`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