On a host with ~/.mosaic but no ~/.mosaic/fleet/agents, the implicit
resolution path passes silently with output byte-identical to a host with
no brain at all. fred traced why this is the shape web1 will be in
(#1288 comment 23133): nothing in product code ever creates
~/.mosaic/fleet/agents — the first fleet write resolves BEFORE creating
(generated-env-boundary), decides legacy, then manufactures the evidence
that keeps the host legacy. The three operator checks all agree and all
point the wrong way; the doctor is the only one that can disagree.
check_brain_home now emits a [NOTE] (not a WARN — nothing is broken yet)
when ~/.mosaic exists at the default config home without fleet/agents,
telling the operator the first 'mosaic fleet regen' locks in the legacy
tree. Explicit MOSAIC_BRAIN_HOME misconfiguration still warns (behavior
unchanged); custom homes stay silent (hermetic).
test-brain-home-check.sh: +3 cases (greenfield note, no-mosaic pass,
stray-mosaic-at-custom-home silence) — 11 total.
`mosaic fleet --help` reads "Manage the local Mosaic tmux fleet" and every
roster the CLI scaffolds sets `transport: tmux`, but neither `tools/install.sh`
nor `tools/_scripts/mosaic-doctor` contained the string "tmux" at all. A
greenfield host therefore came out of the installer able to install a fleet,
start a fleet, and run no seat, with `mosaic fleet ps` as the operator's first
and only signal.
Measured on mosaic-sbx-dev (Debian, no tmux, framework installed): `mosaic-doctor`
reported 11 warnings and not one of them named the reason no seat could launch.
The installer gets a warning, not a `require_cmd` hard failure: tmux is required
by the fleet, not by mosaic. Hosts that install this to run `mosaic claude` and
never scaffold a roster are common, and failing their install over a binary they
do not need would be wrong. The check runs in `--check` mode too — "what is the
state of this host" is the question `--check` is asked.
Both checks read the roster's own `transport:` rather than assuming tmux, so a
host declaring something else is pointed at the binary it actually needs instead
of at the wrong package.
The two implementations are deliberately parallel and each carries a comment
pointing at the other. They are separate because the installer must answer this
before the framework's own scripts are guaranteed to be on disk. One harness
drives BOTH from the shipped text — the functions are extracted from the scripts
by awk rather than copied — so the pair cannot drift silently, and the test
cannot keep passing after the shipped copy changes.
The harness is wired into `test:framework-shell`. Without that it would have
tripped the #1017 enumeration guard as UNENUMERATED, which is the guard doing
its job: a check nothing runs is not a check.
Evidence:
- red: the harness fails against origin/next ("could not extract
fleet_declared_transport"); `grep -ci tmux` on both files at origin/next = 0.
- green on real hosts, all four branches:
- dev (no tmux, no roster) -> WARN naming tmux, points at `mosaic fleet init`
- dev (no tmux, v2 roster) -> WARN naming the roster, points at `mosaic fleet start`
- dev installer --check -> WARN saying start "reports success and no seat comes up"
- canary (tmux present) -> `[OK] Fleet transport available: tmux` under --verbose,
silent by default (pass() is verbose-gated), installer silent
- harness green on node:24-alpine/busybox, the CI base image.
- `bash -n` x3, `pnpm typecheck` 45/45, fleet specs 342 passed,
enumeration guard OK, its self-test OK, prettier clean.
Refs #1240. Upstream of #1237/#1243 and #1241/#1244: a correct fix for either of
those still leaves this host with no live seat.
Zane
jason.woltjeandjarvis
fred