UNVERIFIED. Committed locally to survive a session boundary; not pushed,
not typechecked past the eslint pass, tests not run, B-mutation not done.
`fleet install` now writes 10-brain-home.conf under [email protected],
clearing the inherited ConditionPathExists and re-pointing it at the resolved
brain home. On a split install the shipped condition names the config home
while the reconciler writes the brain home, so every seat is skipped and
`fleet start` still reports rc=0.
The spec's existing coverage could not see this: its fixture never creates
<HOME>/.mosaic/fleet/agents, so resolveBrainHome() only ever reaches legacy
mode. Replaced with three arms - legacy, split (fails without this change),
and stale-override removal with a present-first control.
fred
1a6c8fe0cb