test(search): name the in-brain swap-race tests after what they sample

Review of #172 (rule 9): "LeaksNothing" claims more than a 1.5s
sampled race can prove -- the same overclaim this PR removes from the
"Never" names. Renamed to DoesNotReturn...DuringASampledSwapRace,
and the brainfstest doc now says the target may be inside the brain
(#171) and that observation is over a sampled window.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ingestion/internal/search/brainroot_test.go

@@ -184,7 +184,7 @@ func inBrainTarget(t *testing.T, brain string) string {
 	return brainfstest.WriteSentinelAt(t, filepath.Join(brain, "raw", "s.md"))
 }
 
-func TestQueryLeaksNothingFromAnInBrainTargetUnderASymlinkSwapRace(t *testing.T) {
+func TestQueryDoesNotReturnAnInBrainSymlinkTargetDuringASampledSwapRace(t *testing.T) {
 	brain, facts, _ := searchBrain(t)
 	target := inBrainTarget(t, brain)
 	read := func() string {
@@ -200,7 +200,7 @@ func TestQueryLeaksNothingFromAnInBrainTargetUnderASymlinkSwapRace(t *testing.T)
 	assert.NotContains(t, read(), brainfstest.Sentinel, "static in-brain link")
 }
 
-func TestHydrateRefusesAnInBrainSymlinkAndLeaksNothingUnderASwapRace(t *testing.T) {
+func TestHydrateRefusesAnInBrainSymlinkAndDoesNotReturnItsTargetDuringASampledSwapRace(t *testing.T) {
 	brain, facts, _ := searchBrain(t)
 	target := inBrainTarget(t, brain)
 	require.NoError(t, os.Symlink(filepath.Join("..", "..", "..", "raw", "s.md"), filepath.Join(facts, "inlink.md")))