fix(server): a raising tuning provider no longer takes down get_merged() for everyone (#899) (#904)

One word. server.py's TuningProviderRegistry.get_merged():

    except Exception:
-       logger.exception("tuning provider %r raised during get_merged()", provider_id)
+       log.exception("tuning provider %r raised during get_merged()", provider_id)

There is no `logger` in server.py — the module logger is `log`. So the handler written to
swallow-and-report a bad provider instead raised NameError from inside the except, and that
NameError propagated out of get_merged().

The effect was the exact OPPOSITE of what the handler is for: one misbehaving plugin took
the whole merged-tunings call down for every other provider, AND the traceback named the
wrong problem ("name 'logger' is not defined" rather than the provider that actually blew
up). Doubly silent: nothing was ever logged either, because the logging call was the thing
that crashed.

Found by pyflakes while carving server.py (R3b). It survived because NOTHING exercised the
failure path — no test ever had a provider raise. That is the whole reason this class of
bug is invisible: it lives only on error paths, so the suite is green and the feature is
broken exactly when it matters.

tests/test_tuning_provider_isolation.py is that path:
  * a raising provider must not lose the HEALTHY providers' tunings, nor the defaults
  * and the failure must actually be LOGGED — swallowing is only acceptable if it reports

Bite-tested: restoring `logger` fails both.

(The log assertion attaches caplog's handler to the feedBack logger directly. It sets
propagate=False, so pytest's root capture sees nothing from it — test_plugins.py has a
capture_logger() for this, but it is not importable here: pyproject pins pythonpath to
[".", "lib"], so `tests` is not a package. Three lines beat churning 21 call sites in an
unrelated file to convert that helper into a fixture.)

pytest 2410, pyflakes 0 undefined names in server.py, Codex 0.

Closes #899

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_tuning_provider_isolation.py

@@ -0,0 +1,72 @@
+"""A raising tuning provider must not take down get_merged() for everyone. (#899)
+
+`TuningProviderRegistry.get_merged()` wraps each provider in a try/except precisely so one
+misbehaving plugin cannot break tunings for the rest. The handler called `logger.exception`
+— and there is no `logger` in server.py; the module logger is `log`. So the handler MEANT
+to swallow-and-report instead raised NameError, which propagated out of get_merged().
+
+The net effect was the exact opposite of the handler's purpose: one bad provider took the
+whole merged-tunings call down, and the traceback named the wrong problem.
+
+Nothing exercised the failure path, which is why it survived. This is that path.
+"""
+
+import importlib
+import logging
+import sys
+
+import pytest
+
+
+@pytest.fixture()
+def registry(monkeypatch, tmp_path):
+    monkeypatch.setenv("CONFIG_DIR", str(tmp_path))
+    sys.modules.pop("server", None)
+    mod = importlib.import_module("server")
+    yield mod.TuningProviderRegistry()
+
+
+def test_a_raising_provider_does_not_break_the_others(registry, caplog):
+    """The whole point of the try/except. Before the fix this raised NameError."""
+    def boom():
+        raise RuntimeError("provider exploded")
+
+    def good():
+        return {"guitar": {"My Tuning": [82.41, 110.0, 146.83, 196.0, 246.94, 329.63]}}
+
+    registry.register("bad-plugin", boom)
+    registry.register("good-plugin", good)
+
+    merged = registry.get_merged()          # must NOT raise
+
+    assert "My Tuning" in merged["guitar"], (
+        "the healthy provider's tuning is missing — one raising provider took down the "
+        "merged result for everyone"
+    )
+    # and the default tunings survive
+    assert merged["guitar"], "default tunings were lost"
+
+
+def test_the_failure_is_actually_logged(registry, caplog):
+    """Swallowing is only acceptable if it is reported. A NameError in the handler meant
+    nothing was ever logged — the failure was both fatal AND silent about its real cause."""
+    def boom():
+        raise RuntimeError("provider exploded")
+
+    registry.register("bad-plugin", boom)
+
+    # The feedBack logger sets propagate=False, so pytest's root-logger capture sees
+    # NOTHING from it. Attach caplog's handler directly. (test_plugins.py has a
+    # capture_logger() context manager for this, but it is not importable from here:
+    # pyproject pins pythonpath to [".", "lib"], so `tests` is not a package.)
+    lg = logging.getLogger("feedBack")
+    lg.addHandler(caplog.handler)
+    lg.setLevel(logging.ERROR)
+    try:
+        registry.get_merged()
+    finally:
+        lg.removeHandler(caplog.handler)
+
+    assert any("bad-plugin" in r.getMessage() for r in caplog.records), (
+        "the raising provider was never named in the logs"
+    )