Search cache: preserve falsy provider returns to match original behavior

Line-by-line review of the search lift caught one drift: cache.get_cache_key
was coercing falsy provider returns ('', None, 0) to 'unknown' / False.
Original web_server.py only fell back to those sentinels on exception, not
on falsy success values.

Real-world impact: low — get_active_media_server() and get_primary_source()
return non-empty strings in practice. But cache keys are tuples with no
schema enforcement, so any drift here can silently fragment the cache.
Restored 1:1 parity with original semantics.

Added test covering the falsy-success path so this can't drift again.

789 tests pass, ruff clean.

core/search/cache.py

@@ -78,17 +78,17 @@ def get_cache_key(
     normalized_query = (query or '').strip().lower()
 
     try:
-        active_server = active_server_provider() or 'unknown'
+        active_server = active_server_provider()
     except Exception:
         active_server = 'unknown'
 
     try:
-        fallback_source = fallback_source_provider() or 'unknown'
+        fallback_source = fallback_source_provider()
     except Exception:
         fallback_source = 'unknown'
 
     try:
-        hydrabase_active = bool(hydrabase_active_provider())
+        hydrabase_active = hydrabase_active_provider()
     except Exception:
         hydrabase_active = False
 

tests/search/test_search_cache.py

@@ -119,3 +119,15 @@ def test_key_hydrabase_provider_failure_falls_back_to_false():
                                      fallback_source_provider=lambda: 'spotify',
                                      hydrabase_active_provider=boom)
     assert key[3] is False
+
+
+def test_key_preserves_falsy_provider_returns():
+    """Original behavior: if provider returns None / '' on success, store it
+    as-is. Don't coerce to 'unknown' — that's reserved for exceptions."""
+    key = search_cache.get_cache_key('q', None,
+                                     active_server_provider=lambda: None,
+                                     fallback_source_provider=lambda: '',
+                                     hydrabase_active_provider=lambda: 0)
+    assert key[1] is None
+    assert key[2] == ''
+    assert key[3] == 0