fix(store): read the core version from disk, not from a stale import (#518)

* fix(store): read the core version from disk, not from a stale import

Updating the core to 3.3.0 and then updating plugins refused all eight sports
scoreboards:

    Refusing to install nrl-scoreboard: NRL Scoreboard supports LEDMatrix
    >=3.3.0, but this system is running 3.2.0.

while src/__init__.py on that machine read 3.3.0. Observed on hardware, not
theorised.

The gate ran `from src import __version__ as core_version`, which binds
whatever the process loaded at start. The plugin store's gate lives in the web
UI, a long-lived service of its own, and the update route deliberately restarts
nothing -- it replaces files on disk and asks the user to restart. Its prompt
named only the *display* service, so a user who followed it left the web
process holding the previous number.

Stale by exactly one release is the case that bites: every plugin flooring on
the release you just installed is refused, blaming a core version that is
already correct on disk. It reads as a broken plugin store. 3.3.0 is the first
release where this hits a whole family at once, since all eight scoreboards
floor there.

compatibility.current_core_version() reads the version from the file instead,
falling back to the imported value on any failure -- so it can only ever be as
correct as before, never worse. All four gate call sites use it: three in
store_manager (install, the git-pull update path, install_from_url) and one in
plugin_loader's advisory warning.

The restart prompt now names both services.

Twelve tests, including the hardware failure itself: a process holding 3.2.0
while disk says 3.3.0 refuses hockey, and reading fresh allows it. The inverse
is asserted too -- a genuinely old core still refuses, so the gate has not
become permissive. One test greps both modules for the old import-bound read;
reintroducing that line fails it, which is what stops this coming back.

Not changed: web_interface/__init__.py also imports __version__, but for
display rather than gating, and the API endpoint already reports a fresh
git describe.

* fix: drop the unused os import

Left over from a first draft that joined paths by hand before this used
pathlib. Flagged by CodeRabbit on #518; confirmed dead -- no os. reference
remains in the module.

test/test_core_version_freshness.py

@@ -0,0 +1,122 @@
+"""The gate must read the core version from disk, not from its own import.
+
+`from src import __version__` binds whatever the process loaded at start. The
+web UI is a long-lived service of its own (ledmatrix-web.service), and updating
+the core replaces files on disk without restarting it -- the update route says
+so and asks the user to restart, but its prompt named only the *display*
+service, so a user who followed it left the web process holding the old number.
+
+The plugin store's gate lives in that web process, so being stale by exactly
+one release is the case that bites: every plugin flooring on the release you
+just installed is refused, with a message blaming a core version that is
+already correct on disk.
+
+Observed on hardware: after updating a rig to 3.3.0 and restarting only the
+display service, all eight sports scoreboards were refused with
+"supports LEDMatrix >=3.3.0, but this system is running 3.2.0" while
+src/__init__.py on that machine read 3.3.0.
+"""
+
+import importlib
+import sys
+
+import pytest
+
+from src.plugin_system import compatibility
+
+
+class TestCurrentCoreVersion:
+    def test_it_reads_the_file_rather_than_the_imported_value(self, monkeypatch, tmp_path):
+        # Simulate a process whose import predates the update: the module
+        # object says 3.2.0 while the file on disk says 3.3.0.
+        import src
+        monkeypatch.setattr(src, "__version__", "3.2.0")
+        fake = tmp_path / "__init__.py"
+        fake.write_text('__version__ = "3.3.0"\n', encoding="utf-8")
+        monkeypatch.setattr(compatibility, "_VERSION_FILE", fake)
+        assert compatibility.current_core_version() == "3.3.0"
+
+    def test_it_matches_the_real_file_by_default(self):
+        import src
+        assert compatibility.current_core_version() == src.__version__
+
+    @pytest.mark.parametrize("body", [
+        "__version__ = '3.4.1'\n",
+        '__version__="3.4.1"\n',
+        '"""doc"""\n\n__version__ = "3.4.1"  # trailing comment\n',
+    ])
+    def test_it_tolerates_the_ways_that_line_gets_written(self, monkeypatch, tmp_path, body):
+        fake = tmp_path / "__init__.py"
+        fake.write_text(body, encoding="utf-8")
+        monkeypatch.setattr(compatibility, "_VERSION_FILE", fake)
+        assert compatibility.current_core_version() == "3.4.1"
+
+    def test_a_missing_file_falls_back_to_the_import(self, monkeypatch, tmp_path):
+        # Never worse than before: an unreadable file returns what the old
+        # code would have returned.
+        import src
+        monkeypatch.setattr(src, "__version__", "3.2.0")
+        monkeypatch.setattr(compatibility, "_VERSION_FILE", tmp_path / "gone.py")
+        assert compatibility.current_core_version() == "3.2.0"
+
+    def test_a_file_without_the_line_falls_back(self, monkeypatch, tmp_path):
+        import src
+        monkeypatch.setattr(src, "__version__", "3.2.0")
+        fake = tmp_path / "__init__.py"
+        fake.write_text("# no version here\n", encoding="utf-8")
+        monkeypatch.setattr(compatibility, "_VERSION_FILE", fake)
+        assert compatibility.current_core_version() == "3.2.0"
+
+    def test_it_never_raises(self, monkeypatch, tmp_path):
+        # This runs on the install path; an exception here would surface as a
+        # failed update rather than a version mismatch.
+        bad = tmp_path / "__init__.py"
+        bad.write_bytes(b"\xff\xfe\x00 not utf-8 \xff")
+        monkeypatch.setattr(compatibility, "_VERSION_FILE", bad)
+        assert isinstance(compatibility.current_core_version(), str)
+
+
+class TestTheBugItFixes:
+    def test_a_stale_import_no_longer_refuses_a_compatible_plugin(self, monkeypatch, tmp_path):
+        """The exact hardware failure, as a test."""
+        import src
+        monkeypatch.setattr(src, "__version__", "3.2.0")     # what the process holds
+        fake = tmp_path / "__init__.py"
+        fake.write_text('__version__ = "3.3.0"\n', encoding="utf-8")   # what is on disk
+        monkeypatch.setattr(compatibility, "_VERSION_FILE", fake)
+
+        manifest = {"name": "Hockey Scoreboard", "min_ledmatrix_version": "3.3.0"}
+
+        stale_ok, _ = compatibility.check(manifest, src.__version__)
+        assert stale_ok is False, "precondition: the stale value is what refused it"
+
+        fresh_ok, reason = compatibility.check(
+            manifest, compatibility.current_core_version())
+        assert fresh_ok is True, f"the disk version must allow it, got: {reason}"
+
+    def test_it_still_refuses_when_the_core_really_is_too_old(self, monkeypatch, tmp_path):
+        # The gate must not become permissive: a genuinely old core still says no.
+        fake = tmp_path / "__init__.py"
+        fake.write_text('__version__ = "3.2.0"\n', encoding="utf-8")
+        monkeypatch.setattr(compatibility, "_VERSION_FILE", fake)
+        ok, reason = compatibility.check(
+            {"name": "Hockey", "min_ledmatrix_version": "3.3.0"},
+            compatibility.current_core_version())
+        assert ok is False
+        assert "3.2.0" in (reason or "")
+
+
+class TestCallSites:
+    @pytest.mark.parametrize("module", [
+        "src.plugin_system.store_manager",
+        "src.plugin_system.plugin_loader",
+    ])
+    def test_no_gate_binds_the_version_at_import(self, module):
+        """Catch a future call site reintroducing the stale read."""
+        import inspect
+        mod = importlib.import_module(module)
+        source = inspect.getsource(mod)
+        assert "from src import __version__ as core_version" not in source, (
+            f"{module} binds __version__ at import; use "
+            f"compatibility.current_core_version() so a long-lived process "
+            f"sees a core update.")