AssertNoLeakFrom and the search Query race test passed vacuously when
every symlink swap failed or every read errored. Both now count
successful symlink swaps and reads that returned the inside note and
fail if either is zero; the Query race reader no longer swallows
Query's error.
Verified by flipping: a swapper whose os.Symlink always fails turns
notes, wiki and search race tests red; Query on a missing brain dir
turns the search race test red.
Closes#177
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
