fix: unbreak upgrade path + install-lock race

Three interlocking issues that made 26.11/26.12 effectively
un-upgradable from pre-auth versions without manual pacman +
symlink surgery. Caught while SSH-testing the .196 VM which landed
on a rollback loop after every Update-now click.

1. auth.py imported werkzeug.security, but the target system runs
   core as bare system Python — neither flask nor werkzeug are
   pip-installed. Fresh 26.11+ boxes died on import. Replaced with
   a 50-line stdlib `furtka/passwd.py` using hashlib.pbkdf2_hmac
   for new hashes and parsing werkzeug's `scrypt:N:r:p$salt$hex`
   format for backward-read so existing users.json survives.

2. updater._health_check pinged /api/apps expecting 200. Post-
   auth, /api/apps returns 401 for unauth requests → HTTPError
   caught as URLError → retry loop → 30s timeout → rollback. Now
   any 2xx-4xx counts as "server alive"; only 5xx / connection
   errors fail. Server responding at all is proof it came back up.

3. _do_install released the fcntl lock between sync pre-validation
   and the systemd-run dispatch. A second POST could slip in,
   pass the lock check, return 202, and leave its install-bg child
   to die silently on the in-child lock. Now the API also reads
   install-state.json and refuses 409 on non-terminal stages —
   the state file is the reliable signal, the fcntl lock is
   defence in depth.

Test coverage:
- tests/test_passwd.py (new, 6 cases): roundtrip, salt uniqueness,
  format shape, werkzeug scrypt backward-compat against a real
  hash captured from the .196 box, malformed + non-string
  rejection.
- tests/test_updater.py: +3 cases for _health_check — 4xx=healthy,
  5xx=unhealthy, URLError retry loop.
- tests/test_api.py: +2 cases for install 409 on non-terminal
  state + 202 after terminal.

All 267 tests green, ruff check + format clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,42 @@ This project uses calendar versioning: `YY.N-stage` (e.g. `26.0-alpha` = 2026, r
 
 ## [Unreleased]
 
+## [26.13-alpha] - 2026-04-21
+
+### Fixed
+
+- **Upgrade path from pre-auth releases actually works.** 26.11-alpha
+  introduced `from werkzeug.security import ...` in `furtka/auth.py`,
+  but werkzeug isn't installed on the target system — core runs as
+  system Python with stdlib only, and `flask>=3.0` in `pyproject.toml`
+  is never pip-installed on the box. Fresh boxes from the 26.11/26.12
+  ISO without a manually-installed werkzeug crashed on import; boxes
+  upgrading from pre-26.11 got double-broken by that plus the health
+  check below. Replaced the werkzeug dependency with a stdlib-only
+  `furtka/passwd.py` that uses `hashlib.pbkdf2_hmac` for new hashes
+  and parses werkzeug's `scrypt:N:r:p$salt$hex` format for backward
+  compatibility — existing `users.json` files created on the rare
+  boxes that did have werkzeug keep working after this upgrade, no
+  re-setup needed. `from werkzeug.security import ...` is gone from
+  the import chain entirely; `pyproject.toml`'s flask dep stays only
+  for the live-ISO webinstaller.
+- **Self-update no longer auto-rolls-back when crossing the auth
+  boundary.** `updater._health_check` pinged `/api/apps` and demanded
+  a 200, which meant every 26.10 → 26.11+ upgrade hit the post-restart
+  check, got a 401 (auth guard), and treated that as "server dead"
+  → rollback. Now any 2xx–4xx response counts as "server alive"; only
+  connection-level failures or 5xx fail the check. 5xx still fails
+  rollback because that means the new process is up but broken.
+- **Install lock closes its race window.** `POST /api/apps/install`
+  used to release the fcntl lock immediately after the sync
+  pre-validation so the systemd-run child could re-acquire it —
+  leaving a tiny gap where a second POST could slip in, pass the lock
+  check, and return 202. Both child processes would start, one would
+  win the in-child lock, the other would die silently. Now the API
+  also reads `install-state.json` and refuses with 409 if the stage
+  is non-terminal (`pulling_image`, `creating_volumes`,
+  `starting_container`). The fcntl lock stays as belt-and-suspenders.
+
 ## [26.12-alpha] - 2026-04-21
 
 ### Changed
@@ -243,7 +279,8 @@ First tagged snapshot. Pre-alpha — the installer does not yet boot, but the de
 - **Containers:** Docker + Compose
 - **License:** AGPL-3.0
 
-[Unreleased]: https://forgejo.sourcegate.online/daniel/furtka/compare/26.12-alpha...HEAD
+[Unreleased]: https://forgejo.sourcegate.online/daniel/furtka/compare/26.13-alpha...HEAD
+[26.13-alpha]: https://forgejo.sourcegate.online/daniel/furtka/releases/tag/26.13-alpha
 [26.12-alpha]: https://forgejo.sourcegate.online/daniel/furtka/releases/tag/26.12-alpha
 [26.11-alpha]: https://forgejo.sourcegate.online/daniel/furtka/releases/tag/26.11-alpha
 [26.10-alpha]: https://forgejo.sourcegate.online/daniel/furtka/releases/tag/26.10-alpha

furtka/api.py

@@ -692,6 +692,9 @@ def _do_get_settings(name):
     }
 
 
+_INSTALL_TERMINAL_STAGES = frozenset({"done", "error"})
+
+
 def _do_install(name, settings=None):
     """Kick off an app install. Synchronous sync-phase + async docker-phase.
 
@@ -703,6 +706,22 @@ def _do_install(name, settings=None):
     """
     import subprocess
 
+    # Reject if the state file reports a non-terminal install. The
+    # fcntl lock below catches the same race, but only *after* the API
+    # releases it to let the systemd-run child grab it — a competing
+    # POST can sneak in during that tiny window. Reading the state
+    # first closes that gap: as long as a previous install hasn't
+    # written "done" or "error", we refuse.
+    current_state = install_runner.read_state()
+    current_stage = current_state.get("stage", "") if isinstance(current_state, dict) else ""
+    if current_stage and current_stage not in _INSTALL_TERMINAL_STAGES:
+        return 409, {
+            "error": (
+                f"another install is in progress ({current_state.get('app', '?')}"
+                f" at {current_stage})"
+            )
+        }
+
     # Fast-fail if another install is already in flight. Lock lives under
     # /run/ so a previous reboot clears it automatically.
     try:

furtka/auth.py

@@ -1,15 +1,20 @@
 """Login-guard primitives for the Furtka UI.
 
-One admin, one password. Passwords are PBKDF2-hashed via werkzeug (already
+One admin, one password. Passwords are PBKDF2-SHA256 hashed via
-pulled in by the flask runtime dep), stored in /var/lib/furtka/users.json
+``furtka.passwd`` (stdlib-only — hashlib.pbkdf2_hmac / hashlib.scrypt),
-with mode 0600. Sessions live in memory — a systemctl restart logs
+stored in /var/lib/furtka/users.json with mode 0600. Sessions live in
-everyone out again, which is fine for an alpha single-user box.
+memory — a systemctl restart logs everyone out again, which is fine
+for an alpha single-user box.
 
-On upgrade from 26.10-alpha the users.json file does not exist yet; the
+On upgrade from pre-auth Furtka the users.json file does not exist
-api's GET /login detects this via `setup_needed()` and renders a first-
+yet; the api's GET /login detects this via ``setup_needed()`` and
-run form that POSTs to /login as if it were a setup submit. Fresh installs
+renders a first-run form that POSTs to /login as if it were a setup
-get the file pre-populated by the webinstaller so the setup step is
+submit. Fresh installs get the file pre-populated by the webinstaller
-skipped.
+so the setup step is skipped.
+
+Hash format is compatible with werkzeug.security — 26.11 / 26.12 boxes
+that happened to have werkzeug installed can carry their users.json
+forward without re-setup; see ``furtka.passwd`` for the scrypt reader.
 """
 
 from __future__ import annotations
@@ -20,8 +25,8 @@ import threading
 from dataclasses import dataclass
 from datetime import UTC, datetime, timedelta
 
-from werkzeug.security import check_password_hash, generate_password_hash
+from furtka.passwd import hash_password as _hash_password
-
+from furtka.passwd import verify_password as _verify_password
 from furtka.paths import users_file
 
 COOKIE_NAME = "furtka_session"
@@ -29,13 +34,13 @@ COOKIE_TTL_SECONDS = 7 * 24 * 3600  # one week
 
 
 def hash_password(plain: str) -> str:
-    """PBKDF2-SHA256 via werkzeug. Cost default (~600k iterations)."""
+    """PBKDF2-SHA256 via stdlib. 600k iterations (OWASP 2023)."""
-    return generate_password_hash(plain)
+    return _hash_password(plain)
 
 
 def verify_password(plain: str, hashed: str) -> bool:
-    # werkzeug's check_password_hash is constant-time.
+    """Constant-time compare. Accepts stdlib + legacy werkzeug formats."""
-    return check_password_hash(hashed, plain)
+    return _verify_password(plain, hashed)
 
 
 def load_users() -> dict:

furtka/passwd.py

@@ -0,0 +1,95 @@
+"""Stdlib-only password hashing, compatible with werkzeug's hash format.
+
+Why this exists: 26.11-alpha introduced auth via ``werkzeug.security``,
+but the target system doesn't have ``werkzeug`` installed (Core runs as
+system Python with only the stdlib — pyproject.toml's ``flask>=3.0``
+dep is never pip-installed on the box). Fresh installs from a 26.11 /
+26.12 ISO crashed on import; upgrades from pre-auth versions were
+double-broken by that plus a too-strict updater health check.
+
+Fix: replace werkzeug with stdlib equivalents using the same hash
+**format** so existing ``users.json`` files created by 26.11 / 26.12 on
+the rare boxes that happened to have werkzeug installed (Medion, .196
+after manual pacman) still verify.
+
+Format: ``<method>$<salt>$<hex digest>``
+  - ``pbkdf2:<hash>:<iterations>`` — what we generate by default here
+  - ``scrypt:<N>:<r>:<p>``          — what werkzeug's default produces
+Both are implemented via ``hashlib`` which has been stdlib since 3.6.
+"""
+
+from __future__ import annotations
+
+import hashlib
+import hmac
+import secrets
+
+_PBKDF2_HASH = "sha256"
+_PBKDF2_ITERATIONS = 600_000
+_SALT_LEN = 16
+
+
+def hash_password(password: str) -> str:
+    """Return a ``pbkdf2:sha256:<iter>$<salt>$<hex>`` hash of *password*.
+
+    PBKDF2-SHA256 over UTF-8. 600k iterations — same as werkzeug's
+    default in the 3.x series, roughly OWASP 2023's recommendation.
+    """
+    if not isinstance(password, str):
+        raise TypeError("password must be str")
+    salt = secrets.token_urlsafe(_SALT_LEN)[:_SALT_LEN]
+    dk = hashlib.pbkdf2_hmac(
+        _PBKDF2_HASH, password.encode("utf-8"), salt.encode("utf-8"), _PBKDF2_ITERATIONS
+    )
+    return f"pbkdf2:{_PBKDF2_HASH}:{_PBKDF2_ITERATIONS}${salt}${dk.hex()}"
+
+
+def verify_password(password: str, hashed: str) -> bool:
+    """Constant-time verify *password* against a stored *hashed* value.
+
+    Accepts both our own pbkdf2 hashes and legacy werkzeug scrypt
+    hashes in ``scrypt:N:r:p$salt$hex`` form — so users.json files
+    written by 26.11 / 26.12 keep working after upgrade.
+    """
+    if not isinstance(password, str) or not isinstance(hashed, str):
+        return False
+    try:
+        method, salt, expected = hashed.split("$", 2)
+    except ValueError:
+        return False
+    parts = method.split(":")
+    if not parts:
+        return False
+    algo = parts[0]
+    pw_bytes = password.encode("utf-8")
+    salt_bytes = salt.encode("utf-8")
+    try:
+        if algo == "pbkdf2":
+            if len(parts) < 3:
+                return False
+            inner_hash = parts[1]
+            iterations = int(parts[2])
+            dk = hashlib.pbkdf2_hmac(inner_hash, pw_bytes, salt_bytes, iterations)
+        elif algo == "scrypt":
+            # werkzeug: scrypt:N:r:p, dklen=64, maxmem=132 MiB. Without
+            # the explicit maxmem we'd hit OpenSSL's default memory cap
+            # and throw ValueError on N >= 32768.
+            if len(parts) < 4:
+                return False
+            n = int(parts[1])
+            r = int(parts[2])
+            p = int(parts[3])
+            dk = hashlib.scrypt(
+                pw_bytes,
+                salt=salt_bytes,
+                n=n,
+                r=r,
+                p=p,
+                dklen=64,
+                maxmem=132 * 1024 * 1024,
+            )
+        else:
+            return False
+    except (ValueError, TypeError, OverflowError):
+        return False
+    return hmac.compare_digest(dk.hex(), expected)

furtka/updater.py

@@ -255,13 +255,35 @@ def _run(cmd: list[str]) -> None:
 
 
 def _health_check(url: str, deadline_s: float = 30.0) -> bool:
+    """Poll *url* until we get *any* response from the Python server.
+
+    Treats any 2xx-4xx response as "server is up". A 401 on
+    /api/apps after the 26.11-alpha auth-guard shipped is a perfectly
+    valid signal that the new code imported + the socket is listening
+    — rejecting the request is still "alive". Only 5xx or connection-
+    level failures count as unhealthy.
+
+    Rationale: pre-26.13 this function hit /api/apps and expected 200,
+    which silently broke every upgrade across the auth boundary (26.10
+    → 26.11+) and auto-rolled back. Now we just need proof the new
+    process came up.
+    """
     end = time.time() + deadline_s
     while time.time() < end:
         try:
             with urllib.request.urlopen(url, timeout=3) as resp:
-                if resp.status == 200:
+                # Any 2xx/3xx → alive. urllib follows redirects by
+                # default, so a 302 → /login resolves to /login's 200.
+                if resp.status < 500:
                     return True
+        except urllib.error.HTTPError as e:
+            # 4xx → server is up, just refused us (auth, bad request,
+            # whatever). Counts as healthy for the "did it come back"
+            # check. 5xx → genuinely broken, don't accept.
+            if 400 <= e.code < 500:
+                return True
         except urllib.error.URLError:
+            # Connection refused / DNS / timeout → not up yet, retry.
             pass
         time.sleep(1)
     return False

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "furtka"
-version = "26.12-alpha"
+version = "26.13-alpha"
 description = "Open-source home server OS — simple enough for everyone."
 requires-python = ">=3.11"
 readme = "README.md"

tests/test_api.py

@@ -949,6 +949,36 @@ def test_do_install_returns_409_when_locked(fake_dirs, no_docker, no_systemd_run
         fh.close()
 
 
+def test_do_install_returns_409_when_state_reports_running(fake_dirs, no_docker, no_systemd_run):
+    """Closes the race window where _do_install had already released
+    the fcntl lock (so the systemd-run child could grab it) but a
+    second POST tried to start a new install while the first was still
+    mid-flight. The state file's non-terminal stage is the reliable
+    "someone else is installing" signal."""
+    _, bundled = fake_dirs
+    _write_bundled(bundled, "fileshare", env_example="A=real")
+    api.install_runner.write_state("pulling_image", app="jellyfin")
+    status, body = api._do_install("fileshare")
+    assert status == 409
+    assert "in progress" in body["error"]
+    assert "jellyfin" in body["error"]
+    assert "pulling_image" in body["error"]
+
+
+def test_do_install_goes_through_after_terminal_state(fake_dirs, no_docker, no_systemd_run):
+    """After a successful or failed install, the state file stays at
+    done/error — a new install must be accepted, not blocked."""
+    _, bundled = fake_dirs
+    _write_bundled(bundled, "fileshare", env_example="A=real")
+    api.install_runner.write_state("done", app="previous", version="1.0.0")
+    status, _ = api._do_install("fileshare")
+    assert status == 202
+
+    api.install_runner.write_state("error", app="previous", error="oops")
+    status, _ = api._do_install("fileshare")
+    assert status == 202
+
+
 def test_do_install_status_returns_state(fake_dirs):
     # Write state directly, then GET it via the status handler.
     api.install_runner.write_state("pulling_image", app="jellyfin")

tests/test_passwd.py

@@ -0,0 +1,74 @@
+"""Tests for furtka.passwd — stdlib-only password hashing.
+
+The primary contract: hash/verify roundtrips cleanly, AND the verifier
+accepts the werkzeug hash format that 26.11 / 26.12 boxes wrote to
+``users.json``. Losing that backward compat would lock out existing
+admins after a 26.13+ upgrade.
+"""
+
+from __future__ import annotations
+
+from furtka import passwd
+
+
+def test_hash_roundtrip():
+    h = passwd.hash_password("hunter2")
+    assert passwd.verify_password("hunter2", h)
+    assert not passwd.verify_password("wrong", h)
+
+
+def test_hash_is_salted():
+    # Two separate hashes of the same password must diverge.
+    a = passwd.hash_password("same-pw")
+    b = passwd.hash_password("same-pw")
+    assert a != b
+    assert passwd.verify_password("same-pw", a)
+    assert passwd.verify_password("same-pw", b)
+
+
+def test_generated_hash_format():
+    # Shape is pbkdf2:<hash>:<iter>$<salt>$<hex>
+    h = passwd.hash_password("x")
+    parts = h.split("$", 2)
+    assert len(parts) == 3
+    method, salt, digest = parts
+    assert method.startswith("pbkdf2:sha256:")
+    assert salt
+    # digest is hex of pbkdf2_hmac sha256 → 64 hex chars
+    assert len(digest) == 64
+    assert all(c in "0123456789abcdef" for c in digest)
+
+
+def test_verify_werkzeug_scrypt_hash():
+    """Known werkzeug scrypt hash generated by 26.11 / 26.12 boxes.
+
+    Captured live off a .196 test VM after its auth bootstrap:
+        username=daniel, password=test-admin-pw1
+    Hash format: scrypt:32768:8:1$<salt>$<hex>
+    If this regresses, every existing box that upgraded via 26.11 and
+    set a password gets locked out on the next upgrade.
+    """
+    known = (
+        "scrypt:32768:8:1$yWZUqJodowt9ieI1$"
+        "2d1059b3564da7492b4aa3c2be7fff6fef06085e5e1bfd52e897948c58246b7a"
+        "9603400355b7264f61c4436eba7bf8c947adec3d7a76be03b50efb4227e15a80"
+    )
+    assert passwd.verify_password("test-admin-pw1", known)
+    assert not passwd.verify_password("wrong-password", known)
+
+
+def test_verify_rejects_malformed_hashes():
+    # Empty / missing delimiters / unknown method / bad int — all False.
+    assert not passwd.verify_password("x", "")
+    assert not passwd.verify_password("x", "nothingspecial")
+    assert not passwd.verify_password("x", "pbkdf2:sha256:600000")  # no $salt$digest
+    assert not passwd.verify_password("x", "pbkdf2$salt$digest")  # missing hash + iter
+    assert not passwd.verify_password("x", "bcrypt:12$salt$digest")  # unsupported algo
+    assert not passwd.verify_password("x", "pbkdf2:sha256:abc$salt$digest")  # bad iter int
+
+
+def test_verify_rejects_nonstring_inputs():
+    # Defensive: users.json can be corrupted or have nulls.
+    assert not passwd.verify_password(None, "pbkdf2:sha256:1000$salt$digest")  # type: ignore[arg-type]
+    assert not passwd.verify_password("x", None)  # type: ignore[arg-type]
+    assert not passwd.verify_password("x", 12345)  # type: ignore[arg-type]

tests/test_updater.py

@@ -224,6 +224,76 @@ def test_refresh_caddyfile_substitutes_hostname_placeholder(updater, tmp_path):
     assert updater._refresh_caddyfile(src) is False
 
 
+def test_health_check_treats_4xx_as_healthy(updater, monkeypatch):
+    """26.11+ auth makes /api/apps return 401 on unauth requests. If the
+    health check treated that as "down", every pre-auth → auth upgrade
+    auto-rolls back. Server responding at all is enough signal for the
+    health check."""
+    import urllib.error
+
+    calls = {"n": 0}
+
+    class _FakeResp:
+        def __init__(self, code):
+            self.status = code
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, *a):
+            return False
+
+    def raising_401(url, timeout):
+        calls["n"] += 1
+        raise urllib.error.HTTPError(url, 401, "Unauthorized", {}, None)
+
+    monkeypatch.setattr("urllib.request.urlopen", raising_401)
+    assert updater._health_check("http://127.0.0.1:7000/api/apps", deadline_s=2.0) is True
+    # One call was enough — early exit on 4xx, no retry loop.
+    assert calls["n"] == 1
+
+
+def test_health_check_rejects_5xx(updater, monkeypatch):
+    """500s mean the server is up but broken — that's NOT healthy.
+    Distinguishes auth refusals (4xx = healthy) from real runtime
+    errors (5xx = unhealthy, roll back)."""
+    import urllib.error
+
+    def raising_500(url, timeout):
+        raise urllib.error.HTTPError(url, 500, "Internal Server Error", {}, None)
+
+    monkeypatch.setattr("urllib.request.urlopen", raising_500)
+    assert updater._health_check("http://127.0.0.1:7000/api/apps", deadline_s=1.5) is False
+
+
+def test_health_check_retries_on_connection_refused(updater, monkeypatch):
+    """While furtka-api is still starting, urlopen raises URLError.
+    The loop must keep polling until the server comes up or deadline."""
+    import urllib.error
+
+    calls = {"n": 0}
+
+    def flaky(url, timeout):
+        calls["n"] += 1
+        if calls["n"] < 3:
+            raise urllib.error.URLError("connection refused")
+
+        class _Resp:
+            status = 200
+
+            def __enter__(self):
+                return self
+
+            def __exit__(self, *a):
+                return False
+
+        return _Resp()
+
+    monkeypatch.setattr("urllib.request.urlopen", flaky)
+    assert updater._health_check("http://127.0.0.1:7000/api/apps", deadline_s=10.0) is True
+    assert calls["n"] == 3
+
+
 def test_current_hostname_falls_back_when_file_missing(updater, monkeypatch, tmp_path):
     monkeypatch.setenv("FURTKA_HOSTNAME_FILE", str(tmp_path / "missing"))
     import importlib