diff --git a/CLAUDE.md b/CLAUDE.md
index 2aac70468..704e26c26 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -82,7 +82,7 @@ Only after doing all of the above should you begin writing code.
 # Important commands and conventions:
 
 - Never run `uv sync`, always run `uv sync --all-packages` instead
-- For browser automation, Playwright's Python API is in the root venv (`from playwright.sync_api import sync_playwright`, run via `uv run python`). Chromium installs asynchronously on first container boot (the one-shot `deferred-install` program), so in a fresh workspace confirm it finished -- `supervisorctl status deferred-install` or the marker `/var/lib/minds/deferred-install/done.playwright` -- before launching, or the launch fails with a clear error. It runs as-is under the docker provider's gVisor runtime; if you hit a "No usable sandbox!" error on a runtime without unprivileged user namespaces, pass `chromium.launch(args=["--no-sandbox"])`. See `libs/bootstrap/README.md` for the full deferral contract.
+- For browser automation, Playwright's Python API is in the root venv (`from playwright.sync_api import sync_playwright`, run via `uv run python`). The engine is Fortress (a stealth-patched Chromium fork), not Playwright's own managed Chromium -- pass `executable_path="/opt/fortress/tilion-fortress/tilion"` explicitly to `chromium.launch(...)`, since Playwright's own browser-cache lookup only auto-discovers builds it downloaded itself. It installs asynchronously on first container boot (the one-shot `deferred-install` program), so in a fresh workspace confirm it finished -- `supervisorctl status deferred-install` or the marker `/var/lib/minds/deferred-install/done.fortress` -- before launching, or the launch fails with a clear error. It runs as-is under the docker provider's gVisor runtime; if you hit a "No usable sandbox!" error on a runtime without unprivileged user namespaces, pass `chromium.launch(executable_path="/opt/fortress/tilion-fortress/tilion", args=["--no-sandbox"])`. See `libs/bootstrap/README.md` for the full deferral contract.
 
 # Always remember these guidelines:
 
diff --git a/dev/changelog/deferred-install-fortress-arm64.md b/dev/changelog/deferred-install-fortress-arm64.md
new file mode 100644
index 000000000..91626b41b
--- /dev/null
+++ b/dev/changelog/deferred-install-fortress-arm64.md
@@ -0,0 +1,5 @@
+`scripts/deferred_install.sh` now fetches the Fortress stealth Chromium fork
+per-arch on first container boot instead of vanilla Playwright Chromium: x64
+from Fortress's official `v151.0.7908.0` release, arm64 from a fork build
+(minhtrinh-imbue/fortress, for the aarch64-support PR tiliondev/fortress#29
+until it merges upstream). Both tarballs are SHA256-verified before install.
diff --git a/libs/browser/browser_test.py b/libs/browser/browser_test.py
index e61245af1..ddf6aa3a0 100644
--- a/libs/browser/browser_test.py
+++ b/libs/browser/browser_test.py
@@ -76,11 +76,11 @@ def test_deferred_install_ready_gates_on_marker(
     monkeypatch: pytest.MonkeyPatch, tmp_path: Path
 ) -> None:
     monkeypatch.delenv("BROWSER_SKIP_INSTALL_CHECK", raising=False)
-    play = tmp_path / "done.playwright"
-    monkeypatch.setattr(bsession, "_PLAYWRIGHT_MARKER", play)
+    marker = tmp_path / "done.fortress"
+    monkeypatch.setattr(bsession, "_FORTRESS_MARKER", marker)
     ready, _ = bsession.deferred_install_ready()
     assert ready is False
-    play.write_text("")
+    marker.write_text("")
     ready, reason = bsession.deferred_install_ready()
     assert ready is True
     assert reason == "ready"
diff --git a/libs/browser/changelog/deferred-install-fortress-arm64.md b/libs/browser/changelog/deferred-install-fortress-arm64.md
new file mode 100644
index 000000000..d3bcecaf5
--- /dev/null
+++ b/libs/browser/changelog/deferred-install-fortress-arm64.md
@@ -0,0 +1,6 @@
+The browser fleet's Chromium engine is now Fortress (a from-source, BSD-3,
+stealth-patched Chromium fork) instead of Playwright's own managed Chromium.
+`session.py` and the agents' direct Playwright calls both launch the same
+Fortress binary at `/opt/fortress/tilion-fortress/tilion`, so the whole
+workspace runs one engine. The fleet gates browser launches on the Fortress
+deferred-install marker.
diff --git a/libs/browser/src/browser/session.py b/libs/browser/src/browser/session.py
index d0ee2d6b2..73f445ca7 100644
--- a/libs/browser/src/browser/session.py
+++ b/libs/browser/src/browser/session.py
@@ -105,10 +105,15 @@
 # tab feels snappier. Slightly more bandwidth than skipping frames.
 _SCREENCAST_EVERY_NTH_FRAME = 1
 
-# Deferred-install marker (see scripts/deferred_install.sh). Chromium installs
+# Deferred-install marker (see scripts/deferred_install.sh). Fortress installs
 # asynchronously on first container boot; launching a browser before it exists
 # fails, so callers gate on this. No Xvfb: CDP streaming/input are headless.
-_PLAYWRIGHT_MARKER = Path("/var/lib/minds/deferred-install/done.playwright")
+_FORTRESS_MARKER = Path("/var/lib/minds/deferred-install/done.fortress")
+
+# Fortress's fixed install path (see scripts/deferred_install.sh's
+# _install_fortress). A stealth, C++-patched Chromium fork -- replaces
+# vanilla Chromium as the engine for every browser the fleet launches.
+_FORTRESS_EXECUTABLE = "/opt/fortress/tilion-fortress/tilion"
 
 # Default model. browser-use's own default LLM is ChatBrowserUse (its hosted
 # model), so to drive with the user's Anthropic key we pass ChatAnthropic
@@ -329,7 +334,7 @@ def deferred_install_ready() -> tuple[bool, str]:
     """Return ``(ready, reason)`` once Chromium is installed."""
     if os.environ.get("BROWSER_SKIP_INSTALL_CHECK") == "1":
         return True, "ready"  # host/CI testing without the deferred-install marker
-    if not _PLAYWRIGHT_MARKER.exists():
+    if not _FORTRESS_MARKER.exists():
         return False, "Chromium is still installing in this workspace; try again in a minute."
     return True, "ready"
 
@@ -542,7 +547,10 @@ async def start(
         """
         self._playwright = playwright
         self._input_enabled.set()
-        chromium_path = playwright.chromium.executable_path
+        # Fixed Fortress path, not playwright.chromium.executable_path -- the
+        # fleet's engine is Fortress, not Playwright's own managed Chromium
+        # (which vanilla Playwright calls elsewhere in this image still use).
+        chromium_path = _FORTRESS_EXECUTABLE
         profile_dir = _profile_dir(self.browser_id)
         profile_dir.mkdir(parents=True, exist_ok=True)
         _clear_stale_singleton(profile_dir)  # a prior hard kill may have orphaned a lock
diff --git a/libs/browser/test_browser_integration.py b/libs/browser/test_browser_integration.py
index 6c5b8746c..97a4215be 100644
--- a/libs/browser/test_browser_integration.py
+++ b/libs/browser/test_browser_integration.py
@@ -415,7 +415,7 @@ def test_http_release_requires_ownership(monkeypatch: pytest.MonkeyPatch) -> Non
 
 def test_http_new_browser_blocked_until_chromium_installed(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.delenv("BROWSER_SKIP_INSTALL_CHECK", raising=False)
-    monkeypatch.setattr(bsession, "_PLAYWRIGHT_MARKER", bsession.Path("/nonexistent/marker"))
+    monkeypatch.setattr(bsession, "_FORTRESS_MARKER", bsession.Path("/nonexistent/marker"))
     client = runner.application.test_client()
     resp = client.post("/browsers")
     assert resp.status_code == 503
diff --git a/scripts/deferred_install.sh b/scripts/deferred_install.sh
index c1e1bf8ec..237a2c8bb 100755
--- a/scripts/deferred_install.sh
+++ b/scripts/deferred_install.sh
@@ -66,35 +66,72 @@ _recover_interrupted_dpkg() {
     fi
 }
 
-_install_playwright() {
+# Fortress (tiliondev/fortress) stealth Chromium engine, replacing vanilla
+# Playwright-managed Chromium. x64 from the official release; arm64 has no
+# official release yet (tiliondev/fortress#29, open as of 2026-07-23) so this
+# points at a fork build in the meantime -- swap _FORTRESS_ARM64_URL/_SHA256
+# to the official tiliondev/fortress release once that PR merges.
+# Fork build: https://github.com/minhtrinh-imbue/fortress/releases/tag/linux-arm64-151.0.7908.0-debian12
+# PR:         https://github.com/tiliondev/fortress/pull/29
+readonly _FORTRESS_X64_URL="https://github.com/tiliondev/fortress/releases/download/v151.0.7908.0/tilion-fortress-linux-x64.tar.gz"
+readonly _FORTRESS_X64_SHA256="243238b2b8a8b944b7ba2b63533d2b917da7d569dcb290ce96bf28151294b873"
+readonly _FORTRESS_ARM64_URL="https://github.com/minhtrinh-imbue/fortress/releases/download/linux-arm64-151.0.7908.0-debian12/tilion-fortress-linux-arm64-debian12.tar.gz"
+readonly _FORTRESS_ARM64_SHA256="da6965af8fa8e995d137bcabdca8d163fde7f32ba483eaf5e029223995f19ada"
+readonly _FORTRESS_INSTALL_DIR="/opt/fortress"
+
+_install_fortress() {
     local marker
-    marker="$(_marker_for playwright)"
+    marker="$(_marker_for fortress)"
     if [ -f "$marker" ]; then
-        _log "playwright: marker present at $marker, skipping"
+        _log "fortress: marker present at $marker, skipping"
         return 0
     fi
-    # `playwright install --with-deps` shells out to apt; recover any
-    # interrupted dpkg state first so an install the bake interrupted can
-    # actually complete on retry.
+    # `install-deps` apt-installs the shared libs Chromium needs (libnss3,
+    # libgbm, etc.) -- Fortress is a Chromium build too, same requirement.
+    # Recover any interrupted dpkg state first so a bake-interrupted install
+    # can actually complete on retry.
     _recover_interrupted_dpkg
-    _log "playwright: installing chromium + apt system libs (this may take a few minutes)"
-    # `--with-deps` apt-installs the system libraries chromium needs.
-    # `uv run` uses the workspace venv (the playwright Python wheel is
-    # already installed via the root pyproject.toml's pin). Subshell so
-    # the cwd change does not leak to other `_install_<name>` functions.
-    if (cd "$REPO_ROOT" && uv run playwright install --with-deps chromium); then
-        touch "$marker"
-        _log "playwright: install complete, marker written to $marker"
-    else
-        _log "playwright: install FAILED; marker not written so the next boot retries"
+    _log "fortress: installing apt system libs"
+    if ! (cd "$REPO_ROOT" && uv run playwright install-deps chromium); then
+        _log "fortress: apt install FAILED; marker not written so the next boot retries"
+        return 1
+    fi
+
+    local url sha256
+    case "$(uname -m)" in
+        x86_64) url="$_FORTRESS_X64_URL"; sha256="$_FORTRESS_X64_SHA256" ;;
+        aarch64) url="$_FORTRESS_ARM64_URL"; sha256="$_FORTRESS_ARM64_SHA256" ;;
+        *) _log "fortress: unsupported architecture $(uname -m)"; return 1 ;;
+    esac
+    _log "fortress: downloading $url"
+    local tmp_dir
+    tmp_dir="$(mktemp -d)"
+    # shellcheck disable=SC2064
+    trap "rm -rf '$tmp_dir'" RETURN
+    local asset="$tmp_dir/fortress.tar.gz"
+    if ! curl -fsSL -o "$asset" "$url"; then
+        _log "fortress: download FAILED; marker not written so the next boot retries"
+        return 1
+    fi
+    if [ "$(sha256sum "$asset" | awk '{print $1}')" != "$sha256" ]; then
+        _log "fortress: SHA256 mismatch -- refusing to install"
+        return 1
+    fi
+    rm -rf "$_FORTRESS_INSTALL_DIR"
+    mkdir -p "$_FORTRESS_INSTALL_DIR"
+    if ! tar xzf "$asset" -C "$_FORTRESS_INSTALL_DIR"; then
+        _log "fortress: extract FAILED; marker not written so the next boot retries"
         return 1
     fi
+    chmod +x "$_FORTRESS_INSTALL_DIR/tilion-fortress/tilion"
+    touch "$marker"
+    _log "fortress: install complete (${_FORTRESS_INSTALL_DIR}/tilion-fortress/tilion), marker written to $marker"
 }
 
 main() {
     mkdir -p "$MARKER_DIR"
     local rc=0
-    _install_playwright || rc=$?
+    _install_fortress || rc=$?
     if [ "$rc" -eq 0 ]; then
         _log "all deferred installs complete"
     else