "$formula" | sed -nE 's/^[[:space:]]*version "([^"]+)".*/\1/p' | head -1)
+            if [ "$version" = "$MCPP_PIN" ]; then
+              ready=true
+              break
+            fi
+            echo "Waiting for tap: expected $MCPP_PIN, observed ${version:-unavailable}"
+            sleep 15
+          done
+          [ "$ready" = true ] || { echo "::error::the tap never published mcpp $MCPP_PIN"; exit 1; }
+
       # ① The command README.md documents, on a machine that has never tapped.
       #    Fully qualified, so Homebrew treats it as explicit intent.
       - name: "Documented one-liner installs"
@@ -570,8 +603,8 @@ jobs:
       #    runtime, so a bare symlink into the Cellar would make MCPP_HOME the
       #    versioned Cellar dir and `brew upgrade` would drop every installed
       #    toolchain. Assert the binary on PATH is brew's and reports the
-      #    version the FORMULA declares — not a hardcoded one, which would go
-      #    stale on every release.
+      #    exact release selected for every installation job. Agreement with
+      #    an old formula alone does not validate the new release.
       - name: "Installed binary is brew's, and agrees with the formula"
         run: |
           set -euo pipefail
@@ -583,8 +616,9 @@ jobs:
           formula_version="$(brew info --json=v2 mcpp-community/mcpp/mcpp-m \
                              | python3 -c 'import json,sys; print(json.load(sys.stdin)["formulae"][0]["versions"]["stable"])')"
           echo "formula declares: $formula_version"
+          test "$formula_version" = "$MCPP_PIN"
           mcpp --version
-          mcpp --version | grep -Fq "$formula_version"
+          test "$(mcpp --version)" = "mcpp $MCPP_PIN"
 
       # ③ THE TRUST GATE, from the failing side first.
       #
@@ -620,7 +654,8 @@ jobs:
           brew install mcpp-m                       # short form
           brew uninstall --force mcpp-m
           brew install mcpp-community/mcpp/mcpp     # the `mcpp` alias
-          brew upgrade mcpp-m || true               # no-op when current; must not be refused
+          brew upgrade mcpp-m                       # no-op when current; must not be refused
+          test "$(mcpp --version)" = "mcpp $MCPP_PIN"
 
       # ⑤ The only assertion a user actually cares about: it builds and runs.
       #    Exercises the launcher's MCPP_HOME/MCPP_VENDORED_XLINGS pinning,
 
@@ -114,6 +114,7 @@ jobs:
           GH_TOKEN: ${{ github.token }}
         run: |
           python3 tests/scripts/test_check_workflow_assertions.py
+          python3 tests/scripts/test_release_install_verification.py
           python3 .github/tools/check_workflow_assertions.py --check-open
 
       - name: The release canary runner runs each command under the named bash
 
@@ -0,0 +1,69 @@
+#!/usr/bin/env python3
+"""Run the real Homebrew verification step against controlled command results.
+
+An old formula and its matching old binary must not validate a newer release.
+"""
+from __future__ import annotations
+
+import importlib.util
+import os
+from pathlib import Path
+import subprocess
+import sys
+import tempfile
+import unittest
+
+ROOT = Path(__file__).resolve().parents[2]
+WORKFLOW = ROOT / ".github/workflows/ci-fresh-install.yml"
+spec = importlib.util.spec_from_file_location(
+    "release_ci_assertions", ROOT / ".github/tools/check_workflow_assertions.py"
+)
+parser = importlib.util.module_from_spec(spec)
+sys.modules[spec.name] = parser
+spec.loader.exec_module(parser)
+
+
+def run_guard(formula: str, binary: str) -> subprocess.CompletedProcess[str]:
+    workflow = parser.parse(WORKFLOW)
+    job = next(j for j in workflow.jobs if j.key == "macos-brew-fresh")
+    step = next(s for s in job.steps if s.name.startswith("Installed binary is brew's"))
+    with tempfile.TemporaryDirectory() as directory:
+        prefix = Path(directory) / "brew"
+        bins = prefix / "bin"
+        bins.mkdir(parents=True)
+        (bins / "brew").write_text(r'''#!/bin/sh
+case "$1" in
+  --prefix) printf '%s\n' "$CI_STUB_PREFIX" ;;
+  info) printf '{"formulae":[{"versions":{"stable":"%s"}}]}\n' "$CI_STUB_FORMULA" ;;
+  *) exit 99 ;;
+esac
+''')
+        (bins / "mcpp").write_text(r'''#!/bin/sh
+[ "$1" = --version ] || exit 99
+printf 'mcpp %s\n' "$CI_STUB_BINARY"
+''')
+        for name in ("brew", "mcpp"):
+            (bins / name).chmod(0o755)
+        env = dict(os.environ, PATH=str(bins) + os.pathsep + os.environ["PATH"],
+                   CI_STUB_PREFIX=str(prefix), CI_STUB_FORMULA=formula,
+                   CI_STUB_BINARY=binary, MCPP_PIN="2026.10.21.1")
+        return subprocess.run(["bash", "-c", step.run], env=env,
+                              capture_output=True, text=True, check=False)
+
+
+class ReleasedHomebrewVersion(unittest.TestCase):
+    def test_matching_old_formula_and_binary_do_not_validate_the_new_release(self):
+        result = run_guard("2026.10.19.1", "2026.10.19.1")
+        self.assertNotEqual(result.returncode, 0, result.stdout + result.stderr)
+
+    def test_the_requested_release_passes(self):
+        result = run_guard("2026.10.21.1", "2026.10.21.1")
+        self.assertEqual(result.returncode, 0, result.stdout + result.stderr)
+
+    def test_a_wrong_binary_is_rejected_even_with_the_new_formula(self):
+        result = run_guard("2026.10.21.1", "2026.10.19.1")
+        self.assertNotEqual(result.returncode, 0, result.stdout + result.stderr)
+
+
+if __name__ == "__main__":
+    unittest.main()