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>

server.py

@@ -427,7 +427,12 @@ class TuningProviderRegistry:
                     for name, freqs in names.items():
                         result[instrument][name] = [round(f * scale, 4) for f in freqs]
             except Exception:
-                logger.exception("tuning provider %r raised during get_merged()", provider_id)
+                # `log`, not `logger` — there is no `logger` in this module. This handler
+                # exists so ONE bad provider cannot break tunings for everyone; with the
+                # wrong name it raised NameError from inside the except and did precisely
+                # what it was written to prevent. See #899 and
+                # tests/test_tuning_provider_isolation.py.
+                log.exception("tuning provider %r raised during get_merged()", provider_id)
         return result