Review finding from scooby: this PR added a failure branch the harness
structurally could not reach. The fake tmux answered `has-session` only for
`=_holder:0.0`, so every non-holder agent landed in the session-is-gone branch
no matter what — the `elif` (tmux still reports the session, no pane PID after
the retries) had zero coverage and no way to get any.
That is the same shape as the bug this PR exists to fix, one layer down: a code
path shipped green where the gate that should measure it cannot. Less severe,
because the branch fails closed at exit 69 rather than reporting success — but
"the harness can't reach it" is the sentence that precedes the next silent
regression, so it gets closed here rather than filed.
`MOSAIC_TEST_HELD_SESSIONS` lets a case name targets the shim should also
answer for. It answers them only AFTER `new-session`, and that detail is the
whole trick: the launcher asks `has-session` about the same name twice — once
at line 255 where a yes means "already running, exit 0", and once at 417 where
a yes means "the session survived". A shim answering yes to both short-circuits
at the first and never reaches the branch under test. It would have looked like
coverage while measuring the idempotency path.
Both failure modes were measured, not reasoned about:
- toggle absent (the old shim): `code=pane-did-not-survive` — the case lands on
the wrong branch, which is exactly the unreachability being reported.
- toggle answering unconditionally: launcher exits 0 via the idempotency
short-circuit — "launcher reported success over a session with no resolvable
pane PID".
- toggle gated on new-session: `code=pane-pid-unresolved`, exit 69.
The case also asserts the diagnostic is not `pane-did-not-survive` and does not
mention the heartbeat, so the two pane faults cannot collapse into one message.
Gates: bash -n · launcher harness rc=0 · test-fleet-units.sh (real tmux) rc=0 ·
fleet specs 342 passed.
Refs #1241.
`mosaic fleet start` returned 0 over three dead panes. The launcher knew,
and said the wrong thing at the wrong severity to the wrong layer.
The pane runs `mosaic yolo <runtime>` under PANE_PATH with a cleared
environment. When that binary is absent the pane dies in under a second,
tmux destroys the session, and the diagnostic goes with it. The launcher
then found no PANE_PID, printed a WARNING about the *heartbeat sidecar*,
and exited 0 — so systemd logged "Finished ... successfully" and
`fleet start` reported success. `fleet ps` was the only component telling
the truth.
Two changes, both in start-agent-session.sh:
1. Before any effect, resolve `mosaic` and the roster's runtime against
PANE_PATH — the pane's own view of the path, not the launcher's.
`mosaic yolo <runtime>` calls checkRuntime(runtime) and looks for a
binary named exactly like the runtime, so this asks the same question
the pane will ask a moment later, while an operator can still see the
answer. Absent binary -> exit 69, code=missing-binary, no session
created.
2. Replace the dead-pane WARNING+exit-0. An absent session one second
after new-session is a runtime that died on startup, not a heartbeat
problem -> exit 69, code=pane-did-not-survive, with the command to run
by hand to see why. A present session with no pane PID after five
attempts -> code=pane-pid-unresolved. Neither branch kills the
session; destroying a possibly-live pane on a guess is worse than
leaving it for inspection.
Exit 69 (EX_UNAVAILABLE) is deliberate: the 64s already in this file mean
the projection was bad, and here the data is fine and the host is not
ready. Callers separate the cases by `code=`, the same way fail_env's
codes share 64.
This propagates for free. `fleet start` calls runChecked() for the holder
and each agent, and runChecked throws on non-zero, so layers 4 and 5 stop
lying without a TypeScript change. Two adjacent defects are left for a
follow-up issue rather than widened into this diff: the per-agent loop
aborts on the first failure instead of attempting all and reporting an
aggregate, and runChecked's bare throw surfaces the launcher's message
under a Node unhandled-rejection stack trace because program.parse() is
synchronous.
Tests:
- test-start-agent-session.sh gains three cases: `mosaic` absent from the
pane path, the runtime absent from the pane path, and a pane that does
not survive. Each was verified individually red against the unmodified
origin/next launcher.
- The two cases asserting a valid launch now supply a pane PID. Until now
the suite's one success path was itself a dead pane the launcher
reported as fine.
- The harness fakes `npm` so PANE_PATH stops depending on whatever the
host has installed, and fails loudly if the host provides `mosaic` or
`pi` in the system path, where the missing-binary cases would not be
measurable at all.
- test-fleet-units.sh gains a `pi` shim in its runtime bin. The real-tmux
harness named `pi` in its roster and never installed it; the new
preflight caught it.
Refs #1241
fred
jason.woltje