diff --git a/backend/src/analytics_agent/quickstart.py b/backend/src/analytics_agent/quickstart.py
index 7cdac9c..c6a74e5 100644
--- a/backend/src/analytics_agent/quickstart.py
+++ b/backend/src/analytics_agent/quickstart.py
@@ -309,6 +309,31 @@ def _check_prereqs(port: int) -> None:
     click.echo(f"  ✓ Port {port} available")
 
 
+def _is_stale_demo_db_failure(db_url: str, stderr: str) -> bool:
+    """True when bootstrap failed because the demo-written MySQL DATABASE_URL is unreachable."""
+    # Matches the URL written by _write_demo_config() on both Mac (host.docker.internal)
+    # and Linux (172.17.0.1). The literal datahub:datahub@…/talkster combo is
+    # demo-specific, so a match means we can safely strip the var.
+    if "mysql+aiomysql://datahub:datahub@" not in db_url or "/talkster" not in db_url:
+        return False
+    return "Can't connect" in stderr or "nodename nor servname" in stderr
+
+
+def _strip_env_vars(env_path: Path, keys: set[str]) -> None:
+    """Remove KEY=VALUE lines for the given keys from a .env file."""
+    if not env_path.exists():
+        return
+    kept: list[str] = []
+    for line in env_path.read_text().splitlines():
+        stripped = line.strip()
+        if stripped and not stripped.startswith("#") and "=" in stripped:
+            k, _, _ = stripped.partition("=")
+            if k.strip() in keys:
+                continue
+        kept.append(line)
+    env_path.write_text("\n".join(kept) + ("\n" if kept else ""))
+
+
 def _bootstrap_and_launch(config_dir: Path, port: int, *, open_setup: bool = False) -> None:
     """Run bootstrap (migrations + seeds) then start the server."""
     import subprocess as _sp
@@ -331,6 +356,22 @@ def _bootstrap_and_launch(config_dir: Path, port: int, *, open_setup: bool = Fal
         capture_output=True,
         text=True,
     )
+    if result.returncode != 0 and _is_stale_demo_db_failure(
+        env.get("DATABASE_URL", ""), result.stderr
+    ):
+        click.echo(
+            "  ! Stale demo DATABASE_URL detected (MySQL unreachable). "
+            "Clearing it and falling back to the default SQLite database…",
+            err=True,
+        )
+        _strip_env_vars(env_path, {"DATABASE_URL"})
+        env.pop("DATABASE_URL", None)
+        result = _sp.run(
+            [sys.executable, "-m", "analytics_agent.cli", "bootstrap"],
+            env=env,
+            capture_output=True,
+            text=True,
+        )
     if result.returncode != 0:
         click.echo(result.stderr, err=True)
         sys.exit(result.returncode)
diff --git a/tests/unit/test_quickstart_stale_demo.py b/tests/unit/test_quickstart_stale_demo.py
new file mode 100644
index 0000000..4f27966
--- /dev/null
+++ b/tests/unit/test_quickstart_stale_demo.py
@@ -0,0 +1,86 @@
+"""
+Tests for self-healing recovery when `quickstart` runs against a stale demo
+DATABASE_URL left in ~/.datahub/analytics-agent/.env by a previous `demo` run.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from analytics_agent.quickstart import _is_stale_demo_db_failure, _strip_env_vars
+
+# ── _is_stale_demo_db_failure ────────────────────────────────────────────────
+
+_DEMO_URL_MAC = "mysql+aiomysql://datahub:datahub@host.docker.internal:3306/talkster"
+_DEMO_URL_LINUX = "mysql+aiomysql://datahub:datahub@172.17.0.1:3306/talkster"
+_CONNECT_ERR_MAC = "OperationalError: (pymysql.err.OperationalError) (2003, \"Can't connect to MySQL server on 'host.docker.internal'\")"
+_CONNECT_ERR_DNS = "socket.gaierror: [Errno 8] nodename nor servname provided, or not known"
+
+
+@pytest.mark.parametrize("url", [_DEMO_URL_MAC, _DEMO_URL_LINUX])
+def test_stale_demo_detected_on_mac_and_linux(url):
+    assert _is_stale_demo_db_failure(url, _CONNECT_ERR_MAC)
+    assert _is_stale_demo_db_failure(url, _CONNECT_ERR_DNS)
+
+
+def test_non_demo_mysql_not_treated_as_stale():
+    """A user-supplied MySQL URL must NOT trigger auto-cleanup, even on connect failure."""
+    user_url = "mysql+aiomysql://prod_user:secret@my-db.example.com:3306/analytics"
+    assert not _is_stale_demo_db_failure(user_url, _CONNECT_ERR_MAC)
+
+
+def test_demo_url_but_unrelated_stderr():
+    """Random stderr (e.g. migration syntax error) must not falsely trigger recovery."""
+    assert not _is_stale_demo_db_failure(
+        _DEMO_URL_MAC, "alembic.util.exc.CommandError: Can't locate revision"
+    )
+
+
+def test_empty_db_url():
+    assert not _is_stale_demo_db_failure("", _CONNECT_ERR_MAC)
+
+
+def test_sqlite_url_is_not_stale():
+    assert not _is_stale_demo_db_failure("sqlite+aiosqlite:///x.db", _CONNECT_ERR_MAC)
+
+
+# ── _strip_env_vars ──────────────────────────────────────────────────────────
+
+
+def test_strip_env_vars_removes_only_named_keys(tmp_path: Path):
+    env_file = tmp_path / ".env"
+    env_file.write_text(
+        "ANTHROPIC_API_KEY=sk-ant-xxx\n"
+        "DATABASE_URL=mysql+aiomysql://datahub:datahub@host.docker.internal:3306/talkster\n"
+        "# A comment line\n"
+        "DATAHUB_GMS_URL=http://localhost:8080\n"
+        "\n"
+        "LLM_PROVIDER=anthropic\n"
+    )
+    _strip_env_vars(env_file, {"DATABASE_URL"})
+    remaining = env_file.read_text()
+    assert "DATABASE_URL" not in remaining
+    assert "ANTHROPIC_API_KEY=sk-ant-xxx" in remaining
+    assert "DATAHUB_GMS_URL=http://localhost:8080" in remaining
+    assert "# A comment line" in remaining
+    assert "LLM_PROVIDER=anthropic" in remaining
+
+
+def test_strip_env_vars_multiple_keys(tmp_path: Path):
+    env_file = tmp_path / ".env"
+    env_file.write_text("A=1\nB=2\nC=3\n")
+    _strip_env_vars(env_file, {"A", "C"})
+    assert env_file.read_text() == "B=2\n"
+
+
+def test_strip_env_vars_missing_file_is_noop(tmp_path: Path):
+    """Should not raise when the file doesn't exist."""
+    _strip_env_vars(tmp_path / "nonexistent.env", {"X"})
+
+
+def test_strip_env_vars_key_not_present(tmp_path: Path):
+    env_file = tmp_path / ".env"
+    env_file.write_text("A=1\nB=2\n")
+    _strip_env_vars(env_file, {"DOES_NOT_EXIST"})
+    assert env_file.read_text() == "A=1\nB=2\n"