diff --git a/README.md b/README.md
index 3419597..610987e 100644
--- a/README.md
+++ b/README.md
@@ -153,6 +153,7 @@ The repository now includes the files needed to host the app on Vercel productio
 | `DJANGO_SECRET_KEY` | Required | Required | Use a unique secret per environment. Hosted builds fail fast until this is set. |
 | `DATABASE_URL` | Required | Required | Point previews at an isolated PostgreSQL database or branch database, not production. |
 | `APP_BASE_URL` | `https://deep-workflow.vercel.app` | Optional | Sets the canonical production URL and anchors the production host/origin configuration. |
+| `DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK` | Emergency only | Emergency only | Leave unset for normal deploys. Set to `1` only when intentionally activating the temporary hosted SQLite recovery mode. |
 | `DJANGO_SECURE_HSTS_PRELOAD` | Optional | Optional | Leave unset unless you intentionally want preload and already satisfy the preload requirements (`includeSubDomains` plus at least `31536000` seconds). |
 | `VERCEL_RUN_MIGRATIONS` | Set to `1` only for deliberate schema rollouts | Set to `1` only for isolated preview databases | Build-time migrations are always opt-in. |
 
@@ -181,6 +182,12 @@ Vercel injects `VERCEL_ENV`, `VERCEL_URL`, `VERCEL_BRANCH_URL`, and `VERCEL_PROJ
 4. Let pushes to non-`main` branches create Preview deployments automatically. Leave `VERCEL_RUN_MIGRATIONS` unset for normal deploys; only turn it on for isolated preview databases or a coordinated production schema rollout, then redeploy intentionally.
 5. After each deployment, check `GET /health/ready/` for database readiness and `GET /health/live/` for the lightweight liveness probe.
 
+#### Emergency hosted SQLite recovery
+
+Normal hosted deploys should continue to fail fast if `DATABASE_URL` is missing or broken. If you need a temporary outage recovery mode, you can opt into the hosted SQLite fallback by setting `DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK=1` alongside a SQLite `DATABASE_URL`.
+
+This mode is for emergency recovery only. It moves sessions and flash messages to signed cookies so the app can run from a bundled SQLite snapshot on Vercel, but it should not replace the normal PostgreSQL-backed production path. Only use it when your session and message payloads are small enough to fit within browser cookie limits, and do not treat the cookie contents as secret: signed cookies are tamper-resistant, but their contents remain readable by the client.
+
 ### Health checks and monitoring hooks
 
 - `GET /health/live/` is a cheap liveness probe that does not touch the database.
diff --git a/core/tests/test_deployment.py b/core/tests/test_deployment.py
index b3d5768..bc5d2e1 100644
--- a/core/tests/test_deployment.py
+++ b/core/tests/test_deployment.py
@@ -1,3 +1,8 @@
+import json
+import os
+import subprocess
+import sys
+
 from django.conf import settings
 
 from deep_workflow.deployment import (
@@ -11,6 +16,23 @@
     hsts_preload_enabled,
 )
 
+IMPORT_HOSTED_SETTINGS_COMMAND = (
+    "import environ; "
+    "environ.Env.read_env = staticmethod(lambda *args, **kwargs: None); "
+    "import deep_workflow.settings as settings; "
+    "from django.conf import settings as django_settings; "
+    "print(json.dumps(["
+    "settings.HOSTED_SQLITE_FALLBACK, "
+    "django_settings.SESSION_ENGINE, "
+    "django_settings.MESSAGE_STORAGE"
+    "]))"
+)
+IMPORT_HOSTED_SETTINGS_SNIPPET = (
+    "import environ; "
+    "environ.Env.read_env = staticmethod(lambda *args, **kwargs: None); "
+    "import deep_workflow.settings"
+)
+
 
 def test_build_allowed_hosts_adds_vercel_runtime_hosts() -> None:
     environ = {
@@ -117,3 +139,180 @@ def test_request_id_middleware_precedes_whitenoise() -> None:
     ) < settings.MIDDLEWARE.index(
         "whitenoise.middleware.WhiteNoiseMiddleware",
     )
+
+
+def load_hosted_settings(
+    *,
+    enable_fallback: bool | None,
+    database_url: str | None = "sqlite:///db.sqlite3",
+) -> tuple[bool, str, str]:
+    env = os.environ.copy()
+    env.update(
+        {
+            "DJANGO_DEBUG": "False",
+            "DJANGO_SETTINGS_MODULE": "deep_workflow.settings",
+            "DJANGO_SECRET_KEY": "x" * 64,
+            "VERCEL_ENV": "production",
+            "VERCEL": "1",
+        }
+    )
+    if database_url is None:
+        env.pop("DATABASE_URL", None)
+    else:
+        env["DATABASE_URL"] = database_url
+    if enable_fallback is None:
+        env.pop("DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK", None)
+    else:
+        env["DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK"] = "1" if enable_fallback else "0"
+    command = [
+        sys.executable,
+        "-c",
+        f"import json; {IMPORT_HOSTED_SETTINGS_COMMAND}",
+    ]
+    result = subprocess.run(
+        command,
+        env=env,
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+    return tuple(json.loads(result.stdout))
+
+
+def run_hosted_settings_import(
+    *,
+    database_url: str | None,
+    enable_fallback: bool | None,
+) -> subprocess.CompletedProcess[str]:
+    env = os.environ.copy()
+    env.update(
+        {
+            "DJANGO_DEBUG": "False",
+            "DJANGO_SECRET_KEY": "x" * 64,
+            "VERCEL_ENV": "production",
+            "VERCEL": "1",
+        }
+    )
+    if database_url is None:
+        env.pop("DATABASE_URL", None)
+    else:
+        env["DATABASE_URL"] = database_url
+    if enable_fallback is None:
+        env.pop("DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK", None)
+    else:
+        env["DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK"] = "1" if enable_fallback else "0"
+    return subprocess.run(
+        [sys.executable, "-c", IMPORT_HOSTED_SETTINGS_SNIPPET],
+        env=env,
+        capture_output=True,
+        text=True,
+    )
+
+
+def test_hosted_sqlite_fallback_is_disabled_by_default_when_flag_is_zero() -> None:
+    result = run_hosted_settings_import(
+        database_url="sqlite:///db.sqlite3",
+        enable_fallback=False,
+    )
+    assert result.returncode != 0
+    assert "ImproperlyConfigured" in result.stderr
+    assert "Hosted deployments require one of these database configurations" in (
+        result.stderr
+    )
+    assert "DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK=1" in result.stderr
+
+
+def test_hosted_sqlite_fallback_is_disabled_by_default_when_flag_is_unset() -> None:
+    result = run_hosted_settings_import(
+        database_url="sqlite:///db.sqlite3",
+        enable_fallback=None,
+    )
+    assert result.returncode != 0
+    assert "ImproperlyConfigured" in result.stderr
+    assert "Hosted deployments require one of these database configurations" in (
+        result.stderr
+    )
+    assert "DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK=1" in result.stderr
+
+
+def test_hosted_sqlite_fallback_is_disabled_when_database_url_is_unset() -> None:
+    result = run_hosted_settings_import(
+        database_url=None,
+        enable_fallback=None,
+    )
+    assert result.returncode != 0
+    assert "ImproperlyConfigured" in result.stderr
+    assert "Hosted deployments require one of these database configurations" in (
+        result.stderr
+    )
+    assert "DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK=1" in result.stderr
+
+
+def test_hosted_sqlite_fallback_requires_explicit_opt_in() -> None:
+    hosted_settings = load_hosted_settings(enable_fallback=True)
+    hosted_sqlite_fallback, session_engine, message_storage = hosted_settings
+
+    assert hosted_sqlite_fallback is True
+    assert session_engine == "django.contrib.sessions.backends.signed_cookies"
+    assert message_storage == "django.contrib.messages.storage.cookie.CookieStorage"
+
+
+def test_hosted_sqlite_fallback_requires_explicit_database_url() -> None:
+    result = run_hosted_settings_import(
+        database_url=None,
+        enable_fallback=True,
+    )
+    assert result.returncode != 0
+    assert "ImproperlyConfigured" in result.stderr
+    assert "Hosted deployments require one of these database configurations" in (
+        result.stderr
+    )
+    assert "DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK=1" in result.stderr
+
+
+def test_hosted_sqlite_fallback_flag_ignored_for_postgresql() -> None:
+    hosted_sqlite_fallback, session_engine, message_storage = load_hosted_settings(
+        enable_fallback=True,
+        database_url="postgresql://testuser:testpass@localhost:5432/testdb",
+    )
+
+    assert hosted_sqlite_fallback is False
+    assert session_engine != "django.contrib.sessions.backends.signed_cookies"
+    assert message_storage != "django.contrib.messages.storage.cookie.CookieStorage"
+
+
+def test_hosted_sqlite_fallback_is_not_applied_to_invalid_database_url() -> None:
+    env = os.environ.copy()
+    env.update(
+        {
+            "DJANGO_DEBUG": "False",
+            "DJANGO_SECRET_KEY": "x" * 64,
+            "VERCEL_ENV": "production",
+            "VERCEL": "1",
+            "DATABASE_URL": "invalid://definitely-not-a-supported-database-url",
+            "DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK": "1",
+        }
+    )
+    result = subprocess.run(
+        [
+            sys.executable,
+            "-c",
+            (
+                "import environ; "
+                "environ.Env.read_env = staticmethod(lambda *args, **kwargs: None); "
+                "import deep_workflow.settings"
+            ),
+        ],
+        env=env,
+        capture_output=True,
+        text=True,
+    )
+
+    assert result.returncode != 0
+    assert "ImproperlyConfigured" in result.stderr
+    assert "Hosted deployments require one of these database configurations" in (
+        result.stderr
+    )
+    assert "DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK=1" in result.stderr
+    assert "django.contrib.sessions.backends.signed_cookies" not in result.stderr
+    assert "django.contrib.messages.storage.cookie.CookieStorage" not in result.stderr
diff --git a/deep_workflow/settings.py b/deep_workflow/settings.py
index ab95a21..c70ecf2 100644
--- a/deep_workflow/settings.py
+++ b/deep_workflow/settings.py
@@ -32,6 +32,7 @@
     DJANGO_DB_CONN_MAX_AGE=(int, 60),
     DJANGO_DB_SSL_MODE=(str, "require"),
     DJANGO_DEBUG=(bool, DEFAULT_DEBUG),
+    DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK=(bool, False),
     DJANGO_LOG_LEVEL=(str, "DEBUG" if DEFAULT_DEBUG else "INFO"),
     DJANGO_REQUEST_LOG_LEVEL=(str, "WARNING"),
     DJANGO_SECRET_KEY=(str, "unsafe-local-development-key"),
@@ -63,6 +64,13 @@
 if not DEBUG and SECRET_KEY == "unsafe-local-development-key":
     raise ImproperlyConfigured("Set DJANGO_SECRET_KEY before disabling DJANGO_DEBUG.")
 
+HOSTED_DATABASE_CONFIGURATION_ERROR = (
+    "Hosted deployments require one of these database configurations: "
+    "(1) a valid PostgreSQL DATABASE_URL; or "
+    "(2) for emergency recovery only, DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK=1 "
+    "together with an explicit SQLite DATABASE_URL."
+)
+
 INSTALLED_APPS = [
     "django.contrib.admin",
     "django.contrib.auth",
@@ -107,13 +115,36 @@
 WSGI_APPLICATION = "deep_workflow.wsgi.application"
 
 
-DATABASES = {
-    "default": env.db("DATABASE_URL", default=f"sqlite:///{BASE_DIR / 'db.sqlite3'}")
-}
+try:
+    default_database = env.db(
+        "DATABASE_URL",
+        default=f"sqlite:///{BASE_DIR / 'db.sqlite3'}",
+    )
+except ImproperlyConfigured as exc:
+    if HOSTED_ENV:
+        raise ImproperlyConfigured(HOSTED_DATABASE_CONFIGURATION_ERROR) from exc
+    raise
+
+DATABASES = {"default": default_database}
 DATABASES["default"]["CONN_MAX_AGE"] = env.int("DJANGO_DB_CONN_MAX_AGE", default=60)
 DATABASES["default"]["CONN_HEALTH_CHECKS"] = True
+raw_database_url = os.environ.get("DATABASE_URL", "").strip()
+database_engine = DATABASES["default"].get("ENGINE")
+HOSTED_SQLITE_FALLBACK = (
+    HOSTED_ENV
+    and env.bool("DJANGO_ENABLE_HOSTED_SQLITE_FALLBACK")
+    and bool(raw_database_url)
+    and database_engine == "django.db.backends.sqlite3"
+)
 
-if HOSTED_ENV and DATABASES["default"]["ENGINE"] == "django.db.backends.postgresql":
+if (
+    HOSTED_ENV
+    and database_engine != "django.db.backends.postgresql"
+    and not HOSTED_SQLITE_FALLBACK
+):
+    raise ImproperlyConfigured(HOSTED_DATABASE_CONFIGURATION_ERROR)
+
+if HOSTED_ENV and database_engine == "django.db.backends.postgresql":
     DATABASES["default"].setdefault("OPTIONS", {})
     DATABASES["default"]["OPTIONS"].setdefault(
         "sslmode",
@@ -211,6 +242,10 @@
 LOGIN_REDIRECT_URL = "home"
 LOGOUT_REDIRECT_URL = "login"
 
+if HOSTED_SQLITE_FALLBACK:
+    SESSION_ENGINE = "django.contrib.sessions.backends.signed_cookies"
+    MESSAGE_STORAGE = "django.contrib.messages.storage.cookie.CookieStorage"
+
 LOG_LEVEL = env("DJANGO_LOG_LEVEL").upper()
 REQUEST_LOG_LEVEL = env("DJANGO_REQUEST_LOG_LEVEL").upper()
 LOGGING = {